VDA Band 19.2 English 2010

Packaging means

CG1 - cleanliness zone

CG2 - cleanliness room

Mesh pallet / universal LLC

Permitted if clean (in accordance with in-house Not permitted definition), special measures may be required

Universal LLC made of plastic

Permitted if clean (in accordance with in-house Only those from internal definition), special measures loop permitted may be required

Wooden LLC

Not permitted

Plastic SLC

Permitted if clean (in accordance with in-house definition) SLCs from pool also permitted

Steel SLC (coated)

Not permitted Wooden pallets are not permitted

Pallet

Stainless steel / plastic permitted

Clean SLC with additional measures permitted (in accordance with in-house definition), e.g. secondary packaging

CG3 - Cleanroom

Not permitted

Only those from internal loop permitted

Wooden pallets are not permitted Clean stainless steel / plastic pallets from internal loop permitted

Bag

Permitted in appropriate condition (not soiled or damaged)

Film

Any outer transport film is to be removed before bringing components into the clean area, regardless of cleanliness grade

Cardboard

Coated (hard) cardboard permitted

Special load carriers

Design and materials must be adapted to the cleanliness grade in order to minimize particle emission and displacement from carriers. Special measures may be necessary

Blister / deepdrawing tray


Separating elements

Only permitted if made from No particle-emitting materials permitted (paperboard, low-abrasion materials, cardboard, paper)., e.g. twin-wall sheets, lightweight coated cardboard also board made of PP or PE permitted

Table D.3:

Permitted with secondary Permitted with secondary packaging during transport packaging during transport

Only permitted as far as lock

Not permitted

Permitted with secondary packaging during transport

Overview of packaging means and suitability as outer packaging in dependence upon the cleanliness grade of the assembly area

69

D.3.2

Operative measures

D.3.2.1

Cleaning procedures for packaging

In order to assure the required cleanliness of reusable packaging, it must be cleaned at regular intervals. The type and frequency of cleaning procedure depend upon the cleanliness requirements of the components or aggregates to be packed as well as upon the packaging means or materials used. Cleaning procedures and suitability in dependence upon component cleanliness requirements:

The following table describes standard procedures for cleaning packaging in dependence upon the packaging means and materials used. The procedures are also assessed according to the cleanliness requirements of the components to be packed.. Note:

If reusable containers are used as direct packaging for cleanliness-sensitive components, e.g. SLCs or deep-drawing trays, they should be cleaned at defined intervals using an aqueous process. A defined level of cleanliness cannot be achieved by blowing or sweeping out containers.

Packaging means

Aqueous cleaning process (continuous process with subsequent drying*)

Manual cleaning with pressure washer

SLC

+

-

Only where low cleanliness requirements apply

Mesh pallets **)

-

+

+

Deep-drawing containers

+

-


Blister trays

+

-


Special carriers

+

+


Bags (standard plastic bag)

No cleaning required single-use only

Twin-wall sheets

70

+

-

Dry cleaning process (beating, blowing, suction-cleaning, brushing)


Wetwiping process

-

+

Wooden LLCs **)

-

-

+

-

Hoods **)

-

+

+

+

Universal LLCs made of plastic

+

+


- Procedure is not suitable / cannot be implemented

+ procedure is suitable in principle

*) Drying variations / systems such as centrifugation, vaporization or dry-blowing **) These packaging means are cleaned more to reduce particle displacement in the clean area than to protect products directly because they may not be utilized as direct inner packaging

Table D.4:

Assessment of procedures for cleaning packaging means

Cleaning intervals in dependence upon cleanliness requirements: •

High cleanliness requirements

Reusable containers must be cleaned after each use. Where possible, packaging means are to be cleaned in the immediate vicinity directly before they are used again. If this is not possible, cleaned containers are to be transported and stored in such a way so as to maintain cleanliness levels. If cleaning procedures are not cost-effective, additional single-use inner packaging is to be used (e.g. bags) to prevent cleanliness-sensitive goods from becoming contaminated. •

Average and low cleanliness requirements:

Cleaning procedures are to be carried out and controlled at fixed intervals. D.3.2.2

Inspection of packaging means

Packaging means must be assessed to ensure that they are adequately clean. The manner (visual inspection or test procedure in accordance with VDA 19) and frequency of assessment is determined by the respective cleanliness specification. •

Inspection procedure

Inner (direct) packaging (blisters, bags, films and SLCs):

-

For surfaces coming into contact with the product, pressurerinsing test in accordance with VDA 19 (where possible)

71

-

Alternatively if not possible: Tapelift, wiping test with reference sample (see Chapter F: Assembly equipment )

Outer packaging (e.g. mesh pallets):

-

Visual inspection of surface characteristics using reference samples (image sample)

Described in compliance with the procedures and relevant test parameters laid down in VDA 19, see annex for examples of test specifications for evaluating the cleanliness levels of packaging means. D.3.2.3 Responsibilities – packaging

Responsibilities regarding the provision of cleanliness-suitable containers must be determined by the customer, supplier and logistics provider. From each of the three parties, a person in charge of controlling this is to be named. Elements of the agreement could include: -

Cleanliness requirements (relevant areas of packaging)

-

Method and frequency of cleaning procedures

-

Who is in charge of cleaning packaging and who controls and documents the quality of cleaning processes

-

Method and frequency of control

-

Delivery and storage of cleaned empty containers

-

Further handling of the packaging

-

Identification of cleaned packaging

-

Measures to be taken if cleanliness requirements are not fulfilled

-

Determining transport methods and conditions to and from cleaning location

D.3.2.4

Transport and lock concepts

Internal transportation – fundamentals

Packaging means can displace particles when brought into a clean area and may therefore only be introduced if they are free of critical contamination. Depending on the distance and duration of transport, 72

packaging means may become heavily contaminated. Therefore, the outermost packaging is not permitted in a clean area and must first be removed in a designated unpacking area. To prevent contaminated packaging means from being brought directly into a clean area, material flows must be controlled by an operative or physical barrier. Such barriers are known as locks. Bringing goods into a clean area: •

Cleanliness zone - CG1

If components are brought into the zone in carriers which were not additionally packaged during transport, organizational measures are required to prevent the risk of displacement. Components are to be unpacked and taken out of the container in a place separated from the assembly area. Where appropriate, carrier units can simply be brought to the zone boundary and components transferred into the zone from there. If components are delivered with secondary packaging (e.g. components in bags or SLCs), this must be removed before they are brought into the zone in their inner packaging.

e n r i t a t e l s u l o e t t a p a h h g g s e u e r o g r g b m a

g s n i i n t s i a n d n t a d n e n e o o n k c p i c t t a h p e m l l g n a o u u c p r o n h a b s e e l m c

Fig. D.5:

l o a d i n g s t a t i o n

components transferred to roll cart

cleanliness

storage area for clean packaging means

zone roll cart loaded with aggregates aggregates transferred to mesh pallets

components brought to assembly station

n o i t a t s y l b m e s s a

transfer station

Example of a logistics concept for an assembly facility in a cleanliness zone

73

•

Cleanliness room - CG2

Only packaging means which have been additionally packaged during transport may be brought directly into a cleanliness room after they have been unpacked. The secondary packaging (e.g. hood and stretch film) is removed in a designated unpacking / goods transfer area immediately before the packaging means is brought into the cleanliness room. unpacking/

cleanliness

transfer area

room

SLC containing aggregates is brought out

clean components in SLC on pallets s e n t r i e a t l l s u a e o p t n a t g h g o e r u s o C g r g b L a S

Fig. D.6:

SLC transferred to roll cart

storage area for SLCs and transport pallets


SLC loaded with aggregates SLC brought in via airlock clean components brought in via airlock


component cleaning system with airlock function

Example of a logistics concept for an assembly facility in a cleanliness room

If containers are only utilized in the cleanliness room and unpacking area (i.e. only move back and forth between the component transfer area and cleanliness room) or if load carriers are cleaned appropriately, no secondary packaging is required. The cleaning plant represents a lock. •

Cleanroom - CG3

The secondary packaging, e.g. transport film, is removed immediately before goods enter the material lock. This prevents inadequately clean packaging or contamination from transport from being brought into the locks. Before being brought into the cleanroom, the inner packaging (e.g. SLC, bag) is first brought into the material lock and wiped clean with damp cloths to remove any coarse contamination originating from the outer or 74

secondary packaging. This cleaning step is not required if components are taken out of the inner packaging in the material locks (e.g. from blister trays or bags in the SLC) before being brought into the actual cleanroom assembly area. This requires a double unpacking procedure. The cleaning plant represents a lock because components are brought directly into the cleanroom from the cleaning plant after cleaning. cleanroom

material airlock s e n t r i l e a t l s u a o e t t p a h n g g o e u s r o C g r g b L a S

staff airlock

clean SLC brought in via airloc

SLC containing aggregates brought out via airlock

clean components in SLC on pallets brought in

component transfer



Abb. D.7:



componentcomponentcleaning system with airlock function

Example of a logistics logistics concept for an assembly facility in a cleanroom

Goods leaving clean areas: Aggregates are packaged after assembly to maintain their level of cleanliness. The type of packaging is selected according to the relevant cleanliness requirements. •

Aggregates sensitive to contamination:

Direct component packaging is carried out with the same level of cleanliness as that used for their assembly. The packaging / containers must fulfill the requirements of the packaging means of the respective zone (outer surface) and the product (inner surface). If a component or aggregate requires secondary packaging which does not correspond with the cleanliness grade of the zone, this has to be applied outside the zone. Exception: if the next process step is executed in a zone with a higher CG, packaging must fulfill the higher requirements. 75

•

Aggregates not sensitive to contamination:

When packaging assembled aggregates which are not sensitive to contamination before they leave the clean area, the packaging means must fulfill the requirements of that zone. If necessary, the same measures as those for bringing goods into the zone are to be observed (e.g. packaging area). Examples of such end-products include steering gears and gearboxes. Summary / overview: Step

CG1 – cleanliness zone

Entry via material lock

CG2 – cleanliness room

Regulations for unpacking load carriers without secondary packaging are to be drawn up and observed

Only packaging means which have been wrapped in secondary packaging during previous transportation may be brought into the Remove any secondary cleanliness room packaging (e.g. hood, stretch film) at zone In such cases, boundary before secondary packaging is bringing in to zone to be removed in the unpacking area immediately before goods pass through the material lock Not required for internal load carriers or if the packaging was cleaned before being brought in

Exit via material lock

CG3 - Cleanroom Remove secondary packaging (e.g. hood, stretch film) in the unpacking area immediately before goods pass through the material lock Remove next layer of packaging in the material lock If no additional inner packaging is present, packaging must be cleaned before being brought in

Empty containers exiting the zone and being transported to another area must fulfill the cleanliness requirements of the subsequent zone

Aggregates not sensitive to contamination Exit via material lock

Direct component packaging is carried out in the zone where the aggregates are assembled

Packaging / containers must fulfill the requirements of packaging means of Cleanlinesssensitive aggregates the subsequent zone (influence on exterior environment) and on the product (influence on interior environment) Exception: if the next process step takes place in a zone with a higher CG, packaging must fulfill the higher requirements

Table D.5:

76

Main points to consider when cleanliness-sensitive components and aggregates are brought into / taken out of an assembly area via a material lock in dependence upon the cleanliness grade

Hydac Filtertechnik GmbH

Sulzbach/Saar

J.Eberspächer GmbH & Co. KG

Esslingen

INA Schaeffler oHG

Herzogenaurach

Knorr-Bremse AG

Aldersbach

Mahle Filtersysteme GmbH

Stuttgart

Mann und Hummel

Ludwigsburg

MAN Nutzfahrzeuge

Nürnberg

Maurer Magnetic AG

Grüningen (CH)

Pall GmbH

Dreieich

Robert Bosch GmbH

Schwieberdingen

TRW Lucas Automotive GmbH

Koblenz

Witzenmann GmbH

Pforzheim

Volkswagen AG

Wolfsburg

VOSS Automotive GmbH

Wipperfürth

ZF Friedrichshafen AG

Friedrichshafen

Thanks are also due to all who have provided suggestions for improvement as well as those organizations represented in the editorial circle.

Stuttgart / Berlin, September 2010

VERBAND DER AUTOMOBILINDUSTRIE E. V. (VDA)

6

External transportation - fundamentals

Main points to consider: -

Minimum transport distances and times

-

Low vibration levels

-

Protect products from becoming damaged inside the packaging

-

Protect packaging against damage

-

Additional protection against wetness, humidity and fluctuations in temperature (e.g. open racks conveyed on transport vehicles outside production halls are to be additionally covered)

D.3.2.5

Storage

General information:

Components are to be stored so that the required level of cleanliness is maintained for the duration of storage. Storage areas must be kept separate and their cleanliness grade clearly marked. Packaging has to be weatherproof if stored outside. Protective surface layers, coatings and barriers must be impermeable to water vapor. Goods may only be stored outside if placed on an appropriate underlay (e.g. boards, pallets) in designated, clearly-marked areas. Storing components:

In accordance with surface cleanliness requirements, non-packaged components are to be stored in clean storage areas with the appropriate cleanliness grade. If requirements for inner component surfaces are higher than those for outer surfaces, such components may be stored in areas with a lower cleanliness grade provided all openings are hermetically sealed for the entire storage period. Components made of materials liable to corrode must be protected accordingly, e.g. by packing them in VCI protective foil. Packaged components do not need to be stored in a clean area provided the packaging ensures the required degree of protection. Packaged components may only be stored in a clean area if the packaging itself / unpacking process does not impair the cleanliness grade of the storage area. A sub-domain - adjacent to the clean area but with different requirements - may be used for unpacking purposes.

77

Special storage areas are to be set up and appropriately marked for components rejected because they have been damaged or their surfaces contaminated. Storing packaging means:

Clean / cleaned packaging means are to be stored in accordance with the cleanliness level of the components to be packed inside. Clean containers are to be clearly labeled as such. D.3.2.6

Unpacking and commissioning

In general, packaging is selected (and designed) according to its ability to be opened and closed in a cleanliness-suitable manner. Independent of cleanliness requirements, the following fundamentals are to be considered:

78

-

Each user is responsible for handling packaging correctly.

-

Components and aggregates may only be packed in the prescribed packaging means

-

The covers and lids of containers are to be developed and used in such a way so that any existing (transport) contamination does not enter into the container.

-

Cardboard may not be torn open; it may only be opened at designated sites using tools prescribed for the purpose. This is to be taken into account when designing cardboard packaging. If cutting tools are utilized, care must be taken to ensure that packaged goods do not become damaged.

-

Under no circumstances may members of staff carrying out cleanliness-critical assembly tasks remove packaging. Unpacking and commissioning are also to be carried out separately. If this is not possible, hands are to be washed between tasks (e.g. damp cloth) or disposable gloves worn or changed. Particle-generating and cleanliness-sensitive processes are to be kept strictly separate in order to avoid particle displacement.

-

Clean gloves are to be worn when commissioning components liable to corrosion.

-

Unprotected components are to be unpacked and stored in different areas (separated at least by screens).

-

Once unpacked, components are to be brought immediately into an appropriately clean assembly or storage area. This prevents particle displacement from contaminated packaging materials or containers.

-

Where possible, components are to be unpacked immediately before assembly. Sealing plugs, adhesive films, etc. are to be removed immediately before subsequent processing.

-

Quality control is to be informed if concealed transport damage to packaging / components is discovered. Damaged load carriers and packaging means (e.g. in accordance with reference sample) must be rejected.

-

Packaging waste is to be removed immediately in accordance with the regulations.

-

Due to increased levels of contamination, unpacking areas are to be cleaned using a wet process at regular intervals / more frequently.

-

Any remaining components are to be handled in compliance with relevant cleanliness requirements.

-

Work instructions regarding the opening of packaging are to be observed.

Annex A.D

The cleanliness values shown below are examples of values obtained from cleanliness tests carried out on typical packaging means in various states. The data is only intended to give an impression of potential particle charges on packaging means and does not represent a recommendation or regulation.

79

A.D.1

Small load carriers - SLCs

SLC from pool 250 m c 0 200 0 0 1 r e p 150 t n u o c 100 e l c i t r 50 a P

0 100 - 150 µm

150 - 200 µm

200 - 400 µm

400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.8:

Cleanliness value of SLC from pool

SLC cleaned using defined procedure 250 m c 0 200 0 0 1 r e 150 p t n u o 100 c e l c i t r 50 a P

0 100 - 150 µm

150 - 200 µm

200 - 400 µm

400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.9:

80

Cleanliness value of SLC cleaned using a defined procedure

A.D.2

Plastic bag

New clip closure bag 14 2

m 12 c 0 0 0 10 1 r e 8 p t n u 6 o c e l 4 c i t r a 2 P 0 50 - 100 µm

100 - 150 µm 150 - 200 µm 200 - 400 µm 400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.10:

Cleanliness value of bag with clip-closure

New film tubing 5 2

m c 0 0 0 1 r e p t n u o c e l c i t r a P

4

3

2

1

0 50 - 100 µm

100 - 150 µm 150 - 200 µm 200 - 400 µm 400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.11:

Cleanliness value of film tubing

81

E:

PERSONNEL

E.1

Introduction

This chapter deals with methods of confining and controlling critical particle contamination caused by personnel and deals mainly with workers in direct contact with manufacturing processes and products. First and foremost, the successful and efficient operation of a clean assembly facility requires the commitment and support of management staff right up to the top company management / VDI 2083 / 11 – Cleanroom technology – Quality control. The inclusion of employees in company structures and activities ranges from machine operators and assembly workers to delivery staff. Planners and managers need to take this broad spectrum of potential access and influencing possibilities into careful consideration, e.g. in the form of training courses for a new member of staff from an external company in charge of the regular cleaning of the assembly area, or work instructions regarding personnel conduct during refitting measures or the installation of a new assembly facility. Of all the influencing factors dealt with in the guideline, personnel represents the highest risk as far as the control of critical contamination levels is concerned. Accidental or even intentional misconduct may lead to damage, the cause of which is very difficult to pinpoint or comprehend. This could result in high but avoidable costs spent trying to find the cause and introducing unnecessary or even incorrect failure prevention measures. Example:

82

In a costly failure analysis of several zero kilometer defects, metal particles and abrasive contamination are identified as the cause. They originate from a framework construction no longer in use in the assembly area. Out of laziness, SLCs are not additionally covered when nearby cutting processes are carried out because the parts inside are wrapped in plastic bags in compliance with regulations. On removing the components, the metal particles - which under normal conditions would not be present - are displaced to some of the components. The quality control department of the company is now investigating whether the supplier of the parts may be responsible for the origin of the contamination.

The origin of the damage cannot be located because there is no systematic cause of malfunction but rather a unique chaotic outlier due to personnel misconduct. Personnel attitude is a decisive factor in successfully controlling clean assembly. The complexity of technical cleanliness as a quality characteristic makes it absolutely essential to sensitize the workforce in this regard and to give personnel practical instruction and training. Workers must also take into account the fact that unscheduled activities may affect the cleanliness of products and the environment. If case of uncertainty, further instructions are to be obtained or appropriate measures taken. It is vital for personnel to understand that thoroughness, consistent closed loops and continuity form the basis of a functional clean assembly facility. Any sudden decrease in cleanliness measures (e.g. for reasons of cost or time) may lead to lasting weaknesses in established regulations and impair the credibility of management staff and other persons with a role model function. Recommendations for clothing and conduct within the scope of logistic processes are listed in the following section. They depend upon the cleanliness grade of the assembly area, which is higher than that for component cleanliness (see Chapter C: Environment ). In order to establish the necessary basic stability in a clean area where personnel is present, a number of regulations and measures are required. Recommendations for this can be found in the following paragraphs. Staff members are to be actively included and given responsibilities concerned with cleanliness. Measures and regulations are to be formulated clearly and comprehensively to substantiate the need for / benefits of them. The necessary means and materials are to be made available for this. Personnel activities associated with cleanliness are to be included in the work plan and the time required for them calculated.

83

E.2

FUNDAMENTALS

Personnel plays a major role in assembly cleanliness (see Figure E.1 and Table E.1).

Eliminator

Initiator

Staff Source

Fig. E.1:

84

Carrier

Personnel considered from the point of view of assembly cleanliness

Men as:

Process:

Example:

Activator

Carrying out tasks Assembling components or where critical particles operating load-lifting are / could be equipment. generated

Transmitter

Displacement resulting from tasks involving both clean and contaminated objects

Source

General activity / time Primary: Hair, skin flakes, skin spent in assembly grease, sweat, micro area organisms, droplets of saliva, cosmetic products (skin cream, nail varnish, face powder, etc.).

Example of measure:

Work instruction regarding the avoidance of particle generation or description of cleanliness-suitable process

Handling contaminated Avoid mixed tasks outer packaging or spending time in zone with lower cleanliness grade. Special clothing regulations. Reduce personnel presence to a minimum.

Secondary: Wear and tear of clothing (e.g. fluff) Rectifier

Specific cleanliness action

Removing particles from functional surfaces.

Work instructions

Keeping workstations or operating utilities clean

Table E.1:

Relevance of personnel with regard to assembly cleanliness

Work instructions need to be developed, implemented and their execution verified in a prescribed clean area. Maximum cleanliness measures are required where contamination originating directly from humans (see table, Position 3.) could impair products and associated processes. If the displacement of contamination by personnel can be confined, this may result in a significant stabilization of the degree of cleanliness and minimize defects.

85

E.3

QUALIFICATION AND CLOTHING

E.3.1

Measures and recommendations - conceptual

In the following paragraphs, requirements and measures are described and classified where appropriate. E.3.1.1

Training with focus on assembly cleanliness

Which groups of people reguire training? -

Management, company executives

-

Buyers / procurers of operating utilities

-

Planners (processes and implementation of operating utilities)

-

Design engineers, quality planning and control

-

Personnel for assembly and reworking processes

-

Personnel for component provision and retrieval

-

Machine fitters, repair and maintenance personnel,

-

Building maintenance personnel

-

External companies: e.g. construction workers, service technicians, cleaning companies

Possible training courses: 1.

Basic sensitization: all groups of people are required to attend. The contents of this training course are identical for all groups [see Paragraph B below]; possibly with the exception of external companies. Scope and duration can be adapted to the target group in question.

2.

Rules regarding entering and staying in clean areas: all groups of people are required to attend. The contents of this training course are identical for all groups. Adapted short training courses, especially for employees of external companies who only visit once / sporadically.

3.

Logistics and cleaning maintenance in the vicinity of an assembly facility: this training course is aimed at all members of personnel regularly present in the clean assembly area as well as planners.

86

4.

Cleanliness-suitable assembly: this training course gives information about minimizing and avoiding contamination in assembly and reworking processes. The course is envisaged for all members of personnel regularly present in the clean assembly area as well as for planners.

5.

Main focal points regarding cleanliness: this training course is aimed at selected groups of people and conveys specific information, e.g. maintenance and repair, cleanliness-suitable design of assembly equipment, cleanliness-suitable construction, etc.

No recommendations can be given here regarding the frequency of training measures with a view to updating (further training) or refresher courses (revision). Training concept for basic sensitization (contents of course): -

History, development of the necessity of degree of cleanliness aspects

-

Identifying damaging influences (particles, not chemicals). Contamination (from processes and the environment). Demonstrating the need for everyone to contribute towards cleanliness in the assembly area (despite all previous efforts)

-

Depicting the entire process chain (construction, casting, mechanical processing, cleaning, transport, storage, etc.), also with regard to suppliers and customers

-

Comparing particle sizes, visualization

-

Naming / visualizing defects, subsequent Examples (photos) of parts not in order

-

Specific photographic examples: wrong / right for measures

-

Face-to-face communication: emphasizing the importance of individual contributions from staff members

-

Defined instructions / measures with regard to an assembly task: from the actual assembly process right up to packaging and logistics

-

Certificate of participation

damage,

costs.

87

E.3.1.2

Clothing

Clothing has various functions from the point of view of cleanliness: -

The amount of fluff generated by clothing can be significantly reduced by using suitable textiles

-

If clothing is only worn in the clean area, particle displacement from contaminated areas is decreased.

-

By covering up skin and hair, the quantity of (human) particles given off into the environment is reduced.

-

The type of clothing worn in a clean area is different to that worn in non-controlled areas; this makes personnel more aware of the special rules, requirements and responsibilities regarding cleanliness.

-

In assembly facilities with high staffing percentages, the wearing of low-fluff clothing can considerably reduce dust and fluff levels.

The clothing concepts shown below in dependence upon cleanliness grade have proved to be effective. Clothing requirements in dependence upon cleanliness grade Requirement (in order of increasing cleanliness requirements)

CG0

CG1

SaS2

cleanliness cleanlinesszone room

SaS3

Comment

Cleanroom

Outer clothing 1. Only private day-to-day clothing

+

-

-

-

2. Only conventional work clothing

o

+

-

-

3. Overcoat / overall, only for use in clean area (single-use / reusable), lowfluff

o

o

+

4. Clothing recommended for the corresponding cleanroom class (singleuse / reusable)

o

o

o

88

1)

1)

+

+

1)

Dependent upon use

Clothing requirements in dependence upon cleanliness grade Requirement (in order of increasing cleanliness requirements)

CG0

CG1

SaS2


SaS3

Comment

Cleanroom

Footwear 1. Only private day-to-day / safety footwear

+

+

-

-

2. Private day-to-day / safety footwear in combination with e.g. shoe-cleaning machine or tack mat

o

o

+

-

o

o

o

+

1. None

+

+

+

-

2. Hair net / cap

o

o

o/+

+

o

o

o

o/+

Product dependent

o/+

Product dependent for staff with beards

3. Overshoes, single-use / reusable only for use in clean area Separate footwear , reusable; only for use in clean area

Head gear

3. Hood

4. Mask

o

o

o

If contamination directly generated by staff is critical: Head gear and mask, e.g. to retain skin flakes and loose hairs. Head gear is also to be worn in CG1 and CG2 if members of staff need to bend over exposed products or functional surfaces in order to carry out tasks. Legend: + = suitable / yes

- = unsuitable / no

o = not required

Table E.2: Clothing requirements in dependence upon cleanliness grade

Work safety (e.g. safety footwear, protective gloves or helmets, skin protection means) and also ESD and corrosion protection are to be individually adapted to cleanliness aspects and regulated.

89

Gloves: -

It must be ascertained whether gloves need to be worn to protect goods against particulate contamination (not against corrosion).

-

If the wearing of gloves is mandatory, suitability must be determined with regard cleanliness aspects.

Note:

Particles could collect on the surface of gloves and cause displacement.

-

Conditions regarding the use of gloves are to be laid down in work instructions; e.g. how often they need to be changed.

-

Even where gloves are worn: unnecessary contact with other objects and surfaces is to be avoided.

In some cases, additional rules may apply: -

Contaminated or greasy gloves may not be worn

-

Gloves may not be used to remove contamination

-

Gloves which have fallen on the floor may not be worn again

-

Used gloves are to be removed or clean gloves put on after carrying out cleaning tasks on machines, tools and work stations. This also applies for repair and maintenance tasks.

E.3.1.3

General rules

The following recommendations are mainly concerned with the possible content of work instructions and make no claim to be complete. Shown below, the classification of rules of conduct demonstrates that various measures apply for different cleanliness grades. This substantiates the experience that quality improvement is not necessarily due to the design of a room but rather to the work instructions enforced.

90

Examples of general rules of conduct for clean areas Measure / Requirement

CG0

CG1

CG2

cleanliness cleanliness zone room

1.

2.

3.

4.

5.

6.

7.

CG3 Cleanroom

Unnecessary contact with potentially contaminated surfaces and objects is not permitted

o

+

+

+

Members of staff performing assembly tasks may not come into contact with secondary packaging

o

+

+

+

Prescribed work clothing may not be worn outside the zone

o

o

+

+

Clothing may not come into contact with functional surfaces

o

+

+

+

Prescribed footwear may not be worn outside the zone

Prescribed work clothing must be worn in the zone.

Comment

1)

-

-

o

+

-

1)

+

+

To be cleaned before entering the clean area

+

Food may not be brought into the zone

Only permitted in designated areas Alternative: o

+

+

+

As an exception, only permitted during allocated time period

91


CG0

CG1

CG2


8.

10.

11.

12.

92

All contaminated objects are to be cleaned before bringing them into a zone with a higher cleanliness grade

2)

o

+

2)

+

+

2)

+

+

Staff is responsible for safeguarding cleanliness when using tools, containers and components.

o

+

+

+

o

+

+

+

o

+

+

Exception possible, provided there is no risk of contaminatio n

+

No tasks generating dispersible particles are permitted (e.g. abrasive cutting, blowing)

Awareness of risk of particle detachment from moving and / or painted parts

Comment

Cleanroom

Doors and windows are to be kept closed o

9.

CG3

+

Applies for assembly, maintenance, repair tasks, etc. Where required, take appropriate measures (e.g. suction cleaning, covering surfaces)

Any flaws noticed are to be dealt with in accordance with the regulations


CG0

CG1

CG2


13.

14.

15.

16.

17.

Care is to be taken to ensure that contamination does not fall onto or enter components

Without exception, any components which have been dropped are to be considered as contaminated and subsequently handled specially in accordance with regulations Only necessary tools are to be provided and utilized .

Tools which have been dropped on the floor may not be reused until they have been cleaned During downtimes, oiled or greased parts are to be protected against contamination (e.g. by covering them).

o

o

o

o

+

+

+

+

+

+

+

+

CG3 Cleanroom

+

+

+

+

Products awaiting completion which are located on conveyors are to be covered during assembly downtimes

E.g. packing or unpacking, removing components from shelves, opening machines and equipment Fix further procedures or usage (e.g. disposal, cleaning)

Keep and store tools in a designated place E.g. wipe with clean cloth

3)

o

+

o

3)

o

+

o

3)

o

3)

o

3)

The same principle also applies for thread lock fluid, adhesives, liquid sealing compounds, etc. 18.

Comment

Unless environment al atmosphere has detrimental influence on product

93


CG0

CG1

CG2


19.

20.

21.

22.

