PROJECT R EPORT
MARUTI SUZUKI INDIA LIMITED
SP ATTER REDUCTION
Submitted by
ABHISHEK M ITTAL Roll No. - 101108003
Unde r the Guidance of Mr. Supre et Bhullar Asso ciate Profes sor
Arun K Kuma r De puty Manage r(L-12 )
Department of Mechanical THAPAR UNI VERSI TY, Engineering PATIA LA
June 2014
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DECLARATION
I hereby declare that the project work entitled SPATTER REDUCTION is an authentic record of my own work carried out at MARUTI SUZUKI INDIA LIMITED as requirements of six months project semester for the award of degree of B.E. (Mechanical Engineering), Thapar University, Patiala, under the guidance of Mr. Supreet Bhullar and ER. Arun K umar , during January to June, 2014.
ABHISHEK MITTAL 101108003 Date: ___________________
Certified that the above statement made by the student is correct to the best of our knowledge and be lief.
Mr. Supre et Bhullar
Arun Kumar K
Asso ciate Profes sor
De puty Ma nage r(L-12 )
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ACKNOWLEDGEMENT
I take this opportunity to express my profound gratitude and deep regards to my guide Mr. Arun Kumar K.(Deputy Manager, Weld shop -3 MSIL), for his exemplary guidance, monitoring and constant encouragement throughout the course of this project The blessing, help and guidance given by him time to time shall carry me a long way in the journey of life on which I am about to embark. I also take this opportunity to express a deep sense of gratitude to Mr. Gobinath T (Assistant Manager, Weld shop - 3) andMr.J.Edison (Senior Manager Process Engineering cell MSIL), for his cordial support, valuable information and guidance, which helped me in completing this task through various stages. I am obliged to staff members of MSIL for the valuable information provided by them in their respective fields. I am grateful for their cooperation during the period of my assignment.
ABHISHEK M ITTAL 101108003
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CONTENTS
2
Declaration Acknowledgement
3
Summary
5
About MSIL
6
Weld s hop
24
Spatter Reduction
25
Procedure
29
Implementation Training Module
36
Weld Information Collection System
41
Spot checking
52
Parameter Determination
55
Automation System
70
Result
77
conclusion
78
References
79
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SUMMARY
Reduction of spatter in Ertiga line by maintain proper production process such as avoiding improper face cutting, tip alignment, zero touch up and keeping parameters such as weld time, c urrent and press ure to acceptable limit. Spatter causes huge monetary, productivity, quality losses. The project invo lves parameter determination which is a dominant factor in weld spatter. Also a concept was developed to automate the spatter reduction activities which were earlier done manually.
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Maruti Suzuki India Limited (MSIL) is engaged in the b usiness of manufacture, purchase and sale of motor vehicles, automobile components and spare parts (automobiles).
The other activities of the Company consist of facilitation of pre-owned car sales, fleet management and car financ ing. The Company’s portfolio includes the Maruti 800, Alto 800, Alto K10, A-star, Estilo, WagonR, Ritz, Swift, Swift DZire, SX4, O mni, Eeco, K izashi, Grand Vitara, Gypsy, Ertiga and Stingray.
The Company’s services include Finance, Ins urance, Maruti Ge nuine
Accessories, Maruti Genuine Parts, Maruti Driving School and Autocard. The Company’s subsidiaries include Maruti Ins urance Business Age ncy Limited, Marut i Insurance Distribution Services Limited, True Value Solutions Limited, Maruti Insurance A gency Network Limited, Marut i Insurance Agency Solutions Limited, Maruti Insurance Agency Services Limited, Maruti Insurance Logistic Limited and Maruti Insurance Broker Limited.
Listed in SENSEX ,BSE:532500 AND NSE:MARUTI
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Earlier known as Maruti Udyog Limited, it was incorporated as a Public sector company on 24 Feb,1981 with the following objectives: • Modernization of Indian automobile industry.
•
Production of fuel-efficient vehicles to conserve scarce resources.
•
Production of large number of vehicles which was necessary for economic growth.
Transfer of Technology
Every minute two vehicles roll out of the Maruti Plant. It is therefore impe rative that the transfer of contemporary technology from our partner Suzuki is a smooth process. Great stress is laid on training and motivating the people who man and maintain the eq uipment, since the best equipment alone cannot guarantee high quality and productivity. From the beginning it was a conscious decision to send people to Suzuki Motor Corporation for on-thejob training for line technicians, supervisors and engineers. This helps them to imbibe the culture in a way that merely transferring technology through documents can never replicate. At prese nt 20% of our workforce have been trained under this pro gram. Maruti Code Of Conduct
A code has been developed to assist all the employees in their dealings with those with whom the company does business i.e., customers, dealers, and suppliers and with each other. The code is not a subst itute for the judgment and discretion of individual employee in day-to-day work. Neither is it a replacement for company policies, which will continue to apply. The code contains advice for making decisions in situations where there are no precedents, so that a common set of norms of business behavior can grow throughout the company.
Following are the important points:
•
Integrity
•
Trust
•
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•
Consumer Orientation
•
Ethics
•
Positive Attitude MSIL’S GURGAON PLANT
The manufacturing plant, located about 25-km south of New Delhi in Gurgaon, has an installed capacity of 5,00,000 units per annum. The total area of the plant is 12,02,256 m2 2
with a total covered area of 2,95,293 m . The average daily production is around 2500 vehicles a day. The whole production facility has been divided into 3 plants: 1. Plant I (M800, Omni, Eeco, Ritz, Wagnon R) 2. Plant II ( Zen ESTILO, Swift Dzire) 3. Plant III (Alto) The other activities include research & development and utilities (captive power p lant, water and effluent treatment plant, compressor house, boiler house, air washers and incinerator facilities.
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Managing Director (MD) Join t Managin g Director(JMD)
Director Divisio nal Manager(DVM) Deputy Divisional Manager(DDVM) Departme nt Manager(DPM)
Manager Deputy Manager Asst. Manager Executive Supervisor
Technician `
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The Various divisions in Maruti Udyog Limited are:
• Marketing & Sales • Spares • Engineering • Quality Assurance • Services • Production • Production Engineering • Materials • Information Services • Finance • Personnel and Administration
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To maintain international standards, the Japanese have evolved certain standard quality statements, which are strictly adhered to in the production process. THE 5-S
Seiri
- Proper Selection
Seiton
- Arrangement 11 | Page
Seiso
- Cleaning
Sheiketsu - Cleanliness Shitsuke
- Discipline THE 3-K
Kimerareta Koto Ga - What has been decided Kihin Doro
-
Kichin To Momoru
- must be followed
as per standard
THE 3-G
Genchi
- Actual Place
Genbutsu - Actual Thing Genjitsu
- Actually
(In case of an abnormality, see the actual thing in the actual place) AVOID THE 3-M (Pro ble ms affe cting pro duction)
Muri - Inconvenience Mura - Wastage Muda – Inconsistency
Manufacturingis the productio n of merchandise for use or sale using labor and machines, tools, chemical and biological processing, or formulation. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale. Such finished goods may be used for manufacturing other, more complex products, such as aircraft, household appliances or automobiles, or sold to wholesalers, who
in turn sell them to retailers, who then sell them to end users – the "consumers". Manufacturing takes turns under all types of economic systems. In a free market economy, manufacturing is usually directed toward themass production of products for sale to consumers at a p rofit. In a collectivist economy, manufacturing is more frequently directed by the state to supply a centrallyplanned eco nomy. In mixed market economies, manufacturing occurs under some degree of government re gulation.
