Indu stria l Work Grou p
Group Technology and Cellular Manufacturing
Ramiro Bonaque Rodríguez Jose Luís Gandia Fornés Toni Barberà Pastor
Universita t Jaume I de Castelló
Table of contents 1. Introduction 2. Parts classification and coding 3. Production flow analysis 4. Cellular manufacturing 5. Application considerations in group technology 6. Quantitative analysis in cellular manufacturing
1. Introduction Processes types for batch manufacturing Process type plant layout
Process type group technology Turning Milling Assembly Drilling Shipping Receiving
Machines are arranged by function.
Machines are arranged into cells
1. Introduction Definitions Group technology Group technology is a philosophy in which similar parts are identified and grouped together to take advantage of their similarities in design and production.
Part family Part family is a collection of parts that are similar either because of geometric shape and size or because similar processing steps are required in their manufacture.
Cellular manufacturing Cellular manufacturing is grouping the production equipment into machine cells, where each cell specializes in the production of a particular part family.
1. Introduction Features of group technology Objective • To make batch production more efficient and productive. • To integrate design and manufacturing in a firm. Obstacles • Identifying the part families. • Rearranging production machines into machine cells. Benefits • It promotes standardization • It reduces material handling, setup times and work-in-process • Workers satisfaction and quality work improve
1. Introduction The changeover from a conventional production to group technology Three metho ds to g rou p the parts into familie
s:
1) Visual inspection 2) Parts classification and coding 3) Production flow analysis
1) Visu al ins pectio n
It involves the classification of parts into families by looking at either the physical parts or their photographs and arranging them into groups having similar features.
2. Parts classification and coding Definition Each part family is exclusively identified by an alphanumerical code, which represents their design attributes, manufacturing attributes or both.
Features Advantages
• Design retrieval • Automated process planning • Machine cell design
Methods to obtain the code from a particular part • Looking in tables to match the subject part against the features described. • Using a computerized classification and coding system to reply questions about the part’s features.
2. Parts classification and coding Parts coding systems Opitz
Brisch System
DCLASS
MultiClass
CODE
CUTPLAN
Part Analog System
Types of structures of coding systems Hie rarchical /
mo no cod e
Chain- type / polyco Mixed-mode
de
e.g. MultiClass (by Organization for Industrial Research)
e.g. Opitz Classification System (by H. Opitz)
2. Parts classification and coding Opitz Coding System Digit sequence:
12345
6789
ABCD
For m cod e : design attributes
Supplementa
ry co de : manufacturing attributes
Se cond ar y cod e : operation sequence and particular needs
2. Parts classification and coding Opitz Coding System Digit 1 Part Class
0
L/D ≤ 0,5
1
0,5 < L/D < 3
2 3
R o ta ti o n a l
7 8 9
L/D ≤ 2
A/B ≤ 3
N o n ro ta ito n a l
Digit 5
Rotational Machining
Plane Surface Machining
Additional Holes Teeth and Forming
External Shape Element
Internal Shape Element
Machining of plane surface
Other holes and teeth
Main Shape
Rotational Machining
Machining of plane surface
Other holes, teeth and forming
With deviation
Special
6
Digit 4
Main Shape
Form code
L/D > 2
5
Digit 3
Digits 6
7
8
c o dM eate
S uO pri pniga lsl e h m a p eeo nrf tawa rym a
L/D ≥ 3
With deviation
4
Digit 2
Main Shape
A/C ≥ 4 A/B > 3
Main Shape
A/B ≤ 3 A/C < 4 Special
Main Shape
Main bore and rotational machining
Machining of plane surface
Other holes, teeth and forming
D im e n s i o n s
ri a l
te ri a l s
9
A c c u ra n y
2. Parts classification and coding Opitz Coding System
0
3
Digit 2
Digit 3
Digit 4
Digit 5
External shape, external shape elements
Internal shape, internal shape elements
Plane surface machining
Auxiliary holes and gear teeth
L/D ≤ 0,5
1 2
Digit 1 Part Class
0,5 < L/D < 3
R o t a it o n a l
4
L/D ≥ 3
0 1 2
With deviation L/D ≤ 2
3 4
5
5
6 7 8 9
N o n r-o t a t io n a l
6
Smooth, no shape elements S t No shape elements p e p e d O to r Thread o s n m e o Functional e o n th groove d S te p No shape elements p e d t o Thread b o t h e n Functional groove d s
0 1 2 3 4 5 6
to o n e e n d
No hole, no breakthrough S No shape m o o elements th o Thread r s t e p Functional p e groove d
S t e p No shape elements p e d t o Thread b o t h e n d Functional groove s
7
Functional cone
7
8
Operating thread
8
Operating thread
9
All others
9
All others
Functional cone
0
No surface machining Surface plane and/or
1 2
curved in one direction, external External plane surface related by graduation around the circle
0
No auxiliary hole Axial, not on pitch
1 2 3
3
External groove and/or slot
4
External spline
5
External plane surface and/or slot, external spline
5
6
Internal plane surface and/or slot
6
7
Internal spline
7
8
Internal and external polygon, groove and/or slot
8
9
All others
9
4
circle diameter N Axial on pitch circle o diameter g e a Radial, not on pitch r t e circle diameter e t h Axial and/or radial and/or other directions Axial and/or radial on PCD and/or other directions Spur gear teeth
W it h g e a r te e t h
Bevel gear teeth Other gear teeth
All others
2. Parts classification and coding Opitz Coding System Example
Given this rotational part design, determine the form code in the Opitz parts classification and coding system.
