lrcture number 7 - about Welding.pptx.pdf

Welding

1. GE-105:Basics of Engineering Technology
LECTURE –07
WELDING
9/7/2023
Prepared by:
Prof. Osama Mohammed Irfan & Dr. S.Sivasankaran
Email: [email protected]
Mechanical Engineering
Qassim University

2. Welding Introduction: https://www.youtube.com/watch?v=DJ5Z6cWWJaE
Edge Preparation: https://www.youtube.com/watch?v=8gHVbSYFky0
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3. 1.0INTRODUCTION-WELDING
Weldingisaprocessforjoiningtwosimilarordissimilarmetalsby
fusion.
Itjoinsdifferentmetals/alloys,withorwithouttheapplicationof
pressureandwithorwithouttheuseoffillermetal.
Thefusionofmetaltakesplacebymeansofheat.
Theheatmaybegeneratedeitherfromcombustionofgases,electric
arc,electricresistanceorbychemicalreaction.
Weldingprovidesapermanentjointbutitnormallyaffectsthe
metallurgyofthecomponents.
Itisthereforeusuallyaccompaniedbypostweldheattreatmentfor
mostofthecriticalcomponents.
Theweldingiswidelyusedasafabricationandrepairingprocessin
industries.
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4. 1.1ApplicationsofWelding
Fabricationofships,
Pressurevessels,
Automobilebodies,
Off-shoreplatform,
Bridges,
Weldedpipes
Sealingofnuclearfuelandexplosives,etc.
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5. 1.2Weldability
Theweldabilitymaybedefinedaspropertyofametalwhichindicates
theeasewithwhichitcanbeweldedwithothersimilarordissimilar
metals.
Weldabilityofamaterialdependsuponvariousfactorslikethe
metallurgicalchangesthatoccurduetowelding,changesinhardnessin
andaroundtheweld,gasevolutionandabsorption,extentofoxidation,
andtheeffectoncrackingtendencyofthejoint.
Plainlowcarbonsteel(C-0.12%)hasthebestweldabilityamongst
metals..
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6. 1.3TERMINOLOGICALELEMENTSOFWELDINGPROCESS
Theterminologicalelementsofweldingprocessusedwithcommon
weldingjointssuchasbasemetal,fusionzone,weldface,rootface,root
openingtoeandrootaredepictedinFig.17.1
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7. 1.4EdgePreparation
Forweldingtheedgesofjoiningsurfacesofmetalsarepreparedfirst.
Differentedgepreparationsmaybeusedforweldingbuttjoints,which
aregiveninFig17.2.
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8. 1.5WeldedJoints
SomecommonweldingjointsareshowninFig.17.3.Weldingjointsare
ofgenerallyoftwomajorkindsnamelylapjointandbuttjoint.The
maintypesaredescribedasunder.
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9. (i)Butt-joint(Fig.17.3):
Butt-jointisthejointinwhichthetwoedgesoftheplatesaretobe
budded/touchedtogetherandthenweldingistobecarriedout
Here,thetwoedgesofthepartsaretobewelded.
Beforewelding,thetwoedgesaretobecleanedandpreparedas
showninFig.17.2.
Inbutt-joint,theplaneofthetwosurfacesareinhorizontalposition.
(ii)Lap-joint(Fig,17.3):
Lapjointisthejointinwhichtheplatesaretobeplacedoneoverthe
otherandthentheweldingistobecarriedoutintherequiredportion
Inlap-joint,theplaneoftheworkpiecesareinhorizontalposition
Beforewelding,theplatestobejoinedaretobecleanedandprepared
inwellmanner
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10. (iii)Fillet-joint(Fig.17.3):
Filletjointisthejointinwhichtheplatesaretobeplacedoneoverthe
otherwhoseplanesareinperpendicular.
Beforewelding,theplatestobejoinedaretobecleanedandprepared
inwellmanner
Both,T-jointandCornerjointasshowninFig.17.3arefilletjoint
(ii)Edge-joint(Fig,17.3):
Edgejointisthejointinwhichthetwoedgesoftheplatescanbe
weldedwhoseplanesareinperpendicularasshowninFig.17.3
Beforewelding,theplatestobejoinedaretobecleanedandprepared
inwellmanner
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11. 1.6WeldingPositions
AsshowninFig.17.4,therearefourtypesofweldingpositions,which
aregivenas:
(i)Flatordownhandposition
(ii)Horizontalposition
(iii)Verticalposition
(iv)Overheadposition
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12. (i)Flatordownhandposition
Theflatpositionordownhandpositionisoneinwhichtheweldingis
performedfromtheuppersideofthejointandthefaceoftheweldis
approximatelyhorizontal.
Thisisthesimplestandthemostconvenientpositionforwelding.
Usingthistechnique,excellentweldedjointsatafastspeedwith
minimumriskoffatiguetothewelderscanbeobtained.
(ii)HorizontalWeldingPosition
Inhorizontalposition,theplaneoftheworkpieceisverticalandthe
depositedweldheadishorizontal.
Themetaldepositionrateinhorizontalweldingisnexttothatachieved
inflatordownhandweldingposition.
Thispositionofweldingismostcommonlyusedinweldingvesselsand
reservoirs
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13. (iii)Verticalweldingposition
Inverticalposition,theplaneoftheworkpieceisverticalandtheweldis
depositeduponaverticalsurface.
Itisdifficulttoproducesatisfactoryweldsinthispositionduetothe
effectoftheforceofgravityonthemoltenmetal.
Theweldermustconstantlycontrolthemetalsothatitdoesnotrunor
dropfromtheweld.Verticalweldingmaybeoftwotypesviz.,vertical-
upandvertical-down.
Vertical-upweldingispreferredwhenstrengthisthemajor
consideration.
Thevertical-downweldingisusedforasealingoperationandfor
weldingsheetmetal.
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14. (iv)Overheadweldingposition
Theoverheadpositionisprobablyevenmoredifficulttoweldthanthe
verticalposition.
Herethepullofgravityagainstthemoltenmetalismuchgreater.
Theforceoftheflameagainsttheweldservestocounteractthepullof
gravity.
Inoverheadposition,theplaneoftheworkpieceishorizontal.
Buttheweldingiscarriedoutfromtheunderside.
Theelectrodeisheldwithitsweldingendupward.
Itisagoodpracticetouseveryshortarcandbasiccoatedelectrodesfor
overheadwelding.
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15. 1.7ADVANTAGESANDDISADVANTAGESOFWELDING
Advantages
Weldingismoreeconomicalandismuchfasterprocessascomparedto
otherprocesses(riveting,bolting,castingetc.)
Welding,ifproperlycontrolledresultspermanentjointshavingstrength
equalorsometimesmorethanbasemetal.
Largenumberofmetalsandalloysbothsimilaranddissimilarcanbe
joinedbywelding.
Generalweldingequipmentisnotverycostly.
Portableweldingequipmentscanbeeasilymadeavailable.
Weldingpermitsconsiderablefreedomindesign.
Weldingcanjoinweldingjobsthroughspots,ascontinuouspressure
tightseams,end-to-endandinanumberofotherconfigurations.
Weldingcanalsobemechanized
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16. Disadvantages
Itresultsinresidualstressesanddistortionoftheworkpieces.
Weldedjointneedsstressrelievingandheattreatment.
Weldinggivesoutharmfulradiations(light),fumesandspatter.
Jigs,andfixturesmayalsobeneededtoholdandpositionthepartsto
bewelded
Edgespreparationoftheweldingjobsarerequiredbeforewelding
Skilledwelderisrequiredforproductionofgoodwelding
Heatduringweldingproducesmetallurgicalchangesasthestructureof
theweldedjointisnotsameasthatoftheparentmetal.
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17. 1.8CLASSIFICATIONOFWELDINGANDALLIEDPROCESSES
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18. 2.0GASWELDINGPROCESS
Gasweldingisafusionweldingprocesswhichjoinsmetals,usingthe
heatofcombustionofanoxygen/airandfuelgas(i.e.acetylene,
hydrogenpropaneorbutane)mixture.
Theintenseheat(flame)thusproducedmeltsandfusestogetherthe
edgesofthepartstobewelded,generallywiththeadditionofafiller
metal.
OperationofgasweldingisshowninFig.17.5.
Thefuelgasgenerallyemployedisacetylene;howevergasesotherthan
acetylenecanalsobeusedthoughwithlowerflametemperature.
Oxy-acetyleneflameisthemostversatileandhottestofalltheflames
producedbythecombinationofoxygenandotherfuelgases.
OthergasessuchasHydrogen,Propane,Butane,Naturalgasetc.,may
beusedforsomeweldingandbrazingapplications.
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19. 9/7/2023 19