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Modern manufacturing includes all intermediate processes required for the production and integration of a product's components. Some industries, such assemiconductor and steel manufacturers use the term fabrication instead.
MARUTI SUZUKI MANUFACTURING PROCESS
Blanking is the cutting of a sheet metal part along a closed contour in one step. The piece c ut out is called a blank and may be further processed. Many blanks are often continuously cut out of a sheet or strip. Blanking will waste a certain amount of material. When des igning a sheet metal blanking process, the geometry of the blanks should be nestled as efficiently as possible to minimize material waste. A distinction should be made between the two sheet metal cutting processes of blanking and punching, since essentially they are the same process. In punching, the piece cut out is waste. In blanking, the piece cut out is the work and is kept. It is possible to employ finesheet blanking for many metaliscutting operations, particularly those involving lower total thickness. Finesheet blanking an advanced precision pressworking process that can create cuts having close tolerances and straight smooth edges, without shaving or other secondary processes. A press forces a pressure pad on the sheet metal, holding the work tightly between the lower die and the pressure pad. C lose to, outside and all around the edge of the cut, a v-shaped ring projecting from the bottom of the pressure pad impinges the work piece. This further sec ures the work from movement and restricts metal flow. The cutting punch for this operation has a 13 | Page
very s mall clearance with the lower die, usually 1%. As pressure is applied to the work, the punch cuts through the metal at a s low rate. Simultaneously, another punch app lies force to the other side of the sheet in the opposite direction. The secondary punch delivers less force than the cutting punch. Its p urpose is to help with the cut and to prevent warping o f the ba nk, a common problem in sheet metal blanking operatio ns. The force of the support punch is less than and in the opposite direction of the cutting punch, therefore the summation of both vectors indicates that the total force, (and hence the movement), will be in the direction dictated by the cutting punch.
The press shop can be regarded as the starting point of car manufacturing process. Centrally located between weld1, weld2 and weld3 supplies components to all the three plants. The press shop has a batch production system whereas the plants have a line production system. The press shop maintains an inventory of at least two days. The weld shops as per their requirements pick the finished body parts. These may be divided as A, B & C. ‘A’
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components are large outer components e.g. roof, door panels, front hood etc. These components are manufactured in the press shop at maruti due to design secrecy and huge investment requirements. ‘B’ & ’C’ components are manufactured by joint ventures or
bought from vendors. The press shop can be explained under following headings •
Raw Material
•
Blanking Line
•
Stamping Line
RAW MATERI AL
The raw material is in the form of cold rolled steel coils. It is specified in terms of steel grade and width of coil required. The coils weigh about 15000kg.
BLANKING LINE
There are two blanking lines; ROSL (Rotary Oscillatory Shear Line) for rectangular sheets and the other employing die cutting, for irregular shapes.
The rectangular sheets are obtained on ROSL while dies are employed to obtain the required shape sheets. The sequences of operations on the blanking line are as following: -
•
Uncoiling
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•
Cleaning
•
Leveling
•
Measuring
•
Shearing/cutting
•
Piling/stacking
STAMPING LINE
There are six presses of capacity varying from 1500 tones to 4000 tones. Of these five are transfer presses and one is a semi-automatic press line, wherein the loading is manual. The dies can be changed to obtain different body components. The sequence of operations is as following: •
Destacking
•
Cleaning
•
Drawing
•
Trimming
•
Bending
•
Punching
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Drawing refers to giving the basic shape to the sheet. The dies used for drawing leave margins that are cut by trimming process. Depending upon complexity of the part bending and punching may be done using 2 or 3 dies. Overall the machine provides for an option of 5 dies to be placed. Adjust ing the strokes per minute of the press can vary the rate of product ion.
Transfer
Presses used here have a maximum speed of 60 strokes per minute.
Welding is a materials joining process which produces coalescence of materials by heat ing them to suitable temperatures with or without the application of press ure or by the application of pressure alone, and with or without the use of filler material.
Welding is used for making permanent joints.
It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.
Skyscrapers, exotic cars, rocket launches -- certain things simply demand your attention. Welding, in all likelihood, isn't one of them. You may have gone your whole life w ithout ever having thought about the subject. It might surprise you then, that welding affects an estimated 50 percent of the United States gross national product Without it, none of those amazing skyscrapers, cars or rockets would exist.
There are tons of differe nt welding met hods, and more are being invented all the time. Some methods use heat to essentially melt two pieces of metal together, often adding 17 | Page
a "filler metal" into the joint to act as a binding agent. Other methods rely on pressure to bind metal together, and still others use a combination of both heat a nd pressure. Unlike soldering and brazing, where the metal pieces being joined remain unaltered, the process of welding always changes the work pieces.
This is restricted area and I could not get permission to go inside. A single particle of dust if embedded onto the body the paint would chip off. Hence the entry of non-factory personnel is restricted in order to avoid the entry of dust particles. 18 | Page
However the information regarding the process outline in the paint shop gathered from other sources is as following: I. Pre-treatment: The body is thoroughly washed to remove dirt and oil scales. II. ED coat: This is done by electric deposition method. After applying the ED coat body is baked in ovens. III. Inte rme diate coat: This is done by spray painting method. After applying the coat, the body is dried in the oven. IV. Final coat: For metallic coating, double coats are applied and aluminum flakes provide the shine to metallic paint. This is also done by spray painting method. The PBOK, i.e. Paint Body OK is sent to the assembly shop.
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Painting process I/C & Top Coat painting
Painting
process
Final
Inspection
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The asse mbly shop receives PB-OK i.e. paint body OK from the paint shop. Here the body is loaded on a conveyor on jigs. As the conveyor moves the fitments are made on the body at various stations. The sequencing of models is done by PLC i.e. Program Logic Control. In Plant -1 there are separate assembly lines for each model as compared toPlant-2which has only one U type plant layout for different models. Altering the speed of the conveyor can alter the capacity of shop. The Plant-3 conveyor runs at 2.7m/min. The conveyor belt can run at a maximum speed of 4 m/min. Assembly shops havecontinuous production system. The assembly line can be further subdivided as following: •
Trim
•
Chassis
•
Final
TRIM Tr i m can be fu rt her subdi vided as fol l owi ng: -
1. Trim 1 2. Trim 2 3. Trim 3 Trim 1: This is the beginning of the assembly line conveyor. Here amongst the first tasks
done is attaching the hydraulic supporters for the boot. The asse mbly line check sheet is put inside the body.
.
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Trim 2: It starts with the head light fitting. Other operations done here are vacuum booster/
brake master cylinder fitment, seat belts, fuse box, wiper sprayer and motor, accelerator, clutch, brake pedals, door glasses and a/c panel fitment. Trim 2 ends with the fitment of the instrument panel, which is received from an instrument panel, sub assembly. This sub assembly involves the fitting of the speedometer console, ashtray and stereo system. Besides all these ignition coil for Car800. Trim 3: The fittings done here are rear inside cover for boot, back door glass and windshield,
quarter glasses and connecting pipe between fuel lid and fuel tank. Car800's front coil spring is also fitted here. Steering gear is mounted. For comedienne application on the windshield, Motoman robots are employed. There is a process check at the end of trim line wherein the points in the check sheet are verified and marked ok.
CHASSIS
The chassis receives a trim up body. Here underbody fitments are made; hence body is loaded on overhead jigs. Chassis can be subdivided as following: 1. Chassis 1 2. Chassis 2 Chass is 1: Various fitments made here are rear shock absorbers, brake pipes, front coil spring
with knuckle, steering wheel, tie rods, rear suspension, fuel pipes, fuel tank and rear brake drum. There is a knuckle sub assembly that feeds the line with knuckles for the front suspension system. On front wheels disc brakes are used whereas on rear wheels drum brakes are used. There is a process check at the end of chassis 1.
Chass is 2: The various fitments made here exhaust system (silencer and catalytic converter),
engine cum transmission case assembly, gear shift rod, front and rear bumpers, stabilizer bars and tyres. Radiator of Car800 is fitted here. The tie rod and drive shafts are connected to the knuckle to complete the front suspension system. There is a process check at the end of chassis 2.
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FINAL
Since all the fitments have been made, we will refer the body as vehicle from now onwards. The vehicle is loaded on the conveyor. It can be further subdivided as: •
Final 1
•
Final 2
Final 1: The fitments made here are Spare wheel cover, ID plate, scuff, seats, roo f trim and
carpet, boot carpet, battery and air cleaner. Clutch cable and parking brake connections are made. Brakes are evacuated and brake oil is filled. Coolant is also filled.
Final 2: Five liters of petrol is filled in the vehicle. A/C evacuation and charging is done
here, the refrigerant used here is R134a (400 gm +- 50). Door gaps are checked and adjusted, front grill of Car800 is fitted. There is a process check at the end of this line. Here the vehicle is checked for the following as per the check sheet: •
Final-Engine room
•
Final-Cabin
• •
Final-Pit Final-Side body
Fina l-Eng ine room: Engine oil, brake oil and coolant level. Electrical connections, viz.
ignition coil to distributor, battery terminals, and wiper motor connections. Air cleaner fitment, rad iator hoses &clamp tightening, fuel hoses clamping, rad iator mtg. bolt fitments, clutch cable connection, acce lerator peda l play &choke cable play are checked. Final-Cabin: All lamps viz. head lamp high/low, parking lamp, cabin lamp, wiper water
spray, reverse lamp, ac cooling, blower etc. are checked here. Mirror view, clutch pedal play and brake peda l play & operation of parking levers are checked here. Steering shaft column and shaft nuts and bolts are tightened. 23 | Page
Final-pit: The vehicle is checked for brake oil leakage, coolant leakage, fuel leakage etc.
And these are marked OK on the check sheet. Final-side body: All door fitments checked. Spare wheel fitment and rear seat fitments are
checked. Seat adjustments are checked. The vehicle is said to be AB-OK now. It is sent to vehicle inspection dept. The assembly check sheet is removed. A new check sheet is added to vehicle carrying ABOK stamps. The vehicle is called FC-ON i.e. final check on.
Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020 to 0.118 in) thickness range.
The process uses two shapedcopper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together.
Forcing a large current through the spot will melt the metal and form the weld. The attractive feature of spot welding is that a lot of energy can be delivered to the spot in a very short time (approximately 10 - 100 milliseconds).
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That permits the welding to occur without excessive heating of the remainder of the sheet.
The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current.
The amount of energy is chosen to match the sheet's material properties, its thickness, and type of electrodes.
Applying too little energy will not melt the metal or will make a poor weld. Applying too much energy will melt too much metal, eject molten material, and make a hole rather than a weld.
Another feature of spot welding is that the energy delivered to the spot can be controlled to produce reliable welds.
Weld spatter occurs when small liquid molten metal particles are expelled from the surface of the materials while welding, due to pressure and heat.
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WHY WE NEED TO CONTROL SPATTER ? ??
Deterioration of quality due to metal dust and burrs caused by spatter Spatter can leave marks and also makes spots weak which degrades quality of product ion. Damage of costly PLS , Limit switches , and other se nsors in automation line. Lots of high cost equipments are installed in automation line,spatter can hinder in the working of these instruments also. instruments and in extreme case can lead to fa ilure of these Increased down time due breakdowns related to LS & Sensor damage For company like MSIL ,completing their production targets in time is most important requirement, but spatter can lead to breakdown ,so it is importa nt to co ntrol spatter. Health and safety implications for employees 26 | Page
For MSIL safety comes first and for this we need to control spatter as it can and sk in .
harm eyes
Higher electrical power usage Spatter can be because of wrong parameters like current. Generating more current on spot then required means improper usage of costly resources.
Facto rs Co nt ri bute to we l d s patte r!!
Tip alignment and mismatch problem One of the most common factor that contributes to spatter, mismatch of tip of guns i.e movable and stationary gun. Abnormal Zero touchup Absence of zero touch between body to be welded and stationary gun can make way for spatter because of air gap. Abnormal dressing condition Improper dressing or grinding can also produce spatter because it leads to improper dressing tip. Abnormal gun pressure and welding current. Too low gun pressure or to high current contributes to spatter. Improper location of weld spot Another factor that contributes due to incorrect location of weld spot ,which can be because of overlapping of spots etc.
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1s t Step is collect initial data, follow t hese ste ps: a. Collect the data at standard condition Use standard format for this purpose.
