Design of Fixture for Spot Welding Machine

International Journal of Scientific Research and Engineering Development-– Volume 4 Issue 5, Sep- Oct 2021

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ISSN : 2581-7175 ©IJSRED: All Rights are Reserved Page 573

Design of Fixture for Spot Welding Machine Shantanu Pawar*

*(UG Student, Savitribai Phule Pune University, Pune, Maharashtra, India.

Email: shantanupawar45 @gmail.com)

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Abstract: The project we are going to work is of spot welding machine. The operation being carried out in current

situation is like, there are two operator working alternatively on same machine by sitting on either sides of

machine. The operator has to perform six spot of weld on the workpiece. They have to operate machine by

single foot pedal alternatively.Current fixture requires the hammering action for loading and unloading

purpose . the speed at which it is carried out is very fast which leads to operator fatigue . In this project we

will try to overcome the above problem by designing the new fixture, In which loading and unloading job

will be very easy and accurate. This will also lead to improve the cycle time.

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Introduction : 1. SPOT WELDING

Resistance spot welding (RSW) is a process in which contacting metal surface points are joined by

the heat obtained from resistance to electric current. It is a subset of electric resistance welding. 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 shaped copper 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).

That permits the welding to occur without excessive heating of the remainder of the sheet.

Resistance spot welding is often used in sheet metal production as an important metal joining process. It

has many uses in the automotive, railroad car manufacturing, aerospace and nuclear, electrical and

electronic industries. It can be used in a wide variety of materials, such as low carbon steel, nickel,

aluminum, titanium, copper alloy, and stainless steel, as well as high-strength and low-alloy steel. It also

plays an important role in robotics. Chao stated that the modern vehicle has between 2000 and 5000

welding points. Simplicity, low costs, high speed and automation options are some of the advantages of

this method. Resistance spot welding was invented in 1877 by E. Thomson. It is a method of joining two

or more metal parts by fusing them together at discrete locations on the workpiece interface.

RESEARCH ARTICLE OPEN ACCESS




Fig.1Spotwelding

Fig. 2 Process of spot welding

1.1 FIXTURE:

A fixture is a work-holding or supporting device used in manufacturing. Fixtures are used to safely locate

work (place it in a specific location or orientation) and to assist in work to ensure that all parts

manufactured with the template maintain conformity and interchangeability. The use of an apparatus

improves production economics by allowing smooth operation and rapid transition from one part to

another, reducing the need for skilled labor by simplifying assembly of workpieces and increasing

compliance during a work run. production.

The basic purposes of developing and using suitable fixtures for batch production inmachine shops are:

• Toeliminate marking, punching, positioning, alignments etc.

• Easy, quick and consistently accurate locating, supporting andc lamping the blank in

alignment of the cutting tool Guidance to the cutting tool like drill,reameretc.

• Increase in productivity and maintain product quality consistently

• To Reduce operator‘s labour and skill–requirement




• To Reduce measurement and its cos.t

• Enhancing technological capacity of the machine tools

• Reductionofoverallmachiningcostandalsoincreasesininterchangeability.

Hence, provision of fixtures as production tools provides the following: Manufacture accurately

duplicate and interchangeable parts. Jigs and fixtures are specially designed so that large numbers of

components can be machined or assembled identically, and to ensureinter changeability of

components. Facilitate economical production of engineering components.

1.2.1 Fixture Element Generally, the entire fixture is made up of the following elements Locators:

A locator is typically a permanent component of a fixture. It is used to establish and maintain the position

of a part in a fixture by restricting the part's movement.

Clamps: A clamp is a fixture force-actuating mechanism. The clamps' forces secure a part in the fixture

against all other external forces.

Fixture Body: The fixture body, also known as the tool body, is the main structural element of a fixture. It

keeps the relationship between the fixture elements, such as the Locator, clamps, and supports, and the

machine tool on which the part will be processed, intact.

Supports: A support is a fixed or adjustable component of a fixture. When severe part displacement is

anticipated as a result of imposed clamping and processing.