20. (i)OXYGEN-ACETYLENEGASWELDINGPROCESS
Inthisprocess,acetyleneismixedwithoxygenincorrectproportionsin
theweldingtorchandignited.
Theflameresultingatthetipofthetorchissufficientlyhottomeltand
jointheparentmetal.
Theoxy-acetyleneflamereachesatemperatureofabout3300°Cand
thuscanmeltmostoftheferrousandnon-ferrousmetalsincommon
use.
Afillermetalrodorweldingrodisgenerallyaddedtothemoltenmetal
pooltobuilduptheseamslightlyforgreaterstrength
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21. TYPESOFOXYGEN-ACETYLENEGASWELDINGFLAMES
Inoxy-acetylenewelding,flameisthemostimportantmeanstocontrol
theweldingjointandtheweldingprocess.
Thecorrecttypeofflameisessentialfortheproductionofsatisfactory
welds.
Theflamemustbeofthepropersize,shapeandconditioninorderto
operatewithmaximumefficiency.
Therearethreebasictypesofoxy-acetyleneflames(Fig.17.6):
1.Neutralweldingflame(Acetyleneandoxygeninequalproportions).
2.Carburizingweldingflameorreducing(excessofacetylene).
3.Oxidizingweldingflame(excessofoxygen).
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22. 9/7/2023 22