CG3

Comment

Cleanroom

If gloves used at a “clean workbench” come into contact with external objects (e.g. pulling up a chair), they are to be changed immediately

+

+

+

+

Contamination on covers or housings is to be removed before opening or removing them

o

+

+

+

During machine failures, fitting and maintenance tasks or construction work, load carriers are to be appropriately covered; close plastic bags or film inlays

o

+

+

+

Unprotected cleanlinesssensitive components may not be stored in the packaging area

o

+

+

+

Legend: + = suitable / yes, - = unsuitable / no, o = not required

Table E.3: Examples of general rules and measures

E.3.1.4

Logistics

The following recommendations are mainly concerned with the possible content of work instructions and make no claim to be complete. Examples of measures: logistics in the vicinity of the assembly facility Measure / requirement

CG0

CG1

CG2

CG3

cleanliness Cleanliness Cleanzone room room

1.

94

Each user is responsible for handling packaging carefully and correctly

+

+

+

+

Comment

Examples of measures: logistics in the vicinity of the assembly facility Measure / requirement

CG0

CG1

CG2

CG3

Comment


2.

3.

4.

Components and aggregates may only be packed in the permitted packaging means Damaged load carriers and packaging means are to be rejected

+

+

+

+

+

+

+

+

Secondary packaging may not be removed in the assembly area

o

+

+

+

Assess using reference sample E.g. contamination could fall to the ground and subsequently stirred up into the air and displaced. Exception: only with special measures

5.

6.

7.

8.

Components may not be packed / unpacked in the vicinity of the assembly facility

o

+

+

+

SLCs or stackable containers holding single components, units or completed products may not be deposited directly on the floor

+

+

+

+

Used packaging and covers are to be placed in designated areas

o

+

+

+

Once unpacked, components are to be brought immediately into the prescribed assembly or storage area

o

+

+

+

Only permitted in designated areas Instead: use plastic pallets, transport roll carts, lids, etc.

Reduced risk of cross contamination from contaminated packaging means

95

Verification

A requirement for the cleanliness-suitable design and operation of a facility is an appropriate test technique for locating and evaluating particle sources and for qualifying cleanliness-relevant measures . Suitable test techniques and their implementation are described in Chapter G: Assessing cleanliness factors . As soon as the influence of contamination due to processes carried out on a component can be tested and especially particles from assembly processes analyzed directly at the level of the component or inside it, tried and trusted extraction procedures such as those described in VDA 19 can be implemented. One of the test techniques described in this way for the first time is the use of so-called particle traps to collect particles sedimenting from the environment. It is based on the placement of self-adhesive test surfaces of a defined size for a defined period of time. Depending on the task in question, it is possible to ascertain the quantity of particles generated by each process or the general cleanliness level of the environment, which can then be represented by an overall value. To analyze the particle traps, automated microscopes can be utilized in the same way as for counting analysis filters according to VDA 19. The results and information obtained from the test procedures described in Chapter G: Assessing cleanliness factors can be used to:

26

-

Locate critical particle sources.

-

Verify specific cleanliness-relevant optimizations, e.g. to assembly processes.

-

Assess a manufacturing environment to see if it is suitable for clean assembly.

-

Ascertain whether certain factors have an effect on the cleanliness level of components or aggregates.

-

Gain experience from running processes and to use it to plan new facilities.

-

Visualize and document particle sources.


CG0

CG1

CG2

CG3

Comment


9.

Unprotected components may not be stored directly next to transport pathways, doors, rolling doors, windows or skylights

o

+

+

10. If processes are interrupted, load carriers are to be appropriately covered and plastic bags or film inlays closed

-

+

o

1)

o

1)

11. Load carriers may only be opened immediately before removal of components

-

+

o

1)

o

1)

12. Care is to be taken to ensure that components do not become contaminated by soiled packaging

o

+

+

13. Cardboard boxes may not be torn open; they are to be opened at predetermined points using prescribed tools 14. Folded films and foils with contaminated outer surfaces may not be folded inwards again

o

1)

Unless the environmental atmosphere has detrimental influence on product

+

2)

o

-

+

-

+

2)

+

-

2)

+

Unsealed cardboard materials are not permitted

Instead, leave load carriers open, or use new film / foil or fixed covering hood


Table E.4:

96

Examples of rules relevant to logistics in the vicinity of the assembly facility

E.3.1.5

Keeping work areas clean

Examples of cleaning measures Measure / requirement

CG0

CG1

CG2

CG3

cleanliness zone

Cleanliness room

Cleanroom

Comment

1.

Use of compressed air in manual cleaning processes is not permitted

o

+

+

+

2.

Use of wiping cloths and other cleaning materials which may give off fibers and fluff is not permitted

o

+

+

+

3.

Used wiping cloths and cleaning materials are to be disposed of immediately in designated waste containers and not left lying around

o

+

+

+

May be reused; follow regulations.

4.

The following are to be cleaned after use and as required in accordance with work instructions:

+

+

+

+

Description of when / how to be cleaned must be included in work instructtions as well as a definition of the terms “as required” and “if judged necessary” Measure has a more esthetic / psychological meaning than actual function.

Placement areas, workstations, grab containers, transport containers, workpiece carriers, machines, equipment, etc 5.

The floor in the area of the workstation is to be kept clean

+

+

+

+

6.

Due to increased contamination levels, packing areas are to be cleaned more frequently and wet processes used

o

+

+

+

Instead, use suction cleaning systems or vacuum cleaners


Tabelle E.5:

Regulations concerned with keeping work areas clean

97

E.3.2

Accompanying measures and considerations

Right from the start, staff members are to be included in the planning and design of clean areas. To optimize a clean assembly facility from the staff point of view, the following points should be given priority: 1.

Execution of especially cleanliness-critical assembly steps (also including any necessary rework steps); this is a systematic source of error / direct influencing factor

2.

Control of sensitive component surfaces and active removal of any contamination present; this is a direct influencing factor

3.

Risk of displacement of contamination by workers handling clean functional product surfaces; this is a random source of error / indirect influencing factor. In such cases, it may make sense to separate assembly tasks strictly from ancillary activities (mixed tasks).

Wherever possible or as required, the aspect of degree of cleanliness must always be taken into consideration when designing and organizing an assembly facility. In order for cleanliness measures to be transparent to staff, a number of regulations are required, e.g.: 1.

Staff responsible for clean areas

2.

Rights of access to clean areas; entrance only permitted for limited members of staff

3.

Staff instruction and training with regard to cleanliness requirements. Determination of target groups (e.g. management, workers, cleaning staff, maintenance staff, etc.) and content, dates and frequency of training measures.

4.

Briefing about workstation and surrounding area

5.

Course of action if components have been incorrectly packed, supplied in contaminated load carriers or if components are contaminated.

6.

Written work instructions, e.g. regarding:

98

-

Entering and leaving clean areas and bringing goods in / taking them out

-

The use of special clothing (if required) and changing frequency

-

Rules of conduct in the clean area

-

Handling cleanliness-sensitive goods including auxiliary materials (oil, adhesives, sealing compounds, grease, thread lock fluid, etc.)

-

Carrying out especially contamination-critical assembly steps (also including any necessary rework steps)

-

Assessing / verifying the cleanliness of packaging, load carriers, components and aggregates

-

Opening and closing packaging

-

Using windows, doors, gates and / or locks

-

Eating, drinking and storing foods and beverages

-

Waste disposal

-

Conduct during maintenance, repair work especially when production is in progress

E.3.2.1

/

modifications,

Mixed tasks

On the scale of importance of indirect contamination influences and mechanisms, displacement is one of the greatest risks. Mixed tasks carried out by workers are therefore a key point in the risk analysis and avoidance strategy. The degree of contamination risk associated with mixed tasks carried out on sensitive goods must be assessed and analyzed individually. Contamination may be displaced via hands, gloves, clothing or footwear and transferred to functional surfaces and the direct environment when certain assembly tasks are carried out; e.g. 1. Handling contaminated packaging and load carriers (e.g. removing outer or secondary packaging) 2. Handling non-cleaned or contaminated components and tools 3. Mechanical processing (e.g. scarfing a welded joint) 4. Manual assembly tasks in conjunction with oiled components or handling assembly auxiliary fluids 5. Cleaning (e.g. load carriers, work station) 6. Maintenance and repair tasks

99

Remedy (e. g.): -

Plan work sequences carefully in order to avoid mixed tasks with displacement risks

-

Clean hands after carrying out unclean tasks

-

Wear gloves when carrying out unclean tasks and remove used gloves afterwards

-

Wear disposable gloves when executing unclean tasks and remove used gloves afterwards

E.3.2.2

Displacement through contact

This generally applies to workers handling the sensitive functional surfaces of products. The most important point is: it is prohibited to come into contact with potentially contaminated surfaces which are not related to the task at hand / planned work sequence.

Potentially contaminated surfaces:

• Used wiping cloths

Product area:

• Floor / footwear

Worker:

• Outer packaging (e.g. stretch film/ mesh pallet)

• Hands

• Base of contain ers (e.g. load carriers, vibratory feeders)

• Clothing

• Tools / workpiece receivers

• Gloves

• Components • Tools • Auxiliary aids and materials • Work surface

• Operating u tilities (inside) • Work surfaces • Components of l ower cleanliness class • Upper surfaces of covers / hou sings/ storage sh elves

Abb. E.2:

100

Displacement of contamination through contact

Displacement caused by a worker coming into contact with critical surfaces

Example:

Due to the design of the product and the assembly sequence concerned, a worker may have to handle components which, as far as the assembly function is concerned, are not subject to cleanliness requirements. For example, this could be the non-deburred surface of a non-critical gray iron attachment. Here, it could be stated where the component is to be manually held in order to avoid burr detachment. Single-use cloths could be made available in dispensers to enable workers to clean their hands before touching a sensitive component surface (e.g. seal).

Similar examples are found more often in real assembly scenarios than anticipated during planning. In such cases, the greatest potential for a continuous improvement process (often with relatively simple means or measures) is for a skilled motivated employee to think proactively while working. E.3.2.3

The worker as an activatos and remover of particles

This deals with active measures which can be carried out by staff during assembly. For example, each worker is responsible for checking a specific section of a component or aggregate for possible contamination (visual 100 % check). Sequences are to take into account that n. i. O. findings may occur and that rework may be required (removal of component / aggregate from the zone via the lock, or manual particle removal by the worker). Particle removal techniques which can be integrated into the assembly sequence include: Magnetic rods, suction-cleaning, wiping, etc. Examples of work instructions: -

Discard used screws and use new ones.

-

After pushing in jack, clean Point X of aggregate with hand-held vacuum cleaner.

-

Fit drill bit snugly into screw head to tighten or loosen screws.

101

E.3.2.4

Examples of typical contamination risks

Particles can become detached, disperse into the air and settle on unprotected surfaces in the course of many processes. Such processes are therefore not permitted in clean areas during production. Examples of typical contamination risks Process

Possible remedy

Sweeping

Wet-wiping or suctioncleaning

Cleaning, blowing or drying with compressed air or gas

Suction-blowing or encapsulation with defined suction cleaning

Drafts due to opening doors, windows, skylights or gates

Design and use motor-driven gates (roller gates / swing gates) as locks. Install air conditioning. Lockable windows.

Constructional (renovation) measures

Use curtains to protect assembly areas or stop assembly if necessary. Carefully organize relevant areas before commencing construction work. Clean more often and carry out general clean on completion of construction work.

Table E.6:

102

Comment

Dispersion and sedimentation of contamination onto surrounding structures and clothing

Standard material flows and sequences are often disturbed. Construction area and storage spaces for load carriers and goods intermingle. Displacement of contamination via staff and material.

Examples of typical contamination risks (see Table E.1 Relevance of staff with regard to assembly cleanliness; the worker as an activator))

F:

ASSEMBLY EQUIPMENT

F.1

Introduction

Clean components ready for assembly are generally protected against contamination before they are (further) processed. During assembly, components and products are directly exposed to potentially damaging influences from manufacturing processes, assembly equipment, staff and the environment. For the purposes of simplification, in the guideline operating utilities such as automated devices, machines, manual workstations and assembly stations have been grouped together under the term assembly equipment. In order to take the numerous elements and functions of assembly equipment into account, it has been divided into sub-groups such as tools, auxiliary materials, etc. The construction and scope of assembly equipment depend entirely on the process and product in question. For example, as opposed to the spatial assembly environment, the state of knowledge in December 2009 did not enable the criteria and measures presented here concerning assembly equipment to be clearly delineated or classified with regard to costs and benefits. Therefore, the methods described here regarding cleanliness-suitable design and usage of assembly equipment need to be individually assessed and implemented to the best of one’s knowledge. Example:

In one case, by encapsulating a machine, damaging particles from the environment can be effectively kept out and lead to improved results. In another case, particles generated inside a machine are much more critical and cannot escape, leading to high concentrations inside the housing and significantly poorer results.

Especially in assembly processes , a higher number of particles may be generated and emitted in the vicinity of the product. However, if an intermediate or final cleaning step is integrated at a suitable place, the damaging particles - which were introduced or unavoidable in the past can be largely eliminated (for more information, see also corresponding subchapter ). Methods for characterizing the presence of particles on and in assembly equipment are described in Chapter G: Assessing cleanliness factors .

103

F.2

Fundamentals

As far as the aspect of assembly equipment is concerned, a number of contamination risks are intermeshed: 1. Particle generation due to the assembly process itself with possible consequences: a) Displacement of particles to functional product surfaces (example: during screwing processes, particles are generated in the threads and fall onto the functional areas) b) Emission of particles into the process environment with possible sedimentation directly onto functional surfaces : e.g. abrasion from inserting a drill bit or splinters from a hammering tool (e.g. plastic hammer) c) Corresponding risks may also exist if joins are disconnected during work sequences or processes; e.g. removing screws from bearing seats. 2. Release of particles into the process area a) durch Funktionselemente der Einrichtung (Betriebsmitteltechnik). Häufig: mechanischer Abrieb; z. B. Linearantrieb, Elektromotor, Zustell- und Handhabungsmechanik. b) durch Alterung und zunehmenden Verschleiß von Materialien aspects: • materials

Montagestation Assembly station Environment Umgebung

Bauteile Components

Handling Handhabung

Operating utility Betriebsmittelcomponents komponenten and tools

und Werkzeuge

Feeding

Joining processes

systems Zuführtechnik

Fügeprozesse

Staff Personal

• design • maintenance

Product Erzeugnis

• output • attrition • deterioration

MediaMedien / auxiliary aids / Hilfsstoffe

Load carrier / /packaging Ladungsträger Verpackung

• keeping

clean

• integrated

cleaning •

Fig. F.1:

104

…

Assembly equipment – concurrence of multiple influencing factors

3. Entry of particles into the process area due to a) Material feeding technology (e.g. contaminated conveyor or contaminated workpiece carrier), b) Contaminated outer surfaces of components, tools and load carriers, c) Manual staff involvement (e.g. displacement via hands, sleeves, etc.), d) Airborne / sedimenting particles from the environment (e.g. absence of encapsulation or on opening a machine because of malfunction). When designing assembly equipment from the point of view of cleanliness, aims and strategies strive to maintain the cleanliness of •

Functional component surfaces,

•

Auxiliary materials awaiting processing; e.g. sealing compound,

•

Tools and auxiliary materials / assembly aids utilized; e.g. casing for assembling shaft seals,

•

Objects (general) coming into direct contact with functional surfaces; e.g. measuring sensors

•

Objects and surfaces (general) which have to be touched by the worker, e.g. in order to process cleanliness-sensitive components.

Special attention is to be given to processes and machine parts which are per se active sources of contamination in the direct vicinity of sensitive goods. Note:

This especially concerns the risk of contamination falling directly onto objects requiring protection.

With manual workstations, priority must also be given to the consideration of displacement risks by the worker and his influence on particle generation due to the individual way he uses tools or carries out assembly steps.

105

F.3

Design

F.3.1

Measures and recommendations - constructional

F.3.1.1

Fundamental design principles

The fundamental principles describe potential improvements which can be made to manual workstations and also automated assembly devices. -

As few horizontal surfaces as possible

-

Sloped surfaces (e.g. covering surfaces) to prevent objects from being placed or contamination accumulating on them

-

Smooth surfaces without depressions, gaps, etc.

-

Where possible, rounded corners and edges

-

Easy access for cleaning

The following approaches are recommended for dealing with particle sources (e.g. moving, abrading mechanisms): -

Do not install above sensitive surfaces.  The mechanical elements required for the core process (i.e. particle sources) should be located below work pieces. Figuratively speaking, this equates with a so-called overhead assembly , enabling any particles generated to fall in a downward direction and away from the functional area.

-

Use low-abrasion components / materials

-

Encapsulate and / or install suction-cleaning

-

Eliminate from immediate process area; e.g. use extension cables

-

Implement localized clean air technology to keep away small dispersible particles

Note:

If suction-cleaning units or clean airflows are used, ensure that temperatures remain constant (e.g. hardening of adhesives).

106

Fig. F.2:

F.3.1.2

Methods of installing particle-generating devices

Materials and surfaces

For more information, see corresponding section in Chapter C: Environment. F.3.1.3

Basic design

This is the basic construction for holding the technical equipment. It generally consists of a framework or supporting construction, horizontal surfaces such as placement or installation surfaces, a housing, partitioning walls, locks if required, metal fittings such as handles or hinges, lights, etc. Criteria and measures: -

Horizontal surfaces should have an open, unobstructed construction; especially at work and process level  e.g. burr-free perforated sheeting. In this way, particles fall downwards into a trap (e.g. drawer) where they cause no damage, or onto the floor where they can be removed at regular intervals, e.g. large-surface rotary transfer tables designed as spoked wheels.

-

Avoid protruding screw ends and heads to facilitate cleaning 107

-

Avoid the use of through bolt joints below using blind holes

-

Attach metal fittings and hinges to the exterior of machines or beneath critical areas (such fittings are dirt traps, particle sources)

-

Avoid / remove fixtures which are not (no longer) required for processes. As a rule, only objects necessary for the respective process should be present in the assembly equipment

-

Ensure easy access to installed equipment for cleaning purposes

-

Use standardized interfaces to enable the flexible connection of hand suction cleaners; e.g. Venturi suction systems

-

Where possible, fix housings flush to the floor or mount them in such a way so as to enable easy cleaning access beneath assembly equipment

-

Where possible, exhaust air (e.g. from fans, electromotors or pneumatic cylinders and valves) should not be directed towards the interior of equipment or at least towards sensitive surfaces.

-

Locate as many supply lines (cables, pipes, etc.) as possible outside the direct process area.

-

Apply insulation to conduits condensation could develop.

Fig. F.3:

108

 e.g.

and

fix work surfaces from

machine

parts

Example of a transport system with permeable surface

where

F.3.1.3.1 Housing

Housing is often required for safety reasons. It may be made of acrylic glass or grid elements , or flashing. It not only shields equipment from particles in the environmental atmosphere but also prevents particles generated during manufacturing processes from spreading to the surroundings. If there a number of sources of dispersible particles in the environment (e.g. staff clothing), a housing or encapsulation is highly effective at keeping them out. Clean air technology is not necessarily required in such cases. Housing is to be designed to prevent contamination from accumulating in places where there is a risk of it falling into the machine. The use of grid elements it is to be carefully considered because they trap dust and are difficult to clean. Criteria and measures: -

Mount flaps, covers and doors to prevent contamination from falling into equipment when it is opened / closed

-

Openings for heat dissipation should not be situated in the top covers of machines but rather at the upper section of side walls. Alternatively: use facings to against prevent particles from falling into openings.

Note:

Fig. F.4:

For more information, see previous and following chapters Contamination present on covers / housings is to be removed before opening or closing them.

Example of housing

109

Housing can create a localized area with a different cleanliness grade than that of the environment. Examples: encapsulated blow-cleaning station in an assembly room with a higher cleanliness grade, or a rework station designed as a minienvironment (with or without clean air technology) in an uncontrolled workshop. Assembly equipment and clean air technology :

Where required, assembly stations can be designed as independent minienvironments. This does away with the need to design the entire assembly area as a costly environment such as a cleanroom or a cleanliness room. An important element to consider when using localized clean air technology in assembly equipment is the airflow, which specifically removes airborne particles. Ways of locally confining airborne particles: A. Defined encapsulation of machines, conveyors, goods buffers and / 1) or workstations 2)

B. As in A, but with additional use of localized clean air technology 1)

By encapsulating them (e.g. Perspex housing), machines can be shielded from particles contained in the environmental atmosphere. However, dispersible particles generated inside the equipment have a limited range of movement and form higher concentrations. 2)

A forced airflow may be capable of removing airborne particles generated inside the encapsulation (e.g. due to mechanical abrasion). However, an unfavorable airflow may have the opposite effect and transport (more) generated particles towards functional surfaces. Moving elements in dead spaces are to be avoided as particles accumulate in them.

In both cases, components / products require full protection on leaving the minienvironment if the environmental atmosphere contains damaging particles. If encapsulated devices are opened (e.g. due to malfunction, for refitting), particles may be displaced from the uncontrolled environment. When mounting localized suction-cleaning equipment to remove particles (generated) from the area, it must be considered that incoming air may also contain critical particles.

110

F.3.1.3.2 Manual workstations

At manual workstations, assembly tasks (also rework) are carried out by a member of staff. Examples of such tasks include inserting components and applying auxiliary materials right up to carrying out manual / machine-aided assembly processes. By carefully designing the workstation and related work sequences, the worker can avoid making cleanliness errors. There is a huge error potential due the degree of freedom of the worker as an individual (as opposed to an automated machine) as well as his basic motivation and general state of mind at the time. General rules of conduct are dealt with in Chapter E: Staff . Criteria and measures: -

Avoid material transfer and staff movement on the side facing the product / process material supply e.g. from the rear / side of the workstation

-

Design work plans to avoid workers having to carry out mixed tasks which hold a critical displacement risk.

-

Separate workstation clearly from environment

-

Keep workstation cleaning maintenance separate from assembly tasks (displacement risk)

-

Ensure effective lighting; where possible, use diffuse light to prevent dazzle or shadows.  Also

-

helps to identify and recognize particles.

Ensure that the worker does not have to lean over products in order to reach tools and components  establish

defined gripping sequences (without the worker being able to vary them). -

Where required, place tools so that they are always within easy reach without the worker having to lean over.

-

Define sites for putting tools and auxiliary materials down  including a holder for drinks (if permitted)

-

Where possible, hang up tools and auxiliary assembly materials

111

-

Design placement areas and receivers for tools and components with a minimum surface area. The accumulation of particles can be minimized if a design which is open underneath is used.

Fig. F.5:

-

Example of a workpiece receiver / work surface

Do not mount placement surfaces, load carriers or grab containers directly above the work surface. 

This avoids the worker having to reach over the product at regular intervals -

Do not mount fixations for tools directly above products, open load carriers or grab containers

-

Where feasible, mount grab containers and load carriers with sensitive goods above areas where the worker often has to reach over….(see above)

-

Keep small components in near-closed dispensers (not as open bulk goods)  e.g. stack sealing rings in a tubular dispenser.

-

Used closed shelf systems to prevent contamination from accumulating on the bottom shelf

-

Do not mount grab containers, load carriers and dispensers directly beneath the work area; instead, mount them to one side.

-

Install sieve plates in grab containers  this prevents particles from collecting at the bottom because they fall through the sieve.

112

-

Use closed dispensers for liquids  e.g. principle of a bird feeder: only the amount required is dispensed.

-

In order to protect workpieces and surfaces, apply cushioning to hard placement surfaces.  e.g.

rubber mat beneath stainless steel plate

-

Do not use soft work surfaces  e.g. wood or plastic, as particles could collect and the material abrades slightly

-

Do not use cloth covers for chairs; same principle for wooden chairs  instead, use plastic or metal

-

Do not use ribbed anti-slip mats or insulating matting which allow contamination to accumulate  alternatively: gel matting, non-slip footwear

-

If clean air technology is used, the influence of the worker on airflow guidance / as a particle source has to be taken into account

F.3.1.4 Operating utilities

Operating utilities include all components necessary for a process. They may be installed temporarily or permanently and be actively or passively involved. Examples:

Drives, mechanisms such as transport systems and handling technology, feeding equipment, cylinders, robots, conveyors, grippers (vacuum lifting devices), workpiece receivers, lifting tools, double belts, valve terminals. Also energy chains, linear axes, electromotors, etc.

Equipment and facilities functioning mechanically and constantly in operation are active particle sources. Such elements are often in the immediate vicinity of the product, which further increases the risk of contamination. Another critical aspect is the use of lubricants. Particles may accumulate in a lubricant (e.g. grease on the bushing of a tappet) and then be released into the atmosphere in an uncontrolled way. Where possible, avoid exposed linear axes, drives, brackets, belt drives, ball bearings, etc. F.3.1.4.1 Operating media and media supply technology

This includes media and associated supply components required to operate assembly facilities, e.g. electric current, compressed air / vacuum, hydraulic fluids, water and other fluids for heating and cooling, oils, grease 113

for assembly equipment components, gases (e.g. for welding), fireextinguishing agents (fire safety) etc. Supply technology also includes the devices required to use auxiliary materials, functional fluids and test fluids. Criteria and measures: -

Where possible, supply technology should be installed in false ceilings or walls  e.g. also enclosed in cable channels or corrugated piping.

-

Supply technology installed in the process area should have as few horizontal surfaces as possible and be mounted vertically

-

Care is to be taken with processing media (may contain damaging substances such as particles, oil or water)  e.g. use oil-free, dry, filtered compressed air.

-

Exhaust air from pneumatic units, etc., is to be conducted away from the process area by way of hoses, or filters installed.

-

Hoses and cables (compressed air lines, etc.) of moving elements require fixation to avoid abrasion. Use energy chains.

F.3.1.4.2 Auxiliary materials

These are materials which are either required to carry out assembly processes, form a part of the join itself or are a necessary localized basic supply for a functional group, e.g. -

Oils, grease, soap water and other lubricating agents (as joining aids)

-

Oils, grease and other lubricating agents (as basic supply media for the product)

-

Adhesives, sealants and thread locker fluids; liquids / pastes (as joining elements)

-

Solder and welding wire

Auxiliary materials are often in direct contact with functional surfaces. Fluids and corresponding application aids (e.g. brushes) are always to be kept clean. It is not to be forgotten that particles tend to accumulate on moistened surfaces.

114

Care is to be taken where materials are applied manually, as workers may displace particles via their hands or gloves. Examples include the use of cans to dispense oil via or brushes to apply lubricants. The nebulization and displacement of fluids to nearby surfaces causes contamination to accumulate and gives them a dirty appearance. Contact with contaminated surfaces increases the risk of displacement. Such areas are to be cleaned more frequently. Example:

Brushes, sponges, tampons, sprays (fingers  poor remedy), dispensers, greased bags (e.g. for tumbling a quantity of o-rings or greasing in batches), greasing station (component-adapted; e.g. component placed on ring aperture and greased via dispensing valve), oil can, dipping receptacle (e.g. soaping grommets.) receptacles for fluids.

Criteria and measures: -

Use fluids with defined degree of cleanliness

-

Process-integrated filtration of relevant fluid

-

Ensure that exposed fluids are kept clean

-

Keep auxiliary materials and tools for applying fluids clean

-

Avoid contamination of process environment by the fluid

-

Install housing processes

-

Use silicon brushes or dispensers for greasing instead of brushes made of hair (hairs fall out and adhere to the product)

-

Use alternative materials in order to avoid moistening  e.g. dry functional coating on surfaces; instead of oils, use nano composites because they are highly volatile, extremely thin, almost dry and do not attract dirt

-

Where applicable, if only a short-term lubricating film is required, use highly volatile alcohol

/

suction-cleaning

equipment

around

oiling

Note 1:

Non-volatile rinsing agents may cause seals to shift during pressure tests.

Note 2:

Degrees of cleanliness for fluids in accordance with ISO 4406 do not take particle size into account.  Where appropriate, use more suitable specification.

115

F.3.1.4.3 Test fluids and functional liquids Test fluids: This includes substances implemented in function tests, e.g. liquids and gases used in pressure tests. In some cases, the test fluid remains in the unit and serves as a functional fluid, hydraulic fluid in steering gear, for example. Functional liquids (for initial filling): these are required for the subsequent operation of the aggregate; e.g. hydraulic fluid, oils, coolants or fuel.

The degree of cleanliness of such substances is highly important (e.g. liquids, gases). The degree of cleanliness of such media is to be specified because they are in direct contact with the functional area of the aggregate or may remain inside permanently. They are always used in connection with function test benches and filling stations. Criteria and measure:

-

See also previous section

-

Adapter used to inject or remove test fluids must be kept clean

Test and functional fluids are sometimes used to clean the interior of an aggregate (e.g. pressure tests) (see Subchapter 3.1.6: Assembly integrated cleaning ). Note:

The presence of microorganisms in a fluid circuit may lead to altered fluid characteristics and impair the function of the system (examples: bio diesel, zinc pest)

Function test benches also enable the process-integrated monitoring of contamination inside test pieces: -

Intermittent assessment of particulate residues in processing filters

-

Specific use of analysis filters on downstream side of function test benches

F.3.1.4.4 Transport systems, handling systems, feeding and singularization Transport systems: workpieces are moved along the assembly line by a transport system to different stations and storage areas. Example:

116

Variants with or without pallets: roller-driven, belt-driven, self-driving pallets (workpiece carriers), slides, brush conveyors, suspended rails, turntables, lifting stations, beam conveyors, manual transport carts.

C.3.1.7

Doors, gates, locks, entrances, windows

To reduce disturbing influences (e.g. drafts or entry of outside air), the following are recommended: 1. Always keep skylights and windows closed (locks can be put on windows if required) 2. Only open and close doors as required (not to air rooms) 3. Fix automatic closing systems to doors / gates 4. Install air curtains at doors and / or gates 5. Fit locking systems to prevent doors / gates from being opened at the same time 6. Install gates and doors, for example, as double gates / doors (lock function C.3.1.8

Pathways and storage areas

The following are recommended: 1. Ensure adequate distances between open assembly processes / open carriers and critical or uncontrolled zones (e.g. cutting processes) as well as windows, doors, gates and pathways. 2. If there is a risk of contamination from the environment, sensitive goods are to be wrapped up, covered or sealed to protect them, especially if routine processing is interrupted. 3. Transport pathways and stations with high particle levels are to be cleaned at frequent intervals 4. Transport tasks – especially involving forklift vehicles – are to be kept to a minimum. C.3.1.9

Supply technology / installations

Where possible, supply technology should be installed in false ceilings and walls (suspended or supported ceilings). Where feasible, supply technology installed inside rooms should have as few horizontal surfaces as possible and be mounted vertically. Ceiling lights are to be designed so that no dust may settle on them (e.g. recessed behind glass in the ceiling or as sealed mounted elements). 48

As some transport systems have a large (load) surface, the risk of contamination is high. The systems also connect different stations and thus represent a displacement risk. Handling systems: used to move tools or components inside a station, e.g. robots, linear drives or swivel units. They are generally only in use at one assembly station / workstation. For more information, see also Feeding and singularization devices.