These modular fixture components can be assembled in a variety of configurations to accommodate a

variety of work pieces

2. Problem Statement

Currently there are two operators working alternatively on a same machine by sitting oneither sides of

machine. The operator has to perform six spots of weld on the work piece manually. The speed at

which the operation is carried out is quite fast, which leads too perator fatigue and also the unloading

of




workpieceistime consuming.

Fig.3CurrentConditionofWorking

DESIGNANDCALCULATIONS

3.1 DESIGN CONSIDERATION INFIXTURE DESIGN. The fixture's main frame must be strong enough to allow for as little deflection as possible. This fixture

deflection is caused by cutting forces, clamping of the work piece, or clamping to the machine table. The

fixture's main frame should have enough mass to prevent vibration and chatter. Frames can be constructed

from simple sections so that they can be screwed or welded as needed. Welding can be used on parts of the

frame that will be permanently attached to the fixture. Screws can be used to hold parts that need to be

changed frequently. When the body of the fixture has a complex shape, it may be cast from a good grade

of cast iron. Clamping should be done quickly and with as little effort as possible. Clamps should be

placed in such a way that they are easily accessible and removable. Spring-supported clamps should be

used to keep clamps against the bolt head whenever possible. If the clamp is to swing away from the work,

it should be allowed to swing as far as necessary to remove the work piece. All clamps on the locator



ISSN : 2581-7175 ©IJSRED: All Rights are Reserved 77

should be easily visible to the operator and accessible for cleaning, positioning, or tightening. Provision

should be made for easy chip disposal so that chip storage does not interfere with operation and chip

removal during operation does not interfere with the cutting process.

3.1 DESIGNDEVELOPMENT

Fig.4FixtureonCREO 2.0

Fig.5Differentviewsoffixture

International Journal of Scientific Research and Engineering Development

©IJSRED: All Rights are Reserved

3.2 DEVELOPMENTOFFIXTURE

After suggesting no. of design of fixture design one of it is approved by in

that fixture design. As the design was the finalized we modified the

currently used in industry. As there were three pins on the

pins with attachment of toggle clamp as sho

As per the design, the right pin was reshaped from circular to split pin and is

manner that it would not get press it at the time of welding so that the

neglected at the time of ejection.

The centre pin was reduced in diameter by taking no of trials to avoid fixing of

finally it was repositioned and resize. The left pin was repositioned

attachment of toggle clamp. This clamp is been provided

upper plate.

As per the design we developed the

supervisor of that shop and no further problem was developed of the

hammering action were needed due

International Journal of Scientific Research and Engineering Development-– Volume 4 Issue 5,



Fig.6DevelopedFixtures

After suggesting no. of design of fixture design one of it is approved by in dustry so

As the design was the finalized we modified the existing fixture which is been

currently used in industry. As there were three pins on the fixture we repositioned and resize the

pins with attachment of toggle clamp as shown infig.14.

As per the design, the right pin was reshaped from circular to split pin and is placed in such a

manner that it would not get press it at the time of welding so that the hammering

reduced in diameter by taking no of trials to avoid fixing of job into fixture and

finally it was repositioned and resize. The left pin was repositioned and modified in diameter with

attachment of toggle clamp. This clamp is been provided to the restriction on the

As per the design we developed the fixture and took trials on it and the design was satisfied by the

supervisor of that shop and no further problem was developed of the job was getting stuck and

to easy removal of job.

, Sep- Oct 2021

www.ijsred.com

so we worked on

existing fixture which is been

fixture we repositioned and resize the

placed in such a

hammering action is

job into fixture and

and modified in diameter with

the movement of

was satisfied by the

getting stuck and no




3.3 DESIDNOF TABLE

Inthismanualfeedingmechanismitconsistsofbearingandslidingjointcompletethejob.Itbaseismadeofhollo

wshaftinwhichonedeepgrooveballbearingis fitted with fixed outer race. In the inner race shaft is fitted

which flange coupling at other end. This fange coupling is coupled with circular table for easy rotation

of table.

