IntegratedsimulationoftheinjectionmoldingprocesswithstereolithographymoldsAbstractFunctionalpartsareneededfordesignverificationtesting,fieldtrials,customerevaluation,andproductionplanning.Byeliminatingmultiplesteps,thecreationoftheinjectionmolddirectlybyarapidprototyping(RP)processholdsthebestpromiseofreducingthetimeandcostneededtomoldlow-volumequantitiesofparts.ThepotentialofthisintegrationofinjectionmoldingwithRPhasbeendemonstratedmanytimes.WhatismissingisthefundamentalunderstandingofhowthemodificationstothemoldmaterialandRPmanufacturingprocessimpactboththemolddesignandtheinjectionmoldingprocess.Inaddition,numericalsimulationtechniqueshavenowbecomehelpfultoolsofmolddesignersandprocessengineersfortraditionalinjectionmolding.Butallcurrentsimulationpackagesforconventionalinjectionmoldingarenolongerapplicabletothisnewtypeofinjectionmolds,mainlybecausethepropertyofthemoldmaterialchangesgreatly.Inthispaper,anintegratedapproachtoaccomplishanumericalsimulationofinjectionmoldingintorapid-prototypedmoldsisestablishedandacorrespondingsimulationsystemisdeveloped.Comparisonswithexperimentalresultsareemployedforverification,whichshowthatthepresentschemeiswellsuitedtohandleRPfabricatedstereolithography(SL)molds.KeywordsKKKInjectionmoldingNumericalsimulationRapidprototyping1IntroductionIninjectionmolding,thepolymermeltathightemperatureisinjectedintothemoldunderhighpressure1.Thus,themoldmaterialneedstohavethermalandmechanicalpropertiescapableofwithstandingthetemperaturesandpressuresofthemoldingcycle.Thefocusofmanystudieshasbeentocreatetheinjectionmolddirectlybyarapidprototyping(RP)process.Byeliminatingmultiplesteps,thismethodoftoolingholdsthebestpromiseofreducingthetimeandcostneededtocreatelow-volumequantitiesofpartsinaproductionmaterial.ThepotentialofintegratinginjectionmoldingwithRPtechnologieshasbeendemonstratedmanytimes.ThepropertiesofRPmoldsareverydifferentfromthoseoftraditionalmetalmolds.Thekeydifferencesarethepropertiesofthermalconductivityandelasticmodulus(rigidity).Forexample,thepolymersusedinRP-fabricatedstereolithography(SL)moldshaveathermalconductivitythatislessthanonethousandththatofanaluminumtool.InusingRPtechnologiestocreatemolds,theentiremolddesignandinjection-moldingprocessparametersneedtobemodifiedandoptimizedfromtraditionalmethodologiesduetothecompletelydifferenttoolmaterial.However,thereisstillnotafundamentalunderstandingofhowthemodificationstothemoldtoolingmethodandmaterialimpactboththemolddesignandtheinjectionmoldingprocessparameters.Onecannotobtainreasonableresultsbysimplychangingafewmaterialpropertiesincurrentmodels.Also,usingtraditionalapproacheswhenmakingactualpartsmaybegeneratingsub-optimalresults.Sothereisadireneedtostudytheinteractionbetweentherapidtooling(RT)processandmaterialandinjectionmolding,soastoestablishthemolddesigncriteriaandtechniquesforanRT-orientedinjectionmoldingprocess.Inaddition,computersimulationisaneffectiveapproachforpredictingthequalityofmoldedparts.Commerciallyavailablesimulationpackagesofthetraditionalinjectionmoldingprocesshavenowbecomeroutinetoolsofthemolddesignerandprocessengineer2.Unfortunately,currentsimulationprogramsforconventionalinjectionmoldingarenolongerapplicabletoRPmolds,becauseofthedramaticallydissimilartoolmaterial.Forinstance,inusingtheexistingsimulationsoftwarewithaluminumandSLmoldsandcomparingwithexperimentalresults,thoughthesimulationvaluesofpartdistortionarereasonableforthealuminummold,resultsareunacceptable,withtheerrorexceeding50%.Thedistortionduringinjectionmoldingisduetoshrinkageandwarpageoftheplasticpart,aswellasthemold.Forordinarilymolds,themainfactoristheshrinkageandwarpageoftheplasticpart,whichismodeledaccuratelyincurrentsimulations.ButforRPmolds,thedistortionofthemoldhaspotentiallymoreinfluence,whichhavebeenneglectedincurrentmodels.Forinstance,3usedasimplethree-stepsimulationprocesstoconsiderthemolddistortion,whichhadtoomuchdeviation.Inthispaper,basedontheaboveanalysis,anewsimulationsystemforRPmoldsisdeveloped.Theproposedsystemfocusesonpredictingpartdistortion,whichisdominatingdefectinRP-moldedparts.ThedevelopedsimulationcanbeappliedasanevaluationtoolforRPmolddesignandprocessoptimization.Oursimulationsystemisverifiedbyanexperimentalexample.AlthoughmanymaterialsareavailableforuseinRPtechnologies,weconcentrateonusingstereolithography(SL),theoriginalRPtechnology,tocreatepolymermolds.TheSLprocessusesphotopolymerandlaserenergytobuildapartlayerbylayer.UsingSLtakesadvantageofboththecommercialdominanceofSLintheRPindustryandthesubsequentexpertisebasethathasbeendevelopedforcreatingaccurate,high-qualityparts.Untilrecently,SLwasprimarilyusedtocreatephysicalmodelsforvisualinspectionandform-fitstudieswithverylimitedfunctionalapplications.However,thenewergenerationstereolithographicphotopolymershaveimproveddimensional,mechanicalandthermalpropertiesmakingitpossibletousethemforactualfunctionalmolds.2Integratedsimulationofthemoldingprocess2.1MethodologyInordertosimulatetheuseofanSLmoldintheinjectionmoldingprocess,aniterativemethodisproposed.Differentsoftwaremoduleshavebeendevelopedandusedtoaccomplishthistask.ThemainassumptionisthattemperatureandloadboundaryconditionscausesignificantdistortionsintheSLmold.Thesimulationstepsareasfollows:1Thepartgeometryismodeledasasolidmodel,whichistranslatedtoafilereadablebytheflowanalysispackage.2Simulatethemold-fillingprocessofthemeltintoaphotopolymermold,whichwilloutputtheresultingtemperatureandpressureprofiles.3Structuralanalysisisthenperformedonthephotopolymermoldmodelusingthethermalandloadboundaryconditionsobtainedfromthepreviousstep,whichcalculatesthedistortionthatthemoldundergoduringtheinjectionprocess.4Ifthedistortionofthemoldconverges,movetothenextstep.Otherwise,thedistortedmoldcavityisthenmodeled(changesinthedimensionsofthecavityafterdistortion),andreturnstothesecondsteptosimulatethemeltinjectionintothedistortedmold.5Theshrinkageandwarpagesimulationoftheinjectionmoldedpartisthenapplied,whichcalculatesthefinaldistortionsofthemoldedpart.Inabovesimulationflow,therearethreebasicsimulationmodules.2.2Fillingsimulationofthemelt2.2.1MathematicalmodelingInordertosimulatetheuseofanSLmoldintheinjectionmoldingprocess,aniterativemethodisproposed.Differentsoftwaremoduleshavebeendevelopedandusedtoaccomplishthistask.ThemainassumptionisthattemperatureandloadboundaryconditionscausesignificantdistortionsintheSLmold.Thesimulationstepsareasfollows:1.Thepartgeometryismodeledasasolidmodel,whichistranslatedtoafilereadablebytheflowanalysispackage.2.Simulatethemold-fillingprocessofthemeltintoaphotopolymermold,whichwilloutputtheresultingtemperatureandpressureprofiles.3.Structuralanalysisisthenperformedonthephotopolymermoldmodelusingthethermalandloadboundaryconditionsobtainedfromthepreviousstep,whichcalculatesthedistortionthatthemoldundergoduringtheinjectionprocess.4.Ifthedistortionofthemoldconverges,movetothenextstep.Otherwise,thedistortedmoldcavityisthenmodeled(changesinthedimensionsofthecavityafterdistortion),andreturnstothesecondsteptosimulatethemeltinjectionintothedistortedmold.5.Theshrinkageandwarpagesimulationoftheinjectionmoldedpartisthenapplied,whichcalculatesthefinaldistortionsofthemoldedpart.Inabovesimulationflow,therearethreebasicsimulationmodules.2.2Fillingsimulationofthem