½ – 13 UNC
1,0
0,3
0,5 0,8 1,5
0,7
½ – 13 UNC 1,0
0,3
Form code
0,7
1
5
1
0
0
0,5 0,8 1,5
Digit 1
Digit 2
Part Class
0
L/D ≤ 0,5
1 2 3
0,5 < L/D < 3
R o ta ito n a l
4
L/D ≥ 3
External shape, external shape elements
0 1 2 3 4
5
5
6 7 8 9
N o n ro t a t io n a l
6
Smooth, no shape elements S t No shape elements p e p e d O to r Thread o s n m e o Functional e o n th groove d S te p No shape elements p e d t o Thread b o t h e n Functional groove d s
0 1 2 3 4 5 6
to o n e e n d
Digit 3
Digit 4
Digit 5
Internal shape, internal shape elements
Plane surface machining
Auxiliary holes and gear teeth
No hole, no breakthrough S No shape m o o elements th o Thread r s t e p Functional p e groove d
0
No surface machining Surface plane and/or
1 2
curved in one direction, external External plane surface related by graduation around the circle
0
No auxiliary hole Axial, not on pitch
1 2 3
circle diameter N Axial on pitch circle o diameter g e a Radial, not on pitch r t e circle diameter e t h Axial and/or radial and/or other directions Axial and/or radial on PCD and/or other directions
3 External groove and/or slot Auxiliary External Plane Internal Length-to-diameter surface holes, shape: shape: gear machining: stepped part teeth, contains ratio on etc.: none both none a 4one end ends with4 screw through-hole thread on External=spline L/D 1,5
S t e p No shape elements p e d t o Thread b o t h e n d Functional groove s
7
Functional cone
7
8
Operating thread
8
Operating thread
9
All others
9
All others
Functional cone
5
External plane surface and/or slot, external spline
5
6
Internal plane surface and/or slot
6
7
Internal spline
7
8
Internal and external polygon, groove and/or slot
8
9
All others
9
Spur gear teeth
W it h g e a r te e t h
Bevel gear teeth Other gear teeth
All others
2. Parts classification and coding MultiClass Coding System Coding structure: up to 30 digits divided into 2 regions Region 1
Digit
Function
0 1 2, 3 4 ··· 18
Code system prefix Main shape category External and internal configuration Machined secondary elements · · · Etc. · · · Machined element orientation
Region 2: designed by the user to meet specific needs and requirements.
2. Parts classification and coding MultiClass Coding System
Example
Given this rotational part design, determine the form code in the MultiClass parts coding system.
2. Parts classification and coding MultiClass Coding System
Solution
3. Production Flow Analysis Definition Production flow ana lysis (PFA) is a method for identifying part families and associated machine groupings that uses the information contained on production route sheets rather than on part drawings.
Workparts with identical or similar routings are classified into part families. Then, the families can be used to form logical machine cells in a group technology layout. Possible anomalies • •
Parts whose basic geometries are quite different may nevertheless require similar or even identical process routings. Parts whose geometry are quite similar may nevertheless require process routings that are quite different.
Virtue Require less time than a complete parts classification and coding procedure.