This circular table consists of two stations which means two jobs can be kept at

atime.Amongwhichononestationwillbeundermachineoperationandanotherwillbeof loading and

unloading operation. For rotation of fixture another small dimension bearing is been used which is

fixed in sliding plate. Just at time of spot welding the operator has to slide the sliding plate and rotate

the fixture and carry out six spot weld. After which the job is forward to next station for firstly unload

and then load new jobs. The design is shown in below figure.

Fig.7Assemblydrawing




3.3.1 DETAILEDDRAWINGOFDIFFERENTCOMPONENTS

Fig.16CircularPlateDrawing

Fig.8SlidingPlateDrawing




Fig.9ConnectingShaft Drawing

Fig.10HollowShaft Drawin




Fig.11FlangeCouplingDrawing




3.4Calculations:




Methodology: The project work is bifurcated into various to facilitate independent attention on all




thebasic details related to design, fabrication analysis & calculations. For this, we

havefollowed a methodology which helped us to counter even the smallest issue related

to anyaspectoftheproject.Thesestepsinclude:

4.1 Datacollection

4.2 Materialselection

4.3 Design&Forceanalysis

4.4 ProcessFlaming

4.5 Fabrication

4.1 DATACOLLECTION:

Thissectionofmethodologyincludestheworkofcollectingdata&researchpapersrelatedandrel

evanttooursubject.Forthis,wehavegonethroughvarioussourcesincluding few search

engines, research portals and websites to gather informationregarding our project and

also communicated with the industry personal for what kind

ofproblemstheyarefacingwhile performingthe operation.

4.2 MATERIALSELECTION:

After the step of design and then comes the step of material selection andprocurement.The

selection of a proper material, for engineering purposes, is one ofthe most difficultwork for

the designer. The best mateiial is one which serves thedesired objective at

theminimumcost.Thefollowingfactorsshouldbeconsideredwhileselectingthematerial:

1. Availabilityofthematerials,

2. Suitabilityofthematerials fortheworkingconditionsinservice,and

3. Thecostofthematerials.

Theimportantproperties,whichdeterminetheutilityofthematerialarePhysical,Chemical and

Mechanical properties. All the materials required for the

componentsThereforethematerialselectedare:

EN8 is the material chosen for the fixture. It is an unalloyed medium carbon steel that is used in

applications that require better properties than mild steel but do not justify the purchase of a steel

alloy. EN8 can be flame or induction hardened to provide a good surface hardness and moderate

wear resistance.

For the table Mild steel is a type of carbon steel with a low carbon content; it is also known as

"low carbon steel." Although ranges vary depending on the source, the amount of carbon found

in mild steel is typically 0.05 % to 0.25 % by weight, whereas higher carbon steels are typically




described as having a carbon content ranging from 0.30 % to 2.0 %. If more carbon is added, the

steel will be classified as cast iron.

Mild steel is not an alloy steel, so it does not contain large amounts of other elements besides

iron; it does not contain large amounts of chromium, molybdenum, or other alloying elements.

Because of its low carbon and alloying element content.

Because mild steel contains less carbon, it is more ductile, machinable, and weldable than high

carbon and other steels; however, it is nearly impossible to harden and strengthen through

heating and quenching.The low carbon contentalsomeans it has very little carbon and other

alloying elements to block dislocations in itscrystal structure, generally resulting in less tensile

strength than high carbon and

alloysteels.Mildsteelalsohasahighamountironandferrite,makingitmagnetic

4.3DESIGNCONCEPT

For the design and tis calculations, we had to go through the concept of Design

ofMachineelement,Metallurgy&ProductionScience.Thishelpedusinselectingthe optimum design

procedure and precise production plan to fabricate our product. Thecalculations were done

considering the best possible and optimal conditions so as to make

theproductuserfriendlyandeconomical.Alsotofurtherreducethepriceandcomplexity,wedecidedtom

akethe productas‘mechanical’and robust.

4.3.1 Stepsoffixturedesign

Successfulfixturedesignsbeginwithalogicalandsystematicplan.Withacompleteanalysisof

thefixture'sfunctional requirements,veryfewdesign problemsoccur.Fixturedesignisafive-

stepproblem-solvingprocess.Thefollowingisadetailed analysisofeachstep.