2
nd
Step is Tip alignment & matching
Checking and correction of
Shank alignment
Cap Tip alignment
Tip matching
* Tip alignment and matching to be done in new tip, after dressing * If wear down value is NG then gun mastering to be done
rd
3 Step is Welding Current & pressure calibration
Checking of welding current output vs Input ( by weld checker & Turn ratio setting)
Pressure calibration (by pressure checker )
th
4 Step is Dresser Check
Dresser mounting check
Dresser cutter and holder condition check 29 | Page
Air blow and cutter rotation direction check
Tip condition after Tip Dressing th
5 Step is Zero touch up
Checking and correction of
- Zero touch up with body surface
6th Step is pressure setting correction
Checking and correction of
- Weld pressure as per standard
th
7 Step is Dressing time and dressing frequency setting Checking
and correction of
- Dressing frequency - Dressing time Other than the above procedures following factors also affect the welding condition:
Excessive dust on the welding surface
Gap and mismatch of comp. in jigs
Vibrations in Servo gun & Robot
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Reduced power consumption
Better weld qual ity and less rework
Reduced maintenance costs
Safer and cleaner environment
Lower consumable costs
Increased p roduction up-time
The aim of the project is to re duce spatter an d improve welding process. Spatter free weld shop was motto of this project. 31 | Page
A team was for med including expertise, line su pervisor,summer trainee. A proper checksheet was designed to record daily spatter data. The project started with aim of reducing spatter in YL8 line .During initial data collection spatter percentage was found out to be 42% which was way above acceptable level. A proper procedure to control spatter was followed as discussed above and the results obtained were com mendable. The spatte r percentage of Left side body was reduced from 40% to 5% . 45
S
40
p
35
a
30
t
25
t
20
e
15
40 YL8 Ertiga - LH Side body Spatter control progress
22
10
r %
5
5 0
W1 Jan 14 W2 Jan 14 W3 Jan 14 W4 Jan 14
Period
A view of spatter control checkshe et can be seen below which is updated for each and e very robot in welding shop a nd stepwise sequence was followed to achieve desired results. 32 | Page
And now after 4 months the current spatter and the difference that has been mad e can be seen in below ba r graph:
YL8 LINE SPATTER STATUS AS ON 28.04.2014 S 40 35 P 30 A 25 T 20 T 15 E 10 R 5 0
YL8 Line Feb'14 YL8 Line Mar'14 YL8 Line Apr'14
%
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A standardized process for recording data was for mulated which includes summary sheet of a particular area, supervisor check sheet, monthly data graph which is updated on regular basis. It helps us to analyze spatter data of a particular area and decide ne xt course of action. Given below are t he examples of data colle ction sheets to give the insig ht of how things work.
Monthly Spatter status up date sheet which give us t he monthly
spatter status.
YL8 LSB Line Spatter Status 45
40
S 40 P 35 A 30 T 25 T E 20 R 15 10
%
9
6.6
6
5 0 Jan'14
Feb'14
March'14
April'14
Period
Individual robot wise ch eck sheet updated on regular basis to
know the current spatter st atus of particular ro bot.(Supervisor check sheet.)
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Area wise Summary sheet updated on r egular basis :
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TRAINING M ODULE FOR SPA TTER R EDUCTION
MOS Z was developed for zero touch up training during spatter reduction activities.
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Zero touch up and dressing training module was made for line superviser and workers.
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Below is the step by step instruction for Fanuc robot to conduct zero touch up procedure.
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WELD INF ORMATION CONTROL S YS TEM
INTRODUCTION
As we know, the spots of a car are the most précised work done on a car as their failure can cause accident. So, the company prefers to check the spots of car as it directly refer us to the company quality. But, it was not possible for the company to check the spots of every car as it was a very time consumable process as the processes done to check the spots were hammering test and peeling test. Till now, Maruti Suzuki India Limited was checking the spots of every export car and every 10
th
import car. But this does not give assurance to the
customer for the best quality car as there was no tool for analysis of weld spot quality. So, there was a need to implement a method which would help the company in providing the best quality car. Due to this reason, weld information control system came to being in use.
WELD INF ORMATION CONTROL S YS TEM
Weld information control system is a non-destructive testing technique to check the spots. In this technique, a spot id is given to every spot of the car . The data’s of welding parameters are noted. These data have been fed to the PLC (programmable logic controller). IT department has implemented a server which would be directly linked with the PLC. PLC provides a graphical characteristic of every spot in computer screen with the he lp of server from which we could ensure defective spots on line. Also, the robot line would stop in which problem has occ urred i.e. if the spots does not have the same characteristics as provided to the PLC, the robot would stop working itself and show faults on computer screen. So that, we can correct the spot by taking counter meas ure. Also, this technique will help us in having a control on NG welding flow.
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NG Welding Flow
NG welding flow occ urs at a point where the robot is not ab le to weld the spo t correctly i.e. the weld does not took properly due to following reasons:a) Spatter control b) Spot Miss c) Gun alignment NG d) Tip / Tip Dressing NG e) Half spot f) Spot out of position g) Gun shunting h) Part deformation (part mismatch)
W.I.C.S. FUNCTIONALITY
Prevents NG Welding Flow
Accurate Detection of Faults a) Spatter control b) Spot Miss c) Gun alignment NG d) Tip / Tip Dressing NG e) Half spot f) Spot out of position g) Gun shunting h) Part deformat ion (part mismatch)
Analysis of every weld spot
Storage of weld spot parameters (upto 10 years)
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W.I.C.S. METHODOLOGY
The methodology on which W.I.C.S. depends is to study about the resistance waves as the reason for the spot failure could be known by this methodology.
RESISTANCE WAVES
Resistance waves are the graphical representation between resistance values and the weld time to show that the nugget formed is absolutely correct.
Fig. 3.2. Principle of Resistance Waves
As we ca n see from the above figure 3.2, the resistance value first decreases but as the temp. of base metal is raised the resistance value climb up and form a nugget and as the nugget expansio n takes place with the increase in electrical path, the resistance value again decline.
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BENEFITS FOR OBS ERVING RESISTANCE WAVES
Resistance wave profile is full spot welding, white body check.
Detect the abnormal conditions early.
Prevent NG Welding Flow.
RESULTS OB TAINED B Y OBSERVING RESISTANCE WAVES
By observing the resistance waves, we could get to know the various methods beca use of which the NG Welding Flow occurs. 1. Fault due to get out of parts position.
Fig. 3.3. Fa ult s een due to ge t out of parts position
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From the above fig. 3.3, we can clearly see that the nugget formation takes place at any other position than required.
2. Fault due to bend parts.
Fig. 3.4. Fault see n due to bend pa rts
From the above fig. 3.4, we can clearly see that the nugget formation does not took place correctly as the parts in which the spot was to be applied was bent.
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3. Fault due to get out of position.
Fig. 3.5. Fa ult due to get out of position se en
From the above fig. 3.5, we can clearly see that the nugget formation was formed slightly side from its position due to which spot was not formed as required.
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FAULTS REL ATED T O RESISTANCE WAVES
E79 Resist wave fault
Fault occurs due to low quantity of heat, Tip diameter expansio n, Lack or 2sets of work, Shift of weld position, Gun touch, terrible expulsion etc.
Fig. 3.6. Fault of E79 resistance waves
-Reset possible at reset box -Be cautious that when same control no. a nd same condition has been used continuously, judgment will not be done. NG body don’t stop, even if no check and reset. When you returns weld points before more than 1 weld point by manual operation and you re-welded the weld points, it is possibility existence to stop by fault again.