23. 1.Neutralweldingflame(Acetyleneandoxygeninequalproportions).
Aneutralflameresultswhenapproximatelyequalvolumesofoxygen
andacetylenearemixedintheweldingtorchandburntatthetorchtip.
Thetemperatureoftheneutralflameisoftheorderofabout5900°F
(3260°C).
Ithasaclear,welldefinedinnercone,indicatingthatthecombustionis
complete.
Theinnerconeislightblueincolor.Itissurroundedbyanouterflame
envelope,producedbythecombinationofoxygenintheairand
superheatedcarbonmonoxideandhydrogengasesfromtheinnercone.
ThisenvelopeisUsuallyamuchdarkerbluethantheinnercone.
Aneutralflameisnamedsobecauseitaffectsnochemicalchangeon
themoltenmetaland,thereforewillnotoxidizeorcarburizethemetal.
Theneutralflameiscommonlyusedfortheweldingofmildsteel,
stainlesssteel,castIron,copper,andaluminium
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24. 2.CarburisingorReducingWeldingFlame
Thecarburizingorreducingflamehasexcessofacetyleneandcanbe
recognizedbyacetylenefeather,whichexistsbetweentheinnerconeandthe
outerenvelope.
Theouterflameenvelopeislongerthanthatoftheneutralflameandisusually
muchbrighterincolor.
Withironandsteel,carburizingflameproducesveryhard,brittlesubstance
knownasironcarbide.
Areducingflamemaybedistinguishedfromcarburizingflamebythefactthat
acarburizingflamecontainsmoreacetylenethanareducingflame
Areducingflamehasanapproximatetemperatureof3038°C.
Acarburizing-flameisusedintheweldingofleadandforcarburizing(surface
hardening)purpose.
Areducingflame,ontheotherhand,doesnotcarburizethemetal;ratherit
ensurestheabsenceoftheoxidizingcondition.
Itisusedforweldingwithlowalloysteelrodsandforweldingthosemetals,
(e.g.,non-ferrous)thatdonottendtoabsorbcarbon.Thisflameisverywell
usedforweldinghighcarbonsteel
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25. 3.OxidisingWeldingflame
Theoxidizingflamehasanexcessofoxygenovertheacetylene.
Anoxidizingflamecanberecognizedbythesmallcone,whichisshorter,much
bluerincolorandmorepointedthanthatoftheneutralflame.
Theouterflameenvelopeismuchshorterandtendstofanoutattheend.
Suchaflamemakesaloudroaringsound.
Itisthehottestflame(temperatureashighas6300°F)producedbyanyoxy-
fuelgassource.
Buttheexcessoxygenespeciallyathightemperaturestendstocombinewith
manymetalstoformhard,brittle,lowstrengthoxides.
Moreover,anexcessofoxygencausestheweldbeadandthesurroundingarea
tohaveascummyordirtyappearance.
Forthesereasons,anoxidizingflameisoflimiteduseinwelding.
Itisnotusedintheweldingofsteel.Aslightlyoxidizingflameishelpfulwhen
welding(i)Copper-basemetals(ii)Zinc-basemetalsand(iii)Afewtypesof
ferrousmetalssuchasmanganesesteelandcastiron.
Theoxidizingatmosphereinthesecases,createabasemetaloxidethat
protectsthebasemetal
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26. GASWELDINGEQUIPMENTS
AnarrangementofoxyacetyleneweldingsetupisshowninFig.17.7.
Thebasictoolsandequipmentsusedforoxy-acetyleneweldingare
following:
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27. (i)Gaspressureregulators
Gaspressureregulatorsareemployedforregulatingthesupplyofacetylene
andoxygengasfromcylinders.
Apressureregulatorisconnectedbetweenthecylinderandhoseleadingto
weldingtorch
Apressureregulatorisfittedwithtwopressuregauges,oneforindicationof
thegaspressureinthecylinderandtheotherforindicationofthereduced
pressureatwhichthegasisgoingout
(ii)Weldingtorch
Fig17.8showstheconstructionoftheweldingtorch.Itisatoolformixing
oxygenandacetyleneincorrectproportionandburningthemixtureattheend
ofatip.
Gasflowtothetorchiscontrolledwiththehelpoftwoneedlevalvesinthe
handleofthetorch
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28. (iii)Torchtips
Itistheportionoftheweldingapparatusthroughwhichthegasespassjust
priortotheirignitionandburning.
Agreatvarietyofinterchangeableweldingtipsdifferinginsize,shapeand
constructionareavailablecommercially
(iv)Hosepipes
Thehosepipesareusedforthesupplyofgasesfromthepressureregulators.
Themostcommonmethodofhosepipefittingbothoxygenandacetylenegas
isthereinforcedrubberhosepipe.
Greenisthestandardcolorforoxygenhose,redforacetylene,andblackhose
forotherindustriallyavailableweldinggases.
(v)Goggles
Thesearefittedwithcoloredlensesandareusedtoprotecttheeyesfrom
harmfulheatandultravioletandinfraredrays.
(vi)Gloves
Thesearerequiredtoprotectthehandsfromanyinjuryduetotheheatofwelding
process.
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29. (vii) Spark-lighter
It is used for frequent igniting the welding torch.
(viii) Filler rods
Gasweldingcanbedonewithorwithoutusingfillerrod.
Whenweldingwiththefillerrod,itshouldbeheldatapproximately90
0
tothe
weldingtip.
Fillerrodshavethesameornearlythesamechemicalcompositionasthebase
metal.
(ix) Fluxes
Fluxesareusedingasweldingtoremovetheoxidefilmandtomaintainaclean
surface.
Theseareusuallyemployedforgasweldingofaluminium,stainlesssteel,cast
iron,brassandsiliconbronze.
Theyareavailableinthemarketintheformofdrypowder,paste,orthick
solutions
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30. 4.0ARCWELDINGPROCESSES
Theprocess,inwhichanelectricarcbetweenanelectrodeandaworkpieceor
betweentwoelectrodesisutilizedtoweldbasemetals,iscalledanarcwelding
process.
ThebasicprincipleofarcweldingisshowninFig17.9(a).
HoweverthebasicelementsinvolvedinarcweldingprocessareshowninFig.
17.9(b).
Mostoftheseprocessesusesomeshieldinggaswhileothersemploycoatings
orfluxestopreventtheweldpoolfromthesurroundingatmosphere.
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31. 9/7/2023 31