Due to the load transmission, facilities for large or heavy goods are generally suspended above the work area. Here there is a risk of abraded material falling onto the product. Examples:

Robots, cylinders (pneumatic / hydraulic / electrical), NC axes, hand-guided balancers (torque-jacked and non-torque jacked to relieve weight), linear arms, sleds, swivel units, guide lines, energy chains.

Feed and singularization: grab containers / grab trays (placement areas, receivers), manual / automated singularization of bulk goods, vibratory conveyors, stepped conveyors, etc. Criteria and measures: -

Care is to be taken with regard to particle generation when selecting drive systems.

-

Transport systems are to be checked at regular intervals in order to recognize wear promptly and carry out repairs if necessary.

-

Small permeable surfaces rather than large closed ones

-

Wherever possible, drives, linear axes, cylinders, energy chains and other moveable equipment should be installed beneath critical areas.

-

Turnaround points (e.g. of conveyors) may not be placed above the product

-

Systems for singularizing and feeding small components (e.g. vibratory spiral conveyors): suction nest installed for separated parts or openings in the guide rail to enable loose particles to fall into a collecting receptacle.

117

F.3.1.4.5 Workpiece carriers and workpiece receivers

Components are assembled on the workpiece carrier. In some cases, the workpiece carrier also functions as a means of transport. Where components are identical, they are transported by several carriers from one work station to the next. Sometimes only one workpiece carrier is used. In this case, the component to be assembled is placed on the workpiece carrier, processed there and then lifted off again. There is always a component-specific workpiece receiver on the carrier, e.g. clamping jaws, aligning pins, negative mold / nest, gravity, arrester, swivel unit. Criteria and measures: -

During downtimes, remove workpiece carrier from conveyor or stop conveyor to prevent abrasion between conveyor and workpiece / workpiece carrier

-

Remove burrs at gripping and placement edges of workpieces. Radii are preferred on grippers or workpiece receivers rather than phases.

-

Minimize contact between workpiece carrier and product (care: high point load on product).

F.3.1.4.6 Tools and grippers

Tools are elementary constituents of assembly equipment and assembly processes. It is not possible to make a distinguishable difference between the terms tool and assembly aid. The most important differentiation is made between hand-operated and (semi-) automated tools. Typical handoperated tools include hammers, screwdrivers and brushes for applying fluids. Grippers are generally used to hold components. Example 1:

Adapters (e.g. connection in leak-testing equipment); adapter and contact tools, calipers, measuring tools, aligning and centering tools, molding tools, crimping tools (e.g. pliers for fitting hoses), marking tools (printers, stamps, etc.)

Example 2:

Screw bits, assembly bushings (o-ring / pistons), cutting pliers, peening tools, extrusion dies, bending punches, hammers, cutting dies, wrench sockets, jaw wrenches, riveting tools, wobbling tools, bonding, welding and soldering tools, spindle screw drivers

118

Grippers: vacuum grippers, magnets, form closures (hooks), force closures

Tools are to be kept in good order and replaced promptly if defective. With hand-operated tools , special care is to be taken to ensure the correct use of the right tools. Criteria and measures: -

Suction cleaning integrated into tools via boreholes (e.g. bending punch)

-

No not use sponges to clean tools (particle collectors!)

-

Especially with manual assembly: ensure that joining aids, molding tools or centering aids are provided and utilized  e.g. to avoid damage to constraining contours

-

Beating components  use pressing processes instead

-

Hammers  use guided striking tools instead

-

Hammer with plastic head instead

 plastic

splinters easily. Use brass

-

Tools with wooden handles splinters easily)

 replace

with metal or plastic (wood

-

Automated screw feed (shooting)  holding device for single screws generates abrasion. Alternatively: position screws manually

119

F.3.1.5

Assembly processes

Table F.1 lists typical assembly processes. Assemblyprocess

Screwing

Particle generation

- On locating the screw thread

- Abrasion on inserting screw driver

Characteristic particles

- Exit burrs - Nicks - Coating swarf - Swarf from tools

- Coatings and burrs

detach if screws are shot using compressed air -

- Abrasion /

Particles from screw head Burrs from screw threads

- Weld / solder spatters at start / finish

- Slag, scale

screws

- Thread gauges act like cutting tools

- Damage to threads - Incorrect tension due to increased abrasion; consequence  connections may loosen into components during function tests

- Turbulent welding / - Spherical particles soldering baths cause sputter to land on equipment and components

- Particles from nuts and

- Swarf may be rinsed

detachment of burrs

Welding / soldering

Effects of particles

(welding sputter / solder beads)

- Flake-shaped particles - Flakes of coating - Smoke and soot particles

- Free-flying weld and solder sputter falls into cavities and undercuttings

- Slag, scale falls into cavities

- Leaks

- Plastic particles

- Sedimenting smoke / smoke residue Pressing / crushing / dilating

- Abrasion / detachment of coatings

- Abrasion due to relative movement between tools and components

120

- Pieces of coating -

Generally flakeshaped

- Function of component impaired by jamming

- Impressed particles may detach

Assemblyprocess

Drifting / crimping

Particle generation



- Abrasion on placing - Abrasion / detachment - Burrs may penetrate components in devices

- Chips detach if components are not centered

of burrs

into functional area

- Sickle-shaped chips - Flakes of coatings from tools and components

- Abrasion of tools, components and receivers Calking

- Abrasion from clamping devices

- Abrasion due to deformation or reshaping

- Swarf - Burrs - Chips - Nicks in material

- Burrs, chips, swarf may get into component

- Leaks - Damage to sealing elements

- Detachment of burrs, pieces flake off cast surfaces, small nicks in materials Inserting / sliding in / on, pushing in

- Abrasion /

- Swarf, burrs, particles - Particles between

fragments of components and / or joining components

Chips

- Abrasion from

- Detached particles

centering tools

on work surfaces Fitting / shrinking

Table. F.1:

- Abrasion of tools and receivers

components prevent exact component positioning

- Incorrect fit - Leaks

- Abrasion, swarf, burrs burrs - Component does not - Loose burrs

reach final position

- Jamming

Characterization Characterizat ion of assembly processes

Assembly processes and dismantling steps may generate particles of a critical size and present a much higher risk than contamination from the environmental atmosphere. First of all, it is recommended that optimization measures for the assembly equipment - especially assembly process - are examined with regard to possible contamination risks in order to take any necessary countermeasures. Especially expert planners and experienced assembly technicians are required for this. 121

The relevant critical assembly steps are localized using FMEA or potential analysis and successively detailed during planning. It may be helpful to observe or analyze similar applications in an existing assembly equipment. Objective assessment aids include conventional cleanliness tests and the use of particle traps (see Chapter G: Determination of cleanliness impacts). For reasons of access or in order to exclude atypical dismantling influences, both techniques may need to be carried out on realistic joining models of the product. Computer tomography may be of use to inspect interior functional areas without causing any damage. F.3.1.6 Assembly-integrated cleaning

Assembly-integrated cleaning is implemented to remove particles as they are being generated. Particles may be generated during assembly processes or when handling / separating components. The particles concerned are often only loosely attached to components and can therefore be effectively removed using a simple cleaning procedure. Thus, assembly-integrated cleaning serves principally to clean components or aggregates directly. Cleaning steps can also be integrated into assembly equipment with the aim of keeping facility components clean at all times, e.g. cleaning workpiece carriers, transport conveyors or grippers. This also aims to reduce the displacement of particles from one piece of assembly equipment to another. Assembly-integrated cleaning is a series process and is generally dry – in contrast to conventional component cleaning, which includes the removal of auxiliary materials such as cooling lubricants from mechanical processing steps. As a result, liquid-based cleaning methods are generally implemented in the latter case. c ase. Applications of assembly-integrated cleaning: cleaning: 1. To remove assembly particles from the product immediately after they have been generated 2. For the final cleaning of units / functional systems, systems, e.g. in function test benches 3. To keep facility components clean (e.g. transport conveyors) in order to prevent displacement

122

4. To remove particles emitted recontamination

during processing to prevent

The procedures considered in the guideline also include manual cleaning methods. F.3.1.6.1 Area of application

Assembly-integrated cleaning is the active removal of contamination at process and product level. In the context of this guideline, this primarily means the removal of critical particles . Simple solutions are preferred and are characterized below: •

Adequate cleaning effect / process-reliable

•

On-site implementation, where possible without removal of objects to be cleaned from the actual flow or sequence

•

Where possible, no additional handling, such as repositioning or commissioning (separation or lot-forming) or buffering

•

Where possible, without increasing cycle times

•

No residues of cleaning media or fluids left on the object which could impair end-functions. This is one reason why dry processes are generally implemented.

•

Where possible, (simple) automated processes (e.g. for reasons of reproducibility)

Note:

The (generally manual) cleaning steps implemented to keep workstations, machines, spaces, etc. clean do not form part of assembly-integrated cleaning and are dealt with in later chapters concerned with maintaining cleanliness. Conventional, assembly-near component cleaning technology is also excluded: e.g. bringing bought or in-house produced components into the assembly area via a component-cleaning plant.

The main focus is on the reliable removal of critical contamination . The effectiveness of a planned cleaning process must first be verified through practical tests. This is especially the case if the critical contamination is to be removed from functionally-relevant surfaces directly . If the adequate removal of harmful particles cannot be guaranteed, other measures need to be taken. They may be concerned, for example, with steps to prevent critical joining particles from being generated during an assembly process, or with proving the need to implement more effective (possibly more complex) cleaning measures.

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Application

1. End-product / unit

2. Single component / unit

Component

Process Step

Cleaning Step

Heat exchanger

Pressure test

Internal rinsing with gas

Gear box

End-function tests

Internal rinsing with hydraulic oil

Hydraulic line

After screwing in sensor Internal rinsing with gas

Screw

After singularization

Suction nest

ABS valve

Bevor impression

Suction nest

Crack con rod

After speration

Separating area: suction cleaning or dry ice snow

Housing beneath thread pitch

After loosening screw

Suction cleaning / tape-lift / magnetic probe

Sealing surface of housing

Before application of sealing fluid

a) Brush strip combined with suction cleaning or b) Dry ice snow or c) Atmospheric pressure plasma

3. Assembly process

4. Operating utilities technology

Table. F2:

124

Wobbling tool

During wobbling process Localized suction cleaning

Oiling station

Continuous

Process extraction

Workpiece mount

After calking

Localized suction cleaning

Filter mesh

During confection and pleating

Process extraction / possibly localized clean air technology

Woven hose for heat insulation

On pulling up onto line section


Conveyor belt

Continuous

Suction strip, possible combined with brush or magnetic strip

Workpiece carrier

Immediately after use / before loading

Suction cleaning / wet cleaning / dry ice snow

Tray or SLC


Wiping with damp cloth / suction cleaning / wet cleaning / dry ice snow

Examples of various applications of assembly-integrated cleaning

Integrated cleaning steps are not only associated with components or the product but are also used to prevent direct and indirect recontamination in the vicinity of the product. Examples of different integrated cleaning applications are listed in Table F2. In a planning phase, the respective points in the process sequence and the cleaning alternatives expected to be suitable are narrowed down using FMEA or potential analysis and successively detailed. Here, it may be helpful to observe or analyze similar applications in an existing assembly equipment. Case 1 and 2: Removing recontamination:

Component or product surfaces are specifically treated in order to remove recontamination occurring, for example, during assembly and assembly processes (cleaning immediately after completed assembly step). This also includes the treatment of single components / smaller units, in order to remove particles, e.g. generated during singularization in a vibratory feeder, sedimenting out of the environment or occurring through transport (cleaning immediately before an assembly step). Case 3 and 4: Preventing recontamination:

In these cases, integrated cleaning is implemented to remove contamination in the product area in order to prevent it from spreading and to reduce the risk of it being transferred to the product. Contamination is removed as near as possible to its origin or point of emission (generally via suction). For further information about cleaning, especially with regard to containers (see Chapter D: Logistics ). Note:

See annex for example of a comparison of alternatives for cleaning con rods.

F.3.1.6.2 Characterizing selected cleaning procedures

As far as the requirements or characteristics mentioned are concerned, the spectrum of eligible cleaning procedures is infinite (see Table F3 for examples). The cleaning effect is mainly based on the mechanical elimination of particles, often combined with their defined removal using one or more flowing liquids. Purely mechanical cleaning effects are especially dependent upon the degree particles are bound to the surface (e.g. loose or caked on). 125

Wherever possible, cleaning steps should be carried out during or immediately after the generation of critical particles in order to avoid further displacement or intensive surface bonding, e.g. due to assembly auxiliary materials condensing or drying (e.g. process-related oil film on a workpiece carrier). Note:

Despite considering the optimum interaction of temperature, time and mechanical and chemical effects [Sinner’s circle], most of the cleaning procedures listed are less effective in removing filmy residues (e.g. oil mist). The cleaning effect with regard to particles is good but limited when compared with optimized conventional wet cleaning. This is especially the case with smaller particles because these have a relatively high surface retention force and low detachment force in the surface boundary layer of a flowing liquid.

Caution:

The list in Table F3 is only to be considered as a rough guideline with regard to assessing cleaning effects, especially as far as oil films are concerned (type of fluid / vapor pressure).

Selection of assembly-integrated cleaning procedures: (comparison made based on an easily accessible s urface and particles sized 50 µm and upwards).

Legend: + = high; o = average ; - = low; ? = not known

Relative cleaning effect Procedure

1. Suction 1) cleaning 2. Blowing

1)

3. Internal rinsing with

Cleaning factor Caked Loose Film of particles particles oil mist

Comment

Force of flow

Electrostatic charging possible

126

o

-

Force of flow

Line of sight process, o

+

o

-

+

-

-

o

-

Force of flow

pressurized 1) gas 4. Internal rinsing with negative pressure 1) gas

-

Force of flow





5. Internal rinsing with fluid

1)

6. Brushing


Comment

Force of flow / time / chemical / + (temperature)

Depending on rinsing medium and later use of component, costly internal drying may be required

+

+

Mechanics

Line of sight procedure +

7. Dry ice snow Impulse / temperature / chemical / time

+

-

Electrostatic charging possible. Line of sight procedure,

+

+

+

Electrostatic charging possible, Also for caked films.

8. Vibration with Mechanics / 1) suction force of flow cleaning

-

+/o

-

9. Atmospheric Chemical / time pressure plasma

Electrostatic charging possible Line of sight procedure (in some cases),

-

-

o/+

Cleaning effect depends on chemical composition of film Also for caked films.

10. Damp 1) wiping 11. Tapelift

Mechanics / (chemical) 1)

+

+

+

Adhesion

Low-fluff cloth Line of sight procedure,

+

+

-

Possible residue of adhesive material.

127




12. Magnet

1)

13. Demagneti1) sization


Comment

Field strength

Line of sight procedure,

Field strength

?

?

-

?

?

-

Only works for ferromagnetic particles, Works only for ferromagnetic materials

1)

The cleaning effect is not generally improved by extending the cleaning time of a procedure (without chemical active component). Particles are either detached immediately or not at all. With flow-based procedures, experience has shown that the cleaning effect regarding particles can be increased using a pulsed flow (abrupt, large alterations in velocity). However, with gases this has a weakening effect due to compressibility. Line of sight procedure means that the procedure has a limited scope and the surface concerned must therefore be hit directly . The cleaning probe and object to be cleaned must be positioned / moved towards one another in a defined way ( scanning the surface) if larger surface areas require treatment.

Table. F3:

List of eligible integrable cleaning procedures

Caution:

When selecting a procedure, the possible loss of corrosion protection must be taken into consideration. Consider also the chemical compatibility of the component material with the respective cleaning agent and possible attack on materials through mechanical cleaning forces.

Note:

Electrostatic charging may occur if ionization equipment is used. Earth if required (additionally / only).

When implementing a procedure, ensure that detached / emitted particles are removed carefully in order to prevent cleaned surfaces or the environment from becoming (re-)contaminated. The respective cleaning media must have the required level of cleanliness (blank value). With gases and fluids, this can be proved by filtration (preferably directly at the point of use).

128

With solid cleaning media such as brushes or cloths, the fact that these materials are a potential source of particles must be taken into account; especially when used for longer periods (wear). The repeated use of wiping materials is not recommended because as “particle collectors” they will emit the particles they hold at one time or another (displacement risk!) 1. Suction cleaning: Suction cleaning is the most common procedure implemented and is purely mechanical. In physics, a maximum pressure difference of 1 bar can be used as a potential to generate a flow, although the velocity of flow at the level of the object itself is limited. Methods for generating negative pressure include venturi nozzles operated by compressed air, central process vacuum lines with an air chamber, simple electrically-operated industrial vacuum cleaners or powerful lateral channel blowers. Fields of application range from process suction-cleaning, the capture of larger quantities of air with relatively low flow velocities, right up to suction cleaning in contour-adapted workpiece receivers with relatively high localized flow velocities. The higher the average flow velocity, the better larger (heavy / compact) particles can be detached and removed by the air flow. To process larger areas efficiently, negative pressure sources with a higher capacity may be required. In order to achieve high flow velocities on object surfaces, workpiece receivers should be as closed and contour-adapted as possible. It is essential to achieve a relative optimum between minimum gap width and increased flow resistance. By carefully combining gap widths and openings for the subsequent flow of air, localized areas with an increased flow velocity and thus an increased localized cleaning effect can be created. Note:

The subsequent flow of air may contain critical contamination.

When handling hand-operated probes / vacuum cleaners, the risk of damaging cleaning surfaces and the possibility of generating abrasion particles must be taken into account.

129

2. Blowing: With blowing processes, solely the mechanical cleaning factor of the Sinner circle is utilized. Higher pressures can be used than with suction cleaning and thus greater velocities and cleaning forces attained. Due to expansion, the flow impulse decreases much faster as the distance from the nozzle increases than with liquids. When determining cleaning parameters, static pressure at the level of the cleaning probe is not important but rather the volume flow resulting from the geometry and size of the nozzle used. Together with the distance between the probe and the cleaning surface, this determines the volume flow per component surface and thus the impulse acting on the contamination. In order to prevent the uncontrolled spread of detached contamination, the resulting volume of air must be effectively contained by installing both a housing and process extraction. Cleaning components in blowing / suction cleaning facilities: Volume flow, flow velocity and thus also cleaning forces can be increased significantly in component-adapted suction cleaning systems if compressed air is used additionally. To ensure that no air escapes into the environment, the suction system must be adapted to the shape of the component in order to be hermetically sealed to the outside. With exposed suction cleaning chambers, a high-capacity negative pressure source must be installed to continuously collect the volume flow produced. Alternatively, the flow of compressed air can be pulsed in carefully-calculated intervals. When removing particles from surfaces, the effective impulse of the respective flow velocity is generally more important than the cleaning time. 3. Internal rinsing with pressurized gas: In some cases, this application can be combined with existing pressure and function test benches. The exhaust air charged with contamination can be processed using filters and precipitators, making its removal via a separate process exhaust air line obsolete. Filters can be implemented to specifically remove particles from the inflowing process media (air / gas).

130

4. Internal rinsing with negative pressure gas: In some cases, this application can be combined with existing pressure and function test benches. Filters can be implemented to specifically remove particles from the inflowing process media (air / gas). 5. Internal rinsing with a liquid: Both positive and negative pressure variations are used. By wetting the internal surface, the duration of the process and the chemicals used enhance the mechanical cleaning effect. The higher the flow velocity, the better particles can be detached and removed. Note:

When using this technique for interim cleaning, liquid may be displaced. In some cases, subsequent vacuum filling may no longer be practicable due to outgassing.

Filters can be implemented to specifically remove particles from the inflowing cleaning liquid. In some cases, the cleaning process can be implemented in combination with function test benches and filling stations. 6. Brushing: Brushing is a mechanical procedure. Application methods range from simple manual cleaning using a brush to automated brushing stations. Here again, it is important that particles are not only detached from the object but also efficiently removed. As a rule, the process area or brush is suction-cleaned. In some typical brushing stations, small quantities of liquid are applied. This makes the process gentler on the surfaces to be cleaned, improves particle detachment and prevents electrostatic charging. 7. Dry ice snow: This cleaning technique is based on the use of accelerated CO2 crystals made from liquid carbon dioxide and applied via a special nozzle. This integrable procedure is the most efficient cleaning technique (especially as far as micro particles are concerned). In contrast to a station which uses compressed air, for example, this technique demands a more complex plant technology (e.g. localized supply via gas cylinders). The cleaning medium volatizes spontaneously and leaves no residue (suction required). Due to the

131

way in which the gas is manufactured, the CO2 balance is environmentally neutral. To prevent the uncontrolled spread of detached contamination, the process area needs to be enclosed and suction cleaned (also to remove the carbon dioxide gas).

8. Wet wiping: Wetting improves the cleaning effect and ability of a (low-fluff!) cloth to hold particulate contamination and also makes the process gentler on the surfaces to be treated. Where required, cleaning agents can be selected to enable filmy contamination also to be removed (precipitation of oil mist, etc.). Example:

mixture of isopropanol / water (3:2)

To wet the cloth, simple dispensers ( pump sprays) or laboratory spray / wash bottles can be utilized. To ensure that liquids remain clean, the use of open receptacles to hold the liquids is not permitted. Gloves are to be worn when wet-cleaning. This is for reasons of safety rather than cleanliness (e.g. drying out of skin / allergies). Cleaning liquids should evaporate rapidly and not contain any substances which could leave dry residues on the cleaned surfaces. Fast drying also reduces the risk of any possible recontamination adhering strongly to surfaces on drying. If necessary, the workstation must be adequately ventilated (humidity, vapors from solvents, etc.). In coating technology, a so-called tack cloth is sometimes used to remove dust. As it is a prefabricated wiping agent, it does not need to be moistened before use. In general, a wide range of disposable wet wipes are available on the market; these need to be assessed individually for suitability. This also applies for dry anti-static cloths. When moistened, cotton swabs, available in numerous sizes, shapes and materials, may also be suitable for cleaning small apertures, corners and edges. All types of wiping agents are for single use only and are to be disposed of appropriately directly at the place of use.

132

9. Atmospheric pressure plasma: As explained earlier, only relatively simple applications of atmospheric pressure plasmas, which can be integrated inline and implemented in the environmental atmosphere, are feasible for use. In principle, plasma technology is not intended or suitable for removing macroscopic or anorganic particles. It is mainly implemented to remove filmy organic substances and to enhance the bonding properties of surfaces. Variations also exist which are combined with pressurized gas and therefore aid the removal of particles. 10. Vibration (with suction): Here, the object, component or relatively simple aggregate is subjected to mechanical oscillation. Particles and liquids are detached by inertia. The cleaning effect is improved on combining with suction-cleaning / blowing. To be optimally effective, the workpiece receiver / cleaning equipment should be adapted the object concerned, e.g. to contours and mass. 11. Tapelift: a) Adhesive films coated with a layer of glue or gel are used to lift off particles for analysis purposes or for localized cleaning. In contrast to wiping, the tape is applied to the surface statically and not moved over it. One application has rotatable wheels which work in a similar way to brushes for cleaning clothes in the home. Diverse tests carried out at the Fraunhofer IPA have shown that different tape materials are better suited for removing particles of a specific size. Among other things, this depends on the adhesive coating, the flexibility of the tape and the roughness of the surface to be cleaned. If high particle and surface structures are present on surfaces, this limits the ability of the tape to remove smaller particles. It may be possible to remove a greater number of small particles by repeated the process with new tape. In order to obtain reproducible results, the most important parameter is the force with which the tape is applied to the surface (force per surface area). It therefore makes sense to install Tapelift systems with an adjustable force of application; e.g. in the form of a spring mechanism with an arrester. The duration of contact with the surface is less important. 133

An additional benefit of Tapelift is that the tape can be used to analyze the particles present on it. b) Cleaning mastic: The plastic mass is used to remove particles in precision engineering and electronics. The advantage of this material is that threedimensional or complex structures (especially edges and corners) can be cleaned relatively effectively. The mass is also utilized to remove particles from hands and gloves . It can be used for longer periods of time because the particles removed remain in the mass (caution: greases and oils accumulate successively). 12. Magnet: This type of cleaning probe is only capable of removing ferromagnetic particles and represents an elective form of Tapelifting. With this technique, no mechanical contact with the cleaning surface is required. The collected particles are removed from permanent magnets using brushes, for example (but not in the clean area!) or by wet wiping. Alternatively, tape is applied which holds the collected particles when lifted off. With electromagnets, the particles collected are also removed by switching off the power supply required to generate the magnetic effect. Caution:

undesired magnetization of the cleaned object may occur.

13. Demagnetization: Through demagnetization, the bonding force of particles to metallic surface materials is neutralized. As with component cleanliness inspection (see VDA 19), this may be a necessary or sensible measure to support a subsequent cleaning process. Caution:

loss of desired magnetic properties may occur.

For further information regarding magnetism, see annex.

134

Mesh pallets, coated steel containers, metal pallets and frames: coated steel containers may only be brought into the clean assembly area (CG1) if there is no risk of transferring critical particles to the cleanliness zone. The following measures are to be enforced to prevent the cleanliness zone from becoming contaminated: -

No obviously damaged or soiled mesh pallets may be brought in

-

Boards / molds (so-called saucers) are to be placed underneath mesh pallets to collect particles from the underside; these must be cleaned at regular intervals.

-

Containers may not be brought right up to the assembly line but rather only as far as the relevant zone boundary where components are transferred to roll carts.

-

The same member of personnel may not unpack mesh pallets, take out components and carry out assembly tasks.

Coated steel containers / mesh pallets are not permitted in CG2 and CG3 zones. Uncoated metal frames (e.g. uprights for positioning components in cleaning systems) may be brought into all zones provided they are appropriately clean, e.g. made of stainless steel, no areas of rust or signs of damage. Wooden LLCs (Large Load Carrier) (e.g. overseas transport crates) and wooden pallets: transport crates made of wood may not be used in assembly areas which are subject to cleanliness requirements. Wooden pallets are to be handled in the same way as mesh pallets. Plastic LLCs (e.g. collapsible LLC with integrated pallet) and plastic pallets: LLCs made of plastic may be brought into the cleanliness zone (CG1) if there is no risk of displacing critical particles in the cleanliness zone. These containers require the same measures as mesh pallets.

Only plastic LLCs from an internal loop system may be brought into a cleanliness room (CG2). They must also be covered in secondary packaging during transport outside the clean area (e.g. stretch film). Plastic LLCs are not permitted in cleanrooms (CG3). Only clean plastic pallets may only be brought into CG1 assembly areas. If used in cleanliness rooms and cleanrooms (CG2 and CG3), they may only originate from the internal loop system. 67

14. Other: a) Repositioning / shaking: Due to the force of gravity, larger particles fall off simply by rotating a contaminated component or inverting it. The particles are collected in a tray and disposed of periodically. This method may be suitable for circulating workpiece carriers, for example. Particle detachment can be aided through shaking (e.g. via a vibrating mechanism) or striking the object at non-critical / appropriate sites. Caution: risk of damage and generation of additional particles! b) Ionization: A range of ionic sources can be utilized to prevent static charging, also as a probate means. Ionization eliminates the electrostatic bond between organic fibers / synthetic particles and the product surface. The efficiency of the cleaning procedure requires individual assessment. An objective way of evaluating cleaning success is a before / after comparison of test lots using conventional cleanliness inspection methods (see example in annex and also Chapter G: Assessing cleanliness factors)

135

F.3.2

Measures and recommendations - operative

F.3.2.1

Accompanying / supplementary measures

Requirements and measures regarding the cleanliness of assembly equipment are to be taken into account in the planning phase and fixed with the operating utilities manufacturer as part of the specifications. In order to reduce the risk of contamination during production and packaging, operating utilities are to be carefully planned and designed to ensure that there are no sources of contamination in the later production line. Such sources are especially difficult to eliminate once the plant is in operation. Care is to be taken during planning to ensure that measures are compatible with other rules and regulations (e.g. accident prevention, fire control and property protection). Wherever possible or required, the aspect of cleanliness is to be included in the design and organization of assembly operations. The following points are also to be considered with regard to cleanliness: a) As early as possible during realization of the assembly equipment: o

o

o

o

136

Select joining types contamination risks

and

techniques

with

reduced

Design joining partners with a view to minimizing particle generation or controlling the particles generated (e.g. dimensional accuracy and tolerances, coating systems) Take into account the characteristics of materials as well as the surfaces of joining partners and tools with regard to particle generation Design joining parameters with regard to minimizing particle generation or controlling the particles generated

b) Integrate assembly equipment into the concept of cleanliness grades. Design operating utilities alignment with the requirements of the environment into which it is to be integrated. This means, for example, protecting the environment against contamination from an operating utility and / or vice versa. Possible implementation of (localized) clean air technology to minimize airborne particles from the environment or

from processes; e.g. in the fabrication of filter materials (air filters, oil filters, etc), which may give off significant quantities of particles in some cases. c) Defined (and measurable) cleanliness levels of process and auxiliary media, e.g. lubricants. F.3.2.2

Start up

Requirements of the cleanliness of assembly equipment before it is put into operation are listed in the performance specifications. Before start up, ensure that all equipment has been cleaned and appears clean on visual inspection. This includes particles which have been generated during manufacture of the assembly equipment and also contamination and particles which have accumulated during transport and emitted on installation or fitting. Defined cleaning procedures are carried out and verified in the following areas: -

Contact sites with workpieces (receivers, workpiece carriers, etc.)