E85 Wave Resist Frequent
Fault occurs due to tip dress, etc. - Timers output “E85”, when weld points more than thresholds of a warning level occurred frequently in res. decrease width or aver. res. -Reset possible in reset box
E80 High Resistance
Faults occur due to dust between the tip, power cable break etc.
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Fig. 3.7. Fa ult of E80 high resis tance waves
- Timers output “E80” when it detect resistance value ahead of a threshold of high resistance and it doesn’t send weld current according to the setting value.
-Discontinue the power supply at the detection of the fault - Measures are the basically same as low current fault. - We can reset the fault at a reset box, but it occurs again till the fault state is removed
GRAPHICAL REPRESENTATION OF RESISTANCE WAVES
Fig. 3.8, shows the graphical representation of resistance values at the time of welding.
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Fig. 3.8. Graphical representation of resistance values
This representation shows us the difference in the resistance decreasing width. This is shown by the line arrays o f red, ye llow and blue colour in above fig.
METHOD FOR OBSERVING RESISTANCE WAVEFORM
To measure the transition of resistance value in every 0.5 cycle in welding, we have to calculate the parameter 1 to 4 and supervise them. The parameter to be calculated are as follows:1. Resistance width decrease: - Max. resistance value – final resistance value 2. Average resistance value:- Avera ge of resistance value between 2.5c yc and weld time (setting time) -0.5cyc 3. 3.Max resistance value:- Max value between setting time and weld time (setting time) -1.5cyc 4. Final resistance value:- Resistance Value of weld time (setting time) -0.5cyc 49 | Page
Fig. 3.9 Resistance waveform SETTING OF R ESISTANCE LIM IT
Resistance limits refers us to a position after which alarm would rang. Resistance limits are classified in two levels: -
1. Alarm Level: - When the nugget formatio n does not take properly, limit of alarm level is reached a nd the alarm rang so that the worker or engineer co uld take the counter measure. 2. Fault level: - When the engineer or worker does not take counter meas ure after the alarm, then the line would automatically spot.
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PROBLEMS OCCURING IN OBSERVATION
There is a case when there is not a change of resistance. In this case, only the thin sheet side is weld NG on sheet combination such as thin- thick-thick sheets and in the case of sheet combination of thin-thin sheets. Therefore, there is the case that NG points cannot stop.
Whether fault stops or not depend on a limit setting. Misjudgment occur a lot of times, when limit setting is too rigorous. But it cannot detect weld NG, when limit setting is too indulgent.
Now, we set limits from average and unevenness of the prese nt data which WICS system collect.
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WELD SPOT CHECKING PROCESS STANDARDIZATION
Maruti Operation Standard Inspection
MOS I is known as Maruti Operation Standard Inspection sheet in which a list o f all the spots are made and their robots are mentioned which apply these spots. Cycles are divided according to the application of spots. This sheet has a full spot detail of a car and the cop y of ever y sheet is listed in the file on the line so that any engineer could go on the line and with this sheet could know about the inspection of this spot. The sheet is divided according to main body, main body pit, white body, cowl box, etc. and their cycles.
DESCRIPTION OF MOS I
The first thing that an engineer should know in welding department is the layout of department.
He should know that which robot is working on which car.
He should know which spots can be checked and which cannot be checked.
He should know how many men are needed for checking the spots in a given component.
For this, MOS I has been made so that the engineer have a list of all the spots being implemented on the components of the car.
OBJECTIVES OF M OS I
1. To mark the spots with different colours of different robots working on the component. 2. To mark the G.A. spots and Maru - A spots of the component. 3. To mark the cycle so that we could know how many men are needed for checking the spots? No. of cycles is equal to no. of men needed to check the spots.
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4. To know how many robots are doing welding in a given component and how many spots are there in the given component.
METHODOLOGY ADOPTED
A MOS I sheet was made in which the picture of component with the spots was printed.
The robots which are applying those spots in a given component were noted down along with their spots.
Maru- A spots and G.A. spots were seen and marked on it.
The men working on a given component to check the spots were noted and cycles were made according to their work.
Modified MOS I of Main body checked at white body area 53 | Page
CONCLUSIONS
Easy for engineer to trace back the broken spot robot
Easy to find out the component details with the help of index.
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PARAMETER DETERMINATION
Parameters such as tip pressure, weld current, sq ueeze time and weld time affects weld quality and expulsio ns. Low pressure, high current and weld time were found to be main reasons for weld expulsions.
METHODOLOGY
Stage 1 - calculating pressure at particular current, time, hold time, sheet thickness ratio, material stage 2 - determining current and weld time combination through lobe diagram stage 3 - verifying by peel test nugget size,depth, shear strength stage 4 - spot sample
PRESSURE CALCULATION
Expulsion in welding is determined by many factors involving electrical, thermal, metallurgical, and mechanical processes. Although there are many complicated causes of expulsion, its basic process can be described by the interaction between the forces from the liquid nugget and its surrounding solid containment. Major forces acting on a weld ment during welding are illustrated in Fig. 3. They include the squeezing force provided by the electrodes (F E,applied) and the force from the liquid nugget (FN) onto its solid containment, which is generated by the pressure (P) in the molten metal and a compressive force between the workpieces. There is also a resistance to sheet separation provided by solid diffusion (corona bonding) at the faying interface. This force is usually much smaller than the others and can be neglected in the analysis, as t his model considers extreme expulsion conditions only. Expulsion occurs when the force from the liquid nugget (F N) onto the solid containment equals or exceeds the effective electrode force (FE), i.e., FN≥ FE. In practice, the applied electrode force is rarely collinear with the total force from the liquid nugget because of complications in electrode geometry such as wearing, electrode alignment, and part fitup. Therefore, the applied electrode force, in many cases, is not the same as the one used to contain the liquid nugget from expulsion. The “effective” electrode force is introduced in this situation to accurately represent the force used to suppress the force from the liquid nugget. EVALUATION OF EFFECTIVE ELECTRODE FORCE An effective electrode force, which is usually a portion of the total applied electrode force, is used to balance the force from the liquid nugget. 55 | Page
An offset between the applied electrode force and that from the nugget, which is created by an angular misalignment of electrodes. FE,applied is t he applied electrode force, FN is the total force from the liquid nugget against the solid containment, and Fx is a force imposed by the other workpiece. FE is the effective electrode force, which will be explained in the following. In Fig. 5, d is the distance between the total nugget force a nd the electrode force; r is the distance between FN and the edge of the nugget (it is the radius in the case o f a round weld); x is the distance between force Fx and FE,applied. Moment equilibrium with respect to the acting point of Fx produces the following relationship between FE,applied and FN : FE,applied x = FN (d + X)
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Schematic diagram of simplified forces and theirlocations on one workpiece at expulsion.