32. 4.1TYPESOFARCWELDINGPROCESSES
Thevariousarcweldingprocessesare:
1.CarbonArcWelding
2.ShieldedMetalArcWelding
3.FluxCoredArcWelding
4.GasTungstenArcWelding
5.GasMetalArcWelding
6.PlasmaArcWelding
7.AtomicHydrogenWelding
8.ElectroslagWelding
9.StudArcWelding
10.ElectrogasWelding
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-Important:
* Consumable electrode (i.eelectrode melt)
* Non-consumable electrode (i.eelectrode will not
melt)
•Flux coated electrode
•Bare electrode (i.euncoated0

33. 4.2ARCWELDINGEQUIPMENTS
1.Arcweldingpowersource:
Bothdirectcurrent(DC)andalternatingcurrent(AC)areusedforelectricarc
welding,eachhavingitsparticularapplications.Thefollowingfactorsinfluencethe
selectionofapowersource:
Typeofelectrodestobeusedandmetalstobewelded
Availablepowersource(ACorDC)
Requiredoutput
Dutycycle
Efficiency
Initialcostsandrunningcosts
Availablefloorspace
Versatilityofequipment
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34. 4.2ARCWELDINGEQUIPMENTS–Contd…
2.Weldingcables:
Weldingcablesarerequiredforconductionofcurrentfromthepowersource
throughtheelectrodeholder,thearc,theworkpieceandbacktothewelding
powersource.
Theseareinsulatedcopperoraluminiumcables.
3.Electrodeholder:
Electrodeholderisusedforholdingtheelectrodemanuallyandconducting
currenttoit.
Theseareusuallymatchedtothesizeofthelead,whichinturnmatchedtothe
amperageoutputofthearcwelder.
Electrodeholdersareavailableinsizesthatrangefrom150to500Amps.
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35. 4.2ARCWELDINGEQUIPMENTS–Contd…
4.WeldingElectrodes
Anelectrodeisapieceofwireorarodofametaloralloy,withorwithout
coatings.
Anarcissetupbetweenelectrodeandworkpiece.
Weldingelectrodesareclassifiedintofollowingtypes-.
(1)ConsumableElectrodes
(a)BareElectrodes
(b)CoatedElectrodes
(2)Non-consumableElectrodes
(a)CarbonorGraphiteElectrodes
(b)TungstenElectrodes
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36. 4.2ARCWELDINGEQUIPMENTS–Contd…
(1)Consumableelectrode:
Itismadeofdifferentmetalsandtheiralloys.
Theendofthiselectrodestartsmeltingwhenarcisstruckbetweenthe
electrodeandworkpiece.
Thusconsumableelectrodeitselfactsasafillermetal.
Bareelectrodesconsistofametaloralloywirewithoutanyfluxcoatingon
them.
Coatedelectrodeshavefluxcoatingwhichstartsmeltingassoonasanelectric
arcisstruck.
Thiscoatingonmeltingperformsmanyfunctionslikepreventionofjointfrom
atmosphericcontamination,arcstabilizersetc
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37. 4.2ARCWELDINGEQUIPMENTS–Contd…
(2)Non-Consumableelectrode:
Non-consumableelectrodesaremadeupofhighmeltingpointmaterialslike
carbon,puretungstenoralloytungstenetc.
Theseelectrodesdonotmeltawayduringwelding.
Butpractically,theelectrodelengthgoesondecreasingwiththepassageof
time,becauseofoxidationandvaporizationoftheelectrodematerialduring
welding.
Thematerialsofnonconsumableelectrodesareusuallycoppercoatedcarbon
orgraphite,puretungsten,thoriatedorzirconiatedtungsten
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38. 4.2ARCWELDINGEQUIPMENTS–Contd…
5.Handscreen:
Handscreen(Fig.17.12)usedforprotectionofeyesandsupervisionofweld
bead
6.Chippinghammer:
ChippingHammer(Fig.17.13)isusedtoremovetheslagbystriking
7.Wirebrush:
Wirebrush(Fi.17.14)isusedtocleanthesurfacetobeweld
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39. I-CarbonArcwelding(CAW)
CarbonArcWelding(CAW)isa
weldingprocess,inwhichheatis
generatedbyanelectricarc
struckbetweenancarbon
electrodeandtheworkpiece.
Thearcheatsandmeltsthework
piecesedges,formingajoint.
Carbonarcweldingistheoldest
weldingprocess.
Ifrequired,fillerrodmaybeused
inCarbonArcWelding.Endofthe
rodisheldinthearczone.The
moltenrodmaterialissuppliedto
theweldpool.
Shields(neutralgas,flux)maybe
usedforweldpoolprotection
dependingontypeofwelded
metal.
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40. I-CarbonArcwelding(CAW)–Contd…
AdvantagesofCarbonArcWelding:
Lowcostofequipmentandweldingoperation;
Highlevelofoperatorskillisnotrequired;
Theprocessiseasilyautomated;
Lowdistortionofworkpiece.
DisadvantagesofCarbonArcWelding:
