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外文翻译--对通过塑料注射成型零件的选择性激光融化生产得到的功能梯度材料插入棒的评估 英文版.pdf

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外文翻译--对通过塑料注射成型零件的选择性激光融化生产得到的功能梯度材料插入棒的评估 英文版.pdf

EvaluatingtheuseoffunctionallygradedmaterialsinsertsproducedbyselectivelasermeltingontheinjectionmouldingofplasticspartsVEBeal1,PErasenthiran2,CHAhrens1,andPDickens21UniversidadeFederaldeSantaCaterina,Floriano´polis,Brazil2WolfsonSchoolofMechanicalEngineering,LoughboroughUniversity,Loughborough,UKThemanuscriptwasreceivedon19October2006andwasacceptedafterrevisionforpublicationon9March2007.DOI10.1243/09544054JEM764AbstractThedemandforproductivityandshapecomplexityontheinjectionmouldingindustrynecessitatesnewresearchtoimprovetooldesign,material,andmanufacturing.AresearchfieldisthedevelopmentoffunctionallygradedmaterialsFGMstobuildinjectionmoulds.Forexample,mouldsbuiltwiththeFGMstechniquecanhavedistinctiveregionswithhigherheatconduction.Higherratesofheattransfersfromthickerregionsoftheinjectedpartcanbeusefultoproducebetterandcheaperinjectionmouldedpolymerparts.Itispossibletoobtainmouldswithdifferentialconductivitybyaddinglocally,duringthefabricationofthemould,coppertothemouldbasematerialsuchastoolsteel.Inthiswork,aninvestigationintotheeffectofFGMcopperCutoolsteelmouldinsertoverpolymerinjectedpartsispresented.TheworkisdividedintwopartsanumericalthermalanalysiscomparisonbetweenCutoolsteelgradedandtoolsteelinsertsandaninjectionmouldingexperimentwithcomparisonsbetweenmouldsurfacetemperatureanddegreeofcrystallinityofpolypropyleneparts.Thenumericalmodelwasusedtocomparedifferentbehaviourofthemouldheattransferaccordingtothemouldinsertmaterial.Thereafter,abolsterwasbuilttoholdFGMsandtoolsteelinsertsobtainedbyaselectivelaserfusionprocess.Polypropylenewasinjectedovertheinsertstocomparewiththenumericresults.Toobservetheeffectofthecoolingrateinthepolypropylenepartsusingthegradedinserts,thedegreeofcrystallinityofthepartswasmeasuredbydifferentialscanningcalorimetryDSCtest.Thetemperatureofthemouldwasalsoevaluatedduringtheinjectioncycles.TheresultsshowedthatthegradedCutoolsteelinsertstestedhadlowercapacitytostoreheatenergy.AsCuwasaddedtothetoolsteel,themixtureprovedtotransferheatmoreefficientlybutithadlesscapacitytoabsorbheat.Keywordsfunctionallygradedmaterials,injectionmoulding,rapidmanufacturing,polypropylenecrystallinity1INTRODUCTIONThebenefitofinjectionmouldedpartsdependsonthreegeneralaspectstoolcost,injectionmouldingrawmaterial,andproductivityofthetool.Thistriomakesitdifficulttochangepart/moulddesignwithoutaffectingproductivityandmaterial.Hence,durabilityofthetool,productivity,andcostsmustbeachievedbytheoptimalmaterialrawselectionandpartandmoulddesigns1.Unfortunately,therearerestraintsthatmakeitdifficulttofindthebestcompromisingsolution.Asthecomplexityofamoderninjectionmouldishigh,themoulddesignersconcernishowtosolidifythepartwithoutcausingdistortionsandkeepingthemouldwithhighratesofpartsproducedperhour.Acomplexchannelsnetworkisdesignedtoenablecoolingliquidtoextracttheheatfromthemould.Thedesignofthechannelsisdifficultasitisnecessarytokeeptheejectionsysteminplace.CorrespondingauthorEngenhariaMecaˆnica–CIMJECT,UniversidadeFederaldeSantaCatarina,CaixaPostal476,CampusUniversita´rio–Trindade,Floriano´polis,SantaCatarina88040900,Brazil.emailvalterbealgmail.comJEM764C211IMechE2007Proc.IMechEVol.221PartBJ.EngineeringManufacture945Ejectorpins,slides,andairstreamgatesareusedtoejectthepartfromthemouldcavityavoidingmarksintheaestheticsideofthepart.Dependingonthecomplexityandshapeofthepart,thespaceleftbythecoolingsystemissmallanditisnotfeasibletomanufacturewithoutleavingmarksinthemouldimpression.Inmanycases,whentheheatextractionequilibriumforhomogeneouslyextractingtheheatfromcavityandproductivityarenotachieved,itmightbenecessarytoredesignthepartgeometrytofitmouldlimitations.Analternativetosolvecomplexthermalissuesistheuseofcopper–berylliumCu–Beinserts1.AsCu–Beinsertshavehigherthermalconductivitythantheusualsteelalloys,theyareusedtoextractheatfromregionswherethecoolingchannelsdonothaveaneffectduringtheinjectionmouldingcycles.Nevertheless,theyarenotenvironmentallyfriendly,asberylliumiscitedasahighlycarcinogenicelement2.Anotherlimitationisthatinsertsinthemouldimpressionmightleavemarksinthepartasthemouldsurfacehasavisibleinterfacebetweenthebasematerialandtheinsert.Inaddition,theinsertfeaturesthatareneededtoattachittothebasecontributetoreducingthespaceleftforthecoolingchannels.Inthemid1980s,newmanufacturingtechnologiesknownasSFFsolidfreeformfabricationemerged3.Themaindifferenceofthesetechnologies,asopposedtothetraditionalones,wasthattheywerebasedonthelayeradditiveprinciple.AlsoknownasrapidprototypingRP,thesetechnologiescanproducepartsinlowvolumeproductioninvirtuallyanyformormaterial.Thevarietyofavailablematerialsislimitedhowever,RPprocessescanbuildpartsinmetals,ceramics,andpolymers3.RPtechnologiesarehighlyautomatedandtheyarealsocalledthreedimensional3Dprintersasthemachinesalmostprintsolidpartsfromdatageneratedfromcomputersoftware.Designersandengineerscanbuildandverifydesignedpartswithoutmisunderstandings,inaccuracies,anddelays.ThebasicprincipleofRPtechnologiesistobuild,layerbylayer,materialcorrespondingtothedataofthedesignedpart.Rawmaterialscanbeliquidresins,wires,pastes,powders,andsheets.Thewaytoshapethesematerialsandbondlayerscanbediverseincludingultravioletlasers,lamps,powerlasers,sprayofglue,depositionoffusedmaterial,andothers.TheseadditivelayeredmanufacturingtechnologiesLMTshavealsobeenusedtoproducetoolsforinjectionmoulding.Dependingonthetechnologyandmaterialusedinconstruction,thecomplexityofthemouldimpressioninjectedpart,andtheinjectedmaterial,thesemouldscanbecompetitivetotraditionalcast/milledmoulds.Itispossibletobuildmouldsfrom12to10000partsaccordingtothetechnology,material,andapplication4,5.OneinterestingtechniqueusedwithSFFtobuildinjectionmouldsisconformalcoolingchannels.Thechannelsaredesignedinthemouldimpressionwithouttheconcernsofthelimitationsfromthetraditionalmanufacturingmethod.Theconformalcoolingchannelsmightfollowthemouldimpressionsurface,passingbytheejectorsystemwithfewerlimitationsthantheusualmoulds.Unfortunately,theyarestilllimitedbytheejectionsystemandsomepartfeaturessuchasdeepgrovesmightnotbeaffectedbythecoolingcapabilitiesofthechannels.Toovercomesomeoftheseconstraints,itispossibletousefunctionallygradedmaterialsFGMstobuildinjectionmouldsbySFFtechnologies.FGMshavebeenthesubjectofresearchforthelast25years6.Mostofthenaturalmaterialssuchasmineralsandtissueshaveagradualchangefromonefunctionalregiontoanother.Thisexampleofnatureinspiresintegratedformandfunctiondesignallinthesamecomponent/unit.FGMisnotcompletelynewtothemanufacturingprocesses,butitwasonlyafterthe1980sthatitstartedtoreceivemoreattentionandtobeclassifiedasaspecificresearchsubject.ThebasicideaofFGMistoimprovethepropertiesofthepartbyvaryingthequantityofaningredientinspecificregionsinordertoachievedifferentialproperties.Aningredientcouldbeabasicelementsuchascarbonbeingusedtoincreasethehardnessofasteelpartonlyatthesurface.Anotherexampleistheporosityvariationfromtheoutsidetotheinsideofthemammalsbones.Thelowporosityfromtheoutsideincreasesthestiffnessofthebonebutprovidesinterconnectivitytotheinside.Thecoreoftheboneisporous,therebyallowingweightefficiency.Byusingthisvariationfromonematerialtoanother,optimizedcomponentscanbeobtained.Reducednumberofjointsandfasteners,weightreduction,structuralenhancement,differentialheatextraction,thermalbarriers,embeddedsensors,andbiocompatibleimplantsaresomeofthepotentialadvantagesofusingFGM6–8.FGMsalsocouldgraduallyjoindissimilarmaterialswithdifferentpropertiesinthesamecomponent.Theprincipleissimilartocompositematerials.Thedifferenceisthatcompositeshavedistinctivephasesanddonotvarytheircompositioninthevolumeofthecomponent.DespitetheideaofFGMsbeingverysimple,mostofthepotentialFGMapplicationsarerestrictedtotechnologicallimitationsandhighcost.DifficultiesincontrollinganddepositingthegradientcompositionandproducingcomplexshapeswithcomputeraideddesignCAD,computeraidedmanufacturingCAM,andfiniteelementanalysisFEAintegrationaresomeofthecausesforrestrictionsofuse.TheuseofRPtechnologiestoproduceFGMpartshasbeeninvestigatedbymanyresearchers9.SinceRPtechnologiescanproducefreeformpartsandcanhandledifferentmaterials,itispossibletousethem946VEBeal,PErasenthiran,CHAhrens,andPDickensProc.IMechEVol.221PartBJ.EngineeringManufactureJEM764C211IMechE2007toproduceFGMcomponents.MostoftheresearchersinvestigatingthefabricationofFGMbyLMTsprocessthematerialswiththeheatsourcedeliveredbyalaserbeam.Aslaserscanbeeasilyautomatedandcandeliverhighenergydensitieswithprecisionandspeed,theycanprocessalmostanymaterial10.AnotheraspectofFGMandRPisthefrequentuseofmaterialsintheformofpowdertobefusedorpresinteredunderalaserspot.ThemainissueforusingrapidprocessingandmanufacturingtechnologiesforproducingFGMpartsisthelocalcompositioncontrolLCC.Thisregardstheprincipleforaddingandjoiningthematerialsbycontrollingtheirpercentagesoneachregionofthepartorlayers.Someresearchers11,12usedminiaturehoppernozzlesandcapillarytubestocontrolthedepositionofpowdersinthelayer.Enszetal.13studiedtheoptimizationoftwopowderflowsinthelaserengineeringnetshapingLENSC212processtobuildgradientsfromH13toM300steelalloys.Inaddition,computationalmethodstorepresentthegradedgeometryhavebeenthesubjectofstudy.Choetal.14investigatedtheLLCforthe3Dprintingprocessafterobtaininggeometryandmaterialdatafromfiniteelementandvoxelspacegeometries.Bythismethod,itwaspossibledigitallytorepresentthe3Dpartwithdifferentvolumetricgradients.TheideaofaddinganextrafunctionalmaterialtoabasematerialtoproduceaFGMinjectionmouldhasbeenresearchedinpreviouswork15.AmulticompartmenthopperwasusedtoproducegradedstructuresofH13toolsteelandCu.TheH13iscommonlyusedasmaterialforinjectionmouldsasithasdimensionalstability,toughness,andwearresistanceathightemperature.NeverthelesstheheatconductionofthismaterialislowcomparedwithCukH1324.3W/mKkCu385W/mK16,17.ElementalCupowderwasmixedwithH13inproportionsof12.5,25,37.5,and50wttoproduceFGMbars.Themethodforproducingthesebarswastheselectivelaserfusion