-

Tools

-

Areas above workpieces

The necessary level of cleanliness for this area is determined according to the cleanliness specification of the workpiece. Note:

When operating machines or machine components, abrasion may occur and cause particles to enter constantly into the machine or onto workpieces. Especially in the start-up phase, due to the behavior of machine components during running-in, the quantity of particles generated may be higher and make later cleaning necessary.

137

n o i t a r e n e g e l c i t r a p running-in phase

constant generation of abrasion, etc. due to machine use contamination

operating time Fig. F.6:

Particle generation in relation to length of use If aggregates are filled with fluids during assembly or for test purposes, before they are put into service ensure that (unfiltered) lines are cleaned / rinsed if there is a risk of particle entry.

Note:

Manufacturing ramp-up phase / approval phase / learning phase

After start up, particle generation and particle entry associated with the assembly equipment need to be characterized and optimized and responsibilities determined (planner / operator): -

-

138

Analysis: Where do critical particles originate?

◦

In processes

◦

From equipment

◦

From the environment

Optimization / countermeasures:

◦

Improvements made by suppliers

◦

Optimization of processes, addition of integrated cleaning steps or targeted removal of particles from assembly (e.g. by suction cleaning)

◦

Cleaning plans drawn up by technicians, workers, quality control, planners and / or maintenance. Cleaning plans are also to be incorporated in maintenance plans.

F.3.2.3

Operation

The operator is responsible for the cleanliness of the assembly equipment when it is in operation. However, these responsibilities may be delegated, for example, to maintenance staff, workers, etc. It is imperative that cleaning plans are adhered to and documented during operation of the assembly equipment. Cleaning plans may require optimization. Note:

F.3.2.4

Parallel to operation, cleanliness analyses need to be carried out (monitoring) on equipment, workpieces and / or end-products (depending upon requirements).

Care (cleanliness maintenance)

The following points need to be taken into consideration when cleaning equipment and assembly workstations, irrespective of when cleaning procedures are carried out, e.g. before start up, during operation or after maintenance: -

Only suitable and approved cleaning agents may be used (e.g. fluff-free cloths and cleaning agents compatible with materials)

-

To depict cleaning sites and tasks, cleaning and maintenance plans can be supplemented by viewing catalogues.

-

If visual contamination is generated during operation, maintenance or fitting / installation tasks, it is to be removed by the worker, maintenance staff or fitter who caused it as soon as the work has been completed (polluter principle). These responsibilities may be delegated to other groups of people provided it is appropriately fixed and documented (maintenance or cleaning plan). An FMEA can be carried out to determine where non-visual contamination such as critical micro particles is generated, and additional cleaning measures implemented if required.

F.3.2.5

Maintenance / repair

Maintenance staff is to be sensitized and trained with regard to technical cleanliness. Non-operational staff needs to be instructed accordingly.

139

The aspect of cleanliness is to be incorporated into the maintenance plan and include all relevant persons (e.g. planners). It may encompass the following points: -

Contamination sites generally inaccessible during normal operation need to be cleaned when maintenance work is carried out (e.g. when opening machines or removing covers).

-

Replacement parts are to be cleaned before installation.

-

Only clean tools may be provided and used.

-

Particle abrasion during maintenance work is to be avoided. If this is not possible, for example when separating or machining processes are carried out (abrasive cutting, boring, etc.), such tasks require authorization and appropriate safety measures (covers, extraction, etc.).

-

During maintenance work, care is to be taken to ensure that components / workpieces do not become contaminated. The relevant components are to be removed from the facility or protected against contamination if this is not possible (loss of data in the control system). In some cases, specific components may have to be removed, cleaned and reintroduced or alternatively scrapped if cleaning is not possible.

-

Each maintenance and repair measure is to be documented (traceability.

Note:

Preventative maintenance: if too much contamination is generated, it may be necessary to replace machine components even if they are still functional (increased particle abrasion may occur before a component becomes defective).

F.3.2.6

Installation / (re)fitting

In the same way as for the rules of conduct for maintenance staff, fitters or workers are to be sensitized and instructed about technical cleanliness. Installation instructions are to be observed. The aspect of cleanliness is to be incorporated into installation instructions (drawn up by machine manufacturer and / or planner). After fitting tasks, especially tools, receivers and the direct surroundings need to be cleaned.

140

F.3.2.7

Process approval / clearance for operation

After start up, maintenance, repair, fitting or installation work, the respective equipment is to be approved with regard to cleanliness. Approval is given by the operator: -

In accordance with a checklist

-

Through visual inspection of cleaning work

-

Where necessary, through supplementary cleanliness analysis (e.g. in an escalation level due to a complaint or on the basis of an FMEA)

F.3.2.8

Downtimes

Components must be protected against contamination during downtimes, e.g. overnight, weekends or company holidays: -

Where possible, run assembly equipment until empty

-

The operator / planner determines if there is a threat of particle entry (e.g. due to constructional measures, maintenance work, filter replacement, renovation of flooring, machine installation in the vicinity, or normal particle entry from the environment over a longer period of time) and initiates appropriate protective measures (covers, sealing off, cleaning).

On re-starting, the relevant cleanliness points in Section 3.2.7 Process Approval apply. F.3.2.9

Putting into storage

Machines or devices put into storage during temporary downtimes are to be adequately protected against dust and corrosion. On re-starting, the relevant cleanliness points in Sections 3.2.4 Start up and 3.2.7 Process Approval apply.

141

F.3.2.10 Rework

If components are removed from the manufacturing process for rework and then reinserted, contamination of components and particle entry may take place in the device. Therefore, technical cleanliness is an aspect which needs to be included in the rework concept: -

Rework should be carried out at a separate workstation. If there is a risk of particle generation due to rework, the rework site should be outside the clean assembly area.

-

Caution! Particles may be generated during disassembly (e.g. removing screws)

-

Particles can be generated due to the rework process itself (e.g. particles from deburring)

-

Reconditioned components as well as test components or pseudo rejects may only be reinserted in a permitted state of cleanliness (also applies to small components in feeding technology).

142

Annex A.F A.F.1

Comparison of alternative methods for cleaning con rods

Figure F7 shows results obtained from cleaning the joining surfaces of separated crack con rods immediately before assembly. Different cleaning procedures were implemented depending on the application in question. The state of component cleanliness after cleaning was determined by way of component cleanliness inspection. Comparison of different cleaning methods (shiny metallic particles) t n e n o p m o c r e p t n u o c e l c i t r a P

250

200

150

100

50

0

50 - 100 µm

100 150 µm

150 200 µm

200 400 µm

400 600 µm

600 1000 µm

> 1000 µm

not cleaned (reference)

178,1

97,1

35,1

28,2

2,0

0,9

0,3

cleaned by suction

198,9

89,7

28,5

18,6

1,3

0,1

0,1

cleaned by suction + blowing

153,1

72,1

24,9

12,9

0,5

0,1

0,0

cleaned by suction + CO2

82,9

33,9

9,1

5,1

0,1

0,1

0,0

Fig. F7:

Cleanliness values of comparable test lots after implementing different cleaning procedures

Cleanliness inspection tests were carried out by way of pressure rinsing: 3 test lots were used for each cleaning variant; Size of test lot = 5 x 2 con rod halves. A.F.2

Magnetism as a disturbance variable

In conjunction with contamination risks and magnetism, the following phenomena based on the presence of magnetic forces are of interest: a) Adhesion and accumulation of ferromagnetic particles on surfaces possessing a certain degree of magnetization. 143

b) Adhesion and accumulation of particles possessing a certain degree of magnetization on ferromagnetic surfaces c) A combination of a) and b) Accumulation often occurs on the corners and edges of such objects because the localized stray magnetic field is generally relatively strong here. Due the magnetic force, these particles adhere relatively strongly to the surface. This makes them more difficult to remove than particles adhering normally. As a result, the probability of processing errors, malfunctions or pseudo errors increases. At this stage, no quantitative information can be given regarding respective limiting values. It is advised to include the possible influences of magnetism within the scope of the risk analysis of assembly cleanliness. Note:

This recommendation also applies to the accumulation of electrostatic particles as a potential risk.

Possible causes of magnetization or existing magnetism: •

Lifting magnets

•

Magnetic clamping devices (in machines)

•

Bit holders, screwdrivers, magnetic tool holders

•

Electromotors (e.g. ground conveyors)

•

Machining (especially localized reshaping without the use of lubricants)

•

Welding processes (influenced by continuous current used)

•

Gauge receivers (with permanent magnets for flexible attachment to machines, for example)

•

Cold forming (only partially).

Alterations in the stray magnetic field may occur during transportation or storage of components near a transformer.

144

Possible remedies: •

Replace base material / use non-magnetizable materials

•

Avoid construction of sharp edges

•

Do away with the process or use an alternative

•

Implement well-placed particle-attracting magnets (e.g. magnetic oil drain plugs, magnetic filter cartridges)

•

Active demagnetization (heating via alternating field magnetization)

•

Only activate specific magnetic functions / properties through magnetization at the end of a process

Curie temperature,

G:

DETERMINATION OF CLEANLINESS IMPACTS

G.1

Introduction

or

As described in Chapter B: Designing a clean assembly facility , the following test procedures can be implemented to locate critical particle sources or carry out targeted cleanliness-relevant optimizations e.g. verifying joining techniques. This can be done as part of a process chain analysis (see Chapter B: Designing a clean assembly facility ) or potential analysis (see Chapter K: Analysis of potentials ) and enables experience to be gained from running processes which can be later used in the planning of a new production. A manufacturing environment can also be assessed for suitability as a clean assembly area and enables processes or influencing factors suspected to be active particle sources to be visualized, quantified and documented. Using the procedures described in VDA 19, it is possible to ascertain how certain influences directly affect components or units.

145

G.2

Environmental and air cleanliness

The cleanliness of the environmental atmosphere is especially important if critical particle sources are located near components or aggregates or if functionally-critical areas are unprotected for extended periods of time. Levels of environmental and air cleanliness fluctuate significantly in noncontrolled areas, e.g. through uncontrolled processes, factors such as forklift traffic or seasonal influences. G.2.1

Test techniques

Air particle counters

Air particle counters function according to the principle of scattered light or extinction and are implemented in cleanrooms to monitor air quality and locate particle sources. To achieve this, a defined volume flow of air (usually 1 cubic foot / minute) is sucked in through an optical measuring cell where particles are counted and classified according to size. Air particle counters are not suitable for characterizing the environmental atmosphere for particles >25 µm in cleanliness zones, cleanliness rooms or conventional environments (CG0 - 2) for the following reasons: -

Most devices available on the market are designed for use in cleanrooms. They are capable of measuring particles in the submicrometer range and up to several micrometers in size. The measuring cells are often so sensitive that an uncontrolled environmental atmosphere would cause an overload and contaminate the cell.

-

Even air particle counters, principally capable of detecting larger particles which are determined to be functionally critical by the automobile and supplier industry, can only rarely be implemented effectively. The large particles to be measured are only present in the environmental atmosphere in low quantities with the result that long measuring times are required in order to detect them. In an assembly hall, for example, this would demand full-surface monitoring using numerous particle counters and would be too expensive to carry out.

Where air particle counters are implemented in CG3 areas (cleanrooms), the instructions laid down in ISO 14644-1 are to be followed.

146

Dust measuring devices

With these measuring devices, a suction pump is used to suck in a defined volume flow of air from the test environment via a membrane filter where the particles precipitate (e.g. 8 µm cellulose nitrate, diameter 15 mm). After a defined measuring time, the filter is removed and analyzed using gravimetry, light microscopy or scanning electron microscopy. This enables the total dust mass per air volume, particle size distribution or composition of the dust particle to be ascertained. Particle traps

A method of monitoring air particles which enables them to be correlated to the actual surface charge (e.g. also components stored open), is to use sedimentation surfaces. Here, horizontal sampling surfaces of a specific size are placed in an area for a defined period of time and the particles sedimenting onto it subsequently counted and measured using microscopy. The sedimentation surfaces can be placed in a reclosable carrier which protects them during transport until they can be analyzed microscopically or archived. The combination of sedimentation surface and carrier is called a particle trap. Preferred particle traps are generally made up of a round double-sided adhesive pad with a plastic carrier frame; they are also used for archiving analysis filters from component cleanliness analyses. One side of the adhesive pad is stuck into the plastic carrier. The other adhesive side serves as the sedimentation surface for the particle test (see figure). The protective film on this side is only removed when the test is performed.

147

writing area

transparent lid

protective film

carrier Sedimentation area adhesive on both Ø 47mm

Fig. G.1:

analysis area Ø <47mm

Diagram and photo of a particle trap

The use of this form of particle trap has the following advantages: -

For the sedimentation analysis, the same microscopes can be utilized such as those used by many companies to analyze filters in component cleanliness tests. Analysis in accordance with VDA 19 Chapter F3.

-

The sedimented particles are fixed to the adhesive layer (trap is transportable on completion of test). The particle trap is covered after the test and protected against further particle entry

-

The measuring surface has a defined size

-

Easy to handle

-

Due to the low manufacturing cost of particle traps and the ability to use established microscope systems, the total costs for this analysis technology are very low.

148

-

As well obtaining the automated microscopic analysis (particle size distribution), sedimented particles can also be visually inspected and additional analyses carried out if required (e.g. SEM EDX).

Note 1:

The type of particle trap described here is suitable for analyzing particles >50 µm. If smaller particle sizes are monitored and / or higher microscope magnifications used, the planarity of the sedimentation surface must still be within the depth of field of the microscope lens.

Note 2:

If the level of environmental cleanliness is very high, ensure that the base level of cleanliness of the adhesive surface is high enough to still be able to resolve the low number of sedimented particles (blank value of particle trap).

Instead of using particle traps, the following sedimentation collectors can be implemented: -

Oil-moistened analysis filter membranes. Here, oil binds the particles.

-

Open Petri dishes filled with fluid. The fluid which binds the sedimented particles is subsequently passed through an analysis filter (VDA 19 F1).

In both cases, automated microscopy is used for the analysis.

G.2.2

Procedure

For information regarding the use and handling of particle traps, see Annex A.1. Particle traps can be used for two purposes: -

To investigate processes and characterize particle sources (see Chapter G: Determination of cleanliness impacts ).

-

To perform large-surface tests on an environmental atmosphere to assess different locations in a manufacturing area (hall monitoring).

In the second instance, various measuring sites are selected which are either of interest (paths of movement, storage areas, locks, etc.) or which can be arranged in a grid (see Annex A.2). For this form of monitoring, particle traps are laid out simultaneously for the same period of time (e.g. one week). In order to increase comparability of the test results, all particle traps should be positioned at the same height above the floor (e.g. 1.7m). Note:

The number of particles sedimenting depends upon the height above the floor. The nearer the particle trap is located to the floor, the higher the quantity of particles that will precipitate.

149

G.2.3

Documentation

Particle traps are analyzed microscopically in accordance with VDA 19 F3 and documented as laid down in VDA 19 G 3.2. As a reference value, either the size of the particle trap or a conversion to 1000 cm² is utilized. The measuring time, i.e. the time which the particle trap is laid out for sedimentation, is to be documented. If a comparison of results from different locations is made, the same period of measuring time should be selected. Note:

If required and depending upon the application, additional influencing factors such as operating states are to be documented.

For longer-term monitoring when production is running, the following form of documentation can be selected. Here, the analysis results (particle size distribution) of the various particle size classes are multiplied by a weighting factor and the weighted particle counts then added together. The greater weighting of the larger particles emphasizes the increasing damage potential of the particles. Note:

150

Depending upon the application, it may make sense only to consider or even deliberately exclude specific types of particle (e.g. fluff, metallic particles, etc.).

Particle size [µm]

Size class in accordance with VDA 19

Quadratic weighting factor

5 ≤ x < 15

B

0

15 ≤ x < 25

C

0

25 ≤ x < 50

D

0

50 ≤ x < 100

E

1

100 ≤ x < 150

F

4

150 ≤ x < 200

G

9

200 ≤ x < 400

H

16

400 ≤ x < 600

I

64

600 ≤ x < 1000

J

144

1000 ≤ x

K

400

Table. G.1:

Weighting factors according to particle size when determining sedimentation counts

The resulting sum total is normed to a surface area of 1000cm² and related to a measuring time of one hour. The result is the so-called sedimentation count or Illig value. The use of standardized Illig values has the following advantages. -

The sedimentation results are comparable due to standardized reference values

-

By compressing the results to one number per measuring site, they are easier to document and compare (however, detailed information is lost in the process).

Possible ways of representing Illig values can be found in Annex A.2. The following example shows how the Illig value was calculated for a particle trap with an analysis diameter of 44 mm and a sampling time of one week. The trap was analyzed by way of light microscopy:

151

Men as:

Process:

Example:

Activator

Carrying out tasks Assembling components or where critical particles operating load-lifting are / could be equipment. generated

Transmitter

Displacement resulting from tasks involving both clean and contaminated objects

Source

General activity / time Primary: Hair, skin flakes, skin spent in assembly grease, sweat, micro area organisms, droplets of saliva, cosmetic products (skin cream, nail varnish, face powder, etc.).

Example of measure:

Work instruction regarding the avoidance of particle generation or description of cleanliness-suitable process

Handling contaminated Avoid mixed tasks outer packaging or spending time in zone with lower cleanliness grade. Special clothing regulations. Reduce personnel presence to a minimum.

Secondary: Wear and tear of clothing (e.g. fluff) Rectifier

Specific cleanliness action

Removing particles from functional surfaces.

Work instructions

Keeping workstations or operating utilities clean

Table E.1:

Relevance of personnel with regard to assembly cleanliness

Work instructions need to be developed, implemented and their execution verified in a prescribed clean area. Maximum cleanliness measures are required where contamination originating directly from humans (see table, Position 3.) could impair products and associated processes. If the displacement of contamination by personnel can be confined, this may result in a significant stabilization of the degree of cleanliness and minimize defects.

85

Particle size [µm]

Example of result

Weighting factor

Weighted particle count

5 ≤ x < 15

-

0

0

15 ≤ x < 25

-

0

0

25 ≤ x < 50

1620

0

0

50 ≤ x < 100

374

1

374

100 ≤ x < 150

57

4

228

150 ≤ x < 200

43

9

387

200 ≤ x < 400

15

16

240

400 ≤ x < 600

7

64

448

600 ≤ x < 1000

2

144

288

1000 ≤ x

3

400

1200

Total:

3165

Normed to 1000 cm² and one hour x 0,39 *)

1234

Illig value [1/1000 cm²h]

1234

*) inspection diameter 44 mm: Measuring surface area ( πr²) 15,2 cm² Sampling time (sedimentation time) 1 week = 168 h Norming factor: Table. G.2: Note:

G.3

1h

×

1000 cm

2

Measuringt ime [h ] Measuringarea [cm 2 ]

= 0,39

Determining the sedimentation count (Illig value) The sedimentation count is not intended to describe or characterize component cleanliness (limiting value specifications, inspecting technical cleanliness in accordance with VDA 19).

Surface cleanliness

The test techniques described in this chapter can be applied if the surfaces to be inspected are not suitable for fluid-based testing in accordance with VDA 19 for reasons of size, material, etc.

152

G.3.1

Test technique

Direct measuring procedure:

The only direct measuring procedure for detecting particles (>50 µm) on technical surfaces in a conventional or cleanliness room environment is a scattered light particle counter system. The almost parallel illumination of the surface fades out surface structures, causing particles lying on the surface to appear as bright occurrences. These are recorded by a camera and their size and quantity measured. The small measuring surface makes it necessary to take recordings at numerous measuring points in order to obtain an overall picture of the cleanliness state of a surface.

scattered light

scattered light

surface

Fig. G.2:

Measuring procedure for determining surface particles using scattered light

Indirect measuring procedure:

With the indirect procedure, in a similar way to component cleanliness analysis, particles are removed from the surface and fed to a direct measuring procedure. However, the established method of qualifiable liquid extraction which is used in component cleanliness inspection is not practicable for most surfaces (workstations, machine components, etc). Neither is blowing with air is a suitable analysis method. One way of removing surface particles using air is to suction-clean the relevant surface particles and collect them in a filter clamping unit in the exhaust air flow. The advantage of this procedure is that it is simple to perform and that the analysis filters can be evaluated using standard automated microscopy. This procedure can only be utilized for particles adhering loosely to surfaces. 153

Filter clamping unit with analysis filter

Microscopic analysis oft he analysis filter

Removal of loose particles from surface

Fig. G.3:

Suction sampling with optical evaluation of the analysis filter

A further method of removing particles from surfaces is wiping with a pale carrier (white glove, white cloth). In this way, particles are not only removed from the surface but also accumulated (concentrated on a smaller surface area). This enables the particles to be visualized and assessed by the naked eye as a more or less dark gray value on a pale background. However, efficient removal fluctuates according to how the surface is wiped, the measuring surface is not defined and the analysis (gray value) is subjective. Therefore, the procedure can only be implemented to obtain a qualitative assessment of surface cleanliness. Note:

For a more accurate analysis, the particles wiped off can be removed from the wiping medium by way of an ultrasound bath, for example, and transferred to an analysis filter membrane in the same way as for component cleanliness analysis. Different procedures can then be implemented to analyze the membrane.

Particles can also be transferred to a high-contrast carrier without the accumulation effect of the wiping test. A transparent adhesive strip is applied to the test surface and then removed, in the process of which the particles remain attached to the adhesive strip. For improved visualization and archiving, the adhesive strips are stuck to a base material contrasting well with the particles. However, further analysis e.g. using REM EDX is no longer possible with this method. The adhesive strip test can be standardized if it is carried out as a stamp test and also enables analysis microscopes to be implemented which are typically used in component cleanliness analysis. The following figures show two different sampling stamp constructions and the principles of 154

carrying out the test. With the variation shown on the left, the applied force is defined by a spring element and an arrester. With the variation on the right, the stamp is only applied with the force used by the person carrying out the test. spring

stamp

housing

stamp

cover

cover flexible base

f lexible base adhesive pad Ø 47mm

adhesive pad Ø 47mm

1)

1)

application to surface Defined f orce applied via spring p retensioning

2)

2)

automated microscopic analysis of adhesive p ad

Fig. G.4:

Auf Applied setzen to auf surfac Oberfläche e withoutohne def definierten ined f orce Anpressdruck app lied

alternative: direct analysis of stamp

Sampling with the aid of an adhesive stamp and subsequent optical analysis

155

G.3.2

Procedure

The test is not standardized and is carried out according to the type of technique selected. A recommended procedure for the stamp test is currently being compiled. G.3.3

Documentation

Results are documented in dependence upon the test technique utilized. Results from different test techniques cannot be compared with one another. However, if the same test procedure is used and provided all parameters affecting the results are identical, the results of different tests may be compared with one another. The analysis and documentation of tests analyzed using automated microscopy is to be carried out in accordance with VDA 19. G.4

Cleanliness of liquids

G.4.1

Test set-up

Liquids are often used in assembly processes or tests, for filling aggregates or operating production equipment (hydraulic liquids, cleaning media). The technical cleanliness of such liquids is assessed conform to the procedure laid down in VDA 19. As stated in VDA 19, the analysis fluid is made up of the test sample as well as any rinsing fluids. The quantity of test liquid is to be fixed according to requirements and the task at hand but should be at least 100ml. Particles are separated from the liquid using vacuum or pressure filtration. Filter pore sizes are determined in dependence upon the cleanliness specification (1 / 5 – 1 / 10 of the smallest particle size to be measured). Analysis membranes are also assessed in accordance with VDA 19 using automated microscopy or gravimetry. In the analysis, it is to be taken into consideration that some materials filtered from the test liquid which are shown in analysis results do not represent particulate contamination (e.g. additives in oils). Note:

156

Currently, there is no suitable procedure for analyzing the cleanliness of greases.

G.4.2

Procedure

The procedure for filtering, handling and conditioning analysis filters is carried out conform to VDA 19. In order to speed up filtration, analysis liquids can be diluted with low-viscosity, mixable liquids if required (cleanliness according to blank value criterion). All subsequent surfaces coming into contact with the test liquid (funnel, sampling receptacle, etc.) must be rinsed with a rinsing liquid (cleanliness according to blank value criterion). Determining the blank value: all liquid volumes used to dilute the sample or rinse sampling receptacles or filtration devices are also included in the blank value determination. The same applies for all surfaces coming into contact with the analysis liquid. Note:

G.4.3

When handling highly volatile, combustible, toxic or explosive liquids, the relevant safety guidelines are to be observed.

Documentation

The results from cleanliness analyses are expressed per 100ml test liquid. Volumes of liquids used for diluting or rinsing purposes are not included in the calculation of results. Microscopic counting results are shown accurately to 0.1 particles. With gravimetric analysis, the rounding rules in accordance with VDA 19 apply for each single result. Values are converted to 100 ml after rounding. The following table shows how results from a typical analysis are expressed: -

Test liquid: 700 ml diesel fuel

-

Filtration: vacuum filtration, analysis filter 5 µm PET mesh

-

Rinsing liquid: 200 ml gasoline

-

Microscopic analysis in accordance with VDA 19 F3

157

Particle size

Typical example of analysis result from 700 ml analysis liquid and 200 ml rinsing liquid

Expression of results [particles / 100ml]

5 ≤ x < 15

-

-

15 ≤ x < 25

-

-

25 ≤ x < 50

984

140,6

50 ≤ x < 100

198

28,3

100 ≤ x < 150

73

10,4

150 ≤ x < 200

29

4,1

200 ≤ x < 400

24

3,4

400 ≤ x < 600

9

1,3

600 ≤ x < 1000

2

0,3

1000 ≤ x

0

0

Table. G.3:

Example of determination of cleanliness of a liquid

Permissible blank values are ascertained analog to VDA 19.

G.5

Cleanliness of assembly processes

G.5.1

Test techniques

An important aspect in evaluating cleanliness influences in an assembly equipment and environment is to characterize processes with regard to particle generation. This can be achieved as follows: -

A test component in a defined cleanliness state is subjected to the process step and a subsequent cleanliness analysis is carried out by way of liquid extraction in accordance with VDA 19.

-

Particles generated by a process step can be transferred to an analysis filter membrane in a filter clamping unit as soon as they occur by way of extraction (see Chapter F: Assembly equipment).

-

Particle traps can be placed as close as possible to (and beneath) potential particle sources (e.g. assembly process). The particles generated by the process sediment in the trap and can be then be analyzed.

158

Flüssigextraktion liquid extraction of von Montageassembly oroder process particles

Prozesspartikeln Prüfung nach VDA 19 testing in accordance with VDA 19

Particle traps used to extract assembly or process particles

Particle traps used to collect assembly or process particles

Fig. G.5:

G.5.2

Assembly processes characterized by liquid-based sampling in accordance with VDA 19; sampling by extraction and collection of generated particles in a particle trap

Procedure

Liquid extraction is performed on completion of the respective process step in accordance with VDA 19. Extraction and collection in a particle trap run parallel to the process step and are carried out as near as possible to one another.

159

G.5.3

Documentation

Automated microscopic analysis and documentation of the results are carried out in accordance with VDA 19. It is not useful to express results per unit of measure, e.g. as in component inspection per 1000 cm² or in the analysis of liquids per 100 ml, because this test is concerned with process characterization.

160

Annex A.G A.G.1

Procedure for particle trap tests

1. Positioning the particle trap a) The function of a particle trap is to measure sedimented particles; it should be placed horizontally. b) The particle trap is to be fixed if there is a risk of it slipping during the test, e.g. by applying double-sided adhesive tape (1 x 2 cm) to the underside. Caution: if tape is applied to the whole underside, the particle trap is very difficult to remove and could cause the plastic carrier break as a result. c) If the particle trap is used to characterize a process (in contrast to monitoring environmental cleanliness), it should always be positioned beneath and as close as possible to the particle source under investigation (particles transported by gravity). d) The particle trap can be applied in either a stationary or moving position, e.g. on a workpiece carrier or in transport packaging. e) If necessary, the particle trap should be labeled (warning sign or similar) in order to prevent contamination from being removed by uninformed staff 2. Activating the particle trap a) The particle trap has a writing field to enable later classification of the measuring site in the analysis. This is to be filled out (preferably with waterproof marker) before commencing the test. b) Removing the transparent lid. The lid must be kept in clean additional packaging (e.g. new PE bag) until the test is finished and the lid replaced over the trap. If the lid is contaminated, particles could fall onto the measuring surface / sedimentation area when the trap is covered and falsify results. c) Removing the upper protective film. Use tweezers to lift up and pull off the protective film at the edge of the measuring surface / sedimentation field. Ensure that the measuring surface (adhesive layer) does not become damaged or contaminated. The trap is then armed and sedimenting particles can be collected. The protective film can be discarded. 161

3. Exposure time a) Depending on the particle source under investigation, measuring times may vary. A measuring time of one week has generally proved to be useful in automotive component assembly areas (no extensive particle generation due to chipping, grinding or blasting processes). If a specific sequence is investigated which is related to a specific period of time, e.g. a round trip of a goods carrier or transportation from one place to another, the measuring time is determined by the duration of the process. b) Caution: do not touch the particle trap and avoid nonrepresentative processes above the trap. 4. Deactivating the particle trap, transportation for analysis a) Close the trap with the clean, transparent plastic lid. The lid may not be inadvertently opened until the trap is analyzed (e.g. fixed with a piece of adhesive tape or form-locking packaging in a box…) b) The trap is now disarmed, i.e. no further particles are collected. c) Particle traps are intended for automated microscopic counting. Samples are to be transported to the site of analysis with care. Although the particles are attached to the measuring surface by a strong adhesive layer, if they are agitated they could become detached again. Check the trap when opening it for analysis. 5. Analysis a) The particle trap is analyzed (particle size distribution determined) using automated microscopes such as those used to count analysis filters in component cleanliness analysis (provided they have glancing light illumination). The analysis program and settings can be used b) The microscope table must be fitted with a suitable mount for holding and fixing the particle trap. c) If polarized light is utilized, the lid of the particle trap must be removed for microscopic counting. Ensure that the collecting surface of the trap cannot become contaminated during analysis. d) Additional analyses can be carried out on the opened particle traps, e.g. SEM EDX.