Unstablequalityoftheweld(porosity);
Carbonofelectrodecontaminatesweldmaterialwithcarbides.
CarbonArcWeldinghasbeenreplacedbyTungstenInertGasArcWelding(TIG,
GTAW)inmanyapplications.
TwinCarbonElectrodeArcWelding:
ModificationofCarboneArcWeldingisTwinCarbonElectrodeArcWelding,
utilizingarcstruckbetweentwocarbonelectrodes.
WorkpieceisnotapartofweldingelectriccircuitinTwinCarbonElectrodeArc
Welding,thereforetheweldingtorchmaybemovedfromoneworkpieceto
otherwithoutextinguishingthearc
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41. II-ShieldedMetalArcWelding(SMAW)orManualMetalArcWelding
(MMAW)
Shieldedmetalarcwelding(SMAW)isacommonlyusedarcwelding
processmanuallycarriedbywelder.
Itisanarcweldingprocessinwhichheatforweldingisproduced
throughanelectricarcsetupbetweenafluxcoatedelectrodeandthe
workpiece.
Thefluxcoatingofelectrodedecomposesduetoarcheatandserves
manyfunctions,likeweldmetalprotection,arcstabilityetc.
Innercoreoftheelectrodesupplythefillermaterialformakingaweld.
ThebasicsetupofMMAWisdepictedinFig.17.9(a),(b)andthe
configurationofweldzoneisshowninFig.17.18.
Iftheparentmetalisthickitmaybenecessarytomaketwoorthree
passesforcompletingtheweld.Atypicalmultipassbeadinthiscaseis
showninFig.17.19.arc
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42. II-ShieldedMetalArcWelding(SMAW)orManualMetalArcWelding
(MMAW)–Contd…
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43. II-ShieldedMetalArcWelding(SMAW)orManualMetalArcWelding
(MMAW)–Contd…
AdvantagesofMMAWorSMAW:
ShieldedMetalArcWelding(SMAW)canbecarriedoutinanyposition
withhighestweldquality.
MMAWisthesimplestofallthearcweldingprocesses
Thisweldingprocessfindsinnumerableapplications,becauseofthe
availabilityofawidevarietyofelectrodes.
Bigrangeofmetalsandtheiralloyscanbeweldedeasily.
Theprocesscanbeverywellemployedforhardfacingandmetal
resistanceetc.
Joints(e.g.,betweennozzlesandshellinapressurevessel)which
becauseoftheirpositionaredifficulttobeweldedbyautomatic
weldingmachinescanbeeasilyaccomplishedbyfluxshieldedmetalarc
welding.
TheMMAWweldingequipmentisportableandthecostisfairlylow
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44. LimitationsorDisadvantagesofMMAWorSMAW:
Duetofluxcoatedelectrodes,thechancesofslagentrapmentand
otherrelateddefectsaremoreascomparedtoMIG(metalinertgas)
andTIG(Tungsteninertgas)welding.
Duotofumesandparticlesofslag,thearcandmetaltransferisnotvery
clearandthusweldingcontrolinthisprocessisabitdifficultas
comparedtoMIGwelding.
Duetolimitedlengthofeachelectrodeandbrittlefluxcoatingonit,
mechanizationisdifficult.
Inweldinglongjoints(e.g.,inpressurevessels),asoneelectrode
finishes,theweldistobeprogressedwiththenextelectrode.
Unlessproperlycared,adefect(likeslaginclusionorinsufficient
penetration)mayoccurattheplacewhereweldingisrestartedwiththe
newelectrode
Theprocessusesstickelectrodesandthusitisslowerascomparedto
MIGwelding
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45. ApplicationsofMMAWorSMAW:
Today,almostallthecommonlyemployedmetalsandtheiralloyscanbe
weldedbythisprocess
Shieldedmetalarcweldingisusedbothasafabricationprocessandfor
maintenanceandrepairjobs.
Theprocessfindsapplicationsin
(a)BuildingandBridgeconstruction
(b)Automotiveandaircraftindustry,etc.
(c)Airreceiver,tank,boilerandpressurevesselfabrication
(d)Shipbuilding
(e)Pipesand
(f)Penstockjoininginhydro-powerplant
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46. III-SubmergedArcWelding(SAW)
SubmergedArcWeldingisaweldingprocess,whichutilizesabare
consumablemetallicelectrodeproducinganarcbetweenitselfandthe
workpiecewithinagranularshieldingfluxappliedaroundtheweld.
Thearcheatsandmeltsboththeworkpiecesedgesandtheelectrode
wire.
Themoltenelectrodematerialissuppliedtothesurfacesofthewelded
pieces,fillstheweldpoolandjoinstheworkpieces.
Sincetheelectrodeissubmergedintotheflux,thearcisinvisible.
Thefluxispartiallymeltsandformsaslagprotectingtheweldpool
fromoxidationandotheratmosphericcontaminations.
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47. III-SubmergedArcWelding(SAW)–Contd…
9/7/2023 47

