l3-resistance welding process

8/18/2019 L3-Resistance Welding Process

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IPE 205

ManufacturingProcess I

Resistance Welding

Process(Spot , Seam, Projection & las!

"utt Welding#


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Resistance Welding

Heat is obtained from the resistance of the work to theow of electric current in a circuit of which the work isa part with the application of pressure.

No ller metal is needed


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Two factors/variables responsible for resistance

welding:($# %eat (2# pressure

undamentals of electric resistanceelding

%eat

H ∞ ! " T

H # heat generated $%&' # (urrent $)&' " # "esistance$*&' T #Time $s&

(urrent:H ∞ !

Heat increase with increase of current

+ow current does not give proper fusion. High current heated the entire thickness of the workmetal between the electrodes to the plastic state, theentire thickness reaches the fusion temperature and theelectrodes themselves deepl- into the metal.


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Resistance"

: "esistance of the workpieces

"!: (ontact resistance between the electrodes and

the work."

: "esistance between the fa-ing surfaces of the

two metal pieces to be welded.

0or sound weld' " and "

! should be kept as low as possible

with respect to ".

"' resistance depends on the nature of the workpiece materialand thickness. f w/p material has low electric resistance $)l&'

R2

R'R$


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ime, 0our denite segments or periods of timing during onewelding c-cle

. 12uee3e time!. 4eld time. Hold time5. 67 time

Squeeze time: Time between the initial application ofthe electrode pressure on the work and the initialapplication of current to make the weld. )t the end ofthe s2uee3e time' the welding current is applied.Weld time: 8uring this period the welding current owsthrough the circuit' i.e.' it enters from one electrode'

passes through the work pieces and goes out from thesecond electrode.Hold time: Time during which force acts at the point ofwelding after the last impulse of welding current ceases. The electrode pressure is maintained until the metal hassomewhat cooled.


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Of time: nterval from the end of the hold time to thebeginning of the s2uee3e time for the ne9t$resistance& welding c-cle.


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r ngs e var ous n er aces n o n ma e con acand thus a7ects the contact resistance between the twoworkpieces.$ii& t ensures the completion of the electrical circuitbetween the electrodes and through the work.

$iii& t permits the weld to be made at lowertemperatures.$iv& t provides a forging action and thus reduces weldporosit-.

f too little electrode force is used' the contactresistance between the two workpieces is high and

surface burning and pitting of the electrodes ma-result. f too high electrode force is used' it decreases thecontact resistance of the work metal and thereforereduces the total heat generated between the fa-ingsurfaces of the workpieces b- the welding current.

Too high electrode force ma-' also' s2uee3e softened

hot metal between the surfaces or the work ma- be

Pressure or Electrode orce


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. (urrent.!. ;lectrode pressure.. 4elding time.5. Human element.. (onditions of electrodes and arms.?. (ondition of the material and surfaces ofmaterial.

@. Throat depth.A. Throat height.

)aria*les in Resistance WeldingB


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$i& 0ast rate of production.$ii& No ller rod is needed.$iii& 1emi automatic e2uipments.$iv& +ess skilled workers can do the Cob.$v& Doth similar and dissimilar metals can be welded.$vi& High reliabilit- and reproducibilit- are obtained.$vii& ;limination of warping or distortion of parts.

+dantages of Resistance Welding


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-isadantages of Resistance Welding

$i& The initial cost of e2uipment is high.$ii& 1killed persons are needed for the maintenance ofe2uipment and its controls.$iii& n some materials' special surface preparation is

re2uired.$iv& Digger Cob thicknesses cannot be welded.

+pplications of ResistanceWelding

$i& %oining sheets' bars' rods andtubes.$ii& Eaking tubes and metalfurniture.$iii& 4elding aircraft andautomobile parts.


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Spot Welding

"esistance welding process in which overlapping sheets

are Coined b- local fusion at one or more spots b- theheat generated' b- resistance to the ow of electriccurrent through workpieces that are held togetherunder force b- two electrodes' one above and the otherbelow the two overlapping sheets.


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1tep : )t this stage' the welding current is cut o7. ;9tra

electrode force is then applied or the original force isprolonged. This electrode force or pressure forges theweld and holds it together while the metal cools downand gains strength.