Before metal melts, x = 0 because FN = 0, and FE,applied and Fx have to be collinear. As the liquid nugget grows, FN gets larger (FN is proportional to the area of the nugget at the faying surface) so Fx gets smaller because F x + FN = FE,applied assuming FE,applied = constant. Meanwhile, x goes up as can be derived from a moment equilibrium with respect to the acting point of FE,applied : FN d = Fx x when assuming d = co nstant. Because t he magnitude of FN increases and that of Fx goes down, x has to get larger, or xF gets farther away from the center of the nugget d uring nugget growth. It is reasonable to assume that when Fx moves across the right of the nugget (Point A), thecondition solid losesfor itsexpulsion containment of the nugget. Therefore, x = redge – d can be regarded as a critical to happen. Expulsion condition : FE = (r – d)/r * FE,applied The discrepancy d is usually created by asymmetric loading, suc h as in the case of electrode misalignment (axial and angular misalignments), electrode wear, or improper workpiece fitup. It can be approximated by the distance between the geometric center of the indentation marks and that of the nugget . The force provided by the electrodes is fully used against the nugget force s uch that d = 0 and FE = FE,applied. Figure 6 s hows a case with a ngular misaligned electrodes. The nugget forms around the shortest electrical current path, which is not the same as where the total electrode force is applied because of the angular misalignment. As a result, an offset d is created be tween the applied electrode force a nd the force from the nugget. The location of the applied electrode force is estimated from the surface indentation and the nugget force is at the geometric center of the nugget. A forofselecting electrode force/welding schedule can can be obtained by estimating theguideline conditions extreme an cases. The force from the liquid nugget be calculated with the knowledge of its size and press ure.
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Forces acting on the weldment during resistance spot weldin in idealized
Schematic diagram of the balance of forces considered in the model. FN is the force from the nugget due to liquid pressure and FE is the effective electrode force.
PRESSURE AND FORCES IN LIQUID NUGGET A volume increase occurs during heating in the solid state, solid to liquid phase transformation, and heating in the liquid state. The volume change due to melting happens at the melting point for pure metals and between solidus and liquidus temperatures for alloys (except eutectic alloys). However, a free volume expansion of the nugget during resistance spot welding possible due in to the its surrounding containment and the squeezing of low electrodes. Asisanot result, pressure nugget may solid be significant because of the relatively compressibility of liquids. Another source of pressure in the liquid nugget is the pressure of metal vapors. Such pressure exists because at temperatures above the melting point, a closed system tends to reach liquid/vapor equilibrium according to general thermodynamic principles. In add ition to metal vapor pressure, pressure from gases resulting from thermal decomposition of surface agents should also be considered. Examples of surface agents are lubricants on metal sheets, pretreatment agents, adhesives (in the case of weld-bonding), and
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adsorbed moisture or gases. The pressure can be evaluated by considering the type and amount of gaseous products, and their reactivity with, and solubility in, the liquid alloy. So there are four major components of pressure in a liquid metal during resistance spot welding: solid to liquid phase transformation (melting), expansion in the liquid state, vapors from the liquid metal, and decomposition of surface agents.
P = Pmelt + Pexp + Pvapor + Pdecomp PRESSURE DUE TO MELTING As the result of melting a certain portion of the metal surrounded by the solid phase, compression of the liquid takes place. The relationship between the volume V and pressure P in the liquid nugget at a given absolute temperature T can be described by the coefficient of compressibility
V/ P)T*1/ V
Therefore, for a small increment of volume, the resulting increase in pressure is d P = d V*1/ V Since the molten metal is not allowed to expand freely due to the containment of its solid surrounding and electrode forces, the increase in pressure resulting from melting is approximately the same as that from compressing the liquid metal from VL to VS . This pressure can be obtained by integrating where VS and VL are molar volumes of solid and liquid states, respectively, at the melting temperature. Therefore, the pressure due to melting is Pmelt = 1/ ln( VL/ VS ) So a high volume change during melting results in a high pressure contribution. PRESSURE CHANGE DUE TO LIQUID EXPANSION A quantitative relationship between pressure and temperature under a constant volume can be described by thermal pressure coefficient = 1/P( P/ T)v
Its value is unknown for most liquid metals. However, the partial derivative of ∂P/∂T may be presented as the product of two partial derivatives: (∂P/∂T)v = - (∂V/∂T)p (∂P/∂ V)v By introducing a coefficient of volume thermal expansion, = 1/V(∂V/∂T)r
and using compressibility coefficient , can be expressed b y variables whose values ca n be found in published metallurgical data sources: = (1/P)( /
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Hence, for a small increment of temperature, the increase in pressure is: D dP = ( / dT Integraing the above yields the contribution of pressure due to the expansion of the liquid nugget in the range from melting point Tm to a given temperature T at a consta nt volume in the following form: de Pexp = ( / (T – Tmelt ) Because the contributions of vapor and surface agents to the total pressure are usually small, they can be neglected in estimating liquid pressure and force from the nugget. Therefore P = 1/ ln( VL/ VS ) + ( / (Tavg – Tmelt ) PROCEDURE FOLLOWED IN PRESSURE C ALCULATIONS • Obtain mater ial properties o f the main a lloying elements a nd s urface contaminants. • Obtain information of temperature distribution and value, and dimensions of the nugget. • Calculate pressure components and the total pressure. • Calculate forces in the directions of interest
CURRENT AND WELD TIM E DETERM INATION
Weldability range (lobe) is the area where acceptable welds can be produced using a specific combination of welding current and weld t ime. Welding range is limited b y the minimum acceptable weld size and splash limit. In spot welding, weldability range is usually defined using coordinate axes where weld time is located on one axis and welding current on the other. The electrode force used, electrode geometry and cleanness, and the consistency and thickness of the welded material affect the shape and size of the weldability range. Materials with good welding properties have a large weldability range, which means that welding parameters can be selected from a great number of different combinations. Cold rolled metal sheets usually have a large weldability range. Welding current can vary from 1.0–2.0.kA in common weld times. The alloying of the steel and thick zinc coat ing, in particular, may decrease the weldability range. In this case, the correct use of appropriate welding parameters is very important in terms of producing good spot welds. For a given combination of materials, electrodes, process conditions, and at a particular electrode-force, the weld lobe describes a region of acceptable parameters. The parameter axes are genera lly weld time (duration) & weld welding current. The "lower " boundary is the para meter combination that produces a weld button of minimum acceptable dimensions. The "upper" boundary is defined by expulsion conditions. Expulsion is a probabilistic e vent, so one way to de fine the limit is to find the co nditions that lead to (say) 50% of welds expelling. The area inside the lobe represents the "safe" welding window for new electrodes. Generally the wider the better.