162

position particle trap at measuring site and o en it

remove protective film with tweezers

Test times: one week => 168 h one shift => 8 h

sedimenting particles collect on adhesive test surface

163

close particle trap Transport for analysis

automated microscopic analysis

particle size distribution Analyser einer "Partikelfalle" 60

50

40 l h a z l e 30 k i t r a P

20

10

0 1 5- 25 µm

2 5- 50 µm 5 0- 10 0µm

1 00 150µm

150200µm

200400µm

400600µm

6001000µm

>1000µm

Partikelgrößenkanal

Fig. G.6:

164

Procedure for carrying out tests with a particle trap

A.G.2

Visualizing sedimentation counts (Illig values)

example of visualization of sedimentation counts (Illig values) in a grid containig 30 measuring position

600 500 Illig value

400 300 200 5

100 3

0 A

B

coordinate 2

1 C

coordinate 1

D

E

example of a visualization of sedimentation counts (Illig values) in a grid containing 30 measuring positions

6

Illig value 400-600

5

200-400 0-200

4 coordinate 2

3

2

1 A

B

C D coordinate 1

E

Fig. G7:

165

H:

TERMS AND ABBREVIATIONS

H.1

Terms and definitions

A Aggregate: a functional system (e.g. steering or gear box) or semimanufactured product made up of single parts joined together. Airborne particle : a liquid or solid particle which does not sediment as a result of molecular motion, airflow patterns and / or kinetic energy. It therefore remains in the air for a longer period of time than the statistical average and may stray far from its point of origin. In some cases, airborne particles can be confined using a directed airflow and / or encapsulation. Air quality: describes the state (quality) of the air with regard to contamination. Assembly contamination : contamination caused by an assembly process or generated in the surroundings and which impairs the technical cleanliness of an aggregate. Auxiliary material : a material which is required to carry out an assembly process, form part of the joint or is a necessary localized basic supply for a functional group. Auxiliary packaging material : a packaging element which completes the packaging when used in conjunction with the packaging means, e.g. compartment, filling material [DIN 55405:2006-11]. B Ballistic particle : a particle with a strong sedimentation effect due to its size and density but which spreads from its site of origin as a result of impact momentum. Barrier : a means or measure (physical / operative) of separation [ISO 14644-7:2004, 3.4]. C Clean assembly: cleanliness-suitable assembly. Clean workbench : also minienvironment, a localized area with a higher cleanliness grade than the environment. In general, an encapsulated manual workstation with its own clean air technology to prevent the entry of

166

airborne particles. For automated stations, the term minienvironment has become established in cleanroom technology. room Cleanliness: absence of undesired contamination. Cleanliness grade (CG) : classification of a clean area. Cleanliness maintenance : the removal of contamination from permanently-installed objects or surfaces, principally to prevent particle displacement, transmission via sedimentation and / or to improve visual appearance. Clean area: room or partitioned area of a room which has been constructed for the manufacture, assembly and storage of components and systems and for which appropriate measures have been taken to achieve and maintain surface cleanliness. A clean area can also be formed by packaging or housing. Cleanliness room : room containing fixed installations which contributes towards the maintenance of the technical cleanliness of a product through appropriate design and the implementation of regulations regarding staff, logistics, care and manufacturing processes.

In the VDA 19.2, a cleanliness room is classified as a clean area with a cleanliness grade (CG) of 2. Cleanliness specification : list of cleanliness values for an object combined with a suitable test specification. Cleanliness-suitable: does not affect the state of cleanliness (see VDA 19 Pg. 199) Cleanliness zone : partitioned area which, through appropriate design and implementation of regulations with regard to staff, logistics, care and manufacturing processes, contributes towards maintaining the technical cleanliness of a product.

In VDA 19.2, a clean zone is classified as a clean area with a cleanliness grade (CG) of 1. Cleanroom: a room in which the concentration of airborne particles is controlled. It is constructed and utilized in such a way so as to keep the number of particles brought into or generated and sedimenting in the room to a minimum. Where required, other parameters affecting cleanliness are also controlled, e.g. temperature, humidity and pressure [ISO 14644-1].

In VDA 19.2, a cleanroom is classified as a clean area with a cleanliness grade (CG) of 3.

167

Conventional manufacturing area / assembly facility / environment : a manufacturing area / assembly facility / environment where technical cleanliness is not controlled. Contamination: any particulate, molecular, non-particulate or biological unit which has a detrimental effect on the product or process [ISO 146444:2001, 3.5] Critical particle : a particle which possesses specific properties and whose presence – at the current state of knowledge – impairs the quality of the component D Defined cleaning procedure for packaging means : the removal of contamination using a cleaning procedure with process parameters which have been precisely defined and remain identical, e.g. rinsing pressure and duration in an aqueous cleaning system to achieve a required degree of cleanliness. Displacement: undesired transfer of contamination to other areas and objects. E ESD (Electro Static Discharge): the transfer of a charge between bodies with varying electrostatic potential and caused by direct contact or influenced by an electrostatic field. F Functionally-critical particle: see critical particles. Fiber: a non-metallic shiny particle with a ratio between length and width of < 10 or a degree of compactness of < 30 %. H Housing: the physical encasement of a system with the purpose of protecting the worker or product. I Insert: a molded part used to separate, fix and protect packaged goods inside the packaging or loading unit, e.g. compartment [DIN 55405:200611]. Inner packaging: the surface of the packaging means which is in direct contact with the component, e.g. inner surface of an SLC or bag.

168

K Killer particle: a single highly-critical particle which can cause a component, aggregate or complete system to malfunction. L Load carrier: all forms of container, e.g. SLC, mesh pallet. M Macro particle : a particle with an equivalent diameter or maximum dimension of 5 µm # Mesh pallet: [DIN 15155] Mixed task: the execution of various tasks by the same person. Mixed tasks may cause displacement. O Operating utilities technology : all components required to perform a process. Outer packaging : the part of the packaging whose surface interacts with the environment, adjacent surfaces or staff P Packaged goods : goods to be packaged or which are already packed, e.g. components or aggregates [DIN 55405:2006-11]. Packaging: totality of all packaging materials required to fulfill the packaging task. Serves to protect the packaged goods, people and the environment and to rationalize handling during production [DIN 55405:2006-11]. Packaging material : the material used in the making of the packaging components (packaging means and auxiliary packaging materials) [DIN 55405:2006-11]. Packaging means : forms the main part of the packaging and holds the goods to be packed. It encloses the goods either partially or completely. Being the main part of the packaging, the packaging means has an important protective function. For dimensionally stable packaging means with a high degree of prefabrication (e.g. bottle, tin, crate), the term container is also used [DIN 55405:2006-11].

169

Packaging method : this describes the manner in which packaged goods are put into the packaging, e.g. loose or fixed. Particle: a particle is a solid body composed of metal, plastic, ceramic, mineral, rubber or a salt. Paste-like parts are not considered as particles. Particle source : an object or process which generates and emits particles. Particle trap: adhesive surface for collecting and fixing particles sedimenting out of the environmental atmosphere. Pool container : the common use of a container (e.g. SLC) by several partners in a circulating system. R Recontamination: a reduction in the cleanliness level of a component or aggregate which has been cleaned. S Secondary packaging: additional packaging with the aim of protecting the outer packaging against contamination during transport (second barrier). The secondary packaging must be opened first in order to reach the packaged goods. Size class: particle size class defined in accordance with ISO 16232-10 and VDA 19 Pg. 178. T Tack mat (also dust-attracting mat): floor element (reusable or singleuse) to confine displacements in clean areas. Technical cleanliness: a control surface / functional surface without any functionally-critical contamination originating from manufacturing processes or the environment. U Undefined cleaning of packaging means: removal of contamination with undefined and / or fluctuating parameters, e.g. manual pressure rinsing, brushing or sweeping. There is no guarantee that the desired degree of cleanliness will be attained. User : a person who procures, supplies or uses a machine, e.g. company manager, works or factory manager, department manager.

170

H.2

Abbreviations and symbols

5S: a five-step systematic method to achieve a clean and well-organized work area. It is a key element of the continuous improvement process. The five steps and their basic principles are categorized as follows:

Sort:

clear the work area

Set in order:

designate locations

Shine:

cleanliness and workplace appearance

Standardize:

everyone does things the same way

Sustain:

ingrain the 5S's into the culture

FFU: Filter Fan Unit FMEA: Failure Mode and Effects Analysis: SLC: Small Load Carrier Open-topped, rectangular, rigid, robust, reusable module which can be handled manually or automatically and forms the main element of a small load carrier system [DIN EN 13199-1:2000]. VCI foil: Volatile Corrosive Inhibitor Foil Plastic foil treated with additives which are released during transport or storage with the aim of preventing metal surfaces of packaged goods from corroding [DIN 55405:2006-11]. CG: Cleanliness Grade Classification of a clean area

171

H.3

References

DIN EN 13199: Part 1 to 3:2000-10 Small load carrier systems DIN EN ISO 14644-4:2001; Cleanrooms and associated controlled environments. Part 4: Design, construction and start up (ISO 14644-1: 2001) DIN 15155: Mesh pallets DIN ISO 16232: Road vehicles - Cleanliness of components of fluid circuits DIN 25410: Nuclear facilities – Surface cleanliness of components; April 2001 DIN 55405:2006-11 Packaging – Terminology – Terms and definitions ISO 4406: Hydraulic fluid power - Fluids - Method for coding the level of contamination by solid particles ISO 8573-1: Norm, 2001-02 Compressed air - Part 1: Contaminants and purity VDA Volume 4 Chapter 3: Product and process FMEA VDA Volume 19: Technical cleanliness in the automotive industry – assessing particulate contamination on components VDA 4500:2006-1: Small load carrier (SLC) systems VDI 2083: Cleanroom technology

172

Fig. F.2:

F.3.1.2

Methods of installing particle-generating devices

Materials and surfaces

For more information, see corresponding section in Chapter C: Environment. F.3.1.3

Basic design

This is the basic construction for holding the technical equipment. It generally consists of a framework or supporting construction, horizontal surfaces such as placement or installation surfaces, a housing, partitioning walls, locks if required, metal fittings such as handles or hinges, lights, etc. Criteria and measures: -

Horizontal surfaces should have an open, unobstructed construction; especially at work and process level  e.g. burr-free perforated sheeting. In this way, particles fall downwards into a trap (e.g. drawer) where they cause no damage, or onto the floor where they can be removed at regular intervals, e.g. large-surface rotary transfer tables designed as spoked wheels.

-

Avoid protruding screw ends and heads to facilitate cleaning 107

I:

ANALYSIS OF CLEANLINESS POTENTIALS

I.1

Contents

The chapter contains a list of questions which aim to improve the degree of cleanliness of assembled aggregates and ensure adherence to processreliable cleanliness requirements. The objective is to systematically advise planners and quality control staff about factors (weak points or potentials) influencing component cleanliness. The list focuses on factors affecting the cleanliness of end-products as considered and described in the main chapters of the MontSa guideline. Other points relevant to cleanliness (e.g. development), have been deliberately excluded as they do not form part of the guideline contents. One exception to this is the aspect of component cleaning, as this is an interface between manufacturing and assembly and is sometimes integrated into assembly. I.2

Aim

The question list should be used to help identify weak points in the cleanliness chain in order to develop potentials for improving the degree of cleanliness. The so-called analysis of cleanliness potentials is not to be carried out as part of a process audit such as VDA 6.3 or workstation audit according to the 5S method in the customer / supplier relationship, nor does it replace them. Instead, the analysis of potentials is intended as an internal aid to identify ways of improving efficiency and stabilizing the degree of cleanliness. For this reason, the questions in the chapter have been formulated as openly as possible and should not be evaluated using a point system (e.g. on a scale of 1 to 10). Note that the chapter also does not contain any standardized protocol procedures. With the aid of the open questions, the user of the problem list should be able to verify whether all factors influencing cleanliness have been considered and whether the cleanliness chain in his assembly facility has any gaps or weaknesses. The list of questions is therefore intended as an internal supplement to audits in accordance with VDA 6.3 or 5S.

173

I.3

Procedure

The frequency and scope of an analysis of cleanliness potentials depends upon the individual situation of each cleanliness-critical assembly facility and cannot be bindingly specified. A defined procedure for an analysis of cleanliness potentials is therefore not described and is the responsibility of the person concerned. However, similar basic principles apply as for planning an assembly facility (see Chapter B: Designing a clean assembly facility). An analysis of weak points is recommended if: -

Cleanliness requirements are implemented in existing assembly facilities or for new generations of products

-

Cleanliness requirements for a product have not been fulfilled

-

Processes and sequences in existing assembly facilities are altered

All areas and instances affected by a company’s cleanliness strategy are to be included in the analysis of cleanliness potentials right from the start. A person is also to be named who is responsible for coordinating, executing and evaluating the analysis of cleanliness potentials. I.4

Question List Quality Control

1

What cleanliness requirements exist and which forms of contamination need to be controlled?

2

What are the requirements based on and how do they affect deviations in the end-product?

3

What are the internal consequences of not adhering to cleanliness specifications?

4

What is the procedure for contaminated components and aggregates (control loop escalation)?

5

How is the cleanliness of components verified?

6

What type of plans exist (scope, time intervals) for assessing the cleanliness of components and aggregates for series start-ups and accompanying process controls?

174

Quality Control

7

How is the cleanliness of auxiliary materials verified?

8

What packaging cleanliness specifications exist for delivery and dispatch (components and products)?

9

How are assembly processes assessed / considered with regard to the generation of critical particles?

10

How is the assembly environment assessed / considered with regard to the entry of critical particles?

11

How are staff activities assessed and optimized which are related to mixed tasks / displacement potentials?

12

What preventative measures are taken to avoid or reduce contamination?

13

How is the effectiveness of measures verified and documented?

14

How are regular cleanliness audits carried out, documented and linked to an implementation schedule?

Table. I.1:

Question list about quality control systems

Environment

1

What levels of clean area are planned?

2

How have clean areas been installed?

3

How are clean areas been marked and appropriately separated from one another?

4

What levels of cleanliness have been assigned to the clean areas?

5

Does the design of the clean area comply with the cleanliness grade assigned?

6

Are auxiliary materials appropriate for the cleanliness grade?

7

How has the entry of critical particles from the environment been assessed?

8

What instructions exist for dealing with openings inside the building (doors / gates / windows / skylights)?

9

Is ventilation technology used and how is its function safeguarded?

175

Environment

10

How are adverse effects from possible condensation (humidity) been taken into account? E.g. corrosion, bonding problems in adhesive processes.

11

How are lock concepts organized?

12

Are sufficient suitable storage areas available (components, auxiliary materials, etc.)?

13

Are products on shelves / at workstations / component provision areas protected against the entry of particles?

14

Are there any potential particle sources from the ceiling area (catwalks, ventilation systems, load-lifting equipment) and have appropriate measures been taken to prevent particle entry?

15

Have supply / lifting units located above assembly stations been adequately covered to prevent contamination from falling from them?

16

Is the lighting good enough to enable contamination to be recognized?

17

Is the floor of the assembly facility been designed for easy cleaning?

18

Is there a building maintenance plan for cleaning floors, workstations and storage areas? Have responsibilities been clearly delegated?

19

How have cleaning plans been verified?

20

Do staff members understand the purpose of cleaning? (question staff)

21

Is prescribed clothing worn correctly?

22

Are only low-fluff cleaning cloths utilized?

23

What regulations exist regarding renovation / maintenance measures? How is staff informed about them?

Table. I.2:

176

Question list about the influencing factor »environment«

Logistics

1

How is consistent traceability been planned and documented throughout the entire material flow?

2

What measures have been taken to ensure that no critical particles are brought into the clean area? What does the cleanliness-suitable material flow concept look like?

3

How are the various clean areas screened from one another (e.g. by locks, spaces and / or partitions)?

4

How are material flows of clean and contaminated components kept strictly separate?

5

How is it assured that components are promptly further processed?

6

How are storage areas for contaminated and clean containers kept separate from one another and are they clearly marked?

7

Are there cleaning regulations for storage sites and areas?

8

What unpacking and removal regulations exist which ensure that no particles reach the product?

9

Is the disposal of soiled packaging and the removal of cleanlinesscritical components carried out separately (not directly by the same person) and are responsibilities clearly defined?

10

What regulations exist regarding charging / loading (packing)?

11

Is the packaging concept for the parts, components and aggregates to be processed suitable from the point of view of cleanliness? (protection against contamination, corrosion and damage)

12

Do packaging means fulfill the specified cleanliness grade? (E.g. no cardboard, etc.)

13

What cleanliness regulations exist for packaging means (cleanliness requirements, reference samples, etc.)?

14

How is the cleanliness of packaging means verified?

15

How is the management of packaging means and containers implemented? (inc. keeping clean, control)

16

What cleaning plans exist for load carriers and inserts? How are they ascertained and communicated?

177

Logistics

17

How are clean/cleaned containers protected against contamination?

18

How is recontamination avoided?

19

Are packaging means and packaging incorrectly put down on the floor?

Are load carriers and lifting units used which are potential particle 20 sources? How is transport handling planned to ensure that no damage or contamination occurs? 21

How is it verified that single-use packaging is not reused?

Table. I.3:

Question list about the influencing factor »logistics«

Staff

1

Who is in charge of the clean area?

2

How is cleanliness controlled and how are workstations cleaned? (work instructions)

3

Who is responsible for keeping workstations clean?

4

How are members of staff taught to handle cleanliness-critical products? How are the contents of training courses and staff participation documented?

5

How are external and internal service providers (e.g. maintenance, cleaning) trained and instructed?

6

How are the relevant members of staff taught about 5S?

7

How are instructions given at workstations?

8

How is the topic of contamination fixed in instructions?

9

Have all relevant members of staff received work instructions and are they implemented?

10

How are members of staff informed about the consequences of contamination for the product and for the company?

178

Staff

11

What are the consequences if regulations are not observed?

12

What clothing concept is implemented?

13

How are external and internal service providers (e.g. maintenance, cleaning) trained and instructed?

14

How are the relevant members of staff taught about 5S?

Table. I.4:

Question list about the influencing factor »staff«

Assembly facilities

1

Are processes, measuring devices, auxiliary materials and tools suitable for use in the respective clean areas?

2

Are the materials / parts suitable for further processing (bought parts and own components manufactured at other locations), are cleanliness states known and regulated

3

Are products with different cleanliness requirements assembled on one line?

4

How have assembly processes been verified / assessed with regard to particle generation and entry (procedure/results)?

5

Have assembly facilities (operating utilities / auxiliary materials) been verified / assessed with regard to the generation of critical particles (e.g. particle generation from transport conveyors, tools, lifting devices on guide rails, etc.) and optimized (e.g. as part of an FMEA system)?

6

In accordance with the results from 4 and 5, have assembly facilities been suitably designed from a cleanliness point of view and are they protected against external contamination? Has the assembly position been selected in such a way so as to ensure that generated particles do not reach critical component surfaces?

7

Have magnetic influences on the component been considered? (Magnetization of components from tools and assembly processes)

8

Are components assembled punctually?

9

Are workstations clean?

179

Assembly facilities

10

How are workstations and placement areas protected against contamination from the environment?

11

Are semi-fabricated components / auxiliary materials / single components (especially greased parts) adequately protected during machine shutdowns (e.g. ends of shifts, breaks)?

12

Are tools and measuring devices clean?

13

Are materials and tools stored in appropriate designated locations?

14

Which appropriate measures have been taken to replace/resolve mechanical hammering and beating processes?

15

What facilities / measures for eliminating contamination are available and how are they regulated? (E.g. localized suction-cleaning, magnets, adhesive tape)

16

What measures have been taken to avoid and eliminate contamination in assembly stations?

17

Have responsibilities been designated for maintaining the cleanliness of assembly and workstations?

18

Do cleanliness maintenance plans exist for workstations and assembly facilities in which intervals and procedures have been fixed?

19

What cleaning equipment and agents are available? (e.g. suctioncleaning unit)

20

Have workstations been designed for easy cleaning?

21

Have storage areas and shelves been designed for easy cleaning?

22

If processes are altered, is the effect on cleanliness taken into account?, e.g. production of chips during impressing processes

23

How are cleanliness-critical processes during reworking evaluated and how is this regulated? (E.g. designation of forbidden zones, covers, cleaning, etc.)

24

How is it safeguarded that components are only mechanically reworked and re-cleaned in prescribed zones / rooms?

Table. I.5:

180

Question list about the influencing factor »assembly facilities«

1

Component Cleaning What form of cleaning concept exists for incoming components / intermediate products or end-products in the assembly facility? (external / internal; central / decentral)

2

How / how often is cleaning efficiency verified? (process, product, quality of cleaning media)

3

What maintenance intervals (filter replacement, media control, etc.) have been fixed to ensure that cleaning remains effective?

4

How is it verified that cleaning steps and cleaning media do not have any negative effects on prior or subsequent processes (e.g. particle displacement, oil displacement) to prior and subsequent processes?

5

Has it been assured that materials / surfaces are resistant to the cleaning media used (procedure/results)?

6

Have magnetic influences on cleaning results been considered (procedure/results)?

Table. I.6:

Question list about the influencing factor »component cleaning«

181

J:

PLANNING EXAMPLE

J.1

Overview

The example described in this chapter illustrates how to use the guideline in order to plan a cleanliness-sensitive assembly facility and how to assess and optimize sequences and processes. Although the example is purely fictitious, it is closely related to practical circumstances. The various steps considered here do not necessarily have to be dealt with in chronological order; depending on a company’s internal starting point, they may also be handled in parallel. Furthermore, the example does not state who should be included in the planning phase. For more information, see also Chapter B: Designing a clean assembly facility . The planning sequence and page numbers of relevant paragraphs and chapters contained in the guideline are shown in Fig. J.1. cleanliness specification

design of assembly facili ties, operating utilities, auxiliary materials Pg. 106 - 113 design of assembly processes Pg. 120 - 121 assemblyintegrated cleanin g Pg. 122 - 134 operating assembly facilities and keeping them clean Pg. 134 – 143

selection of CL environmental concept Pg. 33 - 42

design of assembly environment Pg. 42 - 51

development of logistics concept – “outer“ packaging and airlock system Pg. 66 - 69, 72 - 77

“inner“ packaging Pg. 59 - 65

staff: choice an d concept of clothin g Pg. 86 - 90

staff - qualification and sensitization Pg. 86 - 87 verification of cleanliness factors Pg. 88 - 101

Fig. J.1:

182

Flow chart and page numbers showing where to find the relevant information in the guideline

J.2

Introduction

J.2.1

System components

The task is to plan and implement an assembly facility for cleanlinesscritical hydraulic-mechanical functional systems. The systems are composed of four main components :

Fig. J.2:

Cast aluminum housing (left) and steel piston (right)

Fig. J.3:

Steel radial shaft seal with polymer insert (left) and steel pipe with brass screw connection (right)

J.2.2

Construction of the system

The system is constructed by assembling the four main parts. Firstly, the piston is inserted into the aluminum housing. Then the shaft seal is pressed over the piston rod into the housing. The assembly process chain is completed by screwing on two hydraulic pipes and fitting sealing plugs. The final system is shown in Fig. J.4.

183

Fig. J.4:

J.2.3

Assembled hydraulic-mechanical complete system

Cleanliness requirements

Cleanliness specification in accordance with VDA 19: max. 25 particles per 1000 cm² > 200 µm, no particles > 400 µm permitted. As the system mainly reacts critically to abrasive particles, there are separate requirements with regard to anorganic (metals, ceramics and minerals) and organic particles. Organic fibers are also considered separately. The following specifications apply for the system: Particle material

Anorganic (metals, ceramics, minerals)

Particle size

> 200 µm (per 1000 cm² max. 25 particles) > 400 µm not permitted

Organic (plastics, elastomers)

Permissible up to 1000 µm

Organic fibers

Not controlled

Table. J.1:

184

Cleanliness specification for hydraulic-mechanical system

J.3

Assembly environment

J.3.1

Selecting the right cleanliness grade

In the dispersibility diagram (see Chapter C: Environment Fig. C.1 ), details of the critical particle size and particle material have been entered. Anorganic particles sized 400 µm or larger may not be present. A minimum density of the relevant particle material of 2.7 g / cm³ (aluminum) is assumed. When these values are entered into the diagram, it can be seen that a cleanliness zone or cleanliness room is required (see Fig. J.5). Although a cleanroom is not required in this case, a conventional manufacturing environment is not sufficient. compact particles

fiber -shaped particles

] ³ m c / g [ y t i 10 s n e D

CG 1 + 2: cleanliness zone + cleanliness room

5

Aluminum

2

CG0: conventional production environment

CG3: Cleanroom 1 0,5

0,2 0,1 1

2

5

10

20

Examples of materials: p(aluminum) = 2.7 g/cm³ = 7.8 g/cm³ p(steel) p(polystyrene) = 0.02-0.09 g/cm³

Fig. J.5:

50

100

200

500

1000

2000

Particle size [µm]

400

Dispersibility diagram for selecting the correct cleanliness grade

In order to further determine whether a cleanliness zone is adequate or if assembly needs to be carried out in a cleanliness room, the characteristics of both concepts need to be considered in more detail (see Chapter C: Environment, Table C.2 ). It becomes apparent that the cleanliness room is more effective at regulating the entry of particles via the air, staff or packaging. However, in this case the contamination is organic, especially as far as airborne particles and particles generated by staff are concerned, and does not impair the function of the system to be assembled. Therefore, a cleanliness grade CG1 (cleanliness zone) is sufficient for the assembly environment in this example. 185

J.3.2

Design and organization of a cleanliness zone

A cleanliness zone is characterized by: -

Spatial separation: o

o

-

No particle-generating processes inside the cleanliness zone or immediate vicinity.

Regulating logistic processes: o

o

-

Distance away from conventional manufacturing environment

No use of forklift vehicles inside the zone Components may not be brought directly to assembly stations in transport packaging

Skilled staff: o

Assembly workers are specially instructed how to avoid particle displacement

In this case, the cleanliness zone is marked using simple floor-marking. The basic design features of a cleanliness zone are described in Chapter C: Environment 3.1.5 . In the case of the example, the following recommendations are made for constructing the cleanliness zone as an assembly environment: -

Sealed industrial flooring,

-

Appropriately resistant to abrasion, smooth (easy to clean) and pale color,

-

No metal grid walkways above the zone,

-

Sealed ceiling plaster.

J.4

Logistics concept

J.4.1

Outer packaging and lock systems

In compliance with the recommended design criteria, a transfer area is constructed where outer transport packaging is removed or components placed in clean load carriers which are only used in the cleanliness zone.

186

Housings and pistons : because of their size, the housings and pistons are delivered in mesh pallets. A designated worker brings the mesh pallets to the transfer area where he opens the contaminated transport film (secondary packaging). An assembly worker removes individual housing lots as he needs them (without touching the outer packaging) and transports them on a roll cart to the assembly station. Pipes and shaft seals : these are delivered in SLCs, which a designated worker brings to the SLC rack situated at the boundary to the zone where he also removes the contaminated lid. An assembly worker takes out the components contained in the inner packaging (bag or blister pack) without touching the SLC. Assembled system a designated worker brings an empty mesh pallet to the zone boundary and lines it with a plastic bag. An assembly worker brings the completed products in batches on roll carts to the loading station. To protect them against mechanical damage, the products are then packed by the designated worker into compartments with interim layers as separated goods in the lined mesh pallet.

Because the assembled system is finally installed in a CG0, the final packaging does not have to fulfill any cleanliness requirements. The system is completely sealed and is therefore protected against critical recontamination. e n t r i a t l e s u l e o a t p a t g h h g e r u s e g o r m g b a

a d e e r a l l n o r i o t t n c o u c d n o u r p

mesh pallets loading station

roll cart loaded with aggregates

cleanliness zone components transferred to roll cart

e n i l y l b m e s s a

removal of bags / trays mesh pallets transfer station

SLC storage

SLC delivery SLC

Fig. J.6

Lock at delivery area and introduction of cleanliness-critical components into the cleanliness zone

187

J.4.2

Inner packaging of delivered parts

Housings and pistons : the housings and pistons are put separately into the mesh pallet using compartments made of low-abrasion PP twin-wall sheeting. This prevents the generation of particles due to abrasion. The entire mesh pallet is also lined with a tear-resistant plastic bag to protect components against contamination from the environment or from the mesh pallet itself. Shaft seals: the shaft seals are placed in deep-drawing trays with depressions adapted to their shape. The trays are then stacked in the SLC to create a closed package inside it. Pipes: due to the geometry of the pipes in this example, the generation of critical abrasion particles in the interior can be excluded and the pipes can be put into the SLC in layers. The SLC is lined with a plastic bag as inner packaging.

In the example, only SLCs with lids closing on all sides are utilized. Inner lids which can only be opened through tilting are not permitted. Severely contaminated or damaged mesh pallets are rejected (photographs of reference samples are displayed). J.5

Staff

J.5.1

Clothing

Information to assist in the selection of appropriate clothing concepts depending on the cleanliness grade can be found in Chapter E: Staff in Table E.2. As far as cleanliness requirements are concerned in this example, no special clothing concept is necessary to reduce particle emission from the worker or from day-to-day clothing. Here, the clothing concept serves to identify skilled staff working in the clean area and reduce particle displacement:

188

-

Different colored overall and shoes to identify staff working in the clean area,

-

Shoes may not have dark-colored soles as they could leave traces of abrasion in the clean area

-

Overalls and shoes may only be worn in the clean area and are to be stored at the entrance to the cleanliness zone in a wardrobe designated for the purpose,

-

J.5.2

Cleanliness requirements do not demand that gloves, facemasks or hair nets are worn Qualification

Staff working in the cleanliness zone are comprehensively informed about effects of particulate contamination and appropriately motivated with regard to: -

Procedure for putting on and taking off work clothing

-

Avoiding particle displacement: o No unnecessary contact with potentially contaminated surfaces and objects o Defined hand cleaning procedure after contamination

-

Instructions about keeping surfaces clean in and on process stations / workstations

-

Inspection of sensitive component surfaces and active removal of any contamination present (e.g. suction-cleaning, not blowing).

J.6

Assembly processes

Assembly processes may generate critical particles of a certain size which significantly exceed the risk of contamination from the environmental atmosphere or staff. In this example, the optimization of assembly processes is a key issue in assembly planning. J.6.1

Designing assembly processes

The assembly processes necessary to assemble the hydraulic-mechanical system are: -

To insert the piston into the aluminum housing,

-

To press the shaft seal over the piston rod into the housing and

-

To screw both hydraulic pipes into the housing.

