拉深模设计中拉深壁起皱的分析毕业课程设计外文文献翻译.docx

拉深模设计中拉深壁起皱的分析毕业课程设计外文文献翻译.docx

《拉深模设计中拉深壁起皱的分析毕业课程设计外文文献翻译.docx》由会员分享，可在线阅读，更多相关《拉深模设计中拉深壁起皱的分析毕业课程设计外文文献翻译.docx（60页珍藏版）》请在冰豆网上搜索。

拉深模设计中拉深壁起皱的分析毕业课程设计外文文献翻译

AnAnalysisofDraw-WallWrinklinginaStampingDieDesign

F.-K.ChenandY.-C.Liao

DepartmentofMechanicalEngineering,NationalTaiwanUniversity,Taipei,Taiwan

Wrinklingthatoccursinthestampingoftaperedsquarecupsandsteppedrectangularcupsisinvestigated.Acommoncharacteristicofthesetwotypesofwrinklingisthatthewrinklesarefoundatthedrawwallthatisrelativelyunsupported.Inthestampingofataperedsquarecup,theeffectofprocessparameters,suchasthediegapandblank-holderforce,ontheoccurrenceofwrinklingisexaminedusingfiniteelementsimulations.Thesimulationresultsshowthatthelargerthediegap,themoresevereisthewrinkling,andsuchwrinklingcannotbesuppressedbyincreasingtheblank-holderforce.Intheanalysisofwrinklingthatoccurredinthestampingofasteppedrectangularcup,anactualproductionpartthathasasimilartypeofgeometrywasexamined.Thewrinklesfoundatthedrawwallareattributedtotheunbalancedstretchingofthesheetmetalbetweenthepunchheadandthestepedge.Anoptimumdiedesignforthepurposeofeliminatingthewrinklesisdeterminedusingfinite-elementanalysis.Thegoodagreementbetweenthesimulationresultsandthoseobservedinthewrinkle-freeproductionpartvalidatestheaccuracyofthefinite-elementanalysis,anddemonstratestheadvantageofusingfinite-elementanalysisforstampingdiedesign.

Keywords:

Draw-wallwrinkle;Stampingdie;Steppedrectangularcup;Taperedsquarecups

1.Introduction

Wrinklingisoneofthemajordefectsthatoccurinthesheetmetalformingprocess.Forbothfunctionalandvisualreasons,wrinklesareusuallynotacceptableinafinishedpart.Therearethreetypesofwrinklewhichfrequentlyoccurinthesheetmetalformingprocess:

flangewrinkling,wallwrinkling,andelasticbucklingoftheundeformedareaowingtoresidualelasticcompressivestresses.Intheformingoperationofstampingacomplexshape,draw-wallwrinklingmeanstheoccurrenceofwrinklesinthediecavity.Sincethesheetmetalinthewallareaisrelativelyunsupportedbythetool,theeliminationofwallwrinklesismoredifficultthanthesuppressionofflangewrinkles.Itiswellknownthatadditionalstretchingofthematerialintheunsupportedwallareamaypreventwrinkling,andthiscanbeachievedinpracticebyincreasingtheblankholderforce;buttheapplicationofexcessivetensilestressesleadstofailurebytearing.Hence,theblank-holderforcemustliewithinanarrowrange,abovethatnecessarytosuppresswrinklesontheonehand,andbelowthatwhichproducesfractureontheother.Thisnarrowrangeofblank-holderforceisdifficulttodetermine.Forwrinklesoccurringinthecentralareaofastampedpartwithacomplexshape,aworkablerangeofblank-holderforcedoesnotevenexist.

Inordertoexaminethemechanicsoftheformationofwrinkles,Yoshidaetal.[1]developedatestinwhichathinplatewasnon-uniformlystretchedalongoneofitsdiagonals.Theyalsoproposedanapproximatetheoreticalmodelinwhichtheonsetofwrinklingisduetoelasticbucklingresultingfromthecompressivelateralstressesdevelopedinthenon-uniformstressfield.Yuetal.[2,3]investigatedthewrinklingproblembothexperimentallyandanalytically.Theyfoundthatwrinklingcouldoccurhavingtwocircumferentialwavesaccordingtotheirtheoreticalanalysis,whereastheexperimentalresultsindicatedfourtosixwrinkles.NarayanasamyandSowerby[4]

examinedthewrinklingofsheetmetalwhendrawingitthroughaconicaldieusingflat-bottomedandhemispherical-endedpunches.Theyalsoattemptedtorankthepropertiesthatappearedtosuppresswrinkling.

Theseeffortsarefocusedonthewrinklingproblemsassociatedwiththeformingoperationsofsimpleshapesonly,suchasacircularcup.Intheearly1990s,thesuccessfulapplicationofthe3Ddynamic/explicitfinite-elementmethodtothesheetmetalformingprocessmadeitpossibletoanalysethewrinklingprobleminvolvedinstampingcomplexshapes.Inthepresentstudy,the3Dfinite-elementmethodwasemployedtoanalysetheeffectsoftheprocessparametersonthemetalflowcausingwrinklesatthedrawwallinthestampingofataperedsquarecup,andofasteppedrectangularpart.