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CONSRUCTION OF LOBE CURVES
1. First you decide what is Cold, Hot, and OK. I use: Cold = undersize weld button when the coupon is peeled apart, OK = greater than minimum acceptable size. Hot = expulsion occurred during the weld. 2. Select the proper tips, that have a contact size of at least the minimum button size required. 3. Then setup the proper force for the job. 4. Next you condition the tips with 25 welds, this is very important for coated materials. 5. Make a weld in a small coupon, record the current with an acc urate weld current meter, along with the cycle time. 6. Peel the coupon apart, measure button size, length plus width, and divide by two. (Length and width are at a 90 degree axis) 7. Class ify the weld, OK, Hot, or Co ld. Note, if you got expulsion, it is Hot, don’t bother to peel it. 8. Enter the weld current under the appropriate column, there are four columns for OK, three for Cold, and three for Hot, use whatever one you want. 9. Continue with different current levels 10. Then change cycle time to 4 cycles, and entered 7 more welds. 11. Then 6 cycles, then 7 cycles, then 3 cycles. As we fill in the area on the left, a chart is constructed on the right, that is our weld lobe. The spreadsheet also finds which cycle time gave the widest acceptable current range, and announces that is the cycle time to use, along with a current that is about 10% below the expulsion level.
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Weld lobe data collection
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Electrode force = 200kgf/cm2
Elecrode force = 250 kgf/cm2
Elecrode force = 300 kgf/cm2
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SQUEEZE T IME SE TTING
Figure 2 shows how the weld time can be started at different times relating to the force cycle. In the middle example, the welding current comes on too early and the squeeze time is too short to allow sufficient force to build up between components to produce a satisfactory weld. Many welding defects can be attributed to welding with too short a squeeze time.
Examples of different squeeze times in resistance welding The lower example shows a welding cycle where the current is applied late and the peak force has been established for some time. Although acceptable welds may result from this sequence, time is wasted unnecessarily, and in volume production this can add significant costs.
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In the top figure, the squee ze time is adjusted so that the current is initiated just before the peak welding force is achieved. This produces the best quality weld at the highest production rate. Modern programming systems for spot welding equipment enable the welding force current value and the relevant time sequence to be programmed. O n closer inspection the programmed sequence actually performed by the welding gun may differ from the intended welding cycle. This is because of delays in the control system due to mechanical inertia, performance of the pneumatic force cylinder and other mec hanical losses which modify the intended time sequence. It is essential to calibrate not only the forge force and the welding current but also to set the squeeze time correctly. The key forces are displayed on an illuminated bar on the Squeeze Analyser, shown schematically in figure 2. Short squeeze times are indicated by a large gap between the squeeze force and the peak force. Long squeeze times result in the squeeze force and the peak force be ing identical so that no gap in the illuminated bar occurs. Idea l squeeze times s how as a small gap (one unlit light emitting diode) between squeeze and peak force. The simple visual display of the Squeeze Analyser e nables the supervisor q uickly to assess the operating values of a spot welding installation. In practice, it takes minutes to calibrate a gun correctly for optimum operating co nditions. The actual values o f the forces are also indicated on the front panel display. PNUEMATIC VS SERVO GUN
Pneumatic or hydraulic cylinders actuate most spot welding guns. The electrodes move the entire range of the cylinder when the gun opens and closes. Clamping force is normally fixed by a pressure re gulator, and there is usually no means to provide feedback regarding the actual clamping press ure. The motor-controlled servo gun provides var iable electrode openings and programmable regulated pressure. Pneumatic guns often have two cylinders; one is used for short open and the other creates a full open space between electrodes. The servo gun (in position control) provides programmable electrode opening anywhere between the full stroke of the gun. The electrode opening can be programmed to move simultaneously with other axes of the robot. Application flexibility cycle time savings are realized by the servo-gun's ability to open the electrodes only a short distance, or a larger amount, to provide the exact clearance needed around tooling or parts. During the weld, the servomotor switches to torque control and provides a uniform calibrated clamping force. This is easily progra mmed in the robot control and is expressed as a unit of force. The force can be stepped during an individual weld cycle or varied from weld to weld for different material thickness stack-ups. Pneumatic guns close at full clamping force, which creates high impact on the tips. The servo gun controls the rate at which the electrodes close and ramps up to the clamping force. This controlled process extends the life of tips and is a major reason auto manufacturers have been using them. The contro lled clamp force a lso impro ves quality a nd cosmetics, allowing welds to be made on Class A surfaces
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Hence squeeze time for p neumatic guns is set to 3- 4 cycle whereas squeeze time for servo guns can be set to 0 as weld trigger is given only after the application of tip force.
SHEAR STRENGTH CALCULATION The shear strength of a single spot weld can be calculated as follows: Shear strength(N) = 2.6 • t • d • Rm where: t = sheet thickness, mm d = weld diameter, mm Rm = tensile strength of the material, MPa
PEEL TEST This test is conducted to determine nugget size and depth to ascertain the quality of spot weld.
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Chisel test is conducted to check if spots are not broken
SPOT SAMPLE
For final verification spot samples were taken and their shear strength calculated by tensileshear testing machine in R&D lab.
Spot sample j ig
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Spot sample : 0.8-1.2mm sheet combination, current = 6.5, weld time = 15, pressure = 200
Spot sample : 1.2-1.2mm sheet combination, current = 6.5, weld time = 18, pressure = 250
Spot sample : 1.4-1.2mm sheet combination, current = 6.5, weld time = 20, pressure = 300
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AUTOMATIC DETECTION SY STEM There was a consistent problem of tip mis-alignment, improper face cutting and dresser not rotating. As a result these problems were regularly checked by the maintenance and quality department personnel. There was an urgent need to automate this process to avoid any possibility of degradatio n in spot quality due to tip mis-alignment and face cutting.
