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英文原文StressAnalysisofStampingDiesJ.Mater.ShapingTechnoi.19908172291990SpringerVerlagNewYorkInc.R.S.RaoAbstractExperimentalandcomputationalproceduresforstudyingdeflections,flit,andalignmentcharacteristicsofasequenceofstampingdies,housedinatransferpress,arepresented.Dieloadsareactuallymeasuredatallthe12diestationsusingnewloadmonitorsandusedasinputtothecomputationalprocedure.Atypicalstampingdieisanalyzedusingacomputationalcode,MSC/NASTRAN,basedonfiniteelementmethod.Theanalysisisthenextendedtotheotherdies,especiallytheoneswheretheloadsarehigh.Stressesanddeflectionsareevaluatedinthediesforthesymmetricandasymmetricloadingconditions.Basedonourindependentdieanalysis,stressesanddeflectionsarefoundtobereasonablywellwithinthetolerablelimits.However,thissituationcouldchangewhenthestampingdiesareeventuallyintegratedwiththepressasatotalsystemwhichistheultimategoalofthisbroadresearchprogram.INTRODUCTIONSheetmetalpartsrequireaseriesofoperationssuchasshearing,drawing,stretching,bending,andsqueezing.Alltheseoperationsarecarriedoutatoncewhilethedoubleslidemechanismdescendstoworkonthepartsinthediestations,housedinatransferpress1.Materialisfedtothepressasblanksfromastockfeeder.Inoperationthestockismovedfromonestationtothenextbyamechanismsynchronizedwiththemotionoftheslide.Eachdieisaseparateunitwhichmaybeindependentlyadjustedfromthemainslide.Anautomotivepartstampedfromahotrolledsteelblankin12stepswithoutanyintermediateannealsisshowninFigure1.Transferpressesaremainlyusedtoproducedifferenttypesofautomotiveandaircraftpartsandhomeappliances.Theeconomicuseoftransferpressesdependsuponquantityproductionastheirusualproductionrateis500to1500partsperhour2.Althoughproductionisrapidinthisway,closetolerancesareoftendifficulttoachieve.Moreover,thepressesproduceasetofconditionsforoffcenterloadsowingtothedifferentoperationsbeingperformedsimultaneouslyinseveraldiesduringeachstroke.Thus,theformingloadappliedatonestationcanaffectthealignmentandgeneralaccuracyoftheoperationbeingperformedatadjacentstations.Anotherpracticalproblemisthesignificantamountofsetuptimeinvolvedtobringallthediesintoproperoperation.Hence,thebroadgoalofthisresearchistostudythestructuralcharacteristicsofpressanddiescombinationasatotalsystem.Inthispaper,experimentalandcomputationalproceduresforinvestigatingdieproblemsarepresented.Theanalysisofstructuralcharacteristicsofthetransferpresswaspursuedseparately3.Atransferpressconsistingof12diestationswaschosenforanalysis.Typicaldieproblemsareexcessivedeflections,tilt,andmisalignmentoftheupperandlowerdiehalves.Inadequatecushioningandoffcenterloadingmaycausetiltandmisalignmentofthedies.Tiltandexcessivedeflectionsmayalsobecausedbythelackofstiffnessofthediebolsterandthedieitself.Partqualitycanbegreatlyaffectedbythesedieproblems.Therearealotofotherparameterssuchasthediedesign,frictionandlubricationalongthedieworkinterface,speed,etc.thatplayagreatroleinproducingconsistentlygoodparts.Realistically,theanalysisshouldbecardedoutbyincorporatingthediedesignandthedeformingcharacteristicsoftheworkmaterialsuchastheelasticplasticworkhardeningproperties.Inthispreliminarystudy,thelargeplasticdeformationoftheworkpiecewasnotconsideredforthereasonsmentionedbelow.Largedeformationmodelingofasheetstretchingprocesswascardedoutusingthecomputationalcodebasedonanelasticplasticworkhardeningmodelofthedeformationprocess4.Laboratoryexperimentswereconductedonvariouscommercialmaterialsusingahemisphericalpunch.Thecoefficientoffrictionalongthepunchsheetinterfacewasactuallymeasuredintheexperimentandusedasaprescribedboundarytothenumericalmodel.Althoughagoodsolutionwasobtained,itwasrealizedthatthenumericalanalysiswasverysensitivetothefrictionalconditionsalongtheinterface.Inthemostrecentwork,anewfrictionmodelbasedonthemicromechanicsoftheasperitycontactwasdeveloped5.Inthepresentproblem,thereareseveraloperationssuchasdeepdrawing,severalreductiondrawingoperations,andcoining,whichareperformedusingcomplexdiegeometries.Theresourcesandthedurationoftimewerenotadequatetostudythesenonlinearproblems.Hence,thepreliminarystudywaslimitedtodieproblemsbasedonlinearstressanalysis.AdetaileddieanalysiswascarriedoutbyusingMSC/NASTRANcodebasedonfiniteelementmethod.Dieloadswere.measuredatallthestationsusingnewloadmonitors.Suchmeasureddatawereusedinthenumericalmodeltoevaluatestressesanddeflectionsinthediesfornormaloperatingconditionsandforasymmetricloadingconditions.Asymmetricloadingconditionswerecreatedintheanalysisbytiltingthedies.Inrealpractice,itiscustomarytopursuetrialanderrorproceduressuchasplacingshimsunderthedieorbyadjustingthecushionpressuretocorrectthediealignmentproblems.Suchtimeconsumingtaskscanbereducedoreveneliminatedusingthecomputationalandexperimentalprocedurespresentedhere.DIEGEOMETRYANDMATERIALSThedesignofmetalstampingdiesisaninexactprocess.Thereareconsiderabletrialanderroradjustmentsduringdietryoutthatareoftenrequiredtofinishthefabricationofadiethatwillproduceacceptableparts.Itinvolvesnotonlytheproperselectionofdiematerials,butalsodimensions.Inordertowithstandthepressure,adiemusthavepropercrosssectionalareaandclearances.Sharpcomers,radii,fillets,andsuddenchangesinthecrosssectioncanhavedeleteriouseffectsonthedielife.Inthiswork,theanalysiswasdoneontheexistingsetofdies.Thediesweremadeofhighcarbon,highchromiumtoolsteel.ThehardnessofthistoolsteelmaterialisintherangeofRockwellC57to60.Resistancetowearandgallingwasgreatlyimprovedbycoatingthedieswithtitaniumnitrideandtitaniumcarbide.ThediesweresupportedbyseveralothersteelholdersmadeofalloysteelssuchasSAE4140.Thegeometryofatypicalstampingdieisaxisymmetricbutitvariesslightlyfromdietodiedependingontheoperation.Detailedinformationaboutgeometryandmaterialsofareductiondrawingdiestationnumber4wasgatheredfromblueprints.Itwasreproducedinthreedimensionalgeometryusingapreprocessor,PATRAN.OnequadrantofthedieisshowninFigure2.Thedataincludinggeometryandelasticpropertiesofthediematerialwerefedtothenumericalmodel.Theworkmaterialusedwashotrolledaluminumkilledsteel,SAE1008AKSteelandtheblankthicknesswasabout4.5ram.Stampingsusedinunexposedplacesoraspartsofsomedeisgnwherefinefinishisnotessentialareusuallymadefromhotrolledsteel.Theautomotivepartproducedinthisdiesetisacoverforatorqueconverter.Aprincipaladvantageofaluminumkilledsteelisitsminimumstrainaging.EXPERIMENTALPROCEDURESAsmentionedearlier,thisresearchinvolvedmonitotingofdieloadswhichweretobeusedinthenumericalmodeltostaldythestructuralcharacteristicsofdies.Theotheradvantageistoavoidoverloadingthediesinpractice.Offcenterloadingcanbedetectedandalsosetuptimecanbereduced.Thus,anychangesinthethicknessofstock,dullingofthedie,unbalancedloads,oroverloadingscanbedetectedusingdieloadmonitors.StraingagebasedfiatloadcellsmadeofhighgradetoolsteelmaterialwerefabricatedandsuppliedbyIDCCorporation.FouridenticalloadcellswereembeddedinathickrectangularplateasshowninFigure3.Theywerecalibratedbothinthelaboratoryandintheplant.Theplatewasplacedonthetopofthedie.Theknockoutpinslipsthroughtheholeintheplate.Sixsuchplateswereplacedoneachofsixdies.Inthisway,24readingscanbeobtainedatagiventime.Thentheywereshiftedtotheothersixdiesforcompletedata.Allthe12dieloadsarepresentedinTable1.COMPUTATIONALPROCEDURESLinearstaticanalysisusingfiniteelementmethodwasusedtostudytheeffectofsymmetricandasymmetricloadingforthisproblem.Afiniteelementmodelofdiestation4wascreatedusingthegraphicalpreprocessor,PATRAN,andtheanalysiswas
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