注塑模具毕业设计外文翻译3.docx

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注塑模具毕业设计外文翻译3

Integratedsimulationoftheinjectionmoldingprocesswithstereolithographymolds

AbstractFunctionalpartsareneededfordesignverificationtesting,fieldtrials,customerevaluation,andproductionplanning.Byeliminatingmultiplesteps,thecreationoftheinjectionmolddirectlybyarapidprototyping（RP）processholdsthebestpromiseofreducingthetimeandcostneededtomoldlow-volumequantitiesofparts.ThepotentialofthisintegrationofinjectionmoldingwithRPhasbeendemonstratedmanytimes.WhatismissingisthefundamentalunderstandingofhowthemodificationstothemoldmaterialandRPmanufacturingprocessimpactboththemolddesignandtheinjectionmoldingprocess.Inaddition,numericalsimulationtechniqueshavenowbecomehelpfultoolsofmolddesignersandprocessengineersfortraditionalinjectionmolding.Butallcurrentsimulationpackagesforconventionalinjectionmoldingarenolongerapplicabletothisnewtypeofinjectionmolds,mainlybecausethepropertyofthemoldmaterialchangesgreatly.Inthispaper,anintegratedapproachtoaccomplishanumericalsimulationofinjectionmoldingintorapid-prototypedmoldsisestablishedandacorrespondingsimulationsystemisdeveloped.Comparisonswithexperimentalresultsareemployedforverification,whichshowthatthepresentschemeiswellsuitedtohandleRPfabricatedstereolithography（SL）molds.

KeywordsInjectionmoldingNumericalsimulationRapidprototyping

1Introduction

Ininjectionmolding,thepolymermeltathightemperatureisinjectedintothemoldunderhighpressure[1].Thus,themoldmaterialneedstohavethermalandmechanicalpropertiescapableofwithstandingthetemperaturesandpressuresofthemoldingcycle.Thefocusofmanystudieshasbeentocreatethe

injectionmolddirectlybyarapidprototyping（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.Commerciallyavailablesimulationpackagesofthetraditionalinjectionmoldingprocesshavenowbecomeroutinetoolsofthemolddesignerandprocessengineer[2].Unfortunately,currentsimulationprogramsforconventionalinjectionmoldingarenolongerapplicabletoRPmolds,becauseofthedramaticallydissimilartoolmaterial.Forinstance,inusingtheexistingsimulationsoftwarewithaluminumandSLmoldsandcomparingwithexperimentalresults,thoughthesimulationvaluesofpartdistortionarereasonableforthealuminummold,resultsareunacceptable,withtheerrorexceeding50%.Thedistortionduringinjectionmoldingisduetoshrinkageandwarpageoftheplasticpart,aswellasthemold.Forordinarilymolds,themainfactoristheshrinkageandwarpageoftheplasticpart,whichismodeledaccuratelyincurrentsimulations.ButforRPmolds,thedistortionofthemoldhaspotentiallymoreinfluence,whichhavebeenneglectedincurrentmodels.Forinstance,[3]usedasimplethree-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.

2Integratedsimulationofthemoldingprocess

2.1Methodology

InordertosimulatetheuseofanSLmoldintheinjectionmoldingprocess,aniterativemethodisproposed.Differentsoftwaremoduleshavebeendevelopedandusedtoaccomplishthistask.ThemainassumptionisthattemperatureandloadboundaryconditionscausesignificantdistortionsintheSLmold.Thesimulationstepsareasfollows:

1Thepartgeometryismodeledasasolidmodel,whichistranslatedtoafilereadablebytheflowanalysispackage.

2Simulatethemold-fillingprocessofthemeltintoaphotopolymermold,whichwilloutputtheresultingtemperatureandpressureprofiles.

3Structuralanalysisisthenperformedonthephotopolymermoldmodelusingthethermalandloadboundaryconditionsobtainedfromthepreviousstep,whichcalculatesthedistortionthatthemoldundergoduringtheinjectionprocess.

4Ifthedistortionofthemoldconverges,movetothenextstep.Otherwise,thedistortedmoldcavityisthenmodeled（changesinthedimensionsofthecavityafterdistortion）,andreturnstothesecondsteptosimulatethemeltinjectionintothedistortedmold.

5Theshrinkageandwarpagesimulationoftheinjectionmoldedpartisthenapplied,whichcalculatesthefinaldistortionsofthemoldedpart.

Inabovesimulationflow,therearethreebasicsimulationmodules.

2.2Fillingsimulationofthemelt

2.2.1Mathematicalmodeling

Computersimulationtechniqueshavehadsuccessinpredictingfillingbehaviorinextremelycomplicatedgeometries.However,mostofthecurrentnumericalimplementationisbasedonahybridfinite-element/finite-differencesolutionwiththemiddleplanemodel.TheapplicationprocessofsimulationpackagesbasedonthismodelisillustratedinFig.2-1.However,unlikethesurface/solidmodelinmold-designCADsystems,theso-calledmiddle-plane（asshowninFig.2-1b）isanimaginaryarbitraryplanargeometryatthemiddleofthecavityinthegap-wisedirection,whichshouldbringaboutgreatinconvenienceinapplications.Forexample,surfacemodelsarecommonlyusedincurrentRPsystems（generallySTLfileformat）,sosecondarymodelingisunavoidablewhenusingsimulationpackagesbecausethemodelsintheRPandsimulationsystemsaredifferent.Consideringthesedefects,thesurfacemodelofthecavityisintroducedasdatumplanesinthesimulation,insteadofthemiddle-plane.

Accordingtothepreviousinvestigations[4–6],fillinggoverningequationsfortheflowandtemperaturefieldcanbewrittenas:

wherex,yaretheplanarcoordinatesinthemiddle-plane,andzisthegap-wisecoordinate;u,v,warethevelocitycomponentsinthex,y,zdirections;u,varetheaveragewhole-gapthicknesses;andη,ρ,CP（T）,K（T）representviscosity,density,specificheatandthermalconductivityofpolymermelt,respectively.

Fig.2-1a–d.Schematicprocedureofthesimulationwithmiddle-planemodel.aThe3-DsurfacemodelbThemiddle-planemodelcThemeshedmiddle-planemodeldThedisplayofthesimulationresult

Inaddition,boundaryconditionsinthegap-wisedirectioncanbedefinedas:

whereTWistheconstantwalltemperature（showninFig.2a）.

CombiningEqs.1–4withEqs.5–6,itfollowsthatthedistributionsoftheu,v,T,Patzcoordinatesshouldbesymmetrical,withthemirroraxisbeingz=0,andconsequentlytheu,vaveragedinhalf-gapthicknessisequaltothataveragedinwholegapthickness.Basedonthischaracteristic,wecandividethewholecavityintotwoequalpartsinthegap-wisedirection,asdescribedbyPartIandPartIIinFig.2b.Atthesametime,triangularfiniteelementsaregeneratedinthesurface（s）ofthecavity（atz=0inFig.2b）,insteadofthemiddle-plane（atz=0inFig.2a）.Accordingly,finite-differenceincrementsinthegapwisedirectionareemployedonlyintheinsideofthesurface（s）（walltomiddle/center-line）,which,inFig.2b,meansfromz=0toz=b.Thisissingle-sidedinsteadoftwo-sidedwithrespecttothemiddle-plane（i.e.fromthemiddle-linetotwowalls）.Inaddition,thecoordinatesystemischangedfromFig.2atoFig.2btoalterthefinite-element/finite-differencescheme,asshowninFig