48. III-SubmergedArcWelding(SAW)-Contd…
AdvantagesofSubmergedArcWelding(SAW):
Veryhighweldingrate;
Theprocessissuitableforautomation;
Highqualityweldstructure.
DisadvantagesofSubmergedArcWelding(SAW):
Weldmaycontainslaginclusions;
Limitedapplicationsoftheprocess-mostlyforweldinghorizontally
locatedplates.
Applications:Thisprocessisusedforweldinglowcarbonsteel,bronze,
nickelandothernon-ferrousmaterials
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49. IV-MetalInertGas(MIG)WeldingorGasmetalarcwelding(GMAW)
MetalInertGasWelding(GasMetalArcWelding)isaarcwelding
process,inwhichtheweldisshieldedbyanexternalgas(Argon,helium,
CO
2,argon+Oxygenorothergasmixtures).
Consumableelectrodewire,havingchemicalcompositionsimilartothat
oftheparentmaterial,iscontinuouslyfedfromaspooltothearczone.
Thearcheatsandmeltsboththeworkpiecesedgesandtheelectrode
wire.
Thefusedelectrodematerialissuppliedtothesurfacesofthework
pieces,fillstheweldpoolandformsjoint.
Duetoautomaticfeedingofthefillingwire(electrode)theprocessis
referredtoasasemi-automatic.
Theoperatorcontrolsonlythetorchpositioningandspeed.
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50. IV-MetalInertGas(MIG)WeldingorGasmetalarcwelding(GMAW)-
Contd..
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51. IV-MetalInertGas(MIG)WeldingorGasmetalarcwelding(GMAW)-
Contd..
AdvantagesofMetalInertGasWelding(MIG,GMAW):
Continuousweldmaybeproduced(nointerruptions);
Highlevelofoperatorsskillisnotrequired;
Slagremovalisnotrequired(noslag);
DisadvantagesofMetalInertGasWelding(MIG,GMAW):
Expensiveandnon-portableequipmentisrequired;
Outdoorapplicationarelimitedbecauseofeffectofwind,dispersing
theshieldinggas.
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52. V-TungstenInertGasArcWelding(TIG)orGasTungstenArcWelding
(GTAW)
TungstenInertGasArcWelding(GasTungstenArcWelding)isawelding
process,inwhichheatisgeneratedbyanelectricarcstruckbetweena
tungstennon-consumableelectrodeandtheworkpiece.
Theweldpoolisshieldedbyaninertgas(Argon(Ar),helium(He),
Nitrogen(N
2))protectingthemoltenmetalfromatmospheric
contamination.
Theheatproducedbythearcmeltstheworkpiecesedgesandjoins
them.
Fillerrodmaybeused,ifrequired.
TungstenInertGasArcWeldingproducesahighqualityweldofmostof
metals.
Fluxisnotusedintheprocess.
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53. V-TungstenInertGasArcWelding(TIG)orGasTungstenArcWelding
(GTAW)–Contd…
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54. AdvantagesofTungstenInertGasArcWelding(TIG,GTAW):
Weldcompositionisclosetothatoftheparentmetal;
Highqualityweldstructure
Slagremovalisnotrequired(noslag);
Thermaldistortionsofworkpiecesareminimalduetoconcentrationof
heatinsmallzone.
DisadvantagesofTungstenInertGasArcWelding(TIG,GTAW):
Lowweldingrate;
Relativelyexpensive;
Requireshighlevelofoperatorsskill
Applications:Theprocessisgenerallyusedforweldingaluminium,
magnesiumandstainlesssteel
9/7/2023 54

55. 5.0RESISTANCEWELDING
ResistanceWeldingisaweldingprocess,inwhichworkpiecesareweldeddue
toacombinationofapressureappliedtothemandalocalizedheatgenerated
byahighelectriccurrentflowingthroughthecontactareaoftheweld
Heatproducedbythecurrentissufficientforlocalmeltingoftheworkpieceat
thecontactpointandformationofsmallweldpool(”nugget”).
Themoltenmetalisthensolidifiesunderapressureandjoinsthepieces.
Theamountofheatgeneratedintheworkpiecedependonthefollowing
factors:
(1)Magnitudeofthecurrent,
(2)Resistanceofthecurrentconductingpath,and
Mathematically,H=IVt
=I(IR)t
=I
2
Rt
9/7/2023 55
Where H = heat generated in joules
I = current in Amp, R = resistance in ohms
t = time of current flow in seconds

