Applying Metal Inert Gas (MIG) Welding Techniques.ppt

unitamechanicalsystemsandtechnology,lesson7,applyingmetalinertgas(mig)weldingtechniques,nextgenerationscience/commoncorestandardsaddressed!,ccss.elaliteracy.rst.910.1citespecifictextualevidencetosupportanalysisofscienceandtechnicaltexts,attendingtotheprecisedetailsofexplanationsordescriptions.ccss.elaliteracy.rst.910.3followpreciselyacomplexmultistepprocedurewhencarryingoutexperiments,takingmeasurements,orperformingtechnicaltasks,attendingtospecialcasesorexceptionsdefinedinthetext.ccss.math.content.hsgco.d.12makeformalgeometricconstructionswithavarietyoftoolsandmethods(compassandstraightedge,string,reflectivedevices,paperfolding,dynamicgeometricsoftware,etc.).copyingasegment;copyinganangle;bisectingasegment;bisectinganangle;constructingperpendicularlines,includingtheperpendicularbisectorofalinesegment;andconstructingalineparalleltoagivenlinethroughapointnotontheline.,bellwork!,1.explaintheadvantagesofthemetalinertgas(mig)weldingprocess.2.describetheequipment,typesofshieldinggases,andelectrodesusedinthemigweldingprocess.3.describethetypesofmetaltransferpatternsusedinmigweldingandrelatetheirapplications.4.whataretheadvantagesofmigwelding?,terms,burnbackductilityglobulartransferinertgasshortarctransfer,sprayarctransferstickouttransitioncurrenttravelanglewhiskers,haveyouheardthetermmigweldingwhataretheadvantagesofmigwelding?howismigweldingdone?,interestapproach,whataretheadvantagesofthemigweldingprocess?,metalinertgaswelding(mig)isaprocessinwhichaconsumablewireelectrodeisfedintoanarcandweldpoolatasteadybutadjustablerate,whileacontinuousenvelopeofinertgasflowsoutaroundthewireandshieldstheweldfromcontaminationbytheatmosphere.,themigweldingprocesshasseveraladvantageswhichaccountforitspopularityandincreaseduseintheweldingindustries.,migweldingadvantages,a.weldingjobscanbeperformedfasterwiththemigprocess.thecontinuouswirefeedeliminatestheneedtochangeelectrodes.,migweldingadvantages,b.weldcleaningandpreparationtimeislessformigweldingthanforstickelectrodewelds.sincethegaseousshieldprotectsthemoltenmetalfromtheatmosphericgases,thereisnofluxorslag,andspatterisminimal.c.lesstimeisrequiredtoteachindividualshowtomigweld.ifanindividualhaslearnedhowtostickweldtheycanpickuponmigweldingquickly.,migweldingadvantages,d.becauseofthefasttravelspeedatwhichmigweldingcanbedone,thereisasmallerheat-affectedzonethanwiththeshieldedmetalarcweldingprocess.thesmallerheat-affectedzoneresultsinlessgraingrowth,lessdistortion,andlesslossoftemperinthebasemetal.,migweldingadvantages,e.boththickandthinmetalscanbeweldedsuccessfullyandeconomicallywiththemigprocess.f.lesstimeisneededtoprepareweldjointssincethemigweldsaredeeppenetrating.narrowweldjointscanbeusedwithmigweldingandstillsecuresoundweldments.,migweldingadvantages,g.themigweldingprocesscanbeusedtojoinbothferrousandnonferrousmetals.thedevelopmentofelectrodewireandtheuseofspoolgunshasmadethemigprocesswidelyusedforaluminum,stainlesssteel,high-carbon-steel,andalloy-steelfabrication.simplychangethewireandshieldinggastoadapttodifferenttypesofmetal.,migweldingadvantages,h.theweldvisibilityisgenerallygood.thereislesssmokeandfumessooperatorenvironmentisimprovedanditiseasiertoseetheweldformation.,whatequipment,typesofshieldinggases,andelectrodesareusedinthemigweldingprocess?,tounderstandthemigweldingprocess,youmustunderstandtheequipmentneeded.itconsistsofawelder,awirefeedsystem,cableandweldinggunassembly,shieldinggassupply,andelectrodewire.,migwelders,a.mostweldersusedformigweldingaredirectcurrentmachinesoftheconstantvoltagetype.b.migweldingmachinesmustbedesignedtoproduceaconstantvoltage.withaconstantvoltagemigmachine,theoutputvoltagewillchangeverylittlewithlargechangesincurrent.,migwelders,c.weldingvoltagehasaneffectonbeadwidth,spatter,undercutting,andpenetration.d.theconstantvoltageweldingmachinesaredesignedsothatwhenthearcvoltagechanges,thearccurrentisautomaticallyadjustedorself-corrected.wfs+wirefeedspeed,e.mostmigweldingunitshavethreeadjustmentswhichmustbeinbalancetoachieveaqualityweld.thesearevoltagecontrol,wirefeedspeed,andshieldinggasflowrate.,wirefeeder,1.thewirefeedercontinuallydrawsasmalldiameterelectrodewirefromthespoolanddrivesitthroughthecableassemblyandgunataconstantrateofspeed.2.theconstantrateofwirefeedisnecessarytoassureasmoothevenarc.thismustbeadjustabletoprovidefordifferentweldingcurrentsettingsthatmaybedesired.,wirefeeder,3.wirespeedvarieswiththemetalthicknessbeingwelded,typeofjoint,andpositionoftheweld.,wirefeeder,f.tomovetheelectrodewirefromthespooltothemigweldinggun,runthewirethroughaconduitandsystemofdrivewheels.thesedrivewheels,dependingupontheirlocationinthewirefeedunit,areeitherthepushtypeorthepulltype.,wirefeeder,f1.thepull-typedrivewheelsarelocatedrelativelyclosetothemiggunandexertapullingactiononthewire.pull-typedrivewheelsareusedonmostspoolguns.2.withthepush-typedrivewheels,thewiregoesthroughthewheelsandispushedthroughtheelectrodeleadandoutthroughthemiggun.,g.correcttensiononthewirefeeddrivewheelsisveryimportant.,1.toolittletensionresultsindrivewheelslippagewhichcausesthewiretobefedintothepuddleatanunevenrate,givingapoor-qualityweld.,g.correcttensiononthewirefeeddrivewheelsisveryimportant.,2.toomuchtensiononthewirefeedwheelsresultsindeformationofthewireshape.thisalteredwireshapecanmakeitdifficulttothreadtheelectrodethroughtheconduitandthecontacttipinthemiggun.,h.whenablockageorburnbackoccurs,themiggunshouldbeturnedoffimmediatelytoprevententanglement.aburnbackoccurswhentheelectrodewireisfusedtothecontacttip.i.thewirefeedershavedifferentsizeddriverollssotheycanaccommodatedifferentsizesandtypesofwire.,miggun,j.theelectrodeholderiscommonlyreferredtoasthemiggun.themiggunhasatriggerswitchforactivatingtheweldingoperation,agasnozzlefordirectingtheflowoftheshieldinggas,andacontacttip.,miggun,j1.thenozzleonthemiggundirectstheshieldinggasoverthepuddleduringwelding.anozzlethatistoolargeortoosmallmayresultinairfromtheatmospherereachingthepuddleandcontaminatingtheweld.2.thenozzleismadeofcopperalloytohelpremovetheheatfromtheweldingzone.,k.whenweldingoutside,wheretheweldzoneissubjectedtodraftsandwindcurrents,theflowofshieldinggasneedstobestrongenoughsothatdraftsdonotblowtheshieldinggasfromtheweldzone.removalofshieldinggasesbythewindwillleadtocontaminated,weakenedwelds.,l.thecontacttiphelpstoguidethewireelectrodeintothepuddleaswellastransmittheweldcurrenttotheelectrodewire.theelectrodewireactuallytouchesthecontacttipasitisfedthroughthemiggun.duringthiscontact,theweldcurrentistransmittedtotheelectrode.thetipmustmatchthewirediameterbeingusedinthewelder.,m.shieldinggas,theshieldinggasdisplacestheatmosphericairwithacoverofprotectivegas.theweldingarcisthenstruckundertheshieldinggascoverandthemoltenpuddleisnotcontaminatedbytheelementsintheatmosphere,m.shieldinggas,inertandnon-inertgasesareusedforshieldinginmigwelding.aninertgasisonewhoseatomsareverystableandwillnotreacteasilywithatomsofotherelements.,1.argon,hasalowionizationpotentialandthereforecreatesaverystablearcwhenusedasashieldinggas.thearcisquietandsmoothsoundingandhasverylittlespatter.a.argonisagoodshieldinggasforweldingsheetmetalandthinmetalsections.pureargonisalsousedforweldingaluminum,copper,magnesium,andnickel.b.pureargonisnotrecommendedforuseoncarbonsteels.,2.heliumgas,conductsheatwellandispreferredforweldingthickmetalstock.itisgoodforweldingmetalsthatconductheatwell,suchasaluminum,copper,andmagnesium.a.heliumrequireshigherarcvoltagesthanargon.b.helium-shieldedweldsarewider,havelesspenetrationandmorespatterthanargon-shieldedwelds.c.heliumisquiteoftenusedalongwithfluxcoredmigweldingwire.,3.carbondioxide,themostoftenusedgasinmigweldingbecauseitgivesgoodbeadpenetration,widebeads,noundercuttingandgoodbeadcontouranditcostsmuchlessthanargonorhelium.a.themainapplicationofcarbondioxideshieldinggasisweldinglowandmediumcarbonsteels.b.whenusingcarbondioxideshieldinggas,thearcisunstable,whichcausesalotofspatter.,3.carbondioxide,c.carbondioxidegashasatendencytodisassociate.athightemperaturesencounteredinthearczone,carbondioxidewillpartiallybreakupintooxygenandcarbonmonoxide.d.goodventilationisessentialtoremovethisdeadlygas,4.gasmixtures,argon/oxygenisusedquiteoftenwhenweldingstainlesssteel.theoxygengashelpstostabilizethearcandeliminatemuchoftheweldsplatter.,4.gasmixtures,b.anargon-heliummixtureisusedforweldingthicknon-ferrousmetals.thismixturegivesthesamearcstabilityaspureargonwithverylittlespatter,andproducesadeeppenetratingbead.,4.gasmixtures,c.theargon-carbondioxidemixtureisusedmainlyforcarbonsteels,lowalloysteels,andsomestainlesssteel.thegasmixturehelpstostabilizethearc,reducespatter,eliminateundercuttingandimprovemetaltransferstraightthroughthearc.,n.gascylinderandgauges,thetanksupplyingtheshieldinggaswillhaveagaugeandagasflowmeter.thevolumeofgasdirectedovertheweldzoneisregulatedbytheflowmeter.,o.electrodewire,theselectionofthecorrectelectrodewireisanimportantdecisionandthesuccessoftheweldingoperationdependsonthecorrectselection.,o.electrodewire,therearefactorstoconsiderwhenselectingthecorrectelectrode.1.considerthetypeofmetaltobeweldedandchooseafillerwiretomatchthebasemetalinanalysisandmechanicalproperties.,o.electrodewire,2.considerthejointdesign.thickermetalsandcomplicatedjointdesignsusuallyrequirefillerwiresthatprovidehighductility.ductilityistheabilitytobefashionedintoanewformwithoutbreaking.,o.electrodewire,3.examinethesurfaceconditionofthemetaltobewelded.ifitisrustyorscaly,itwillhaveaneffectonthetypeofwireselected.4.considertheservicerequirementsthattheweldedproductwillencounter.5.migweldingisnoteffectiveonrustyorpaintedsurfacesasthelowervoltageisnoteffectiveascouringthesurfaceinthesamemannerasastickelectrode.,p.electrodewireclassification,migelectrodewireisclassifiedbytheamericanweldingsociety(aws).anexampleiser70s6.forcarbon-steelwire,the“e”identifiesitasanelectrode“r”notesthatitisarodnotemigwireisavailableindifferentdiameters.thediameterofthewiremustmatchthedrivewheelsandtheguntip.,p.electrodewireclassification,thefirsttwodigitsrelatethetensilestrengthin1,000lbs.psithe“s”signifiestheelectrodeisasolidbarewireanyremainingnumberandsymbolsrelatethechemicalcompositionvariationsofelectrodes.,whatarethetypesofmetaltransferpatternsusedinmigweldingandwhenaretheyused?,metaltransferpatterns,inmigwelding,themetalfromthewireelectrodeistransferredacrossthearcplasmatothepuddlebyglobular,shortarc,orspraytransferpatterns.thetypeoftransferusedforanygivenwelddependsuponthearcvoltage,current,kindofshieldinggasused,anddiameterofthewireelectrode.,a.globulartransferpatterns,whenthemoltenmetalfromthewireelectrodetravelsacrossthearcinlargedroplets,itisintheglobulartransferpattern.1.globulartransferpatternoccursatlowwirefeedrates,lowcurrent,andlowarcvolt-agesettings.,a.globulartransferpatterns,3.themoltenglobulesaretwotothreetimeslargerthanthediameteroftheelectrode.surfacetensionholdstheglobulesontheendofthewireelectrode.whentheglobulesbecometooheavytoremainontheelectrode,theydropoffandmoveacrossthearc.theglobulesdonotmoveacrossthearcinanevenpattern.,a.globulartransferpatterns,4.weldsmadewithglobulartransferhavepoorpenetrationandexcessivespatterandareusedlittleinmigwelding.,b.shortarctransferpattern,isactuallyaseriesofperiodicshortcircuitsthatoccurasthemoltentipoftheadvancingwireelectrodecontactstheworkpieceandmomentarilyextinguishesthearc.,b.shortarctransferpattern,1.thedropletformsontheendoftheelectrodeandbeginstosagwhilethearcisignited.thedropletsagsfurtherandtouchesthemoltenpuddle.whenthedroplettouchesthepuddle,thearcisshort-circuitedandextinguished.,migweldingprocedures,b.long,coiledcablesactasreactorsandsetupstraymagneticfieldsthataffectarcaction.2.checkthatthewiretype,wiresize,andshieldinggasarecorrectforthemetaltobewelded.3.settheshieldinggasflowrate,properamperage,andwirespeedforthemetalbeingwelded.,b.shortarctransferpattern,thedropletcontinuestomeltandbreaksofftheendofthewireelectrode.atthisinstant,thearcreignitesandanewdropletbeginstoform.2.newdropletformationandarcshortingmayoccurfrom20to200timespersecond.,b.shortarctransferpattern,3.shortarctransferisalsoknownasshortcircuitingtransferanddiptransfer.a.shortarctransferisespeciallygoodforweldinginthehorizontal,vertical,andoverheadpositionswherepuddlecontrolisusuallyhardtomaintain.b.shortarcweldingismostfeasibleatcurrentlevelsbelow200ampsandwithsmall-diameterelectrodewire.,c.sprayarctransferpattern,isasprayofveryfinedroplets.1.sprayarctransferisahigh-heatmethodofweldingwitharapiddepositionofmetal.itisusedforweldingallcommonmetalsfrom3/32inchtoover1inchinthickness.2.thistransferoccursonlywithargonorargon-oxygenmixtureofshieldinggas.,whatisthecorrecttechniqueforstarting,controlling,andstoppinganmigweld?,followproperprocedureswhenstarting,controlling,andstoppinganmigweld.,migweldingprocedures,a.preparingtostartweldingwiththemigwelderrequiresyoutomakeadjustmentstothemachine.1.besurethegunandgroundcablesareproperlyconnected.a.ifpossible,attachthegrounddirectlytotheworkpieceandweldawayfromtheground.b.long,coiledcablesactasreactorsandsetupstraymagneticfieldsthataffectarcaction.2.checkthatthewiretype,wiresize,andshieldinggasarecorrectforthemetaltobewelded.3.settheshieldinggasflowrate,properamperage,andwirespeedforthemetalbeingwelded.,b.whenreadytostarttheweldingprocess,travelspeed,stickout,andgunangleareimportantconsiderations.,migweldingprocedures,1.thespeedatwhichthearcismovedacrossthebasemetalaffectsthepuddle.propercontrolofthepuddleprovidesforgoodpenetration,withcorrectbeadwidthandbeadheight,andpreventsundercutting.a.travelspeedmayalsoaffectarcstabilityandthemetaltransferpattern.,migweldingprocedures,b.travelspeedsvarywiththesizeoftheelectrodewire,currentdensity,metalthickness,weldposition,andkindofmetalbeingfabricated.2.thetip-to-workdistancecanaffectweldpenetrationandweldshape,andisknownasstickout.a.shortstickoutdistances(3/8inchorless)aredesirableonsmall-wire,low-amperageapplications.,migweldingprocedures,3.holdingthemiggunatthecorrectangleisveryimportantsinceitcontrolsshieldinggasdistribution,puddlecontrol,andbeadformation.twoangleswhichmustbecorrecttomakeaqualityweldarethetravelangleandtheworkangle.,a.travelangle,theangleatwhichthemiggunleanstowardorawayfromthedirectionofmovement.i.atravelangleof10degreesto20degreesisusedformostwelding.ii.travelangleissometimesreferredtoasdragangle.,b.theworkangle,isperpendiculartothelineoftravelandvariesconsiderably,dependinguponthetypeofweldbeingmadeandtheweldingposition.theworkangleforaflatpositionsurfacingweldshouldbe15degreesto25degrees.,4.themiggunmaybeheldthreedifferentways.,a.perpendiculartothebasemetal.,4.themiggunmaybeheldthreedifferentways.,b.leaninginthedirectionoftravel,alsoknownasthebackhandorpullposition.,4.themiggunmaybeheldthreedifferentways.,c.leaningoppositethedirectionoftravel,alsoknownastheforehandorpushposition.,c.iftheweldcurrentisstoppedinstantly,theweldpuddlefreezes,gasesbecomeentrappedinthebead,andporosityresults.,stoppingtheweld,1.thebeststopisachievedbyallowingtheweldcurrenttotaperdown.2.stoppingthewirefeedasquicklyaspossibleafterthemigguntriggerisoffisdesirable.3.stoppingtheflowofshieldinggasisthelastthingtobedonewhenstoppingaweld.theshieldinggasneedstoflowoverthepuddleuntilitisfullysolidified,howisthemigwelderadjustedandmaintained?,a.mostmigmachineshaveavoltageadjustmentinadditiontothewirefeedcontrol.,1.determinewhatthevoltageshouldbesetforthekindandthicknessofmetalandtheshieldinggasbeingused.2.fineadjustmentsmaythenneedtobemadesoweldingoccurswiththerightsound,beadpenetration,shape,andcontour.,b.checkspecificationstoseewhatthecorrectgasvolumeshouldbefortheweld.,1.standtoonesideoftheregulator,openthetankvalvecompletely.2.adjusttheflowmetertothepredeterminedgasvolume.3.holdthemiggun“on”tosettothecorrectoperatingvolume.,d.thenozzleshouldbekeptcleanandfreeofspatterinordertoproperlydirecttheflowofshieldinggasesoverthepuddle.,1.iffilledwithspatter,thenozzlemaybecleanedwithanozzlereameroraroundfile.becarefulnottodeformthetipwhilecleaning.2.anti-spatterdiporspraymaybeputonthenozzletohelppreventspatterbuild-upandtomakecleaningeasier.,e.contacttipsneedtobesizedtofitthediameterofelectrodewirebeingused.,1.thecurrentistransmittedtothewireelectrodeinthecontacttip.2.tipsareusuallythreadedintothemiggunsothatgoodelectricalcontactismade.,whatarethesafetypracticesthatareobservedinmigwelding?,safetypracticesandprocedures,a.makesurethatallweldingcablesandtheirconnectionsareingoodrepair.donotusecablesthatarecrackedorcutorhavedamagedinsulation.electricalconnectionsoneachcableshouldbetightandnothavefrayedendsorbarewiresexposed.,safetypracticesandprocedures,b.wearweldinggloves,helmet,leatherapron,weldingchaps,leathershoes,andotherpersonalprotectiveequipmenttohelppreventweldburns.,safetypracticesandprocedures,c.whenoperatingamigwelder,nevertouchanelectricalconnection,abarewire,oramachinepartwhichmaycauseelectricalshock.neverweld