Step1:DefineRequirements

To initiate the fixture-design process, clearly state the problem to besolved or needs to

bemet. State these requirements as broadly as possible, butSpecifically enough to define

thescopeofthe designprojectortoimprove existingproduction.

So we got the problem of loading and ejection and proper clamping of part 2 over

theplate (as showninstandardpartdesign)

Step2:Gather/AnalyzeInformation

Collect all relevant data and assemble it for evaluation. The main sources of

informationarethepartprintprocesssheets,andmachinespecifications.Makesurethatpartdocu

ments and records are current. Four categories of designconsiderations need to betaken

into account at this time: work piece specifications,operation variables,

availabilityofequipmentandpersonnel.

So we have gathered the No. of parts produced, time cycle, rejection rate as shown




intablebelow.

Particulars Collected Data

No.ofpartsproducedperday 2200

No.ofspotsoneachjob 6

Cycletime 26seconds

No.ofoperators 2

No.ofpartsrejectedperday 34

RejectionRate 1.59%

Step3:Develop SeveralOptions

This phase of the fixture-design process requires the most creativity. Atypical work piececan

belocated and clamped several differentways.The naturaltendency is to think ofone solution,

then develop and refine it while blocking outother, perhaps better solutions.A designer

should brainstorm for several good toolingalternatives, not just choose onepath right away.

During this phase, the designer‘sgoal should be adding options, notdiscarding them. In the

interest of economy,alternative designs should be developed onlyfarenoughtomakesure

theyarefeasibleandtodoacostestimate.

And followingareseveralsolutionsdeveloped.

Firstsolution–inthisnesttypefixturepositioningoflowerplateisproperbutsecondor upper plate

isnotgetting exactas itis requiredin assembly . alsowith fixturejamming or adhesion of the

workpiece may take place with the wall and this will not leadtoeasyremovalofworkpiece,

sowemovedtonextsolution.Itisshowninbelowfig.

Fig. 12 TrialFixture1

International Journal of Scientific Research and Engineering Development

ISSN : 2581-7175

Second solution – in this the drawbacks of above solution were solved and properplacing of

the jobs were taking place . In this easy ejection of

hammering action needed for existing fixture. But the only problem inthisfixture we came

across was, when spot were being carried out from right side the upperplate was getting

lifted up so we needed to restrict one mo

platesgetlocked.Itisasshowninbelowfigure

Third solution – here in this solution all the drawbacks were over

was been finalized. The detailed

Step 4:Choose the Best Option:

As discussed with our guide and industrial coordinator, the solution third was been fixed

after all the considerations were

International Journal of Scientific Research and Engineering Development-– Volume 4 Issue



in this the drawbacks of above solution were solved and properplacing of

the jobs were taking place . In this easy ejection of job also successfully donerather than



lifted up so we needed to restrict one more movement so that allmovementofboththe

platesgetlocked.Itisasshowninbelowfigure

Fig. 13TrialFixture2

here in this solution all the drawbacks were overcomed and this fixture

detailed in formation and design iscoveredinchapter3.

Fig. 14TrialFixture3

Option:


were studied.

Volume 4 Issue 5, Sep- Oct 2021

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Page 589

in this the drawbacks of above solution were solved and properplacing of

job also successfully donerather than



re movement so that allmovementofboththe

d and this fixture

iscoveredinchapter3.





The reason for finalizing the fixture was all the needs or requirements were fulfilled inthis

case i.e. proper alignment of jobs due to which the rejections of job reduce with it easy

removal of work piece also reduces time cycle.

Step5:Implement the Design

The final phase of the fixture-design process consists of turning the chosen design approach

into reality. The following guidelines should be considered during the final-design process to

make the fixture less costly while improving its efficiency.

These rules are amix of practical considerations.[11]

i. Use standard components: The economics of standard parts apply

totoolingcomponentsas wellas tomanufacturedproducts.

ii. Useprefinishedmaterials:PrefinishedandpreformedmaterialsshouldbeusedWherePossib

le tolowercostsandsimplifyconstruction,

iii. Eliminatefinishingoperations:Finishingoperationsshouldneverbeperformedforcosmeti

c purposes.Makinga fixturelookbetteroftencandoubleitscost.