1tep 5: The electrode pressure is released to removethe spot welded workpieces.


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%eat S!rin.age in SpotWelding

1pot welding usuall- leaves slight depressions or indentationson the workpieces and these are often undesirable on the showside of the nished products such as refrigerators.

;lectrodes being under pressure prevent an- vertical movementof material' which' then' naturall- e9pands in the hori3ontal

plane and causes a slight ridge. )fter welding' as the workcools' contraction takes place in the vertical plane' i.e.' alongthe line of the least resistance' thereb- resulting in the concavesurface or the depression.

These depressions can

be minimi3ed b- thefollowing techni2ues.$a& Gse larger si3edelectrode tips on theshow side.

S!o

Side


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Spot Welda*leMetals

errous Metals $i& +ow carbon steel $mildsteel&$ii& Hardenable steels$iii& High speed steel$iv& 1tainless steels

$v& (oated steel sheets

/onferrous Metals

$i&)luminium$ii& )luminium Eagnesium )llo-s$iii& )luminium Eanganese)llo-s$iv& (opper$v& Nickel' Nickel allo-s andEonel Eetal

Spot Welding Met!ods

$i& 8irect$ii& ndirect $or series&$iii& ush pull


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$i& 8irect 4eldst is a welding method in which one or more electrodes opposeeach other' contacting both sides of the work and with the

current passing from the electrodes on one side directl-through the work into the electrodes on the other side andback to the welding transformer.

$ii& 1eries 4eldst is a welding method in which two or more spots areproduced simultaneousl- with onl- one common but indirectcurrent path. n series welding' a portion of the secondar-current b- passes $shunts& an- weld nugget being formed. This shunt current passes through one of the panels being

welded.


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$iii& ush ull 4elds) push pull s-stem

emplo-s transformerswith an electricall-reversed polarit-arrangement whereintwo transformers

complement each otherto form circulatingwelding current circuit.6pposing electrodes areconnected to di7erent

transformers and are ofopposite polarit-. Twospot welds ma- beobtained simultaneousl-.


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$i& +ow cost$ii& High speed of welding$iii& 8ependabilit-$iv& +ess skilled worker will do

$v& Eore general elimination of warping ordistortion of parts$vi& High uniformit- of products$vii& 6peration ma- be made automatic orsemiautomatic

$viii& No edge preparation is needed

+dantages of Spot Welding


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$i& 1pot welding of two !.< mm thick steel plates has

been done satisfactoril- as a replacement for riveting.

$ii& Ean- assemblies of two or more sheet metal

stampings that do not re2uire gas tight or li2uid tight

Coints can be more economicall- Coined b- spot weldingthan b- mechanical methods.

$iii& (ontainers such as receptacles and tote bo9es

fre2uentl- are spot welded.

$iv& The attachment of braces' brackets' pads or clips

to formed sheet metal parts such as cases' covers'

bases or tra-s is another application of spot welding.

$v& 1pot welding nds application in automobile and

aircraft industries.

+pplications of Spot Welding


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Seam WeldingHeat obtained from resistance to electric current $ow&

through the work parts held together under pressure b-electrodes."esulting weld is a series of overlapping resistanceBspotwelds made progressivel- along a Coint b- rotating thecircular electrodes.


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Principle of 1peration 1eam welding is similar to spot welding' e9cept thatcircular rolling electrodes are used to produce acontinuous airBtight seam of overlapping welds.6verlapping $spot& welds are produced b- the rotatingelectrodes and a regularl- interrupted current. 4orkpieces cleaned' overlapped suitabl- and placedbetween the two circular electrodes' which clamp the

workpieces together b- the electrode force. (urrent impulse is applied through the rollers to thematerial in contact with them' heat generated andpressure from the electrodes completes the weld )s the rst current impulse is applied' the power driven

circular electrodes are set in rotation and the workpiecessteadil- move forward. Throughout the welding period' the electrodes revolveand the work passes through them at a specic speed. ntermittent current: 6n for a denite length of time and

o7 for another denite and short period.


