机械行业电子类文献原文英文版DOC 12页.docx

机械行业电子类文献原文英文版DOC 12页.docx

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机械行业电子类文献原文英文版DOC12页

机械行业电子类文献原文（英文版）（DOC12页）

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,theratio13βofthetwoprincipalstrainsisintroduced,βbeingεmin/εmax,whereεmaxandεminarethemajorandtheminorprincipalstrains,respectively.HosfordandCaddell[5]haveshownthatiftheabsolutevalueofβisgreaterthanacriticalvalue,wrinklingissupposedtooccur,andthelargertheabsolutevalueofβ,thegreateristhepossibilityofwrinkling.

Theβvaluesalongthecross-sectionM–Natthesamedrawingheightforthethreesimulatedshapeswithdifferentdiegaps,asmarkedinFig.4,areplottedinFig.5.ItisnotedfromFig.5thatseverewrinklesarelocatedclosetothecornerandfewerwrinklesoccurinthemiddleofthedrawwallforallthreedifferentdiegaps.Itisalsonotedthatthebiggerthediegap,thelargeristheabsolutevalueofβ.Consequently,increasingthediegapwillincreasethepossibilityofwrinklingoccurringatthedrawwallofthetaperedsquarecup.

3.2EffectoftheBlank-HolderForce

Itiswellknownthatincreasingtheblank-holderforcecanhelptoeliminatewrinklinginthestampingprocess.Inordertostudytheeffectivenessofincreasedblank-holderforce,thestampingofataperedsquarecupwithdiegapof50mm,whichisassociatedwithseverewrinklingasstatedabove,wassimulatedwithdifferentvaluesofblank-holderforce.Theblank-holderforcewasincreasedfrom100kNto600kN,whichyieldedablank-holderpressureof0.33MPaand1.98MPa,respectively.Theremainingsimulationconditionsaremaintainedthesameasthosespecifiedintheprevioussection.（Anintermediateblank-holderforceof300kNwasalsousedinthesimulation.）

Thesimulationresultsshowthatanincreaseintheblankholderforcedoesnothelptoeliminatethewrinklingthatoccursatthedrawwall.Theβvaluesalongthecross-sectioncomparedwithoneanotherforthestampingprocesseswithblank-holderforceof100kNand600kN.Thesimulationresultsindicatethatthe_valuesalongthecross-sectionM–Narealmostidenticalinbothcases.Inordertoexaminethedifferenceofthewrinkleshapeforthetwodifferentblank-holderforces,fivecross-sectionsofthe

drawwallatdifferentheightsfromthebottomtothelineM–N,asmarkedinFig.4,areplottedinFig.6forbothcases.ItisnotedfromFig.6thatthewavinessofthecross-sectionsforbothcasesissimilar.Thisindicatesthattheblank-holderforcedoesnotaffecttheoccurrenceofwrinklinginthestampingofataperedsquarecup,becausetheformationofwrinklesismainlyduetothelargeunsupportedareaatthedrawwallwherelargecompressivetransversestressesexist.Theblankholderforcehasnoinfluenceontheinstabilitymodeofthematerialbetweenthepunchheadandthediecavityshoulder.

Distance（mm）

Fig.5.β-valuealongthecross-sectionM–Nfordifferentdiegaps.

Fig.6.Cross-sectionlinesatdifferentheightsofthedrawwallfor

differentblank-holderforces.（a）100kN.（b）600kN.

4.SteppedRectangularCup

Inthestampingofasteppedrectangularcup,wrinklingoccursatthedrawwalleventhoughthediegapsarenotsosignificant.Figure1（b）showsasketchofapunchshapeusedforstamping