TIP ALIGNMENT DETECTION
CONTRUCTION AND WORKING This device consists of a mild steel strip of dimension 30 X 100 resting on cast iron rods. There is a pressure sensor below one o f the rod. Dur ing tip dress ing the tips will exert a vertical force in oppos ite d irection on the plate. Any misalignment will cause a moment in the plate which in turn would increase or decrease the force exerted by the rod on the pressure sensor. Tip separated by x Mild steel strip Mx Cast iron hollow rods Force sensor F R
W
F
R
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TIP FORC E DETERMINATION Usually for steel design, the yield strength is used with a factor of safety, or, alternatively, a load factor is applied to t he design load, and bending stresses must not exceed the yield stress. The bending stiffness is equal to the product of the elastic modulus E and the area moment of inertia I of the beam cross-section about the axis of interest. In other words, the bending stiffness is EI . According to elementary beam theory, the relationship between the applied bending moment M and the resulting curvature K of the beam is M = EIK The flexure of the plate depends on: 1. The plate thickness 2. The elastic properties of the plate 3. The applied load or force As flexural rigidity of the plate is determined by the Young's modulus, Poisson's ratio and cube of the plate's elastic thickness, it is a governing factor in both (1) and (2). Flexural Rigidity, D = (Ehe3 )/12(1 – v2 ) E = Young's Modulus he = elastic thickness (~10 –15 km) v = Poisson's Ratio Flexural rigidity of a plate has units of Pa·m3 , i.e. one dimension of length less from the one for the rod, as it refers to the moment per unit length per unit of curvature, and not the total moment. I is termed as moment of inertia.J is denoted as 2nd moment of inertia/polar moment of inertia Factor of safety for mild steel = 3 Bending stress b = (MY)/I Where M(X) = Bending Moment at X Y = Maximum distance from the neutral axis Ix = second moment of area = (bh 3 )/12 = 6.86* 10-12 Sheet thickness = 1.4, length = 100 mm, breadth = 30 mm x = Maximum distance betwee n misaligned weld tips in X direction = 15 mm = 1.5*10-2 Bending moment ,M(Nm) = F(50) – F(50 + X) Y = 1.4/2 = 0.7 mm = 7* 10-4 m Maximum bending stress will be at the bottom most point. b = (Fx*7* 10-4 )/I
=( F*1.5*10-2 *7* 10-4)/( 6.86* 10-12) F = b /1.53*106 71 | Page
Bending stress has to be less than allowable tensile stress Allowable tensile stress = Young’s modulus(E)/FOS
E for mild steel = 420 Mpa Allowable stress , t = 420/3 = 140 Mpa F = 140*10 6 /1.53*106 = 93 N
MISALIGNMENT CALIBRATION Mx = 0 0 = 50(1500) – 1500(50+X) – RB(100) RB = 15x RB can be determined from the load cell reading. Accordingly x is calculated to determine the degree of misalignment. Tips can be adjusted using L keys. 5 full rotation moves the tip 1mm towards the fixed tip. FACE CUTTING D ETECTION
Proper dress ing is required to bring the tip diameter to the required level. This is necessary so that the required current density is maintained. It is also necessary to remove any carbon deposits that may obstruct the flow of current during welding. The device consists of component locating pin which is paced at the top of the meta l strip. The Robot gun travels a certain perpendicular distance from a datum until the gun tip touches the locating pin. The distance is recorded to de termine whether there is any hole at the tip centre due to improper dressing. To check the tip diameter after dressing the tip is made to e xert certa in force over the gauge pressure sensor. If the tip diameter is less pressure exerted would be high and hence improper dressing would be detected.
X
Datum
Locating
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The material used is cast iron. Since the minimum force detectable from the load cell is very less available cone with tip diameter 1.5 mm is feasible. The compressive stress developed would be very less. ROBOT PROGRAMM ING Tip dressing programm was modified in accordance with the se nsor requirement. For e.g. programm was made for the additional path robot follows after dressing, giving different pressure schedule during testing and logic was given to check the conditions for proper process in macro module.
1: !*** 371A TIP DRESS *** ; 2: ; 3: UTOOL_NUM = 1 ; 4: UFRAME_NUM = 0 ; 5: $USEUFRAME = 0 ; 6: PAYLOAD[1] ; 7: ; 8: !*** IO_RESET *** ; 9: CALL IO_RESET ; 10: ; 11: !*** AROUND HOME POSITION *** ; 12:L PR[2] 2000mm/sec FINE ; 13: ; 14: Reset Tip Wdn ; 15: ; 16: LBL[1] ; 17: R[17] = 0 ; 18: DO[213] = ON ; 19: ; 20:L P[3] 2000 mm/sec FINE ; 21: ; 22: !*** BEFORE DRESS POSITION *** ; 23:L P[4] 2000 mm/sec FINE ; 24: ; 25: DO[221] = ON ; 26: R[99] = $MCR.$GENOVERRIDE ; 27: O VERRIDE = 100% ; 28: ; 29: !*** DRESS POSITION *** ; 30:L P[5] 200mm/sec FINE PRESS_MOTION P=[99,89] ; 73 | Page
31: ; 32: WAIT 0.50(sec) ; 33: WAIT DI[203] = ON ; 34: ; 35: !*** BEFORE DRESS POSITION *** ; 36:L P[4] 300mm/sec CNT0 ; 37: ; 38: DO[221] = OFF ; 39: DO[213] = OFF ; 41: ; 42:L P[3] 1000mm/sec CNT10 ; 43: ; 44: CALL TWD ; 45: ; 46:L P[3] 1000mm/sec CNT10 ; 47: ; 48: DO[210] = ON ; 49: ; 50: !*** Tip Change Request *** ; 51: IF DI[210] = ON,JMP LBL[10] ; 52: ; 54: ; 55: DO[210] = OFF ; 56: WAIT 0.50(sec) ; 57: ; 58: CALL WDN_CHK ; 59: ; 60:L PR[2] 2000mm/sec CNT100 ; 61: ; 62: CALL IO_RESET ; 63: ; 64: !*** HOME POSITION *** ; 65:L PR[1] 2000mm/sec FINE ; 66: ; 67: !*** IO_RESET *** ; 68: CALL IO_RESET ; 69: ; 70: IF R[17] = 1,JMP LBL[1] ; 71: ; 72: END ; 73: ; 74: LBL[10] ; 75: ; 76: ; 77: !*** Tip Change Position *** ; 78:L P[9] 2000 mm/sec FINE ; 79: ; 80: Reset Tip Wdn ; 81: ; 74 | Page
82: DO[64] = ON ; 83: WAIT DI[64] = ON ; 84: DO[64] = OFF ; 85: ; 86: ; 87: JMP LBL[1] ; 88:
RESULT
COST PER PIECE Cost of mild steel strip = Rs 5 Cost of force sensor = Rs 400 Cost of 4 hollow rods = Rs 20 Cost of locating pins = Rs 90 Cost of pressure sensor = Rs 600 Total cost per piece = Rs 1105 EFFECT ON QUALITY AND PRODUCTIVITY There would be a huge affect in quality aspects of the spot weld as tip misalignment and improper face cutting are the major reasons for defects such as spot pinning, spot burr. Chances of weld spatter will reduce which is a major factor for excessive tip wear o ut. Productivity will increase with the reduction in jig related breakdown such Limit switch fault, PLS fault , solenoid vacuum fault. The major contributor to s uch faults is we ld expulsion. Hence overall line efficiency = Total time – breakdown time would significantly improve. EFFECT OF SPATTER REDUCTION ACTIVITIES Reduction in no. of spot burr cases per month = 1500 Cost of repairing spot burr defect = cost of tool = cost of sander wheel Life of sander wheel = 40 spots Reduction in cost of repairing = 1500/40*60 = Rs 2250
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CONCLUSION Spatter reduction activities were a huge success. We reached our target o f 5 % in 4 weld areas in Ertiga line. Parameter determination for different sheet combination helped us achieve the required spot quality at low current and weld time.
REFERENCES 1. Expulsion Prediction in Resistance Spot Welding by J. SENKARA, H. ZHANG, AND S. J. HU 2. Spot Weld Properties When Welding With Expulsion— A Comparative Study by M. Kimchi 3. Ruukki-Resistance-welding-manual 4. Miller Handbook for Resistance Spot Welding 5. http://www.updatetechnology.com/
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