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-ierent t3pes ofseams produced

V

Electrodewheel

Overlapping weld

nuggets

Sheet metal

parts

V

Individual weld

nuggets

V

Continuous weld

seam

Conventional resistance seam welding Roll spot welding

Continuous resistance seam


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Roller motion control

4ontinuous motion met!od6;lectrodes rotate at a constant speed(urrent ows continuousl- or are

interrupted

Intermittent motion met!od6;lectrodes travel the distance necessar- for each

successive weld and then stop. The current is then switched on and the weld made


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Seam elding mac!ines

$i& (ircular: 0aces of the electrode wheels are at rightangles to the throat of the machine. Gsed for circularwork' such as welding the heads on containers and forat work re2uiring long seams.

$ii& +ongitudinal: 0aces of the electrode wheels areparallel to the throat of the machine. Gsed for weldingshort seams in containers' etc.

$iii& Gniversal: ;lectrode wheels ma- beBset in eitherthe circular or longitudinal position b- the use of aswivel t-pe upper head in which the upper wheel andits bearing can be swiveled @A degrees.


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+dantages of Seam Welding$i& t can produce gas tight or li2uidBtight Coints.

$ii& 6verlap can be less than for spot or proCection welds.$iii& ) single seam weld or several parallel seams ma- beproduced simultaneousl-.-isadantages of Seam Welding$i& 4elding can be done onl- along a straight or uniforml-curved line.

$ii& t is dicult to weld thicknesses greater than mm.$iii& ) change in the design of electrode wheels is re2uired toavoid obstructions along the path of the wheels duringwelding.+pplications of Seam Welding$i& Iirth welds can be made in round'

s2uare or rectangular parts.$ii& ;9cept for copper and high copperallo-s' most other metals of commonindustrial use can be seam welded.$iii& Desides lap welds' seamBwelding canbe used for making butt seam welds too.


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las! "utt Welding lash produced during the

process.

robabl-' ash weldingprocess was developed fromresistance butt welding b-accident in attempts to increasethe capacit- of the butt weldingmachines b- raising the voltageand appl-ing pressureintermittentl-.

Heat obtained fromresistance to electric current

between the two surfaces' and

b- the application of pressure

after heating is substantiall-

completed.


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Principle of 1peration $i& 0lash butt weldsare made on a

machine having onestationar- and oneopposing movableplaten' on which aremounted the ashB

welding dies orclamps. These clampssecurel- hold thetwo workpieces to

be welded whilesimultaneousl-serving to conductthe welding currentthrough theseworkpieces.


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$ii& Eovable platen isbrought towards the one

gripped in the stationar-platen until the two come inlight contact. 4eldingcurrent $with voltagesucientl- high& is turned

on' ashing is established.Eovable platen keeps movewith a constant speed. Theend of the workpieces burno7 as graduall- the

temperature raised intowelding temperature.$iii& ressure of the movingclamp is 2uickl- increased to forge the parts togetherand e9pel the molten metallater.


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Welda*le metal6

$i& +ow carbon steels.$ii& Eedium strength and high strength lowallo- steels.$iii& Tool steels.$iv& 1tainless steels.

$v& )luminium allo-s $with thickness greaterthan .!< mm&.$vi& (opper allo-s $with high 3inc content&.$vii& Eagnesium allo-s.$viii& Eol-bdenum allo-s.$i9& Nickel allo-s.$9& Titanium allo-s.


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$i& Ean- dissimilar metals with di7erent meltingtemperatures can be ash welded.

$ii& 0lash welding o7ers strength factors up to AAJ.$iii& Ienerall- no special preparation of the weldsurface is re2uired.$iv& las! elding can *e used for t!e elding oft!ose !ig!l3 allo3ed steels !ic! cannot *e

elded satisfactoril3 *3 an3 ot!er process8 This is because' in ash welding' under correctl-controlled conditions' the heating is not onl- even bute9tremel- local' so that the cooling stresses aremaintained at a minimum, this avoids hardening and

cracking in highl- allo-ed steels.$v& The process is cheap' i.e.' the cost of current perweld is small.(i# las! elding is faster t!an man3 ot!ermet!ods.$vii& las! elding gies a smaller upset8

+dantages of las! Welding


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-isadantages of las! Welding$i& The most undesirable feature of ash welding isthe ashing operation during which it is impossible toprotect the welding machine and the surrounding areafrom these particles' which can burn into slide wa-bearings' insulation etc. This necessitates morefre2uent maintenance.$ii# !e process presents a considera*le 9re

!a:ard8 6perators need be protected from -ingparticles.$iii& 4oncentricit3 and straig!tness ofor.pieces during welding is often dicult tomaintain.