56. ThefollowingmetalsmaybeweldedbyResistanceWelding:
Lowcarbonsteels-thewidestapplicationofResistanceWelding
Aluminumalloys
Mediumcarbonsteels,highcarbonsteelsandAlloysteels(maybewelded,but
theweldisbrittle)
AdvantagesofResistanceWelding:
Highweldingrates;
Lowfumes;
Costeffectiveness;
Easyautomation;
Nofillermaterialsarerequired;
Lowdistortions.
DisadvantagesofResistanceWelding:
Highequipmentcost;
Lowstrengthofdiscontinuouswelds;
Thicknessofweldedsheetsislimited-upto1/4”(6mm);
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57. ApplicationsofResistanceWelding(RW):
Itcanbeusedforjoiningvehiclebodyparts,fueltanks,domesticradiators,
pipesofgasoilandwaterpipelines,wireends,turbineblades,railwaytracks.
5.1TypesofResistancewelding
Themajortypesofresistanceweldingaregivenasunder:
(1)SpotWelding
(2)SeamWelding
(3)ProjectionWelding
(4)ResistanceButtWelding
(5)FlashButtWelding
(6)PercussionWelding
(7)HighFrequencyResistanceWelding
(8)HighFrequencyInductionWelding
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58. I–SPOTWELDING
SpotWeldingisaResistanceWelding(RW)process,inwhichtwoor
moreoverlappedmetalsheetsarejoinedbyspotwelds.
Themethodusespointedcopperelectrodesprovidingpassageof
electriccurrent.
Theelectrodesalsotransmittpressurerequiredforformationofstrong
weld.
Diameteroftheweldspotisintherange1/8”-1/2”(3-12mm).
Spotweldingiswidelyusedinautomotiveindustryforjoiningvehicle
bodyparts
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59. I–SPOTWELDING-Contd…
Themajortypesofresistanceweldingaregivenasunder:
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60. II–FlashWelding(FW)
FlashWeldingisaResistanceWelding(RW)process,inwhichendsof
rods(tubes,sheets)areheatedandfusedbyanarcstruckbetween
themandthenforged(broughtintoacontactunderapressure)
producingaweld.
Theweldedpartsareheldinelectrodeclamps,oneofwhichis
stationaryandthesecondismovable
FlashWeldingmethodpermitsfast(about1min)joiningoflargeand
complexparts.
WeldedpartareoftenannealedforimprovementofToughnessofthe
weld.
Steels,Aluminumalloys,Copperalloys,Magnesiumalloys,Copperalloys
andNickelalloysmaybeweldedbyFlashWelding.
Thickpipes,endsofbandsaws,frames,aircraftlandinggearsare
producedbyFlashWelding
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61. 9/7/2023 61

62. III–ResistanceButtWelding
ResistanceButtWeldingisaResistanceWeldingprocess,inwhichends
ofwiresorrodsareheldunderapressureandheatedbyanelectric
currentpassingthroughthecontactareaandproducingaweld
TheprocessissimilartoFlashWelding,howeverinButtWelding
pressureandelectriccurrentareappliedsimultaneouslyincontrastto
FlashWeldingwhereelectriccurrentisfollowedbyforgingpressure
application.
Buttweldingisusedforweldingsmallparts.
Theprocessishighlyproductiveandclean.
IncontrasttoFlashWelding,ButtWeldingprovidesjoiningwithnoloss
oftheweldedmaterials.
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63. 9/7/2023 63

64. IV–ResistanceSeamWelding
SeamWeldingisaResistanceWelding(RW)processofcontinuous
joiningofoverlappingsheetsbypassingthembetweentworotating
electrodewheels.
Heatgeneratedbytheelectriccurrentflowingthroughthecontactarea
andpressureprovidedbythewheelsaresufficienttoproducealeak-
tightweld.
SeamWeldingishighspeedandcleanprocess,whichisusedwhen
continuoustightweldisrequired(fueltanks,drums,domesticradiators)
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65. 9/7/2023 65

66. 6.0SOLIDSTATEWELDING
SolidStateWeldingisaweldingprocess,inwhichtwoworkpiecesarejoined
underapressureprovidinganintimatecontactbetweenthemandata
temperatureessentiallybelowthemeltingpointoftheparentmaterial.
Bondingofthematerialsisaresultofdiffusionoftheirinterfaceatoms.
AdvantagesofSolidStateWelding:
Weld(bonding)isfreefrommicrostructuredefects(pores,non-metallic
inclusions,segregationofalloyingelements)
Mechanicalpropertiesoftheweldaresimilartothoseoftheparentmetals
Noconsumablematerials(fillermaterial,fluxes,shieldinggases)arerequired
Dissimilarmetalsmaybejoined(steel-aluminumalloysteel-copperalloy).
DisadvantagesofSolidStateWelding:
Thoroughsurfacepreparationisrequired(degreasing,oxidesremoval,
brushing/sanding)
Expensiveequipment.
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67. 6.1TYPESOFSOLIDSTATEWELDING
ForgeWelding(FOW)
ColdWelding(CW)
FrictionWelding(FRW)
ExplosiveWelding(EXW)
DiffusionWelding(DFW)
UltrasonicWelding(USW)
ElectronBeamwelding(EBW)
I-FORGEWELDING:
Forgeweldingisasolidstateweldingprocessinwhichboththeplatesare
heatedquitebelowitsmeltingtemperature.
Thisheatingdeformstheworkpiecesplastically.
Nowarepeatedhammeringorhighpressurizeloadisappliedontheseplates
together.
Duetothishighpressureandtemperature,inter-moleculardiffusiontakes
placeattheinterfacesurfaceoftheplateswhichmakeastrongweldjoint.
Thisisbasicprincipleofforgewelding
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68. I-FORGEWELDING–Contd…
9/7/2023 68

69. II-COLDWELDING:
Coldweldingprocessdonebyapplyinghighpressurebetweencleancontacting
surfacesatroomtemperature
Cleaningusuallydonebydegreasingandwirebrushingimmediatelybefore
joining
Noheatisapplied,butdeformationraisesworktemperature
Atleastoneofthemetals,preferablyboth,mustbeveryductile
SoftaluminumandcoppersuitedtoCW
Applications:makingelectricalconnections
9/7/2023 69

70. III-FRICTIONWELDING:
Frictionweldingisaprocessinwhichcoalescenceisachievedbyfrictionalheat
combinedwithpressure
Whenproperlycarriedout,nomeltingoccursatfaying/joiningsurfaces
Nofillermetal,flux,orshieldinggasesnormallyused
ProcessyieldsanarrowHAZ
Itcanbeusedtojoindissimilarmetals
Widelyusedcommercialprocess,amenabletoautomationandmass
production
9/7/2023 70