3. Production Flow Analysis Procedure 1. Scope of the analysis : The production flow analysis must begin defining the scope of the study (population of parts to be analyzed). 2. Data collection: The minimum data needed in the analysis are the part number and operation sequence. Additional data: lot size, time standards, and annual demand might be useful. 3. Sortation of process routings : Parts are arranged into groups according to the similarity of their process routings. To make this: a) All operations or machines are reduced to code numbers; b) For each part, operation codes are listed in the order they are performed c) A sortation procedure is then used to arrange parts into packs.
3. Production Flow Analysis Procedure 4. PFA Chart : The processes used for each pack are then displayed in a PFA chart. PFA chart has been referred aspart-machine incidence matrix.
xij = 1 Part i requires processing on machine j xij = 0
Part i is not processed on machine j
3. Production Flow Analysis Procedure 5. Cluster an alysis : From the pattern of data in the PFA chart, related groupings are identified an rearranged into a new pattern that brings together packs with similar machine sequences. - Different machine groupings are indicated with blocks. - The blocks might be considered as possible machine cells.
Weakness The data used in the technique are derived form existing production route sheets. The routings may contain operations that are nonoptimal, illogical or unnecessary.
4. Cellular Manufacturing Definition Cel lular manufacturin g is an application of group technology in which dissimilar machines or processes have been aggregated into cells, each of which is dedicated to the production of a part or product family or limited groups of families.
Objectives •
To shorten manufacturing lead times.
•
To reduce work in process inventory.
•
To improve quality.
•
To simplify production scheduling.
•
To reduce setup times.
4. Cellular Manufacturing 4.1. Composite Part Concept Definition Com pos ite Pa rt Concept is a hypothetical part for a given family which includes all of the design and manufacturing attributes of the family.
An individual part in the family will have some features that characterize the family but not all of them. The composite part possesses all of them. Production cell design A production cell designed for the part family would include all the machines required to make the composite part. Such a cell would be capable of producing any member of the family, simply by omitting those operations corresponding to features not possessed by the particular part. The cell would also be designed to allow size variations within the family as well as feature variations.
4. Cellular Manufacturing
4. Cellular Manufacturing 4.2. Machine cell design Types of Machine Cells and Layouts Manufacturing cells can be classified according to the number of machines and the degree to which the material flow is mechanized between machines. Four common GT cell configurations: 1. Single machine cell : Consists on one machine plus supporting fixtures and tooling. This type of cell can be applied to workparts whose attributes allow them to be made on one basic type of process such as turning or milling.
4. Cellular Manufacturing 2. Group machine cell with manual handling: an arrangement of more than one machine used collectively to produce one or more part families. - There is no provision for mechanized parts movement between the machines in the cell. Instead, the human operators who run the cell perform the material handling function. - The cell is often organized into a U-shaped layout. This layout is appropriate when there is variation in the work flow and to allow the multifunctional workers in the cell to move easily between machines.
4. Cellular Manufacturing 3. Group machine cell with semi-integrated handling: uses a mechanized handling system to move parts between machines in the cell. 4. Flexible manufacturing system (FMS): combines a fully integrated material handling system with automated processing stations. - FMS is the most highly automated of the group technology machines cell. - Variety of layouts: U-shape, in-line, loop, and rectangular.
4. Cellular Manufacturing Cell design Part movement Four types of part movement: 1. Repeat o peration : a consecutive operation is carried out on the same machine so the part does not actually move. 2. In-sequence move: the part moves from the current machine to an immediate neighbor in the forward direction. 3. By-passing move: the part moves forward from the current machine to another machine that is two or more machines ahead. 4. Backtracking move: the part moves from the current machine in the backward direction to another machine.
4. Cellular Manufacturing Movement
Layout
Repeat operations
Multiple stations (machines)
In-sequence move
In-line layout / U-shaped layout
Passing moves Backtracking move
U-shaped layout Loop or rectangular layout
Additional factors Additional factors that must be accounted for in the cell design: •
Quantity of work to be done by the cell : number of parts per year and processing time per part at each station. Determine the workload and therefore the number of machines that must be included.
•
Part size, shape, weight, and other physical attributes : determine the size and type of material handling and processing equipment that must be used.
4. Cellular Manufacturing Key machine concept Key machine is a certain machine in a cell that is more expensive to operate than the other machines or that performs certain critical operations in the plant.
The other machines are referred to as supporting machines, and they should be organized in the cell to keep the key machine busy. In a sense, the cell is designed so that the key machine becomes the bottleneck of the system.
