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WeldingSimulationofCastAluminiumA356

X-T.Pham*,P.GougeonandF-O.Gagnon

AluminiumTechnologyCentre,NationalResearchCouncilCanadaChicoutimi,Quebec,Canada

Abstract

Weldingofcastaluminiumhollowpartsisanewpromisingtechnicaltrendforstructuralassemblies.However,biggapbetweencomponents,weldporosity,largedistortionandriskforhotcrackingneedtobedealtwith.Inthispaper,theMIGweldingofaluminiumA356castsquaretubesisstudied.Thedistortionoftheweldedtubeswaspredictedbynumericalsimulations.Agoodagreementbetweenexperimentalandnumericalresultswasobtained.

Introduction

Aluminiumstructuresbecomemoreandmorepopularinindustriesthankstotheirlightweights,especiallyintheautomotivemanufacturingindustry.Moreover,weldingofcastaluminiumhollowpartsisanewpromisingtechnicaltrendforstructuralassemblies[1-3].However,itmaybeverychallengingduetomanyproblemssuchasbiggapbetweencomponents,weldporosity,largedistortionandriskforhotcracking[4,5].Duetolocalheating,complexthermalstressesoccurduringwelding;residualstressanddistortionresultafterwelding.Inthispaper,thealuminiumA356casttubeMIGweldingisstudied.ThesoftwareSysweld[6]wasusedforweldingsimulations.Theobjectiveistovalidatethecapabilityofthissoftwareinpredictingthedistortionoftheweldedtubesinthepresenceoflargegaps.Inthiswork,theporosityofweldswascheckedafterweldingusingtheX-raytechnique.Theheatsourceparameterswereidentifiedbasedontheweldcross-sectionsandweldingparameters.Full3Dthermalmetallurgicalmechanicalsimulationswereperformed.ThedistortionspredictedbythenumericalsimulationswerecomparedtoexperimentalresultsmeasuredafterweldingbyaCMMmachine.

Experiments

Experimentalsetup

TwosquaretubesaremadeofA356bysandcastingandthenmachined.TheyareassembledbyfourMIGwelds,namedW1toW4.TheirdimensionsandtheweldingconfigurationaredepictedinFigure1.Bothsmall（inner）andlarge（outer）tubesarewellpositionedonafixtureusingv-blocksasshowninFigure2.Thedimensionsofthetubesmakeaperipheralgapof1mmbetweenthem.Thisfixtureisfixedonapositionerthatallowstheweldingprocesstobecarriedoutalwaysinthehorizontalposition.Thelengthofeachweldisof35mm.TheFroniusweldinghead,whichismountedonaMotomanrobot,wasusedfortheMIGweldingprocess.Table1indicatestheparametersoftheweldingprocessforthisweldingconfiguration.

Table1:

MIGweldingparameters.

Voltage

Amperage

Speed

Thick1

Thick2

Gap

（V）

（A）

（m/min.）

（mm）

（mm）

（mm）

23

260

1.25

4

4

1

a）

b）

Figure1:

Tubeweldingconfiguration:

a）cross-sectionview,b）tubedimensions

Figure2:

Experimentalsetupfortubewelding

Testing

TheporosityofweldswasobservedbeforeandafterweldingusingtheX-raytechniquetocheckthequalityoftheseweldsaccordingtothestandardASTME155.ThewholeweldedtubeswerethentestedbytractiononaMTStestingmachine.ThefinaldimensionsoftheweldedtubesaremeasuredonaCMMmachineatmanypointsonthetubes.Thedistortionoftheweldedtubesisdeterminedbycomparingthefinalpositionswiththeinitialpositionsofthetubes.

Numericalanalysis

InSysweld,aweldinganalysisisperformedbasedonaweak-couplingformulationbetweentheheattransferandmechanicalproblems.Onlythethermalhistorywillaffectonthemechanicalproperties,butnotinreversedirection.Therefore,athermalmetallurgicalmechanicalanalysisisdividedintotwosteps.Thefirststepisathermalmetallurgicalanalysis,inwhichtheheattransferredfromtheweldingsourcemakesphasechangesduringtheweldingprocess.Theresultsoftemperatureandphasechangesfromthefirststeparethenusedasinputforthesecondanalysis.Itisapurethermo-elasto-plasticsimulation[6].

Heatsourcemodelidentification

Beforerunningaweldingsimulation,itisnecessarytodeterminetheparametersoftheheatsourcemodel.Thisiscalledheatsourcefitting.Actually,itisathermalsimulationusingthisheatsourcemodelinthesteadystate,whichiscombinedwithanoptimizationtooltoobtaintheparametersoftheheatsource.Figure3presentstheformofa3DconicalheatsourceofwhichtheenergydistributionisdescribedinEq

（1）asfollows:

F=Q0exp（-r²/r0²）

（1）

inwhichQ0denotesthepowerdensity;andr，r0aredefinedby

r²=（x-x0）²+（x-x0-vt）²

（2）

and

r0=re-（re-ri）（ze-z+z0）/（ze-zi）（3）

where（x0,y0,z0）istheoriginofthelocalcoordinatesystemoftheheatsource;reandritheradiusoftheheatsourceatthepositionszeandzi,respectively;vtheweldingspeedandtthetime.

Inthisstudy,ametallographiccross-sectionhasbeenusedtoidentifytheheatsourceparametersasshowninFigure4.Theuseofa3Dconicalheatsourcefitsverywelltheweldcross-section.Themeshsizeinthecross-sectionisaround0.5mmforthiscase.Thefineristhemesh,themoreaccurateistheshapeofthemeltingpool,butthelongeristhesimulation.