Ataperedsquarecup,asshowninFig.1（a）,hasaninclineddrawwalloneachsideofthecup,similartothatexistinginaconicalcup.Duringthestampingprocess,thesheetmetalonthedrawwallisrelativelyunsupported,andisthereforepronetowrinkling.Inthepresentstudy,theeffectofvariousprocessparametersonthewrinklingwasinvestigated.Inthecaseofasteppedrectangularpart,asshowninFig.1（b）,anothertypeofwrinklingisobserved.Inordertoestimatetheeffectivenessoftheanalysis,anactualproductionpartwithsteppedgeometrywasexaminedinthepresentstudy.Thecauseofthewrinklingwasdeterminedusingfinite-elementanalysis,andanoptimumdiedesignwasproposedtoeliminatethewrinkles.Thediedesignobtainedfromfinite-elementanalysiswasvalidatedbyobservationsonanactualproductionpart.

Sketchesof（a）ataperedsquarecup.

Sketchesof（b）asteppedrectangularcup.

Fig.1.

2.Finite-ElementModel

Thetoolinggeometry,includingthepunch,dieandblankholder,weredesignedusingtheCADprogramPRO/ENGINEER.Boththe3-nodeand4-nodeshellelementswereadoptedtogeneratethemeshsystemsfortheabovetoolingusingthesameCADprogram.Forthefinite-elementsimulation,thetoolingisconsideredtoberigid,andthecorrespondingmeshesareusedonlytodefinethetoolinggeometryandarenotforstressanalysis.ThesameCADprogramusing4-nodeshellelementswasemployedtoconstructthemeshsystemforthesheetblank.Figure2showsthemeshsystemforthecompletesetoftoolingandthesheet-blankusedinthestampingofataperedsquarecup.Owingtothesymmetricconditions,onlyaquarterofthesquarecupisanalysed.Inthesimulation,thesheetblankisputontheblank-holderandthedieismoveddowntoclampthesheetblankagainsttheblank-holder.Thepunchisthenmoveduptodrawthesheetmetalintothediecavity.

Inordertoperformanaccuratefinite-elementanalysis,theactualstress–strainrelationshipofthesheetmetalisrequiredaspartoftheinputdata.Inthepresentstudy,sheetmetalwithdeep-drawingqualityisusedinthesimulations.Atensiletesthasbeenconductedforthespecimenscutalongplanescoincidingwiththerollingdirection（0°）andatanglesof45°and90°totherollingdirection.Theaverageflowstressσ,calculatedfromtheequationσ=（σ0+2σ45+σ90）/4,foreachmeasuredtruestrain,asshowninFig.3,isusedforthesimulationsforthestampingsofthetaperedsquarecupandalsoforthesteppedrectangularcup.

AllthesimulationsperformedinthepresentstudywererunonanSGIIndigo2workstationusingthefinite-elementprogramPAMFSTAMP.Tocompletethesetofinputdatarequiredforthesimulations,thepunchspeedissetto10ms_1andacoefficientofCoulombfrictionequalto0.1isassumed.

Fig.2.Finite-elementmesh.

Fig.3.Thestress–strainrelationshipforthesheetmetal.

3.WrinklinginaTaperedSquareCup

AsketchindicatingsomerelevantdimensionsofthetaperedsquarecupisshowninFig.1（a）.AsseeninFig.1（a）,thelengthofeachsideofthesquarepunchhead（2Wp）,thediecavityopening（2Wd）,andthedrawingheight（H）areconsideredasthecrucialdimensionsthataffectthewrinkling.Halfofthedifferencebetweenthedimensionsofthediecavityopeningandthepunchheadistermedthediegap（G）inthepresentstudy,i.e.G=Wd-Wp.Theextentoftherelativelyunsupportedsheetmetalatthedrawwallispresumablyduetothediegap,andthewrinklesaresupposedtobesuppressedbyincreasingtheblank-holderforce.Theeffectsofboththediegapandtheblank-holderforceinrelationtotheoccurrenceofwrinklinginthestampingofataperedsquarecupareinvestigatedinthefollowingsections.

3.1EffectofDieGap

Inordertoexaminetheeffectofdiegaponthewrinkling,thestampingofataperedsquarecupwiththreedifferentdiegapsof20mm,30mm,and50mmwassimulated.Ineachsimulation,thediecavityopeningisfixedat200mm,andthecupisdrawntothesameheightof100mm.Thesheetmetalusedinallthreesimulationsisa380mm×380mmsquaresheetwiththicknessof0.7mm,thestress–straincurveforthematerialisshowninFig.3.

Fig.4.Wrinklinginataperedsquarecup（G=50mm）.

Thesimulationresultsshowthatwrinklingoccurredinallthreetaperedsquarecups,andthesimulatedshapeofthedrawncupforadiegapof50mmisshowninFig.4.ItisseeninFig.4thatthewrinklingisdistributedonthedrawwallandisparticularlyobviousatthecornerbetweenadjacentwalls.Itissuggestedthatthewrinklingisduetothelargeunsupportedareaatthedrawwallduringthestampingprocess,also,thesidelengthofthepunchheadandthediecavityopeningaredifferentowingtothediegap.Thesheetmetalstretchedbetweenthepunchheadandthediecavityshoulderbecomesunstableowingtothepresenceofcompressivetransversestresses.Theunconstrainedstretchingofthesheetmetalundercompressionseemstobethemaincauseforthewrinklingatthedrawwall.Inordertocomparetheresultsforthethreedifferentdiegaps,theratioβofthetwoprincipalstrainsisintroduced,βbeingεmin/εmax,whereεmaxandεminarethemajorandtheminorprincipalstrains,respectively.HosfordandCaddell[5]haveshownthatiftheabsolutevalueofβisgreaterthanacriticalvalue,wrinklingissupposedtooccur,andthelargertheabsolutevalueofβ,thegreater