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
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