Figure3:

3Dconicalheatsource（Sysweld）.

a）

b）

Figure4:

（a）Metallographiccross-section,（b）Meltingpoolcross-section.

Analysismodel

ThemeshofthetubeswascreatedinHypermesh7.0.Sysweld2007hasbeenusedassolverandpre/postprocessor.Afull3Dthermalmetallurgicalmechanicalanalysiswithbrickandprismelements.TwoweldingsequenceshavebeendonesuchasW1/W2/W3/W4andW1/W3/W2/W4.Thetubesareclampedusingfourv-blocksduringthewelding,twoforeachtube.Inthesimulations,thepositionswherethetubesareincontactagainstthesurfacesofthev-blocksareconsideredasfixedconditions（i.e.Ux=Uy=Uz=0）.Inthereleasephase,thetubesarefreefromthev-blocks.

Results

Thedistortionoftheweldedtubeismeasuredwhenitisreleasedfromtheconstraints.Thedistortionisdeterminedbymeasuringthedisplacementofthesmalltubeonthetopandlateralsurfacesalongthecentrelineofthetube.Thesemeasuresarerelativetothelargetube.Figures5a-bdepictthedistortionpredictedbythenumericalsimulationsofthesequenceW1/W2/W3/W4andW1/W3/2/W4,respectively.GoodagreementsbetweenexperimentalandnumericalresultswereobtainedinthetwoweldingsequencesasindicatedinTables2-3,inboththedistortiontendencyanddistortionrangeoftheprocessvariation.

a）

b）

Figure5:

Tubedistortion（NormU）:

（a）SequenceW1/W2/W3/W4,（b）SequenceW1/W3/W2/W4.

Table2:

Distortionresultcomparison（weldingsequenceW1/W2/W3/W4）

Displacements（mm）

Uy

Uz

Experimrntal

From-0.4to-0.59

From-0.35to-0.51

3Dsimulation

-0.4

-0.51

Table3:

Distortionresultcomparison（weldingsequenceW1/W3/W2/W4）

Displacements（mm）

Uy

Uz

Experimrntal

From-0.07to-0.11

From-0.12to-0.21

3Dsimulation

-0.05

-0.26

a）

b）

Figure7:

StateofstressesSxy（a）Clamped,（b）Released.（Red=positive,Blue=negative）

a）

b）

Figure8:

StateofstressesSxz（a）Clamped,（b）Released.（Red=positive,Blue=negative）

Figures6-8showsthestateofthestressesoftheweldedtubesatroomtemperatureforthesequenceW1/W2/W3/W4afterweldingwhenclampledandreleasedfromconstraints（xisthedirectionalongtheaxeoftheweldedtube）.Toshowhowtheweldedtubeisdistorted,positive-negativevaluesareusedinsteadofthetruevaluesofstresses.Thedistortionoftheweldedtubecanbeexplainedasthenewequilibriumpositionduetotheresidualstresseswhenthereisnoexternalload.Itisremarkedthatinthepresenceoflargegaps,thedistortionoftheweldedtubeisverylikelyintherotationalmodearoundlocalwelds.

Conclusions

TheMIGweldingisverygoodforassemblingaluminiumcasttubes（hollowparts）inthepresenceoflargegaps.

The3DthermalmetallurgicalmechanicalsimulationofthecasttubeweldingusingSysweldhasbeenvalidated.Averygoodagreementbetweennumericalandexperimentalresultswasobtainedforboththedistortiontendencyanddistortionrange.

Theweldingsequencehasamajorinfluenceonthedistortionoftheweldedstructure.Itturnsoutthattheoptimizationoftheweldingsequencesforareasonabledistortionofaweldedstructurewithalargenumberofweldsbecomesveryimportant.

Acknowledgments

TheauthorswouldliketothankgratefullyRioTintoAlcanandGeneralMotorforfinancialandtechnicalsupports,particularlyMartinFortierandPei-ChungWang.Also,theauthorsaregratefultoWeldingTeamatATC（AudreyBoily,MartinLarouche,FrançoisNadeauandMarioPatry）forexperimentalworks.

References

1.K-H.VonZengen,Aluminiuminfuturecars–Achallengeformaterialsscience,MaterialsScienceForum,519-521（Part2）,1201-1208（2006）.

2.S.WiesnerS.,M.RethmeierandH.Wohlfart,MIGandlaserweldingofaluminiumalloypressurediecastpartswithwroughtprofiles,WeldingInternational,19

（2）,130-133（2005）.

3.R.Akhter,L.Ivanchev,C.V.Rooyen,P.KazadiandH.P.Burger,LaserweldingofSSMCastA356aluminiumalloyprocessedwithCSIR-Rheotechnology,SolidStatePhenomena,116-117,173-176（2006）.

4.J.F.Lancaster,Metallurgyofwelding,AbingtonPublishing（1999）.

5.Φ.Grong,Metallurgicalmodellingofwelding,Theinstituteofmaterials（1997）.

6.Sysweld,Sysweldreferencemanual,ESIGroup（2005）.

译文

铸造A356铝合金的焊接模拟

X-T.Pham*,P.GougeonandF-O.Gagnon

AluminiumTechnologyCentre,NationalResearchCouncilCanadaChicoutimi,Quebec,Canada

摘要：

空心铝铸造件的焊接是一个很有前途的新结构组件技术的趋势。

然而，组件之间的差距较大，焊接孔隙度，大变形和热裂需要处理的风险。

在这篇文章中，对铸造A356铝合金的方管的MIG焊接进行了研究。

并对焊接管弯曲变形进行了数值模拟预测。

实验结果和数值模