/meltingSLForSLMusingahighpowderNdYAGpulsedlaser.Thelaserprocessedthemulticompositionpowderbedthatwaspreviouslyloadedwithpowdersfromthemulticompartmenthopper.Asthelaserscannedthepowderbed,thepowderwasfusedandbondedtothepreviousaddedlayers.Afterprocessingalayer,thepowderbedwasloweredandthepowderswerespreadoverthepreviouslayerandthelaserwassettofusethepowdertoformanewlayer.Thisprocesswasnumericallycontrolledandcontinueduntilthecompletionofthepart.Thefusionprocess,usingthislaser,leftaroughsuperficialaspectandrequiredsomepostprocessingincludingtheremovalofthesubstratethatwasusedtobondthefirstlayersoftheparttothepowderbedplatform.Attheendoftheprocess,gradedpartsofH13andCucouldbeobtained.Therefore,FGMscouldbeusedoninjectionmouldstocreatehighheatconductivityregionstoimproveheatextraction.Asthecooling/heatingchannelscanbelimitedbymanufacturabilityandtheejectorsystem,someregionsoftheimpressioncouldbeoverheated.Thisdifferentialheatextractionfromthepartmightcausewarpage,sinkandcoldweldingmarks,andpoorsurfacequality,andcouldreducetheproductionrateofthepart.AnotherapplicationofFGMonmouldsistobuildthecavityedgeswithgradientsoftoolsteelandtungstencarbide.Thiscouldimprovethepartqualitybyreducingdefectssuchasflashingcausedbywearinthemouldedges1.TheuseofFGMtoobtainperformanceinjectionmouldswasoneofthestimuliforthisresearch.Despitethelimitationsofthelaserandlayerdepositionsystemsusedinthiswork,theseexperimentswereplannedtoevaluatetheinfluenceoftheCuadditiontotheH13matrix.TheeffectoftheadditionofCuonthemouldtemperatureandontheinjectedpolymerpartcrystallinitydegree,comparedwiththeH13basematerial,wasanalysed.Intheory,theadditionofCuwouldincreasethethermalconductivityofthemould.Theworkwasdividedintwopartsnumericalmodellingoftheheattransferandexperimentalinjectionmoulding.Thefirstpartpresentsthenumericalmodeloftheheattransferfromtheinjectedparttothemouldandthemetallicinserts.Themodelevaluatedthetemperaturetimestamp,simulatingmouldinsertsindifferentmaterialsH13,Cu,andH13þ50Cu.Intheinjectionmouldingexperiment,FGMbarsmouldinsertsweremanufacturedbylaserfusionandplacedinastereolithographySLmould.PolypropylenePPpartswereproducedbyinjectingthepolymeroverthesemetallicinserts.TwooutputswereanalysedfromthisexperimenttemperatureofthemouldsurfaceandcrystallinitydegreeofthePPparts.Thetemperatureofthemouldwasmeasuredbythermocouplesintheexactsamepositiontakeninthenumericalmodel.Thedegreeofcrystallinityoftheparts,mouldedwithdifferentinserts,wasanalysedbydifferentialscanningcalorimetryDSC.TheDSCtestwasperformedtoidentifyifthepartsmouldedoverdifferentinsertshaddifferentcoolingrates.Asaconsequence,thedegreeofcrystallinityofthepartscouldbedifferenttoo.Thelowerthecoolingrate,thegreateristheorganizationofthepolymerchainsreflectinginthecrystallinitydegreeofthePP.Arapidcoolingratehelpsthepolymertoholdanamorphousstructure.Whenheatingaplastic,moreheatwillbenecessarytodissolvethecrystalsmorestableandlowerenergystateuntiltheplasticiscompletelymelted.ThisphenomenoncanbeseenintheDSCcurvesmeasuringtheenergyabsorbedbythesamplebeforemelting18.Evaluatingtheuseoffunctionallygradedmaterialsinserts947JEM764C211IMechE2007Proc.IMechEVol.221PartBJ.EngineeringManufacture2METHODOLOGY2.1NumericalmodelTheinjectionmouldingcycleisatransientphenomenaandthermalconductivityisnottheonlymaterialpropertythatcountswhenanalysingtheheattransfer.Densityandspecificheatcapacityalsodeterminethecapabilityofthematerialtostoreortotransportenergy19.Consideringvolumecontrol,theenergystateisobtainedbythebalanceoftheenergythatisabsorbed,generated,andlost.Thisvariationoftheenergyaccumulatedbythemassinsidethevolumecanbemodelledbyequation1.Theenergythatenters_Einplustheenergygenerated_Egeninsidethevolumeminustheenergylost_EouttothesurroundingsisequaltothevariationofenergyEofthemassinsidethevolumewithrespecttotimet._EinC0_Eoutþ_Egen¼dEdtC12C12C12C12vcð1ÞInthecaseofamould,inthemomentsafterthemeltedmaterialfillsthemouldimpression,thereisnoheatgeneratedindefinedvolumecontrol.Consideringtheheattransferinonedirection,equation1becomesfurthersimplifiedfortheheatfluxthroughanareaA,generatingequation2.Simplifyingthearea,equation3isgenerated.Intheseequations,q00representstheheatfluxes,risthematerialdensity,cpsymbolizesthespecificheat,Tisthetemperature,andxistheaxisofthedirectionoftheheatflux.qin00AC0qout00Aþ0¼ZxrcpTtAdxð2Þqin00C0qout00¼ZxrcpTtdxð3ÞThetemperatureinthemould,awayfromtheimpression,couldbeconsideredconstant.Takingthisintoconsideration,inaveryshortperiodtheheatfluxescanbeconsideredconstantandcanbedescribedasinequation4,wherekistheheatconductioncoefficient.q00¼kTxC12C12C12C12xð4ÞThereisnoeasysolutionforsolvingequations3and4andanumericalmodelisusuallynecessarytosolvethemforcomplexshapes.Atwodimensional2DmodelofaninjectionmouldedpartinsideaSLmouldincontactwithametallicinsertisshowninFig.1.Thismodelconsiderednocontactresistancebetweentheparts,moulds,andinsertsurfaces.TheinitialconditionswerethatthetemperatureinthenodesinsidetheareathatrepresentsthehotPPinjectedpartwas195˚Candthetemperatureforallothernodes,includingtheconnectednodesofthepartwithotherareas,was20˚C.Temperaturewascalculatedbyemployingaquadrangularmeshformedbyplanarfournodeelements.ThenodeschosentobeanalysedareindicatedinFig.1.Thermocoupletemperature,Ttc,matchedthesamepositionintheexperimentalworkandinsertsurfacetemperature,Tis,matchedtheregionfromwhereDSCsamplesweretakeninthePPpart.ThemodelandanalysiswereperformedusingAnsyssoftware.Forinputtingthematerialpropertiesdensity,specificheat,andthermalconductivityinthenumericalmodel,tabledvalueswereusedfortheH1316.However,theH13þ50percentmaterialpropertiesvalueswereestimatedbasedontheVoightandReussrulesofmixtures5,6.ThebasicruleofmixturesVoightispresentedinequation5.Anequivalentproperty«ofthemixtureformedbyaandbphasesiscalculatedbythesummationofthepropertyofeachphaseandthevolumefractionVofthephasesinthemixture,resultinginalinearvariationbetweeneachphasevalueproperty.Thesecondruleexpressedinequation6ismoreelaborate,butneitherrulecountsthephaseinteraction,phasegeometry,spacedistribution,andotherfactorsthataffectthefinalpropertyofthemixture.Nevertheless,thesecondruleismoreconservativethanthefirstone.ThematerialpropertiesusedinthenumericalmodelarepresentedinTable1.Voight¼VaaþVbbð5ÞReuss¼baVabþVbað6ÞIntotal,sixsimulationsofthetimeversustemperatureinthenodesTtcandTisrefertoFig.1weremadeusingdifferentinsertmaterialsspecifiedinTable1.ThefirstfoursimulationswereperformedFig.12DmodelfortheheattransferofaninjectedpartincontactwithametallicinsertinaSLmouldinitialtemperatureindicatedforeachareaofthemodel948VEBeal,PErasenthiran,CHAhrens,andPDickensProc.IMechEVol.221PartBJ.EngineeringManufactureJEM764C211IMechE2007

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