Byusing thisfixturetheactualtask isperformed andwehavego thefollowing result.

No. of parts

produced

Timerequired No. of parts

rejected

Oldfixture 2200 26 sec 32

Newfixture 2200 24 sec 8

Table2

Step 6:ActuationMethod:

After the successful implementation of fixture we have to its actuation method. As we

have to remove the skill operator and instead unskilled operator should do the task we

have also design the actuation mechanism.

By using this we have reduced the fatigue of operator, rejection rate, cycle time and thus

increased the production rate.

The difference with and without the mechanism is shown in table below.




No.ofpartsproduced Timerequired

Withoutmechanism 2200 8hours

Withmechanism 2200 6.7hours

Table3

5.0GANTTCHART

Table5:GanttChart

7.0FUTURESCOPE

Our project is manually operated currently but in future this machine can be




fullyautomated by means of using various modes of actuation i.e rotation of circular table

,rotation of fixture andlifting of table by actuating cylinders eitherhydraulically

orpneumatically. Below are the details of the part which may be used for the means

ofdoingfullautomation.

Full autoamation process this can also be integrated in three methods.

Basicscomponents will remain same i.e. servo motor , stepper motor , pneumatic

actuators

orhydraulicactuatorsanddifferentkindsofsensors.Butonlychangeinthereconfrigrationswillb

rtheresoastomake the process easier.

Followingarethemethodsoffullautomationprocess,

First method will be consisting of one servo motor one stepper motor and

onepneumatic actuator. Among which servowillbe usedforrotating table

stepperforrotatingfixture and actuator for lifting of table.This all will beintegrated

tomachinewith PLC along with this many sensors will be used like timmer sensor,

positioningsensor,proximitysensor,etc.The arrangementasshowninbelowfig.

Fig.15Method1




Second methods will be consisting of four motors with no need of actuator in

thismethod. If we keep three stations i.e. three fixture on the table so each station

willemployed with one stepper motor for purpose of rotating fixture individually. This

willfulfill thepurposr of rotatingfixtureandremainingrotatingtablewill

achievedbyanotherstepper motor.But the drawback of this system is that the system

becomeshighlycomplexandbulky.Anddueitscomplexstructureitscontrollingandprogrammi

ngbecomes difficult.

Fig.16Method2

Third method consists of only one stepper or servo motor along with

infrareddedsensor for getting positioning of job. This is the most simplestmethod of

matching thearc of the circle of table with arc of the job andusing only onemotor for

rotation oftable. Its programming alsogets easier as the no. of components gets

reduced.Thearrangementas shown inbelowfigure.




Fig.17Method3

8. CONCLUSION

The main objective of the project was to unskill the operator and making the operation

abit easier for operator. So as to reduce the stress level as well as the co-ordination

levelbetween the two operator. So as a result of our study, we weresuccessfully able

toeliminate one skill operator and also making operation easier. Along with this we

haddone development of fixture which tends to reduce the work for operator resulting

inreduce in cycle time also. Two operators which are required now in which one is for

onlyloadingandunloadingthejob,soforany unskill personis suitable andremainingoperation

is done by skilled person or we can say semiskilled person. The skill levelwhichwas

expectedbeforeis notrequirednow.

Due to implementation of new fixture the accuracy so job also increased which leads

toreduction in rejection rate , due to whichproduction also increased. This will

alsoreduce the costing of job as the time, skill operator and power consumption gets

reduce.Thefollowingobservationswererecordedasbelow,




SR NO PARAMETER BEFORE

PROJECT

AFTER

PROJECT

1 Partsproduced 2200 2618

2 Productionrate 19%

3 Rejectionrate 1.59% 1%

3 Cycletime 26 sec 21 sec

4 Timerequired 8hours 6.7hours

5 Trainingperiod 45days 5days

6 Powerconsumption 13817units 11572units

7 Electricitycost Rs.98106 Rs.82409

8 Labourcost Rs.249600 Rs.211200

TOTALCOSTSAVING Rs.54097/year

Table.6

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Design of Fixture for Spot Welding Machine

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