The risks associated with these processes are described in Chapter F: Assembly facilities 3.1.5 .

189

Process

Screwing

Particle generation

- On searching for screw thread




Effect of particles

- Exit burrs

- Thread gauges act

- Coating swarf - Swarf from


- Abrasion due to

- Damage to threads - Incorrect tension due to increased abrasion; consequence  connections may loosen

tools

detach if screws are - Particles from shot using screw heads compressed air - Burrs from - Abrasion / screw threads detachment of burrs Pressing / crushing / dilating

like cutting tools

- Nicks

- Pieces of

- Swarf may be rinsed into components during function tests

- Component function

coating - Generally flake-shaped

impaired by jamming


relative movement between tools and components Inserting / sliding in / on, pushing in

- Abrasion / broken

- Swarf, burrs,

- Particles between

fragments of particles components and / or joining components - Chips - Detached particles - Abrasion of centering tools on work surfaces

components prevent exact positioning of component Incorrect fit

- Leaks

Table J.2:

Extract from characterization list of joining procedures

The following points are relevant for the three joining procedures considered: Screwing in pipes : when screwing in pipes, the worker must put screws in straight and not at an angle. The screw joint may not be reopened because any trapped particles generated would enter the interior of the housing directly and thus reach the critical area.

190

Inserting the piston : if the piston is inserted incorrectly, particle abrasion due to the relative movement between both joining partners may occur and cause a leak. This is avoided by accurately centering the piston on insertion without tilting it. The outer surface of the piston is greased before insertion. Pressing in shaft seal : in order to minimize particle generation, the shaft seal must also be accurately centered when pressing it in. If it is inserted at an angle, it may not be removed. In such a case, the unit must be rejected. J.6.2

In-line cleaning

Assembly-integrated cleaning methods are described in Chapter F: Assembly facilities 3.1.6 and areas of application and limitations of use explained. Due to the shape of the system (interior critical surfaces) and experience gained from pre-series, the following two assembly-integrated cleaning steps are implemented: 1. Suction-cleaning through pipes when screwing them in Before screwing a pipe in, a suction nozzle is attached to the end of the pipe. Any particles generated during the screwing process are thus effectively removed. 2. Rinsing the complete systems The end-product is then tested on a test bench for the presence of leaks. At the same time, the interior of the system is also rinsed with hydraulic test fluid in order to remove any loose particles.

J.7

Operating utilities

J.7.1

Assembly station

In the following, a cleanliness-suitable design of the necessary assembly station is described for the process of joining the piston rod and housing. Beforehand, a similar assembly station already in operation is first evaluated with the aid of particle traps (see Fig. J.7 left). The design of the existing system and implementation of the cleanliness-optimized system is shown in Figure J.7 (right).

191

The following alterations were made: -

Overhead assembly: the opening of the housing is now underneath so that the piston can be inserted from below

-

The moving components (gripper, linear axes, energy chain) have been installed next to or below the product

-

Due to the low risk of recontamination from the environment (cleanliness zone), covers over component transfer stretches are not required

-

The open light construction causes any particles generated to fall into non-critical areas.

Furthermore, the following basic principles have been implemented: -

Placement surfaces are slanted to prevent the accumulation of particles.

-

Easy-to-clean design, no inaccessible corners, edges, protruding screw heads, etc.

-

Corners and edges of workpiece receivers and grippers are rounded.

-

Parts are provided one at a time, so the worker does not have to lean over the workstation.

Existing station

Fig. J.7:

192

Improved station

Examples of a potentially critical and improved mechanical design of an assembly station for impressing shaft seals

J.7.2

Feeding technique / singularization

Before the pipes are screws together, metal seals are automatically inserted into the screw depressions. Supplied as bulk goods, the metals seals are poured into a vibratory spiral feeder where they are singularized and fed via a linear track. Configured in this way, the actual assembly step (insertion) is non-critical from the point of view of recontamination because insertion is carried out friction-free in a defined manner without any material deformation. Although the metal seals are supplied in a clean state, there is a risk that they could transfer particles to the hydraulic area. This is because particles are generated during singularization and feeding as a result of impaction of the seals against one another. To prevent such particles from being brought into the hydraulic area with the components, a suction/blowing station is integrated into the linear track downstream from the vibratory feeder. In order to verify the necessity and efficiency of this measure, metal seals were placed as bulk goods in the vibratory feeder and three test lots, each containing one thousand pieces, were removed at the end of the linear track and tested for cleanliness. With the first test lot, the suction/blowing station was completely turned off. The second test lot was only suctioncleaned and the third test lot suction-cleaned and simultaneously blowcleaned. A reference sample of seals in their delivery state was also tested. Particles on metal seals after singularization in vibratory feeder 250

s l t a n e s u l o t c a e e l c m i t r 0 a 0 P 1 r e p

State on delivery 200

Without suction-cleaning With suction-cleaning

150

With suction- and blow cleaning

100 50 0

20 - 400 µm

400 - 600 µm

600 - 1000 µm

> 1000 µm

24

0

0

0

243

9

3

2

With suction-cleaning

88

7

2

0

With suction- and blow cleaning

43

3

0

0

State on delivery Without suction-cleaning

Fig. J.8:

Cleanliness values of the metal seals after singularization in vibratory spiral feeder

193

From the results, it can be seen that critical particles are generated by the singularization and feeding process. Although the majority of particles remain in the feeder, some particles do leave the feeder with the seals. Simple suction-cleaning removes most of the particles; if the seals are additionally blow-cleaned at the same time, the seals are almost as clean as they were on delivery. In order to prevent particles from accumulating in the vibratory feeder, the floor of the latter has also now been fitted with a perforated metal sheet, thus enabling particles to fall through. As a supplementary measure, the vibratory feeder, especially the spiral, is to be wipe-cleaned with a moist cloth at the end of each shift. J.8

Determining and assessing cleanliness influences

The environmental atmosphere in the realized cleanliness zone and also particle generation from installed operating utilities are assessed with the aid of particle traps (see Chapter G: Determination of cleanliness impacts 2.1 and Chapter C: Environment Annex A.1 ).

J.8.1

Environment

For the duration of one week, five particle traps are placed at measuring locations which are undisturbed by workers (on top of switching cabinets, assembly stations, etc.). The particle traps are then analyzed using reflected light microscopy in accordance with the procedure laid down in VDA 19. Particle coun t per measuring site > 400 µ m

Particle coun t per measuring site > 100 µm 50

60 Particles > 100 µm (wit hout fibers) Organic fibers > 100 µm

50

t n t u n 40 o u c o c e l e lc 30 c i t ritr a a P P 20

Particles > 100 µm (shiny, met allic)

C s s C L e L e v S v l S l e n e n h h O s O s

Fig. J.8.1:

194

Organic fibers > 400 µm

t 40 n t u n o u c 30 o c e l e l c i c t ritr 20 a a P P

Particles > 400 µm (shiny, m etallic)

10

10 0

Particles > 400 µm (witho ut fibers)

g t g n e n i n i t h i h e b c c t a i it in c b w w s s a c n n O O

A A nn oio i t ata t stS nn O O

l l l e o r o r n t ntn ale oo pn cc a nn p OO

BB nn oo i i t atta t sS nn O O

0

s s C C e L e L v v S l l S e e n n h h O s O s

g g t e n n i n i i t h h e b c c tit a in i c b w w s a s c n n O O

A A n n o i io t t a a t t s S n n O O

Particle entry via the environmental atmosphere

ll l o e o r t tr n l n e n a p o n o c a c n p n O O

BB nn oo i tit ata t sS nn O O

The results show that only a very small number of critical particles > 100 µm are introduced. On considering the results of particles > 400 µm, only organic fibers are found in the particle traps. Particle entry via the environmental atmosphere is non-critical. J.8.2

Assembly station

Figure J.9 shows the results of an assessment of the assembly station (insertion of the piston) before optimization. For evaluation purposes, particle traps were positioned beneath moving elements close to the product inside the assembly station (pneumatic cylinders, linear axes, energy chains). The subsequent procedure and assessment is carried out in the same way. Particle count per measuring site > 100 µm 250

Particle count per measuring site > 400 µm 80 Particles > 400 µm (without fibers)

Particles > 100 µm (without fibers) org. fibers > 100 µm

200

t n u o 150 c e l c i t r 100 a P

Particles > 100 µm (shiny, metallic)

50 0

s i x a r a e n i l r e d n U

Fig. J.9:

is x a r a e in l r e d n U

c c i t it a a m m r u u e e e d n n i n p p l r r y e e c d d n n U U

r e d n il y c

g g a r a r d d e n le l b b i a a a h c c c r r e e d d n n U U

n i a h c

r e p p i r g r e d n U

r e p p i r g r e d n U

org. fibers > 400 µm

t 60 n u o c e l c 40 i t r a P 20

0

Particles > 400 µm (shiny, metallic)

s s i x ix a a r r a a e e n in i l l r r e e d d n n U U

c i ic t t a a m r r m e u e u e d d e n n n i n il p l p y r y r c e c e d d n n U U

g g a a r r d d e le i l n i b n b a a a a h c h c c r c r e e d d n n U U

rr ee pp pp i i rr gg rr ee dd nn U U

Particles captured using particle traps placed at selected sites inside assembly stations

The particle trap beneath the linear axis is of interest. It is clear that metallic particles > 100 µm and even > 400 µm were generated here. As this represented a constant particle source, the station was optimized as illustrated in Figure J.7.

195

Quality Management in the Automotive Industry

The current version of the published VDA volumes on quality management in the automotiv industry (QAI) can be found in the Iternet at http://www.vda-qmc.de. You can also order directly from this homepage.

Order from: Verband der Automobilindustrie e.V. (VDA) Qualitäts Management Center (QMC) 10117 Berlin, Behrenstr. 35 Germany

Telephone : Telefax : E-Mail : Internet :

196

+49 (0) 30 89 78 42-235 +49 (0) 30 89 78 42-605 [email protected] www.vda-qmc.de

Summary of direct contamination mechanisms due to packaging

The following table summarizes possible ways of minimizing the contamination of packaged goods by optimizing packaging methods, packaging means and materials. Contamination mechanism

Description

Component is #1 Entry of particles from the contaminated by particles entering the environment packaging from the atmosphere #2 Displacement from packaging to the packaged goods

Packaging contaminated through storage or prior transport; transfer of particles to components

Packaging means gives #3 Particle off particles to abrasion from packaging means components; alternatively, components damage surface of packaging means through abrasion during transport and thus become contaminated #4 Particle abrasion at component level

Components damage and thus contaminate one another

Example

Countermeasures

Natural dust

Seal load carriers

Particles from production processes

Use bags inside container

Hairs, fibers from workers Contaminated packaging means which has been delivered and directly reused Incorrect storage of packaging means

Clean and control load carriers regularly Use clean bag inserts (nonreturnable packaging) Use conductive materials

Electrostatically charged packaging means attract contamination

Use easy-to-clean materials and shapes

Bulk goods, non-secured layered goods and loose separated goods with sharp edges in packaging which is too soft or brittle, e.g. wood, cardboard or porous plastics

Fix components in place Ensure maximum packing density for layered goods in LC Use vacuum bags for bulk goods if this aids stability Use low-abrasion materials Do not use damaged packaging means

Bulk goods and nonPack components as secured layered goods with separated goods (e.g. with sharp edges compartments) or separately Use vacuum bags for bulk goods

#5 Componentcorrosion

Table D.2:

Components corrode during packaging processes, transport, storage

Components made of nonalloy or low-alloy steel

Use VCI materials as packaging means or corrosion protection agents Only handle components with gloves

Contamination mechanisms of packaged goods due to packaging means and transport, and ways to avoid or reduce them

65

Outer packaging:

Where packaging requirements depend upon the cleanliness grade, the main priority to consider is not the protection of the packaged components but rather the effect of the packaging on the external environment in the room. The most important aspect is the emission of particles and contamination into the manufacturing environment, which in turn could lead to their displacement of particles to the components stored or to be assembled or packaged there. The higher the cleanliness grade of the zone (see Chapter C: Environment) components are brought into, the higher the cleanliness requirements of packaging means and auxiliary materials. A load carrier or container is considered to be clean if relevant in-house cleanliness requirements have been fulfilled. Packaging should have the following properties: -

Its surfaces should generate or emit as little contamination as possible.

-

Its surfaces should be tear-free and impermeable

-

Its surfaces should be as resistant as possible to abrasion and the formation of chips

-

It should have geometries which are easy to clean

The outer packaging is selected in dependence upon the cleanliness grade of the assembly area. SLCs: Empty SLCs may be brought into the cleanliness zone (CG1) provided there is no risk of transferring critical particles to the clean area.

SLCs brought into a cleanliness room (CG2) must be additionally packaged during transport outside the clean area, e.g. by wrapping them in stretch film or using hoods. The use of interim layers (e.g. twin-wall sheets, coated abrasion-resistant cardboard) will also prevent the transport pallet from contaminating the first or bottom-most layer of SLCs. In a cleanroom (CG3), only clean SLCs from a defined in-house loop may be brought in. The SLCs must be regularly cleaned and controlled (no undefined load carriers from the user pool system). During transport outside the clean area, SLCs must again be covered in secondary packaging, e.g. wrapping or sealing in film or covering with a hood. 66

Deep-drawing / blister trays and bags: blister trays and bags may be brought into CG1 cleanliness zones provided there is no risk of transferring critical particles to the zone.

If blister packs and bags are brought into a cleanliness room or cleanroom (CG2 or CG3), they must be wrapped in secondary packaging during transport, e.g. in a closed SLC or sealed in an additional bag. Special load carriers: The material and design of special load carriers must be adapted to the cleanliness grade in order to minimize particle emission from them and the transfer of particles to the clean assembly area. Film (as secondary packaging, e.g. for SLCs): film used as secondary packaging must be removed and discarded before goods contained in direct inner packaging are brought into the clean area. To avoid displacement, the same member of personnel may not unwrap the film, remove components and carry out assembly tasks. Cardboard: boxes, separating elements or linings made of coated (hard) cardboard may be brought into a cleanliness zone. No cardboard may be brought into zones with a higher cleanliness grade.

The following table lists common packaging means and assesses their suitability for use as outer packaging in dependence upon the cleanliness grade of the assembly facility.

68

Packaging means

CG1 - cleanliness zone

CG2 - cleanliness room

Mesh pallet / universal LLC

Permitted if clean (in accordance with in-house Not permitted definition), special measures may be required

Universal LLC made of plastic

Permitted if clean (in accordance with in-house Only those from internal definition), special measures loop permitted may be required

Wooden LLC

Not permitted

Plastic SLC

Permitted if clean (in accordance with in-house definition) SLCs from pool also permitted

Steel SLC (coated)

Not permitted Wooden pallets are not permitted

Pallet

Stainless steel / plastic permitted

Clean SLC with additional measures permitted (in accordance with in-house definition), e.g. secondary packaging

CG3 - Cleanroom

Not permitted

Only those from internal loop permitted

Wooden pallets are not permitted Clean stainless steel / plastic pallets from internal loop permitted

Bag


Film

Any outer transport film is to be removed before bringing components into the clean area, regardless of cleanliness grade

Cardboard

Coated (hard) cardboard permitted

Special load carriers

Design and materials must be adapted to the cleanliness grade in order to minimize particle emission and displacement from carriers. Special measures may be necessary

Blister / deepdrawing tray


Separating elements

Only permitted if made from No particle-emitting materials permitted (paperboard, low-abrasion materials, cardboard, paper)., e.g. twin-wall sheets, lightweight coated cardboard also board made of PP or PE permitted

Table D.3:

Permitted with secondary Permitted with secondary packaging during transport packaging during transport

Only permitted as far as lock

Not permitted

Permitted with secondary packaging during transport

Overview of packaging means and suitability as outer packaging in dependence upon the cleanliness grade of the assembly area

69

D.3.2

Operative measures

D.3.2.1

Cleaning procedures for packaging

In order to assure the required cleanliness of reusable packaging, it must be cleaned at regular intervals. The type and frequency of cleaning procedure depend upon the cleanliness requirements of the components or aggregates to be packed as well as upon the packaging means or materials used. Cleaning procedures and suitability in dependence upon component cleanliness requirements:

The following table describes standard procedures for cleaning packaging in dependence upon the packaging means and materials used. The procedures are also assessed according to the cleanliness requirements of the components to be packed.. Note:

If reusable containers are used as direct packaging for cleanliness-sensitive components, e.g. SLCs or deep-drawing trays, they should be cleaned at defined intervals using an aqueous process. A defined level of cleanliness cannot be achieved by blowing or sweeping out containers.

Packaging means

Aqueous cleaning process (continuous process with subsequent drying*)

Manual cleaning with pressure washer

SLC

+

-


Mesh pallets **)

-

+

+

Deep-drawing containers

+

-


Blister trays

+

-


Special carriers

+

+


Bags (standard plastic bag)

No cleaning required single-use only

Twin-wall sheets

70

+

-

Dry cleaning process (beating, blowing, suction-cleaning, brushing)


Wetwiping process

-

+

Wooden LLCs **)

-

-

+

-

Hoods **)

-

+

+

+

Universal LLCs made of plastic

+

+


- Procedure is not suitable / cannot be implemented

+ procedure is suitable in principle

*) Drying variations / systems such as centrifugation, vaporization or dry-blowing **) These packaging means are cleaned more to reduce particle displacement in the clean area than to protect products directly because they may not be utilized as direct inner packaging

Table D.4:

Assessment of procedures for cleaning packaging means

Cleaning intervals in dependence upon cleanliness requirements: •

High cleanliness requirements

Reusable containers must be cleaned after each use. Where possible, packaging means are to be cleaned in the immediate vicinity directly before they are used again. If this is not possible, cleaned containers are to be transported and stored in such a way so as to maintain cleanliness levels. If cleaning procedures are not cost-effective, additional single-use inner packaging is to be used (e.g. bags) to prevent cleanliness-sensitive goods from becoming contaminated. •

Average and low cleanliness requirements:

Cleaning procedures are to be carried out and controlled at fixed intervals. D.3.2.2

Inspection of packaging means

Packaging means must be assessed to ensure that they are adequately clean. The manner (visual inspection or test procedure in accordance with VDA 19) and frequency of assessment is determined by the respective cleanliness specification. •

Inspection procedure

Inner (direct) packaging (blisters, bags, films and SLCs):

-

For surfaces coming into contact with the product, pressurerinsing test in accordance with VDA 19 (where possible)

71

-

Alternatively if not possible: Tapelift, wiping test with reference sample (see Chapter F: Assembly equipment )

Outer packaging (e.g. mesh pallets):

-

Visual inspection of surface characteristics using reference samples (image sample)

Described in compliance with the procedures and relevant test parameters laid down in VDA 19, see annex for examples of test specifications for evaluating the cleanliness levels of packaging means. D.3.2.3 Responsibilities – packaging

Responsibilities regarding the provision of cleanliness-suitable containers must be determined by the customer, supplier and logistics provider. From each of the three parties, a person in charge of controlling this is to be named. Elements of the agreement could include: -

Cleanliness requirements (relevant areas of packaging)

-

Method and frequency of cleaning procedures

-

Who is in charge of cleaning packaging and who controls and documents the quality of cleaning processes

-

Method and frequency of control

-

Delivery and storage of cleaned empty containers

-

Further handling of the packaging

-

Identification of cleaned packaging

-

Measures to be taken if cleanliness requirements are not fulfilled

-

Determining transport methods and conditions to and from cleaning location

D.3.2.4

Transport and lock concepts

Internal transportation – fundamentals

Packaging means can displace particles when brought into a clean area and may therefore only be introduced if they are free of critical contamination. Depending on the distance and duration of transport, 72

packaging means may become heavily contaminated. Therefore, the outermost packaging is not permitted in a clean area and must first be removed in a designated unpacking area. To prevent contaminated packaging means from being brought directly into a clean area, material flows must be controlled by an operative or physical barrier. Such barriers are known as locks. Bringing goods into a clean area: •

Cleanliness zone - CG1

If components are brought into the zone in carriers which were not additionally packaged during transport, organizational measures are required to prevent the risk of displacement. Components are to be unpacked and taken out of the container in a place separated from the assembly area. Where appropriate, carrier units can simply be brought to the zone boundary and components transferred into the zone from there. If components are delivered with secondary packaging (e.g. components in bags or SLCs), this must be removed before they are brought into the zone in their inner packaging.

e n r i t a t e l s u l o e t t a p a h h g g s e u e r o g r g b m a

g s n i i n t s i a n d n t a d n e n e o o n k c p i c t t a h p e m l l g n a o u u c p r o n h a b s e e l m c

Fig. D.5:

l o a d i n g s t a t i o n

components transferred to roll cart

cleanliness


zone roll cart loaded with aggregates aggregates transferred to mesh pallets

components brought to assembly station


transfer station

Example of a logistics concept for an assembly facility in a cleanliness zone

73

•

Cleanliness room - CG2

Only packaging means which have been additionally packaged during transport may be brought directly into a cleanliness room after they have been unpacked. The secondary packaging (e.g. hood and stretch film) is removed in a designated unpacking / goods transfer area immediately before the packaging means is brought into the cleanliness room. unpacking/

cleanliness

transfer area

room

SLC containing aggregates is brought out

clean components in SLC on pallets s e n t r i e a t l l s u a e o p t n a t g h g o e r u s o C g r g b L a S

Fig. D.6:

SLC transferred to roll cart





component cleaning system with airlock function

Example of a logistics concept for an assembly facility in a cleanliness room

If containers are only utilized in the cleanliness room and unpacking area (i.e. only move back and forth between the component transfer area and cleanliness room) or if load carriers are cleaned appropriately, no secondary packaging is required. The cleaning plant represents a lock. •

Cleanroom - CG3

The secondary packaging, e.g. transport film, is removed immediately before goods enter the material lock. This prevents inadequately clean packaging or contamination from transport from being brought into the locks. Before being brought into the cleanroom, the inner packaging (e.g. SLC, bag) is first brought into the material lock and wiped clean with damp cloths to remove any coarse contamination originating from the outer or 74

secondary packaging. This cleaning step is not required if components are taken out of the inner packaging in the material locks (e.g. from blister trays or bags in the SLC) before being brought into the actual cleanroom assembly area. This requires a double unpacking procedure. The cleaning plant represents a lock because components are brought directly into the cleanroom from the cleaning plant after cleaning. cleanroom

material airlock s e n t r i l e a t l s u a o e t t p a h n g g o e u s r o C g r g b L a S

staff airlock

clean SLC brought in via airloc

SLC containing aggregates brought out via airlock

clean components in SLC on pallets brought in

component transfer



Abb. D.7:



componentcomponentcleaning system with airlock function

Example of a logistics logistics concept for an assembly facility in a cleanroom

Goods leaving clean areas: Aggregates are packaged after assembly to maintain their level of cleanliness. The type of packaging is selected according to the relevant cleanliness requirements. •

Aggregates sensitive to contamination:

Direct component packaging is carried out with the same level of cleanliness as that used for their assembly. The packaging / containers must fulfill the requirements of the packaging means of the respective zone (outer surface) and the product (inner surface). If a component or aggregate requires secondary packaging which does not correspond with the cleanliness grade of the zone, this has to be applied outside the zone. Exception: if the next process step is executed in a zone with a higher CG, packaging must fulfill the higher requirements. 75

•

Aggregates not sensitive to contamination:

When packaging assembled aggregates which are not sensitive to contamination before they leave the clean area, the packaging means must fulfill the requirements of that zone. If necessary, the same measures as those for bringing goods into the zone are to be observed (e.g. packaging area). Examples of such end-products include steering gears and gearboxes. Summary / overview: Step

CG1 – cleanliness zone

Entry via material lock

CG2 – cleanliness room

Regulations for unpacking load carriers without secondary packaging are to be drawn up and observed

Only packaging means which have been wrapped in secondary packaging during previous transportation may be brought into the Remove any secondary cleanliness room packaging (e.g. hood, stretch film) at zone In such cases, boundary before secondary packaging is bringing in to zone to be removed in the unpacking area immediately before goods pass through the material lock Not required for internal load carriers or if the packaging was cleaned before being brought in

Exit via material lock

CG3 - Cleanroom Remove secondary packaging (e.g. hood, stretch film) in the unpacking area immediately before goods pass through the material lock Remove next layer of packaging in the material lock If no additional inner packaging is present, packaging must be cleaned before being brought in

Empty containers exiting the zone and being transported to another area must fulfill the cleanliness requirements of the subsequent zone

Aggregates not sensitive to contamination Exit via material lock

Direct component packaging is carried out in the zone where the aggregates are assembled

Packaging / containers must fulfill the requirements of packaging means of Cleanlinesssensitive aggregates the subsequent zone (influence on exterior environment) and on the product (influence on interior environment) Exception: if the next process step takes place in a zone with a higher CG, packaging must fulfill the higher requirements

Table D.5:

76

Main points to consider when cleanliness-sensitive components and aggregates are brought into / taken out of an assembly area via a material lock in dependence upon the cleanliness grade

External transportation - fundamentals

Main points to consider: -

Minimum transport distances and times

-

Low vibration levels

-

Protect products from becoming damaged inside the packaging

-

Protect packaging against damage

-

Additional protection against wetness, humidity and fluctuations in temperature (e.g. open racks conveyed on transport vehicles outside production halls are to be additionally covered)

D.3.2.5

Storage

General information:

Components are to be stored so that the required level of cleanliness is maintained for the duration of storage. Storage areas must be kept separate and their cleanliness grade clearly marked. Packaging has to be weatherproof if stored outside. Protective surface layers, coatings and barriers must be impermeable to water vapor. Goods may only be stored outside if placed on an appropriate underlay (e.g. boards, pallets) in designated, clearly-marked areas. Storing components:

In accordance with surface cleanliness requirements, non-packaged components are to be stored in clean storage areas with the appropriate cleanliness grade. If requirements for inner component surfaces are higher than those for outer surfaces, such components may be stored in areas with a lower cleanliness grade provided all openings are hermetically sealed for the entire storage period. Components made of materials liable to corrode must be protected accordingly, e.g. by packing them in VCI protective foil. Packaged components do not need to be stored in a clean area provided the packaging ensures the required degree of protection. Packaged components may only be stored in a clean area if the packaging itself / unpacking process does not impair the cleanliness grade of the storage area. A sub-domain - adjacent to the clean area but with different requirements - may be used for unpacking purposes.

77

Special storage areas are to be set up and appropriately marked for components rejected because they have been damaged or their surfaces contaminated. Storing packaging means:

Clean / cleaned packaging means are to be stored in accordance with the cleanliness level of the components to be packed inside. Clean containers are to be clearly labeled as such. D.3.2.6

Unpacking and commissioning

In general, packaging is selected (and designed) according to its ability to be opened and closed in a cleanliness-suitable manner. Independent of cleanliness requirements, the following fundamentals are to be considered:

78

-

Each user is responsible for handling packaging correctly.

-

Components and aggregates may only be packed in the prescribed packaging means

-

The covers and lids of containers are to be developed and used in such a way so that any existing (transport) contamination does not enter into the container.

-

Cardboard may not be torn open; it may only be opened at designated sites using tools prescribed for the purpose. This is to be taken into account when designing cardboard packaging. If cutting tools are utilized, care must be taken to ensure that packaged goods do not become damaged.

-

Under no circumstances may members of staff carrying out cleanliness-critical assembly tasks remove packaging. Unpacking and commissioning are also to be carried out separately. If this is not possible, hands are to be washed between tasks (e.g. damp cloth) or disposable gloves worn or changed. Particle-generating and cleanliness-sensitive processes are to be kept strictly separate in order to avoid particle displacement.

-

Clean gloves are to be worn when commissioning components liable to corrosion.

-

Unprotected components are to be unpacked and stored in different areas (separated at least by screens).

-

Once unpacked, components are to be brought immediately into an appropriately clean assembly or storage area. This prevents particle displacement from contaminated packaging materials or containers.

-

Where possible, components are to be unpacked immediately before assembly. Sealing plugs, adhesive films, etc. are to be removed immediately before subsequent processing.

-

Quality control is to be informed if concealed transport damage to packaging / components is discovered. Damaged load carriers and packaging means (e.g. in accordance with reference sample) must be rejected.

-

Packaging waste is to be removed immediately in accordance with the regulations.

-

Due to increased levels of contamination, unpacking areas are to be cleaned using a wet process at regular intervals / more frequently.

-

Any remaining components are to be handled in compliance with relevant cleanliness requirements.

-

Work instructions regarding the opening of packaging are to be observed.

Annex A.D

The cleanliness values shown below are examples of values obtained from cleanliness tests carried out on typical packaging means in various states. The data is only intended to give an impression of potential particle charges on packaging means and does not represent a recommendation or regulation.

79

A.D.1

Small load carriers - SLCs

SLC from pool 250 m c 0 200 0 0 1 r e p 150 t n u o c 100 e l c i t r 50 a P

0 100 - 150 µm

150 - 200 µm

200 - 400 µm

400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.8:

Cleanliness value of SLC from pool

SLC cleaned using defined procedure 250 m c 0 200 0 0 1 r e 150 p t n u o 100 c e l c i t r 50 a P

0 100 - 150 µm

150 - 200 µm

200 - 400 µm

400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.9:

80

Cleanliness value of SLC cleaned using a defined procedure

A.D.2

Plastic bag

New clip closure bag 14 2

m 12 c 0 0 0 10 1 r e 8 p t n u 6 o c e l 4 c i t r a 2 P 0 50 - 100 µm

100 - 150 µm 150 - 200 µm 200 - 400 µm 400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.10:

Cleanliness value of bag with clip-closure

New film tubing 5 2

m c 0 0 0 1 r e p t n u o c e l c i t r a P

4

3

2

1

0 50 - 100 µm

100 - 150 µm 150 - 200 µm 200 - 400 µm 400 - 600 µm 600 - 1000 µm

> 1000 µm

Particle size

Fig. D.11:

Cleanliness value of film tubing

81

E:

PERSONNEL

E.1

Introduction

This chapter deals with methods of confining and controlling critical particle contamination caused by personnel and deals mainly with workers in direct contact with manufacturing processes and products. First and foremost, the successful and efficient operation of a clean assembly facility requires the commitment and support of management staff right up to the top company management / VDI 2083 / 11 – Cleanroom technology – Quality control. The inclusion of employees in company structures and activities ranges from machine operators and assembly workers to delivery staff. Planners and managers need to take this broad spectrum of potential access and influencing possibilities into careful consideration, e.g. in the form of training courses for a new member of staff from an external company in charge of the regular cleaning of the assembly area, or work instructions regarding personnel conduct during refitting measures or the installation of a new assembly facility. Of all the influencing factors dealt with in the guideline, personnel represents the highest risk as far as the control of critical contamination levels is concerned. Accidental or even intentional misconduct may lead to damage, the cause of which is very difficult to pinpoint or comprehend. This could result in high but avoidable costs spent trying to find the cause and introducing unnecessary or even incorrect failure prevention measures. Example:

82

In a costly failure analysis of several zero kilometer defects, metal particles and abrasive contamination are identified as the cause. They originate from a framework construction no longer in use in the assembly area. Out of laziness, SLCs are not additionally covered when nearby cutting processes are carried out because the parts inside are wrapped in plastic bags in compliance with regulations. On removing the components, the metal particles - which under normal conditions would not be present - are displaced to some of the components. The quality control department of the company is now investigating whether the supplier of the parts may be responsible for the origin of the contamination.

