反应釜毕业设计外文翻译.doc

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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-s