$iv& Metal is lost during as!ing and upsetting.$v& S!ape of t!e or.pieces to *e as! eldeds!ould *e similar8$vi& t is generall- not recommended for welding 3incand its allo-s' cast iron' lead and its allo-s.


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+pplications of las!Welding $i& 0lash welding is applied primaril- in the butt

welding of metal sheets' tubing' bars' rods' forgings'ttings etc.$ii& 0lash welding nds applications in automotiveand aircraft products' household appliances'refrigerators and farm implements.$iii& The process is also used for welding the bandsaw blades into continuous loops' and Coining of toolsteel drill' tap and reamer bodies to low carbon steeland allo- steel shanks.

$iv& 0lash welding is used to produce assembliesthat otherwise would re2uire more costl- forgings orcastings.


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Projection Welding

Heat obtained from resistance to electric current owthrough the work parts held together under pressure b-electrodes. "esulting welds are locali3ed at predetermined pointsb- proCections' embossments or intersections.


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Principle of 1perationroCection welding is similar to spotwelding e9cept that

$i& The electrodes' instead of being tips asin spot welding' are at and relativel-large in surface area. ;lectrodes arecooled as in spot welding.

$ii& 1ince a number of welds are made ateach operation' both the electrical power$kK)& and mechanical pressure must becorrespondingl- greater' as compared witha spot welder.

1uccess of proCection welding depends onthe surface preparation of the workBpiecesto be welded.roCections' small deformations that willtouch the surface of the material to be

welded are formed on the weld areas b-


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These proCections serve to concentrate $locali3e& thewelding heat at these areas and facilitate fusion withoutthe necessit- of emplo-ing a large current.$i& The proCection in the upper piece is held in contact

with the lower piece under electrode pressure.$ii& The current ows and being locali3ed to the regionaround the proCection' heats the metal in that area tothe plastic state.$iii& The heated and softened proCection collapses under

the pressure of the electrodes thereb- forming the weld.


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Metals Welded

$i& +ow carbon $A.!AJ ( ma9& steels$ii& (oated metals such as galvani3ed steel' terneplate' tin plate' etc.$iii& Naval brass' Eonel $NiB(u& allo-s

$iv& 1tainless steel$v& Titanium allo-s


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+dantages of Projection Welding

$i& /um*er of elds can *e made simultaneousl3.$ii& Projection elds can *e made in metals t!at are too

t!ic. to *e joined *3 spot elding8$iii& 1cale' rust' oil and workBmetal coatings interfere less withproCection welding than with spot welding.$iv# Projection elding electrodes possess longer lifethan spot welding ones because of less wear andmaintenance resulting from fusion and overheating.

$v& S!osides of t!e jo*s can *e produced it! noelectrode mar.ing' thus making it possible to paint or platethem without grinding.$vi& )n- two surfaces which can be brought together to giveline or point contact can be proCection welded, proCectionwelding is not limited to sheet Bsheet Coints,

$vii& Projection elding locates t!e elds at certaindesired points8$viii& ) better heat balance can be obtained in dicultBtoBweld combinations of compositions and thicknesses.$i9& roCection welding lowers the amount of current andpressure needed to form a good bond between two surfaces. This reduces the chances of shrinkage and distortion around

-isadantages of Projection Welding


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-isadantages of Projection Welding

$i& !e projection elding is limited tocom*inations of metal t!ic.ness and composition

!ic! can *e em*ossed8$ii& Metals t!at are not strong enoug! to supportproCections $e.g.' some brasses' or copper& cannot beproCection welded satisfactoril-.$iii& orming of projection on one of t!eor.pieces is an e;tra operation8$iv& 0or proper elding, all projections must *e oft!e same !eig!t8$v& 1ince there is no possibilit- of using postBweldcurrent pulses for heatBtreatment $as is possible in spotwelding& weld assemblies in hardenable materials must

be heatBtreated in a furnace.plications

omobiless production workB refrigerator' condenser' crossed wire welding etc.


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Thank Lou

l3-resistance welding process

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