The key machine concept is sometimes used to plan the GT machine cell. The approach is to decide what parts should be processed through the key machine and then determine what supporting machines are required.
4. Cellular Manufacturing Utilization measures Two measures of utilization: 1. Utilization of the key machine: using the usual definition. The utilization of each of the other machines can also be evaluated similarly. 2. Utilization of the overall cell: obtained by taking a simple arithmetic average of all the machines in the cell.
5. Application considerations in group technology 5.1. Applications of Group Technology 5.1.1. Manufacturing Applications Informal scheduling and routing of
1. Formation of cells
similar parts through selected machines Virtual machine cells Formal machine cells
2. Process planning of new parts 3. Family tooling 4. Parametric programming
5. Application considerations in group technology 5.1. Application of Group Technology 5.1.2. Product Design Applications
1. Use of design retrieval systems
Design savings
• Simplify design procedures • Reduce part proliferation 2. Simplification and standardization of design parameters
• Reduce the required number of tools • Reduce the amount of data and information that the company must deal with
5. Application considerations in group technology 5.2. Survey of Industry Practice Rank
Reason for installing Manufacturing Cells
1
Reduce throughput time (Manuf. Lead time)
2
Reduce work-in-process
3
Improve part and/or product quality
4
Reduce response time for customer orders
5
Reduce move distances
6
Increase manufacturing flexibility
7
Reduce unit costs
8
Simplify production planning and control
9
Facilitate employee involvement
10
Reduce setup times
11
Reduce finished goods inventory
5. Application considerations in group technology 5.2. Survey of Industry Practice
Rank
Costs of Introducing Cellular Manufacturing
1
Relocation and installation of machines
2
Feasibility studies, planning and design
3
New equipment and duplication of equipment
4
Training
5
New tooling and fixtures
6
Programmable controllers, computers and software
7
Material handling equipment
8
Lost production time during installation
9
Higher operator wages
6. Quantitative analysis in cellular manufacturing •
Quantitative techniques have been developed to deal with problem areas in GT Grouping parts and machines into families
•
Two main problem areas
Rank order clustering Arranging machines in a GT cell
An heuristic approach by Hollier
6. Quantitative analysis in cellular manufacturing 6.1. Rank Order Clustering Technique • Specially applicable in production flow analysis • It works by reducing the part-machine incidence matrix to a set of diagonalized blocks that represent part families and machine cells. • Algorithm
1. Read each row of the matrix as a binary number and reorder them in decreasing order. 2. Do the same with the columns of the matrix 3. Repeat steps 1 and 2 until no change in the matrix is needed.
6. Quantitative analysis in cellular manufacturing 6.1. Rank Order Clustering Technique 6.1.2. Example
Parts
Machines
A
1
1
B
1
3
1
1
D
E
F
Machines
A
F
D
1
1
1
1
1
1
4
1
1
1
1
2
4
C
Parts
1
1
B
E
C
3
1
1
1
2
1
1
6. Quantitative analysis in cellular manufacturing 6.1. Rank Order Clustering Technique 6.1.2. Example
Parts
Parts Machines
A
F
D
B
1
1
1
1
1
4
1
1
3
1
2
1
1
E
C
1 1
1
Machines
A
F
D
B
E
1a
1
1
4
1
1
3
1
1
1
1b
1
1
2
1
1
C
1
6. Quantitative analysis in cellular manufacturing 6.2. Hollier Method to Arrange Machines in a GT Cell • Uses data contained in From-To charts • Maximizes the proportion of in-sequence moves within the cell • Algorithm
1. Develop the From-To chart 2. Determine the From/To ratio for each machine 3. Arrange machines in order of decreasing From/To ratio
6. Quantitative analysis in cellular manufacturing 6.2. Hollier Method to Arrange Machines in a GT Cell 6.2.2. Example
• 50 parts processed on 4 machines. To: From:
1
2
3
4
“From”
Sums
From/To Ratio
1
0
5
0
25
30
0.60
2
30
0
0
15
45
1.0
3
10
40
0
0
50
4
10
0
0
0
10
“To” Sums
50
45
0
40
0.25
6. Quantitative analysis in cellular manufacturing 6.2. Hollier Method to Arrange Machines in a GT Cell 6.2.2. Example
• Flow diagram 10 50 in
3
40
15 2
30
1
25
5
Percentages of in-sequence moves = 70.4% Percentages of backtracking moves = 11.1%
4
30 out
10 20 out
Questions