The origin of the damage cannot be located because there is no systematic cause of malfunction but rather a unique chaotic outlier due to personnel misconduct. Personnel attitude is a decisive factor in successfully controlling clean assembly. The complexity of technical cleanliness as a quality characteristic makes it absolutely essential to sensitize the workforce in this regard and to give personnel practical instruction and training. Workers must also take into account the fact that unscheduled activities may affect the cleanliness of products and the environment. If case of uncertainty, further instructions are to be obtained or appropriate measures taken. It is vital for personnel to understand that thoroughness, consistent closed loops and continuity form the basis of a functional clean assembly facility. Any sudden decrease in cleanliness measures (e.g. for reasons of cost or time) may lead to lasting weaknesses in established regulations and impair the credibility of management staff and other persons with a role model function. Recommendations for clothing and conduct within the scope of logistic processes are listed in the following section. They depend upon the cleanliness grade of the assembly area, which is higher than that for component cleanliness (see Chapter C: Environment ). In order to establish the necessary basic stability in a clean area where personnel is present, a number of regulations and measures are required. Recommendations for this can be found in the following paragraphs. Staff members are to be actively included and given responsibilities concerned with cleanliness. Measures and regulations are to be formulated clearly and comprehensively to substantiate the need for / benefits of them. The necessary means and materials are to be made available for this. Personnel activities associated with cleanliness are to be included in the work plan and the time required for them calculated.

83

E.2

FUNDAMENTALS

Personnel plays a major role in assembly cleanliness (see Figure E.1 and Table E.1).

Eliminator

Initiator

Staff Source

Fig. E.1:

84

Carrier

Personnel considered from the point of view of assembly cleanliness

E.3

QUALIFICATION AND CLOTHING

E.3.1

Measures and recommendations - conceptual

In the following paragraphs, requirements and measures are described and classified where appropriate. E.3.1.1

Training with focus on assembly cleanliness

Which groups of people reguire training? -

Management, company executives

-

Buyers / procurers of operating utilities

-

Planners (processes and implementation of operating utilities)

-

Design engineers, quality planning and control

-

Personnel for assembly and reworking processes

-

Personnel for component provision and retrieval

-

Machine fitters, repair and maintenance personnel,

-

Building maintenance personnel

-

External companies: e.g. construction workers, service technicians, cleaning companies

Possible training courses: 1.

Basic sensitization: all groups of people are required to attend. The contents of this training course are identical for all groups [see Paragraph B below]; possibly with the exception of external companies. Scope and duration can be adapted to the target group in question.

2.

Rules regarding entering and staying in clean areas: all groups of people are required to attend. The contents of this training course are identical for all groups. Adapted short training courses, especially for employees of external companies who only visit once / sporadically.

3.

Logistics and cleaning maintenance in the vicinity of an assembly facility: this training course is aimed at all members of personnel regularly present in the clean assembly area as well as planners.

86

4.

Cleanliness-suitable assembly: this training course gives information about minimizing and avoiding contamination in assembly and reworking processes. The course is envisaged for all members of personnel regularly present in the clean assembly area as well as for planners.

5.

Main focal points regarding cleanliness: this training course is aimed at selected groups of people and conveys specific information, e.g. maintenance and repair, cleanliness-suitable design of assembly equipment, cleanliness-suitable construction, etc.

No recommendations can be given here regarding the frequency of training measures with a view to updating (further training) or refresher courses (revision). Training concept for basic sensitization (contents of course): -

History, development of the necessity of degree of cleanliness aspects

-

Identifying damaging influences (particles, not chemicals). Contamination (from processes and the environment). Demonstrating the need for everyone to contribute towards cleanliness in the assembly area (despite all previous efforts)

-

Depicting the entire process chain (construction, casting, mechanical processing, cleaning, transport, storage, etc.), also with regard to suppliers and customers

-

Comparing particle sizes, visualization

-

Naming / visualizing defects, subsequent Examples (photos) of parts not in order

-

Specific photographic examples: wrong / right for measures

-

Face-to-face communication: emphasizing the importance of individual contributions from staff members

-

Defined instructions / measures with regard to an assembly task: from the actual assembly process right up to packaging and logistics

-

Certificate of participation

damage,

costs.

87

E.3.1.2

Clothing

Clothing has various functions from the point of view of cleanliness: -

The amount of fluff generated by clothing can be significantly reduced by using suitable textiles

-

If clothing is only worn in the clean area, particle displacement from contaminated areas is decreased.

-

By covering up skin and hair, the quantity of (human) particles given off into the environment is reduced.

-

The type of clothing worn in a clean area is different to that worn in non-controlled areas; this makes personnel more aware of the special rules, requirements and responsibilities regarding cleanliness.

-

In assembly facilities with high staffing percentages, the wearing of low-fluff clothing can considerably reduce dust and fluff levels.

The clothing concepts shown below in dependence upon cleanliness grade have proved to be effective. Clothing requirements in dependence upon cleanliness grade Requirement (in order of increasing cleanliness requirements)

CG0

CG1

SaS2


SaS3

Comment

Cleanroom

Outer clothing 1. Only private day-to-day clothing

+

-

-

-

2. Only conventional work clothing

o

+

-

-

3. Overcoat / overall, only for use in clean area (single-use / reusable), lowfluff

o

o

+

4. Clothing recommended for the corresponding cleanroom class (singleuse / reusable)

o

o

o

88

1)

1)

+

+

1)

Dependent upon use

Clothing requirements in dependence upon cleanliness grade Requirement (in order of increasing cleanliness requirements)

CG0

CG1

SaS2


SaS3

Comment

Cleanroom

Footwear 1. Only private day-to-day / safety footwear

+

+

-

-

2. Private day-to-day / safety footwear in combination with e.g. shoe-cleaning machine or tack mat

o

o

+

-

o

o

o

+

1. None

+

+

+

-

2. Hair net / cap

o

o

o/+

+

o

o

o

o/+

Product dependent

o/+

Product dependent for staff with beards

3. Overshoes, single-use / reusable only for use in clean area Separate footwear , reusable; only for use in clean area

Head gear

3. Hood

4. Mask

o

o

o

If contamination directly generated by staff is critical: Head gear and mask, e.g. to retain skin flakes and loose hairs. Head gear is also to be worn in CG1 and CG2 if members of staff need to bend over exposed products or functional surfaces in order to carry out tasks. Legend: + = suitable / yes

- = unsuitable / no

o = not required

Table E.2: Clothing requirements in dependence upon cleanliness grade

Work safety (e.g. safety footwear, protective gloves or helmets, skin protection means) and also ESD and corrosion protection are to be individually adapted to cleanliness aspects and regulated.

89

Gloves: -

It must be ascertained whether gloves need to be worn to protect goods against particulate contamination (not against corrosion).

-

If the wearing of gloves is mandatory, suitability must be determined with regard cleanliness aspects.

Note:

Particles could collect on the surface of gloves and cause displacement.

-

Conditions regarding the use of gloves are to be laid down in work instructions; e.g. how often they need to be changed.

-

Even where gloves are worn: unnecessary contact with other objects and surfaces is to be avoided.

In some cases, additional rules may apply: -

Contaminated or greasy gloves may not be worn

-

Gloves may not be used to remove contamination

-

Gloves which have fallen on the floor may not be worn again

-

Used gloves are to be removed or clean gloves put on after carrying out cleaning tasks on machines, tools and work stations. This also applies for repair and maintenance tasks.

E.3.1.3

General rules

The following recommendations are mainly concerned with the possible content of work instructions and make no claim to be complete. Shown below, the classification of rules of conduct demonstrates that various measures apply for different cleanliness grades. This substantiates the experience that quality improvement is not necessarily due to the design of a room but rather to the work instructions enforced.

90


CG0

CG1

CG2


1.

2.

3.

4.

5.

6.

7.

CG3 Cleanroom

Unnecessary contact with potentially contaminated surfaces and objects is not permitted

o

+

+

+

Members of staff performing assembly tasks may not come into contact with secondary packaging

o

+

+

+

Prescribed work clothing may not be worn outside the zone

o

o

+

+

Clothing may not come into contact with functional surfaces

o

+

+

+

Prescribed footwear may not be worn outside the zone

Prescribed work clothing must be worn in the zone.

Comment

1)

-

-

o

+

-

1)

+

+

To be cleaned before entering the clean area

+

Food may not be brought into the zone

Only permitted in designated areas Alternative: o

+

+

+

As an exception, only permitted during allocated time period

91


CG0

CG1

CG2


8.

10.

11.

12.

92

All contaminated objects are to be cleaned before bringing them into a zone with a higher cleanliness grade

2)

o

+

2)

+

+

2)

+

+

Staff is responsible for safeguarding cleanliness when using tools, containers and components.

o

+

+

+

o

+

+

+

o

+

+

Exception possible, provided there is no risk of contaminatio n

+

No tasks generating dispersible particles are permitted (e.g. abrasive cutting, blowing)

Awareness of risk of particle detachment from moving and / or painted parts

Comment

Cleanroom

Doors and windows are to be kept closed o

9.

CG3

+

Applies for assembly, maintenance, repair tasks, etc. Where required, take appropriate measures (e.g. suction cleaning, covering surfaces)

Any flaws noticed are to be dealt with in accordance with the regulations


CG0

CG1

CG2


13.

14.

15.

16.

17.

Care is to be taken to ensure that contamination does not fall onto or enter components

Without exception, any components which have been dropped are to be considered as contaminated and subsequently handled specially in accordance with regulations Only necessary tools are to be provided and utilized .

Tools which have been dropped on the floor may not be reused until they have been cleaned During downtimes, oiled or greased parts are to be protected against contamination (e.g. by covering them).

o

o

o

o

+

+

+

+

+

+

+

+

CG3 Cleanroom

+

+

+

+

Products awaiting completion which are located on conveyors are to be covered during assembly downtimes

E.g. packing or unpacking, removing components from shelves, opening machines and equipment Fix further procedures or usage (e.g. disposal, cleaning)

Keep and store tools in a designated place E.g. wipe with clean cloth

3)

o

+

o

3)

o

+

o

3)

o

3)

o

3)

The same principle also applies for thread lock fluid, adhesives, liquid sealing compounds, etc. 18.

Comment

Unless environment al atmosphere has detrimental influence on product

93


CG0

CG1

CG2


19.

20.

21.

22.

CG3

Comment

Cleanroom

If gloves used at a “clean workbench” come into contact with external objects (e.g. pulling up a chair), they are to be changed immediately

+

+

+

+

Contamination on covers or housings is to be removed before opening or removing them

o

+

+

+

During machine failures, fitting and maintenance tasks or construction work, load carriers are to be appropriately covered; close plastic bags or film inlays

o

+

+

+

Unprotected cleanlinesssensitive components may not be stored in the packaging area

o

+

+

+


Table E.3: Examples of general rules and measures

E.3.1.4

Logistics

The following recommendations are mainly concerned with the possible content of work instructions and make no claim to be complete. Examples of measures: logistics in the vicinity of the assembly facility Measure / requirement

CG0

CG1

CG2

CG3


1.

94

Each user is responsible for handling packaging carefully and correctly

+

+

+

+

Comment


CG0

CG1

CG2

CG3

Comment


2.

3.

4.

Components and aggregates may only be packed in the permitted packaging means Damaged load carriers and packaging means are to be rejected

+

+

+

+

+

+

+

+

Secondary packaging may not be removed in the assembly area

o

+

+

+

Assess using reference sample E.g. contamination could fall to the ground and subsequently stirred up into the air and displaced. Exception: only with special measures

5.

6.

7.

8.

Components may not be packed / unpacked in the vicinity of the assembly facility

o

+

+

+

SLCs or stackable containers holding single components, units or completed products may not be deposited directly on the floor

+

+

+

+

Used packaging and covers are to be placed in designated areas

o

+

+

+

Once unpacked, components are to be brought immediately into the prescribed assembly or storage area

o

+

+

+

Only permitted in designated areas Instead: use plastic pallets, transport roll carts, lids, etc.

Reduced risk of cross contamination from contaminated packaging means

95


CG0

CG1

CG2

CG3

Comment


9.

Unprotected components may not be stored directly next to transport pathways, doors, rolling doors, windows or skylights

o

+

+

10. If processes are interrupted, load carriers are to be appropriately covered and plastic bags or film inlays closed

-

+

o

1)

o

1)

11. Load carriers may only be opened immediately before removal of components

-

+

o

1)

o

1)

12. Care is to be taken to ensure that components do not become contaminated by soiled packaging

o

+

+

13. Cardboard boxes may not be torn open; they are to be opened at predetermined points using prescribed tools 14. Folded films and foils with contaminated outer surfaces may not be folded inwards again

o

1)

Unless the environmental atmosphere has detrimental influence on product

+

2)

o

-

+

-

+

2)

+

-

2)

+

Unsealed cardboard materials are not permitted

Instead, leave load carriers open, or use new film / foil or fixed covering hood


Table E.4:

96

Examples of rules relevant to logistics in the vicinity of the assembly facility

E.3.1.5

Keeping work areas clean

Examples of cleaning measures Measure / requirement

CG0

CG1

CG2

CG3

cleanliness zone

Cleanliness room

Cleanroom

Comment

1.

Use of compressed air in manual cleaning processes is not permitted

o

+

+

+

2.

Use of wiping cloths and other cleaning materials which may give off fibers and fluff is not permitted

o

+

+

+

3.

Used wiping cloths and cleaning materials are to be disposed of immediately in designated waste containers and not left lying around

o

+

+

+

May be reused; follow regulations.

4.

The following are to be cleaned after use and as required in accordance with work instructions:

+

+

+

+

Description of when / how to be cleaned must be included in work instructtions as well as a definition of the terms “as required” and “if judged necessary” Measure has a more esthetic / psychological meaning than actual function.

Placement areas, workstations, grab containers, transport containers, workpiece carriers, machines, equipment, etc 5.

The floor in the area of the workstation is to be kept clean

+

+

+

+

6.

Due to increased contamination levels, packing areas are to be cleaned more frequently and wet processes used

o

+

+

+

Instead, use suction cleaning systems or vacuum cleaners


Tabelle E.5:

Regulations concerned with keeping work areas clean

97

E.3.2

Accompanying measures and considerations

Right from the start, staff members are to be included in the planning and design of clean areas. To optimize a clean assembly facility from the staff point of view, the following points should be given priority: 1.

Execution of especially cleanliness-critical assembly steps (also including any necessary rework steps); this is a systematic source of error / direct influencing factor

2.

Control of sensitive component surfaces and active removal of any contamination present; this is a direct influencing factor

3.

Risk of displacement of contamination by workers handling clean functional product surfaces; this is a random source of error / indirect influencing factor. In such cases, it may make sense to separate assembly tasks strictly from ancillary activities (mixed tasks).

Wherever possible or as required, the aspect of degree of cleanliness must always be taken into consideration when designing and organizing an assembly facility. In order for cleanliness measures to be transparent to staff, a number of regulations are required, e.g.: 1.

Staff responsible for clean areas

2.

Rights of access to clean areas; entrance only permitted for limited members of staff

3.

Staff instruction and training with regard to cleanliness requirements. Determination of target groups (e.g. management, workers, cleaning staff, maintenance staff, etc.) and content, dates and frequency of training measures.

4.

Briefing about workstation and surrounding area

5.

Course of action if components have been incorrectly packed, supplied in contaminated load carriers or if components are contaminated.

6.

Written work instructions, e.g. regarding:

98

-

Entering and leaving clean areas and bringing goods in / taking them out

-

The use of special clothing (if required) and changing frequency

-

Rules of conduct in the clean area

-

Handling cleanliness-sensitive goods including auxiliary materials (oil, adhesives, sealing compounds, grease, thread lock fluid, etc.)

-

Carrying out especially contamination-critical assembly steps (also including any necessary rework steps)

-

Assessing / verifying the cleanliness of packaging, load carriers, components and aggregates

-

Opening and closing packaging

-

Using windows, doors, gates and / or locks

-

Eating, drinking and storing foods and beverages

-

Waste disposal

-

Conduct during maintenance, repair work especially when production is in progress

E.3.2.1

/

modifications,

Mixed tasks

On the scale of importance of indirect contamination influences and mechanisms, displacement is one of the greatest risks. Mixed tasks carried out by workers are therefore a key point in the risk analysis and avoidance strategy. The degree of contamination risk associated with mixed tasks carried out on sensitive goods must be assessed and analyzed individually. Contamination may be displaced via hands, gloves, clothing or footwear and transferred to functional surfaces and the direct environment when certain assembly tasks are carried out; e.g. 1. Handling contaminated packaging and load carriers (e.g. removing outer or secondary packaging) 2. Handling non-cleaned or contaminated components and tools 3. Mechanical processing (e.g. scarfing a welded joint) 4. Manual assembly tasks in conjunction with oiled components or handling assembly auxiliary fluids 5. Cleaning (e.g. load carriers, work station) 6. Maintenance and repair tasks

99

Remedy (e. g.): -

Plan work sequences carefully in order to avoid mixed tasks with displacement risks

-

Clean hands after carrying out unclean tasks

-

Wear gloves when carrying out unclean tasks and remove used gloves afterwards

-

Wear disposable gloves when executing unclean tasks and remove used gloves afterwards

E.3.2.2

Displacement through contact

This generally applies to workers handling the sensitive functional surfaces of products. The most important point is: it is prohibited to come into contact with potentially contaminated surfaces which are not related to the task at hand / planned work sequence.

Potentially contaminated surfaces:

• Used wiping cloths

Product area:

• Floor / footwear

Worker:

• Outer packaging (e.g. stretch film/ mesh pallet)

• Hands

• Base of contain ers (e.g. load carriers, vibratory feeders)

• Clothing

• Tools / workpiece receivers

• Gloves

• Components • Tools • Auxiliary aids and materials • Work surface

• Operating u tilities (inside) • Work surfaces • Components of l ower cleanliness class • Upper surfaces of covers / hou sings/ storage sh elves

Abb. E.2:

100

Displacement of contamination through contact

Displacement caused by a worker coming into contact with critical surfaces

Example:

Due to the design of the product and the assembly sequence concerned, a worker may have to handle components which, as far as the assembly function is concerned, are not subject to cleanliness requirements. For example, this could be the non-deburred surface of a non-critical gray iron attachment. Here, it could be stated where the component is to be manually held in order to avoid burr detachment. Single-use cloths could be made available in dispensers to enable workers to clean their hands before touching a sensitive component surface (e.g. seal).

Similar examples are found more often in real assembly scenarios than anticipated during planning. In such cases, the greatest potential for a continuous improvement process (often with relatively simple means or measures) is for a skilled motivated employee to think proactively while working. E.3.2.3

The worker as an activatos and remover of particles

This deals with active measures which can be carried out by staff during assembly. For example, each worker is responsible for checking a specific section of a component or aggregate for possible contamination (visual 100 % check). Sequences are to take into account that n. i. O. findings may occur and that rework may be required (removal of component / aggregate from the zone via the lock, or manual particle removal by the worker). Particle removal techniques which can be integrated into the assembly sequence include: Magnetic rods, suction-cleaning, wiping, etc. Examples of work instructions: -

Discard used screws and use new ones.

-

After pushing in jack, clean Point X of aggregate with hand-held vacuum cleaner.

-

Fit drill bit snugly into screw head to tighten or loosen screws.

101

E.3.2.4

Examples of typical contamination risks

Particles can become detached, disperse into the air and settle on unprotected surfaces in the course of many processes. Such processes are therefore not permitted in clean areas during production. Examples of typical contamination risks Process

Possible remedy

Sweeping

Wet-wiping or suctioncleaning

Cleaning, blowing or drying with compressed air or gas

Suction-blowing or encapsulation with defined suction cleaning

Drafts due to opening doors, windows, skylights or gates

Design and use motor-driven gates (roller gates / swing gates) as locks. Install air conditioning. Lockable windows.

Constructional (renovation) measures

Use curtains to protect assembly areas or stop assembly if necessary. Carefully organize relevant areas before commencing construction work. Clean more often and carry out general clean on completion of construction work.

Table E.6:

102

Comment

Dispersion and sedimentation of contamination onto surrounding structures and clothing

Standard material flows and sequences are often disturbed. Construction area and storage spaces for load carriers and goods intermingle. Displacement of contamination via staff and material.

Examples of typical contamination risks (see Table E.1 Relevance of staff with regard to assembly cleanliness; the worker as an activator))

F:

ASSEMBLY EQUIPMENT

F.1

Introduction

Clean components ready for assembly are generally protected against contamination before they are (further) processed. During assembly, components and products are directly exposed to potentially damaging influences from manufacturing processes, assembly equipment, staff and the environment. For the purposes of simplification, in the guideline operating utilities such as automated devices, machines, manual workstations and assembly stations have been grouped together under the term assembly equipment. In order to take the numerous elements and functions of assembly equipment into account, it has been divided into sub-groups such as tools, auxiliary materials, etc. The construction and scope of assembly equipment depend entirely on the process and product in question. For example, as opposed to the spatial assembly environment, the state of knowledge in December 2009 did not enable the criteria and measures presented here concerning assembly equipment to be clearly delineated or classified with regard to costs and benefits. Therefore, the methods described here regarding cleanliness-suitable design and usage of assembly equipment need to be individually assessed and implemented to the best of one’s knowledge. Example:

In one case, by encapsulating a machine, damaging particles from the environment can be effectively kept out and lead to improved results. In another case, particles generated inside a machine are much more critical and cannot escape, leading to high concentrations inside the housing and significantly poorer results.

Especially in assembly processes , a higher number of particles may be generated and emitted in the vicinity of the product. However, if an intermediate or final cleaning step is integrated at a suitable place, the damaging particles - which were introduced or unavoidable in the past can be largely eliminated (for more information, see also corresponding subchapter ). Methods for characterizing the presence of particles on and in assembly equipment are described in Chapter G: Assessing cleanliness factors .

103

F.2

Fundamentals

As far as the aspect of assembly equipment is concerned, a number of contamination risks are intermeshed: 1. Particle generation due to the assembly process itself with possible consequences: a) Displacement of particles to functional product surfaces (example: during screwing processes, particles are generated in the threads and fall onto the functional areas) b) Emission of particles into the process environment with possible sedimentation directly onto functional surfaces : e.g. abrasion from inserting a drill bit or splinters from a hammering tool (e.g. plastic hammer) c) Corresponding risks may also exist if joins are disconnected during work sequences or processes; e.g. removing screws from bearing seats. 2. Release of particles into the process area a) durch Funktionselemente der Einrichtung (Betriebsmitteltechnik). Häufig: mechanischer Abrieb; z. B. Linearantrieb, Elektromotor, Zustell- und Handhabungsmechanik. b) durch Alterung und zunehmenden Verschleiß von Materialien aspects: • materials

Montagestation Assembly station Environment Umgebung

Bauteile Components

Handling Handhabung

Operating utility Betriebsmittelcomponents komponenten and tools

und Werkzeuge

Feeding

Joining processes

systems Zuführtechnik

Fügeprozesse

Staff Personal

• design • maintenance

Product Erzeugnis

• output • attrition • deterioration

MediaMedien / auxiliary aids / Hilfsstoffe

Load carrier / /packaging Ladungsträger Verpackung

• keeping

clean

• integrated

cleaning •

Fig. F.1:

104

…

Assembly equipment – concurrence of multiple influencing factors

3. Entry of particles into the process area due to a) Material feeding technology (e.g. contaminated conveyor or contaminated workpiece carrier), b) Contaminated outer surfaces of components, tools and load carriers, c) Manual staff involvement (e.g. displacement via hands, sleeves, etc.), d) Airborne / sedimenting particles from the environment (e.g. absence of encapsulation or on opening a machine because of malfunction). When designing assembly equipment from the point of view of cleanliness, aims and strategies strive to maintain the cleanliness of •

Functional component surfaces,

•

Auxiliary materials awaiting processing; e.g. sealing compound,

•

Tools and auxiliary materials / assembly aids utilized; e.g. casing for assembling shaft seals,

•

Objects (general) coming into direct contact with functional surfaces; e.g. measuring sensors

•

Objects and surfaces (general) which have to be touched by the worker, e.g. in order to process cleanliness-sensitive components.

Special attention is to be given to processes and machine parts which are per se active sources of contamination in the direct vicinity of sensitive goods. Note:

This especially concerns the risk of contamination falling directly onto objects requiring protection.

With manual workstations, priority must also be given to the consideration of displacement risks by the worker and his influence on particle generation due to the individual way he uses tools or carries out assembly steps.

105

F.3

Design

F.3.1

Measures and recommendations - constructional

F.3.1.1

Fundamental design principles

The fundamental principles describe potential improvements which can be made to manual workstations and also automated assembly devices. -

As few horizontal surfaces as possible

-

Sloped surfaces (e.g. covering surfaces) to prevent objects from being placed or contamination accumulating on them

-

Smooth surfaces without depressions, gaps, etc.

-

Where possible, rounded corners and edges

-

Easy access for cleaning

The following approaches are recommended for dealing with particle sources (e.g. moving, abrading mechanisms): -

Do not install above sensitive surfaces.  The mechanical elements required for the core process (i.e. particle sources) should be located below work pieces. Figuratively speaking, this equates with a so-called overhead assembly , enabling any particles generated to fall in a downward direction and away from the functional area.

-

Use low-abrasion components / materials

-

Encapsulate and / or install suction-cleaning

-

Eliminate from immediate process area; e.g. use extension cables

-

Implement localized clean air technology to keep away small dispersible particles

Note:

If suction-cleaning units or clean airflows are used, ensure that temperatures remain constant (e.g. hardening of adhesives).

106

-

Avoid the use of through bolt joints below using blind holes

-

Attach metal fittings and hinges to the exterior of machines or beneath critical areas (such fittings are dirt traps, particle sources)

-

Avoid / remove fixtures which are not (no longer) required for processes. As a rule, only objects necessary for the respective process should be present in the assembly equipment

-

Ensure easy access to installed equipment for cleaning purposes

-

Use standardized interfaces to enable the flexible connection of hand suction cleaners; e.g. Venturi suction systems

-

Where possible, fix housings flush to the floor or mount them in such a way so as to enable easy cleaning access beneath assembly equipment

-

Where possible, exhaust air (e.g. from fans, electromotors or pneumatic cylinders and valves) should not be directed towards the interior of equipment or at least towards sensitive surfaces.

-

Locate as many supply lines (cables, pipes, etc.) as possible outside the direct process area.

-

Apply insulation to conduits condensation could develop.

Fig. F.3:

108

 e.g.

and

fix work surfaces from

machine

parts

Example of a transport system with permeable surface

where

F.3.1.3.1 Housing

Housing is often required for safety reasons. It may be made of acrylic glass or grid elements , or flashing. It not only shields equipment from particles in the environmental atmosphere but also prevents particles generated during manufacturing processes from spreading to the surroundings. If there a number of sources of dispersible particles in the environment (e.g. staff clothing), a housing or encapsulation is highly effective at keeping them out. Clean air technology is not necessarily required in such cases. Housing is to be designed to prevent contamination from accumulating in places where there is a risk of it falling into the machine. The use of grid elements it is to be carefully considered because they trap dust and are difficult to clean. Criteria and measures: -

Mount flaps, covers and doors to prevent contamination from falling into equipment when it is opened / closed

-

Openings for heat dissipation should not be situated in the top covers of machines but rather at the upper section of side walls. Alternatively: use facings to against prevent particles from falling into openings.

Note:

Fig. F.4:

For more information, see previous and following chapters Contamination present on covers / housings is to be removed before opening or closing them.

Example of housing

109

Housing can create a localized area with a different cleanliness grade than that of the environment. Examples: encapsulated blow-cleaning station in an assembly room with a higher cleanliness grade, or a rework station designed as a minienvironment (with or without clean air technology) in an uncontrolled workshop. Assembly equipment and clean air technology :

Where required, assembly stations can be designed as independent minienvironments. This does away with the need to design the entire assembly area as a costly environment such as a cleanroom or a cleanliness room. An important element to consider when using localized clean air technology in assembly equipment is the airflow, which specifically removes airborne particles. Ways of locally confining airborne particles: A. Defined encapsulation of machines, conveyors, goods buffers and / 1) or workstations 2)

B. As in A, but with additional use of localized clean air technology 1)

By encapsulating them (e.g. Perspex housing), machines can be shielded from particles contained in the environmental atmosphere. However, dispersible particles generated inside the equipment have a limited range of movement and form higher concentrations. 2)

A forced airflow may be capable of removing airborne particles generated inside the encapsulation (e.g. due to mechanical abrasion). However, an unfavorable airflow may have the opposite effect and transport (more) generated particles towards functional surfaces. Moving elements in dead spaces are to be avoided as particles accumulate in them.

In both cases, components / products require full protection on leaving the minienvironment if the environmental atmosphere contains damaging particles. If encapsulated devices are opened (e.g. due to malfunction, for refitting), particles may be displaced from the uncontrolled environment. When mounting localized suction-cleaning equipment to remove particles (generated) from the area, it must be considered that incoming air may also contain critical particles.

