外文翻译--冲压模具的受力分析.doc

英文原文StressAnalysisofStampingDiesJ.Mater.ShapingTechnoi.(1990)8:17-2291990Springer-VerlagNewYorkInc.R.S.RaoAbstract:Experimentalandcomputationalproceduresforstudyingdeflections,flit,andalignmentcharacteristicsofasequenceofstampingdies,housedinatransferpress,arepre-sented.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,thepressesproduceasetofconditionsforoff-centerloadsowingtothedifferentoperationsbeingperformedsimultaneouslyinseveraldiesduringeachstroke.Thus,theformingloadappliedatonestationcanaffectthealignmentandgeneralaccuracyoftheoperationbeingperformedatadjacentstations.Anotherpracticalproblemisthesignificantamountofset-uptimeinvolvedtobringallthediesintoproperoperation.Hence,thebroadgoalofthisresearchistostudythestructuralcharacteristicsofpressanddiescombinationasatotalsystem.Inthispaper,experimentalandcomputationalproceduresforinvestigatingdieproblemsarepresented.Theanalysisofstructuralcharacteristicsofthetransferpresswaspursuedseparately3.Atransferpressconsistingof12diestationswaschosenforanalysis.Typicaldieproblemsareexcessivedeflections,tilt,andmisalignmentoftheupperandlowerdiehalves.Inadequatecushioningandoffcenterloadingmaycausetiltandmisalignmentofthedies.Tiltandexcessivedeflectionsmayalsobecausedbythelackofstiffnessofthediebolsterandthedieitself.Partqualitycanbegreatlyaffectedbythesedieproblems.Therearealotofotherparameterssuchasthediedesign,frictionandlubricationalongthedieworkinterface,speed,etc.thatplayagreatroleinproducingconsistentlygoodparts.Realistically,theanalysisshouldbecardedoutbyincorporatingthediedesignandthedeformingcharacteristicsoftheworkmaterialsuchastheelastic-plasticworkhardeningproperties.Inthispreliminarystudy,thelargeplasticdeformationoftheworkpiecewasnotconsideredforthereasonsmentionedbelow.Largedeformationmodelingofasheetstretchingprocesswascardedoutusingthecomputationalcodebasedonanelastic-plasticworkhardeningmodelofthedeformationprocess4.Laboratoryexperimentswereconductedonvariouscommercialmaterialsusingahemisphericalpunch.Thecoefficientoffrictionalongthepunch-sheetinterfacewasactuallymeasuredintheexperimentandusedasaprescribedboundarytothenumericalmodel.Althoughagoodsolutionwasobtained,itwasrealizedthatthenumericalanalysiswasverysensitivetothefrictionalconditionsalongtheinterface.Inthemostrecentwork,anewfrictionmodelbasedonthemicromechanicsoftheasperitycontactwasdeveloped5.Inthepresentproblem,thereareseveraloperationssuchasdeepdrawing,severalreductiondrawingoperations,andcoining,whichareperformedusingcomplexdiegeometries.Theresourcesandthedurationoftimewerenotadequatetostudythesenonlinearproblems.Hence,thepreliminarystudywaslimitedtodieproblemsbasedonlinearstressanalysis.AdetaileddieanalysiswascarriedoutbyusingMSC/NASTRANcodebasedonfiniteelementmethod.Dieloadswere.measuredatallthestationsusingnewloadmonitors.Suchmeasureddatawereusedinthenumericalmodeltoevaluatestressesanddeflectionsinthediesfornormaloperatingconditionsandforasymmetricloadingconditions.Asymmetricloadingconditionswerecreatedintheanalysisbytiltingthedies.Inrealpractice,itiscustomarytopursuetrial-and-errorproceduressuchasplacingshimsunderthedieorbyadjustingthecushionpressuretocorrectthediealignmentproblems.Suchtimeconsumingtaskscanbereducedoreveneliminatedusingthecomputationalandexperimentalprocedurespresentedhere.DIEGEOMETRYANDMATERIALSThedesignofmetalstampingdiesisaninexactprocess.Thereareconsiderabletrial-and-erroradjustmentsduringdietryoutthatareoftenrequiredtofinishthefabricationofadiethatwillproduceacceptableparts.Itinvolvesnotonlytheproperselectionofdiematerials,butalsodimensions.Inordertowithstandthepressure,adiemusthavepropercross-sectionalareaandclearances.Sharpcomers,radii,fillets,andsuddenchangesinthecrosssectioncanhavedeleteriouseffectsonthedielife.Inthiswork,theanalysiswasdoneontheexistingsetofdies.Thediesweremadeofhighcarbon,highchromiumtoolsteel.ThehardnessofthistoolsteelmaterialisintherangeofRockwellC57to60.Resistancetowearandgallingwasgreatlyimprovedbycoatingthedieswithtitaniumnitrideandtitaniumcarbide.ThediesweresupportedbyseveralothersteelholdersmadeofalloysteelssuchasSAE4140.Thegeometryofatypicalstampingdieisaxisymmetricbutitvariesslightlyfromdietodiedependingontheoperation.Detailedinformationaboutgeometryandmaterialsofareductiondrawingdie(stationnumber4)wasgatheredfromblueprints.Itwasreproducedinthree-dimensionalgeometryusingapreprocessor,PATRAN.OnequadrantofthedieisshowninFigure2.Thedataincludinggeometryandelasticpropertiesofthediematerialwerefedtothenumericalmodel.Theworkmaterialusedwashotrolledaluminumkilledsteel,SAE1008A-KSteelandtheblankthicknesswasabout4.5ram.Stampingsusedinunexposedplacesoraspartsofsomedeisgnwherefinefinishisnotessentialareusuallymadefromhotrolledsteel.Theautomotivepartproducedinthisdiesetisacoverforatorqueconverter.Aprincipaladvantageofaluminum-killedsteelisitsminimumstrainaging.EXPERIMENTALPROCEDURESAsmentionedearlier,thisresearchinvolvedmonitotingofdieloadswhichweretobeusedinthenumericalmodeltostaldythestructuralcharacteristicsofdies.Theotheradvantageistoavoidoverloadingthediesinpractice.Off-centerloadingcanbedetectedandalsoset-uptimecanbereduced.Thus,anychangesinthethicknessofstock,dullingofthedie,unbalancedloads,oroverloadingscanbedetectedusingdieloadmonitors.StraingagebasedfiatloadcellsmadeofhighgradetoolsteelmaterialwerefabricatedandsuppliedbyIDCCorporation.FouridenticalloadcellswereembeddedinathickrectangularplateasshowninFigure3.Theywerecalibratedbothinthelaboratoryandintheplant.Theplatewasplacedonthetopofthedie.Theknockoutpinslipsthroughtheholeintheplate.Sixsuchplateswereplacedoneachofsixdies.Inthisway,24readingscanbeobtainedatagiventime.Thentheywereshiftedtotheothersixdiesforcompletedata.Allthe12dieloadsarepresentedinTable1.COMPUTATIONALPROCEDURESLinearstaticanalysisusingfiniteelementmethodwasusedtostudytheeffectofsymmetricandasymmetricloadingforthisproblem.Afiniteelementmodelofdiestation4wascreatedusingthegraphicalpreprocessor,PATRAN,andtheanalysiswas