71. 9/7/2023 71
Figure.Frictionwelding(FRW):(1)rotatingpart,nocontact;(2)partsbrought
intocontacttogeneratefrictionheat;(3)rotationstoppedandaxialpressure
applied;and(4)weldcreated

72. IV-EXPLOSIVEWELDING:
Itisaprocessinwhichrapidcoalescence/joiningoftwometallicsurfacesis
causedbytheenergyofadetonatedexplosive
Nofillermetalused
Noexternalheatapplied
Nodiffusionoccurs-timeistooshort
Bondingismetallurgical,combinedwithmechanicalinterlockingthatresults
fromarippledorwavyinterfacebetweenthemetals
Commonlyusedtobondtwodissimilarmetals,inparticulartocladonemetal
ontopofabasemetaloverlargeareas
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73. 9/7/2023 73

74. V-ELECTRONBEAMWELDING:
ElectronBeamWeldingisaweldingprocessutilizingaheatgeneratedbya
beamofhighenergyelectrons.
Theelectronsstriketheworkpieceandtheirkineticenergyconvertsinto
thermalenergyheatingthemetalsothattheedgesofworkpiecearefused
andjoinedtogetherformingaweldafterSolidification.
Theprocessiscarriedoutinavacuumchamberatapressureofabout0.00013
to0.0013Pa
Suchhighvacuumisrequiredinordertopreventlossoftheelectronsenergyin
collisionswithairmolecules.
Theelectronsareemittedbyacathode(electrongun).
Duetoahighvoltage(about150kV)appliedbetweenthecathodeandthe
anodetheelectronsareacceleratedupto30%-60%ofthespeedoflight.
Kineticenergyoftheelectronsbecomessufficientformeltingthetargeted
weld.
Electronsacceleratedbyelectricfieldarethenfocusedintoathinbeaminthe
focusingcoil.Deflectioncoilmovestheelectronbeamalongtheweld.
9/7/2023 74

75. ElectronBeamiscapabletoweldworkpieceswiththicknessfrom0.01mmup
to150mmofsteelandupto500mmofaluminum.
ElectronBeamWeldingmaybeusedforjoininganymetalsincludingmetals,
whicharehardlyweldablebyotherweldingmethods:refractorymetals
(tungsten,molybdenum,niobium)andchemicallyactivemetals(titanium,
zirconium,beryllium).
ElectronBeamWeldingisalsoabletojoindissimilarmetals.
9/7/2023 75

76. 9/7/2023 76

77. 6.0WELDINGDEFECTS:
9/7/2023 77

78. 6.0WELDINGDEFECTS–Contd…
9/7/2023 78

79. 6.0WELDINGDEFECTS–Contd…
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80. 9/7/2023 80

81. 6.0WELDINGDEFECTS–Contd…
1.LackofPenetration(Fig.17.31(i))
Itisthefailureofthefillermetaltopenetrateintothejoint.Itisdueto
(a)Inadequatede-slagging,(b)Incorrectedgepenetration
(c)Incorrectweldingtechnique.
2.LackofFusion(Fig.17.31(ii))
Lackoffusionisthefailureofthefillermetaltofusewiththeparentmetal.Itis
duoto(a)Toofastatravel,(b)Incorrectweldingtechnique,(c)Insufficientheat
3.Porosity(Fig.17.31(iii))
Itisagroupofsmallholesthroughouttheweldmetal.Itiscausedbythe
trappingofgasduringtheweldingprocess,dueto
(a)Chemicalsinthemetal,(b)Dampness,(c)Toorapidcoolingoftheweld.
4.SlagInclusion(Fig.17.31(iv))
Itistheentrapmentofslagorotherimpuritiesintheweld.Itiscausedby
(a)Slagfrompreviousrunsnotbeingcleanedaway,(b)Insufficientcleaningand
preparationofthebasemetalbeforeweldingcommences
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82. 6.0WELDINGDEFECTS–Contd…
5.Undercuts(Fig.17.31(v))
Thesearegroovesorslotsalongtheedgesoftheweldcausedby(a)Toofasta
travel,(b)Badweldingtechnique,(c)Toogreataheatbuild-up.
6.Cracking(Fig.17.31(vi))
Itistheformationofcrackseitherintheweldmetalorintheparentmetal.Itis
dueto(a)Unsuitableparentmetalsusedintheweld,(b)Badweldingtechnique.
7.PoorWeldBeadAppearance(Fig.17.31(vii))
Ifthewidthofweldbeaddepositedisnotuniformorstraight,thentheweld
beadistermedaspoor.
Itisduetoimproperarclength,improperweldingtechnique,damaged
electrodecoatingandpoorelectrodeandearthingconnections.Itcanbe
reducedbytakingintoconsiderationstheabovefactors.
8.Distortion(Fig.17.31(viii))
Distortionisduetohighcoolingrate,smalldiameterelectrode,poorclamping
andslowarctravelspeed
9/7/2023 82

83. Note:Kindlyrefer/studytheTextBooksothatyou
canenhanceyourknowledge
Foracademicpointofview/gradepointofview,
myslides,importantquestionswithanswerare
enough
Pleasedon’tthinkthatthematerialswhichyouare
learning/goingtolearninthissubjectarenothuge
content.Itisyourdutytostudyandknowallthe
information's.