110

F.3.1.3.2 Manual workstations

At manual workstations, assembly tasks (also rework) are carried out by a member of staff. Examples of such tasks include inserting components and applying auxiliary materials right up to carrying out manual / machine-aided assembly processes. By carefully designing the workstation and related work sequences, the worker can avoid making cleanliness errors. There is a huge error potential due the degree of freedom of the worker as an individual (as opposed to an automated machine) as well as his basic motivation and general state of mind at the time. General rules of conduct are dealt with in Chapter E: Staff . Criteria and measures: -

Avoid material transfer and staff movement on the side facing the product / process material supply e.g. from the rear / side of the workstation

-

Design work plans to avoid workers having to carry out mixed tasks which hold a critical displacement risk.

-

Separate workstation clearly from environment

-

Keep workstation cleaning maintenance separate from assembly tasks (displacement risk)

-

Ensure effective lighting; where possible, use diffuse light to prevent dazzle or shadows.  Also

-

helps to identify and recognize particles.

Ensure that the worker does not have to lean over products in order to reach tools and components  establish

defined gripping sequences (without the worker being able to vary them). -

Where required, place tools so that they are always within easy reach without the worker having to lean over.

-

Define sites for putting tools and auxiliary materials down  including a holder for drinks (if permitted)

-

Where possible, hang up tools and auxiliary assembly materials

111

-

Design placement areas and receivers for tools and components with a minimum surface area. The accumulation of particles can be minimized if a design which is open underneath is used.

Fig. F.5:

-

Example of a workpiece receiver / work surface

Do not mount placement surfaces, load carriers or grab containers directly above the work surface. 

This avoids the worker having to reach over the product at regular intervals -

Do not mount fixations for tools directly above products, open load carriers or grab containers

-

Where feasible, mount grab containers and load carriers with sensitive goods above areas where the worker often has to reach over….(see above)

-

Keep small components in near-closed dispensers (not as open bulk goods)  e.g. stack sealing rings in a tubular dispenser.

-

Used closed shelf systems to prevent contamination from accumulating on the bottom shelf

-

Do not mount grab containers, load carriers and dispensers directly beneath the work area; instead, mount them to one side.

-

Install sieve plates in grab containers  this prevents particles from collecting at the bottom because they fall through the sieve.

112

-

Use closed dispensers for liquids  e.g. principle of a bird feeder: only the amount required is dispensed.

-

In order to protect workpieces and surfaces, apply cushioning to hard placement surfaces.  e.g.

rubber mat beneath stainless steel plate

-

Do not use soft work surfaces  e.g. wood or plastic, as particles could collect and the material abrades slightly

-

Do not use cloth covers for chairs; same principle for wooden chairs  instead, use plastic or metal

-

Do not use ribbed anti-slip mats or insulating matting which allow contamination to accumulate  alternatively: gel matting, non-slip footwear

-

If clean air technology is used, the influence of the worker on airflow guidance / as a particle source has to be taken into account

F.3.1.4 Operating utilities

Operating utilities include all components necessary for a process. They may be installed temporarily or permanently and be actively or passively involved. Examples:

Drives, mechanisms such as transport systems and handling technology, feeding equipment, cylinders, robots, conveyors, grippers (vacuum lifting devices), workpiece receivers, lifting tools, double belts, valve terminals. Also energy chains, linear axes, electromotors, etc.

Equipment and facilities functioning mechanically and constantly in operation are active particle sources. Such elements are often in the immediate vicinity of the product, which further increases the risk of contamination. Another critical aspect is the use of lubricants. Particles may accumulate in a lubricant (e.g. grease on the bushing of a tappet) and then be released into the atmosphere in an uncontrolled way. Where possible, avoid exposed linear axes, drives, brackets, belt drives, ball bearings, etc. F.3.1.4.1 Operating media and media supply technology

This includes media and associated supply components required to operate assembly facilities, e.g. electric current, compressed air / vacuum, hydraulic fluids, water and other fluids for heating and cooling, oils, grease 113

for assembly equipment components, gases (e.g. for welding), fireextinguishing agents (fire safety) etc. Supply technology also includes the devices required to use auxiliary materials, functional fluids and test fluids. Criteria and measures: -

Where possible, supply technology should be installed in false ceilings or walls  e.g. also enclosed in cable channels or corrugated piping.

-

Supply technology installed in the process area should have as few horizontal surfaces as possible and be mounted vertically

-

Care is to be taken with processing media (may contain damaging substances such as particles, oil or water)  e.g. use oil-free, dry, filtered compressed air.

-

Exhaust air from pneumatic units, etc., is to be conducted away from the process area by way of hoses, or filters installed.

-

Hoses and cables (compressed air lines, etc.) of moving elements require fixation to avoid abrasion. Use energy chains.

F.3.1.4.2 Auxiliary materials

These are materials which are either required to carry out assembly processes, form a part of the join itself or are a necessary localized basic supply for a functional group, e.g. -

Oils, grease, soap water and other lubricating agents (as joining aids)

-

Oils, grease and other lubricating agents (as basic supply media for the product)

-

Adhesives, sealants and thread locker fluids; liquids / pastes (as joining elements)

-

Solder and welding wire

Auxiliary materials are often in direct contact with functional surfaces. Fluids and corresponding application aids (e.g. brushes) are always to be kept clean. It is not to be forgotten that particles tend to accumulate on moistened surfaces.

114

Care is to be taken where materials are applied manually, as workers may displace particles via their hands or gloves. Examples include the use of cans to dispense oil via or brushes to apply lubricants. The nebulization and displacement of fluids to nearby surfaces causes contamination to accumulate and gives them a dirty appearance. Contact with contaminated surfaces increases the risk of displacement. Such areas are to be cleaned more frequently. Example:

Brushes, sponges, tampons, sprays (fingers  poor remedy), dispensers, greased bags (e.g. for tumbling a quantity of o-rings or greasing in batches), greasing station (component-adapted; e.g. component placed on ring aperture and greased via dispensing valve), oil can, dipping receptacle (e.g. soaping grommets.) receptacles for fluids.

Criteria and measures: -

Use fluids with defined degree of cleanliness

-

Process-integrated filtration of relevant fluid

-

Ensure that exposed fluids are kept clean

-

Keep auxiliary materials and tools for applying fluids clean

-

Avoid contamination of process environment by the fluid

-

Install housing processes

-

Use silicon brushes or dispensers for greasing instead of brushes made of hair (hairs fall out and adhere to the product)

-

Use alternative materials in order to avoid moistening  e.g. dry functional coating on surfaces; instead of oils, use nano composites because they are highly volatile, extremely thin, almost dry and do not attract dirt

-

Where applicable, if only a short-term lubricating film is required, use highly volatile alcohol

/

suction-cleaning

equipment

around

oiling

Note 1:

Non-volatile rinsing agents may cause seals to shift during pressure tests.

Note 2:

Degrees of cleanliness for fluids in accordance with ISO 4406 do not take particle size into account.  Where appropriate, use more suitable specification.

115

F.3.1.4.3 Test fluids and functional liquids Test fluids: This includes substances implemented in function tests, e.g. liquids and gases used in pressure tests. In some cases, the test fluid remains in the unit and serves as a functional fluid, hydraulic fluid in steering gear, for example. Functional liquids (for initial filling): these are required for the subsequent operation of the aggregate; e.g. hydraulic fluid, oils, coolants or fuel.

The degree of cleanliness of such substances is highly important (e.g. liquids, gases). The degree of cleanliness of such media is to be specified because they are in direct contact with the functional area of the aggregate or may remain inside permanently. They are always used in connection with function test benches and filling stations. Criteria and measure:

-

See also previous section

-

Adapter used to inject or remove test fluids must be kept clean

Test and functional fluids are sometimes used to clean the interior of an aggregate (e.g. pressure tests) (see Subchapter 3.1.6: Assembly integrated cleaning ). Note:

The presence of microorganisms in a fluid circuit may lead to altered fluid characteristics and impair the function of the system (examples: bio diesel, zinc pest)

Function test benches also enable the process-integrated monitoring of contamination inside test pieces: -

Intermittent assessment of particulate residues in processing filters

-

Specific use of analysis filters on downstream side of function test benches

F.3.1.4.4 Transport systems, handling systems, feeding and singularization Transport systems: workpieces are moved along the assembly line by a transport system to different stations and storage areas. Example:

116

Variants with or without pallets: roller-driven, belt-driven, self-driving pallets (workpiece carriers), slides, brush conveyors, suspended rails, turntables, lifting stations, beam conveyors, manual transport carts.

As some transport systems have a large (load) surface, the risk of contamination is high. The systems also connect different stations and thus represent a displacement risk. Handling systems: used to move tools or components inside a station, e.g. robots, linear drives or swivel units. They are generally only in use at one assembly station / workstation. For more information, see also Feeding and singularization devices.

Due to the load transmission, facilities for large or heavy goods are generally suspended above the work area. Here there is a risk of abraded material falling onto the product. Examples:

Robots, cylinders (pneumatic / hydraulic / electrical), NC axes, hand-guided balancers (torque-jacked and non-torque jacked to relieve weight), linear arms, sleds, swivel units, guide lines, energy chains.

Feed and singularization: grab containers / grab trays (placement areas, receivers), manual / automated singularization of bulk goods, vibratory conveyors, stepped conveyors, etc. Criteria and measures: -

Care is to be taken with regard to particle generation when selecting drive systems.

-

Transport systems are to be checked at regular intervals in order to recognize wear promptly and carry out repairs if necessary.

-

Small permeable surfaces rather than large closed ones

-

Wherever possible, drives, linear axes, cylinders, energy chains and other moveable equipment should be installed beneath critical areas.

-

Turnaround points (e.g. of conveyors) may not be placed above the product

-

Systems for singularizing and feeding small components (e.g. vibratory spiral conveyors): suction nest installed for separated parts or openings in the guide rail to enable loose particles to fall into a collecting receptacle.

117

F.3.1.4.5 Workpiece carriers and workpiece receivers

Components are assembled on the workpiece carrier. In some cases, the workpiece carrier also functions as a means of transport. Where components are identical, they are transported by several carriers from one work station to the next. Sometimes only one workpiece carrier is used. In this case, the component to be assembled is placed on the workpiece carrier, processed there and then lifted off again. There is always a component-specific workpiece receiver on the carrier, e.g. clamping jaws, aligning pins, negative mold / nest, gravity, arrester, swivel unit. Criteria and measures: -

During downtimes, remove workpiece carrier from conveyor or stop conveyor to prevent abrasion between conveyor and workpiece / workpiece carrier

-

Remove burrs at gripping and placement edges of workpieces. Radii are preferred on grippers or workpiece receivers rather than phases.

-

Minimize contact between workpiece carrier and product (care: high point load on product).

F.3.1.4.6 Tools and grippers

Tools are elementary constituents of assembly equipment and assembly processes. It is not possible to make a distinguishable difference between the terms tool and assembly aid. The most important differentiation is made between hand-operated and (semi-) automated tools. Typical handoperated tools include hammers, screwdrivers and brushes for applying fluids. Grippers are generally used to hold components. Example 1:

Adapters (e.g. connection in leak-testing equipment); adapter and contact tools, calipers, measuring tools, aligning and centering tools, molding tools, crimping tools (e.g. pliers for fitting hoses), marking tools (printers, stamps, etc.)

Example 2:

Screw bits, assembly bushings (o-ring / pistons), cutting pliers, peening tools, extrusion dies, bending punches, hammers, cutting dies, wrench sockets, jaw wrenches, riveting tools, wobbling tools, bonding, welding and soldering tools, spindle screw drivers

118

Grippers: vacuum grippers, magnets, form closures (hooks), force closures

Tools are to be kept in good order and replaced promptly if defective. With hand-operated tools , special care is to be taken to ensure the correct use of the right tools. Criteria and measures: -

Suction cleaning integrated into tools via boreholes (e.g. bending punch)

-

No not use sponges to clean tools (particle collectors!)

-

Especially with manual assembly: ensure that joining aids, molding tools or centering aids are provided and utilized  e.g. to avoid damage to constraining contours

-

Beating components  use pressing processes instead

-

Hammers  use guided striking tools instead

-

Hammer with plastic head instead

 plastic

splinters easily. Use brass

-

Tools with wooden handles splinters easily)

 replace

with metal or plastic (wood

-

Automated screw feed (shooting)  holding device for single screws generates abrasion. Alternatively: position screws manually

119

F.3.1.5

Assembly processes

Table F.1 lists typical assembly processes. Assemblyprocess

Screwing

Particle generation

- On locating the screw thread



- Exit burrs - Nicks - Coating swarf - Swarf from tools


detach if screws are shot using compressed air -

- Abrasion /

Particles from screw head Burrs from screw threads

- Weld / solder spatters at start / finish

- Slag, scale

screws

- Thread gauges act like cutting tools

- Damage to threads - Incorrect tension due to increased abrasion; consequence  connections may loosen into components during function tests

- Turbulent welding / - Spherical particles soldering baths cause sputter to land on equipment and components

- Particles from nuts and

- Swarf may be rinsed

detachment of burrs

Welding / soldering


(welding sputter / solder beads)

- Flake-shaped particles - Flakes of coating - Smoke and soot particles

- Free-flying weld and solder sputter falls into cavities and undercuttings

- Slag, scale falls into cavities

- Leaks

- Plastic particles

- Sedimenting smoke / smoke residue Pressing / crushing / dilating


- Abrasion due to relative movement between tools and components

120

- Pieces of coating -

Generally flakeshaped

- Function of component impaired by jamming


Assemblyprocess

Drifting / crimping

Particle generation



- Abrasion on placing - Abrasion / detachment - Burrs may penetrate components in devices

- Chips detach if components are not centered

of burrs

into functional area

- Sickle-shaped chips - Flakes of coatings from tools and components

- Abrasion of tools, components and receivers Calking

- Abrasion from clamping devices

- Abrasion due to deformation or reshaping

- Swarf - Burrs - Chips - Nicks in material

- Burrs, chips, swarf may get into component

- Leaks - Damage to sealing elements

- Detachment of burrs, pieces flake off cast surfaces, small nicks in materials Inserting / sliding in / on, pushing in

- Abrasion /

- Swarf, burrs, particles - Particles between

fragments of components and / or joining components

Chips

- Abrasion from

- Detached particles

centering tools

on work surfaces Fitting / shrinking

Table. F.1:

- Abrasion of tools and receivers

components prevent exact component positioning

- Incorrect fit - Leaks

- Abrasion, swarf, burrs burrs - Component does not - Loose burrs

reach final position

- Jamming

Characterization Characterizat ion of assembly processes

Assembly processes and dismantling steps may generate particles of a critical size and present a much higher risk than contamination from the environmental atmosphere. First of all, it is recommended that optimization measures for the assembly equipment - especially assembly process - are examined with regard to possible contamination risks in order to take any necessary countermeasures. Especially expert planners and experienced assembly technicians are required for this. 121

The relevant critical assembly steps are localized using FMEA or potential analysis and successively detailed during planning. It may be helpful to observe or analyze similar applications in an existing assembly equipment. Objective assessment aids include conventional cleanliness tests and the use of particle traps (see Chapter G: Determination of cleanliness impacts). For reasons of access or in order to exclude atypical dismantling influences, both techniques may need to be carried out on realistic joining models of the product. Computer tomography may be of use to inspect interior functional areas without causing any damage. F.3.1.6 Assembly-integrated cleaning

Assembly-integrated cleaning is implemented to remove particles as they are being generated. Particles may be generated during assembly processes or when handling / separating components. The particles concerned are often only loosely attached to components and can therefore be effectively removed using a simple cleaning procedure. Thus, assembly-integrated cleaning serves principally to clean components or aggregates directly. Cleaning steps can also be integrated into assembly equipment with the aim of keeping facility components clean at all times, e.g. cleaning workpiece carriers, transport conveyors or grippers. This also aims to reduce the displacement of particles from one piece of assembly equipment to another. Assembly-integrated cleaning is a series process and is generally dry – in contrast to conventional component cleaning, which includes the removal of auxiliary materials such as cooling lubricants from mechanical processing steps. As a result, liquid-based cleaning methods are generally implemented in the latter case. c ase. Applications of assembly-integrated cleaning: cleaning: 1. To remove assembly particles from the product immediately after they have been generated 2. For the final cleaning of units / functional systems, systems, e.g. in function test benches 3. To keep facility components clean (e.g. transport conveyors) in order to prevent displacement

122

4. To remove particles emitted recontamination

during processing to prevent

The procedures considered in the guideline also include manual cleaning methods. F.3.1.6.1 Area of application

Assembly-integrated cleaning is the active removal of contamination at process and product level. In the context of this guideline, this primarily means the removal of critical particles . Simple solutions are preferred and are characterized below: •

Adequate cleaning effect / process-reliable

•

On-site implementation, where possible without removal of objects to be cleaned from the actual flow or sequence

•

Where possible, no additional handling, such as repositioning or commissioning (separation or lot-forming) or buffering

•

Where possible, without increasing cycle times

•

No residues of cleaning media or fluids left on the object which could impair end-functions. This is one reason why dry processes are generally implemented.

•

Where possible, (simple) automated processes (e.g. for reasons of reproducibility)

Note:

The (generally manual) cleaning steps implemented to keep workstations, machines, spaces, etc. clean do not form part of assembly-integrated cleaning and are dealt with in later chapters concerned with maintaining cleanliness. Conventional, assembly-near component cleaning technology is also excluded: e.g. bringing bought or in-house produced components into the assembly area via a component-cleaning plant.

The main focus is on the reliable removal of critical contamination . The effectiveness of a planned cleaning process must first be verified through practical tests. This is especially the case if the critical contamination is to be removed from functionally-relevant surfaces directly . If the adequate removal of harmful particles cannot be guaranteed, other measures need to be taken. They may be concerned, for example, with steps to prevent critical joining particles from being generated during an assembly process, or with proving the need to implement more effective (possibly more complex) cleaning measures.

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Application

1. End-product / unit

2. Single component / unit

Component

Process Step

Cleaning Step

Heat exchanger

Pressure test

Internal rinsing with gas

Gear box

End-function tests

Internal rinsing with hydraulic oil

Hydraulic line

After screwing in sensor Internal rinsing with gas

Screw

After singularization

Suction nest

ABS valve

Bevor impression

Suction nest

Crack con rod

After speration

Separating area: suction cleaning or dry ice snow

Housing beneath thread pitch

After loosening screw

Suction cleaning / tape-lift / magnetic probe

Sealing surface of housing

Before application of sealing fluid

a) Brush strip combined with suction cleaning or b) Dry ice snow or c) Atmospheric pressure plasma

3. Assembly process

4. Operating utilities technology

Table. F2:

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Wobbling tool

During wobbling process Localized suction cleaning

Oiling station

Continuous

Process extraction

Workpiece mount

After calking

Localized suction cleaning

Filter mesh

During confection and pleating


Woven hose for heat insulation

On pulling up onto line section


Conveyor belt

Continuous

Suction strip, possible combined with brush or magnetic strip

Workpiece carrier


Suction cleaning / wet cleaning / dry ice snow

Tray or SLC


Wiping with damp cloth / suction cleaning / wet cleaning / dry ice snow

Examples of various applications of assembly-integrated cleaning

Integrated cleaning steps are not only associated with components or the product but are also used to prevent direct and indirect recontamination in the vicinity of the product. Examples of different integrated cleaning applications are listed in Table F2. In a planning phase, the respective points in the process sequence and the cleaning alternatives expected to be suitable are narrowed down using FMEA or potential analysis and successively detailed. Here, it may be helpful to observe or analyze similar applications in an existing assembly equipment. Case 1 and 2: Removing recontamination:

Component or product surfaces are specifically treated in order to remove recontamination occurring, for example, during assembly and assembly processes (cleaning immediately after completed assembly step). This also includes the treatment of single components / smaller units, in order to remove particles, e.g. generated during singularization in a vibratory feeder, sedimenting out of the environment or occurring through transport (cleaning immediately before an assembly step). Case 3 and 4: Preventing recontamination:

In these cases, integrated cleaning is implemented to remove contamination in the product area in order to prevent it from spreading and to reduce the risk of it being transferred to the product. Contamination is removed as near as possible to its origin or point of emission (generally via suction). For further information about cleaning, especially with regard to containers (see Chapter D: Logistics ). Note:

See annex for example of a comparison of alternatives for cleaning con rods.

F.3.1.6.2 Characterizing selected cleaning procedures

As far as the requirements or characteristics mentioned are concerned, the spectrum of eligible cleaning procedures is infinite (see Table F3 for examples). The cleaning effect is mainly based on the mechanical elimination of particles, often combined with their defined removal using one or more flowing liquids. Purely mechanical cleaning effects are especially dependent upon the degree particles are bound to the surface (e.g. loose or caked on). 125

Wherever possible, cleaning steps should be carried out during or immediately after the generation of critical particles in order to avoid further displacement or intensive surface bonding, e.g. due to assembly auxiliary materials condensing or drying (e.g. process-related oil film on a workpiece carrier). Note:

Despite considering the optimum interaction of temperature, time and mechanical and chemical effects [Sinner’s circle], most of the cleaning procedures listed are less effective in removing filmy residues (e.g. oil mist). The cleaning effect with regard to particles is good but limited when compared with optimized conventional wet cleaning. This is especially the case with smaller particles because these have a relatively high surface retention force and low detachment force in the surface boundary layer of a flowing liquid.

Caution:

The list in Table F3 is only to be considered as a rough guideline with regard to assessing cleaning effects, especially as far as oil films are concerned (type of fluid / vapor pressure).




1. Suction 1) cleaning 2. Blowing

1)

3. Internal rinsing with


Comment

Force of flow


126

o

-

Force of flow

Line of sight process, o

+

o

-

+

-

-

o

-

Force of flow

pressurized 1) gas 4. Internal rinsing with negative pressure 1) gas

-

Force of flow





5. Internal rinsing with fluid

1)

6. Brushing


Comment

Force of flow / time / chemical / + (temperature)

Depending on rinsing medium and later use of component, costly internal drying may be required

+

+

Mechanics

Line of sight procedure +

7. Dry ice snow Impulse / temperature / chemical / time

+

-

Electrostatic charging possible. Line of sight procedure,

+

+

+

Electrostatic charging possible, Also for caked films.

8. Vibration with Mechanics / 1) suction force of flow cleaning

-

+/o

-

9. Atmospheric Chemical / time pressure plasma

Electrostatic charging possible Line of sight procedure (in some cases),

-

-

o/+

Cleaning effect depends on chemical composition of film Also for caked films.

10. Damp 1) wiping 11. Tapelift

Mechanics / (chemical) 1)

+

+

+

Adhesion

Low-fluff cloth Line of sight procedure,

+

+

-

Possible residue of adhesive material.

127




12. Magnet

1)

13. Demagneti1) sization


Comment

Field strength

Line of sight procedure,

Field strength

?

?

-

?

?

-

Only works for ferromagnetic particles, Works only for ferromagnetic materials

1)

The cleaning effect is not generally improved by extending the cleaning time of a procedure (without chemical active component). Particles are either detached immediately or not at all. With flow-based procedures, experience has shown that the cleaning effect regarding particles can be increased using a pulsed flow (abrupt, large alterations in velocity). However, with gases this has a weakening effect due to compressibility. Line of sight procedure means that the procedure has a limited scope and the surface concerned must therefore be hit directly . The cleaning probe and object to be cleaned must be positioned / moved towards one another in a defined way ( scanning the surface) if larger surface areas require treatment.

Table. F3:

List of eligible integrable cleaning procedures

Caution:

When selecting a procedure, the possible loss of corrosion protection must be taken into consideration. Consider also the chemical compatibility of the component material with the respective cleaning agent and possible attack on materials through mechanical cleaning forces.

Note:

Electrostatic charging may occur if ionization equipment is used. Earth if required (additionally / only).

When implementing a procedure, ensure that detached / emitted particles are removed carefully in order to prevent cleaned surfaces or the environment from becoming (re-)contaminated. The respective cleaning media must have the required level of cleanliness (blank value). With gases and fluids, this can be proved by filtration (preferably directly at the point of use).

128

With solid cleaning media such as brushes or cloths, the fact that these materials are a potential source of particles must be taken into account; especially when used for longer periods (wear). The repeated use of wiping materials is not recommended because as “particle collectors” they will emit the particles they hold at one time or another (displacement risk!) 1. Suction cleaning: Suction cleaning is the most common procedure implemented and is purely mechanical. In physics, a maximum pressure difference of 1 bar can be used as a potential to generate a flow, although the velocity of flow at the level of the object itself is limited. Methods for generating negative pressure include venturi nozzles operated by compressed air, central process vacuum lines with an air chamber, simple electrically-operated industrial vacuum cleaners or powerful lateral channel blowers. Fields of application range from process suction-cleaning, the capture of larger quantities of air with relatively low flow velocities, right up to suction cleaning in contour-adapted workpiece receivers with relatively high localized flow velocities. The higher the average flow velocity, the better larger (heavy / compact) particles can be detached and removed by the air flow. To process larger areas efficiently, negative pressure sources with a higher capacity may be required. In order to achieve high flow velocities on object surfaces, workpiece receivers should be as closed and contour-adapted as possible. It is essential to achieve a relative optimum between minimum gap width and increased flow resistance. By carefully combining gap widths and openings for the subsequent flow of air, localized areas with an increased flow velocity and thus an increased localized cleaning effect can be created. Note:

The subsequent flow of air may contain critical contamination.

When handling hand-operated probes / vacuum cleaners, the risk of damaging cleaning surfaces and the possibility of generating abrasion particles must be taken into account.

129

2. Blowing: With blowing processes, solely the mechanical cleaning factor of the Sinner circle is utilized. Higher pressures can be used than with suction cleaning and thus greater velocities and cleaning forces attained. Due to expansion, the flow impulse decreases much faster as the distance from the nozzle increases than with liquids. When determining cleaning parameters, static pressure at the level of the cleaning probe is not important but rather the volume flow resulting from the geometry and size of the nozzle used. Together with the distance between the probe and the cleaning surface, this determines the volume flow per component surface and thus the impulse acting on the contamination. In order to prevent the uncontrolled spread of detached contamination, the resulting volume of air must be effectively contained by installing both a housing and process extraction. Cleaning components in blowing / suction cleaning facilities: Volume flow, flow velocity and thus also cleaning forces can be increased significantly in component-adapted suction cleaning systems if compressed air is used additionally. To ensure that no air escapes into the environment, the suction system must be adapted to the shape of the component in order to be hermetically sealed to the outside. With exposed suction cleaning chambers, a high-capacity negative pressure source must be installed to continuously collect the volume flow produced. Alternatively, the flow of compressed air can be pulsed in carefully-calculated intervals. When removing particles from surfaces, the effective impulse of the respective flow velocity is generally more important than the cleaning time. 3. Internal rinsing with pressurized gas: In some cases, this application can be combined with existing pressure and function test benches. The exhaust air charged with contamination can be processed using filters and precipitators, making its removal via a separate process exhaust air line obsolete. Filters can be implemented to specifically remove particles from the inflowing process media (air / gas).

130

4. Internal rinsing with negative pressure gas: In some cases, this application can be combined with existing pressure and function test benches. Filters can be implemented to specifically remove particles from the inflowing process media (air / gas). 5. Internal rinsing with a liquid: Both positive and negative pressure variations are used. By wetting the internal surface, the duration of the process and the chemicals used enhance the mechanical cleaning effect. The higher the flow velocity, the better particles can be detached and removed. Note:

When using this technique for interim cleaning, liquid may be displaced. In some cases, subsequent vacuum filling may no longer be practicable due to outgassing.

Filters can be implemented to specifically remove particles from the inflowing cleaning liquid. In some cases, the cleaning process can be implemented in combination with function test benches and filling stations. 6. Brushing: Brushing is a mechanical procedure. Application methods range from simple manual cleaning using a brush to automated brushing stations. Here again, it is important that particles are not only detached from the object but also efficiently removed. As a rule, the process area or brush is suction-cleaned. In some typical brushing stations, small quantities of liquid are applied. This makes the process gentler on the surfaces to be cleaned, improves particle detachment and prevents electrostatic charging. 7. Dry ice snow: This cleaning technique is based on the use of accelerated CO2 crystals made from liquid carbon dioxide and applied via a special nozzle. This integrable procedure is the most efficient cleaning technique (especially as far as micro particles are concerned). In contrast to a station which uses compressed air, for example, this technique demands a more complex plant technology (e.g. localized supply via gas cylinders). The cleaning medium volatizes spontaneously and leaves no residue (suction required). Due to the

131

way in which the gas is manufactured, the CO2 balance is environmentally neutral. To prevent the uncontrolled spread of detached contamination, the process area needs to be enclosed and suction cleaned (also to remove the carbon dioxide gas).

8. Wet wiping: Wetting improves the cleaning effect and ability of a (low-fluff!) cloth to hold particulate contamination and also makes the process gentler on the surfaces to be treated. Where required, cleaning agents can be selected to enable filmy contamination also to be removed (precipitation of oil mist, etc.). Example:

mixture of isopropanol / water (3:2)

To wet the cloth, simple dispensers ( pump sprays) or laboratory spray / wash bottles can be utilized. To ensure that liquids remain clean, the use of open receptacles to hold the liquids is not permitted. Gloves are to be worn when wet-cleaning. This is for reasons of safety rather than cleanliness (e.g. drying out of skin / allergies). Cleaning liquids should evaporate rapidly and not contain any substances which could leave dry residues on the cleaned surfaces. Fast drying also reduces the risk of any possible recontamination adhering strongly to surfaces on drying. If necessary, the workstation must be adequately ventilated (humidity, vapors from solvents, etc.). In coating technology, a so-called tack cloth is sometimes used to remove dust. As it is a prefabricated wiping agent, it does not need to be moistened before use. In general, a wide range of disposable wet wipes are available on the market; these need to be assessed individually for suitability. This also applies for dry anti-static cloths. When moistened, cotton swabs, available in numerous sizes, shapes and materials, may also be suitable for cleaning small apertures, corners and edges. All types of wiping agents are for single use only and are to be disposed of appropriately directly at the place of use.

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VDA Band 19.2 English 2010

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