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JournalofMaterialsProcessingTechnology187–1882007690–693AdaptivesystemforelectricallydriventhermoregulationofmouldsforinjectionmouldingˇB.Nardina,∗,B.Zagara,∗,A.Glojeka,D.KriˇajbzaTECOS,ToolandDieDevelopmentCentreofSlovenia,KidriˇevaCesta25,3000Celje,SloveniacbFacultyofElectricalEngineering,Ljubljana,SloveniaAbstractOneofthebasicproblemsinthedevelopmentandproductionprocessofmouldsforinjectionmouldingisthecontroloftemperatureconditionsinthemould.Precisestudyofthermodynamicprocessesinmouldsshowed,thatheatexchangecanbemanipulatedbythermoelectricalmeans.Suchsystemupgradesconventionalcoolingsystemswithinthemouldorcanbeastandaloneapplicationforheatmanipulationwithinit.Inthepaper,theauthorswillpresentresultsoftheresearchproject,whichwascarriedoutinthreephasesanditsresultsarepatentedinA686\2006patent.Thetestingstage,theprototypestageandtheindustrializationphasewillbepresented.Themainresultsoftheprojectweretotalandrapidonlinethermoregulationofthemouldoverthecycletimeandoverallinfluenceonqualityofplasticproductwithemphasisondeformationcontrol.Presentedapplicationcanpresentamilestoneinthefieldofmouldtemperatureandproductqualitycontrolduringtheinjectionmouldingprocess.©2006ElsevierB.V.Allrightsreserved.KeywordsInjectionmouldingMouldcoolingThermoelectricmodulesFEMsimulations1.Introduction,definitionofproblemDevelopmentoftechnologyofcoolingmouldsviathermoelectricalTEMmeansderivesoutoftheindustrialpraxisandproblems,i.e.atdesign,toolmakingandexploitationoftools.Currentcoolingtechnologieshavetechnologicallimitations.TheirlimitationscanbelocatedandpredictedinadvancewithfiniteelementanalysesFEAsimulationpackagesbutnotcompletelyavoided.Resultsofadiversestateoftheartanalysesrevealedthatallexistingcoolingsystemsdonotprovidecontrollableheattransfercapabilitiesadequatetofitintodemandingtechnologicalwindowsofcurrentpolymerprocessingtechnologies.Polymerprocessingisnowadayslimitedintermofshorteningtheproductioncycletimeandwithinthatreducingcostsonlywithheatcapacitymanipulationcapabilities.Otherproductionoptimizationcapabilitiesarealreadydriventomechanicalandpolymerprocessinglimitations3.1.1.ThermalprocessesininjectionmouldingplasticprocessingPlasticprocessingisbasedonheattransferbetweenplasticmaterialandmouldcavity.Withincalculationofheattransferoneshouldconsidertwomajorfactsfirstisallusedenergywhichisbasedonfirstlawofthermodynamicslawofenergyconservation1,secondisvelocityofheattransfer.Basictaskatheattransferanalysesistemperaturecalculationovertimeanditsdistributioninsidestudiedsystem.Thatlastdependsonvelocityofheattransferbetweenthesystemandsurroundingsandvelocityofheattransferinsidethesystem.Heattransfercanbebasedasheatconduction,convectionandradiation1.1.2.CoolingtimeCompleteinjectionmouldingprocesscyclecomprisesofmouldclosingphase,injectionofmeltintocavity,packingpressurephaseforcompensatingshrinkageeffect,coolingphase,mouldopeningphaseandpartejectionphase.Inmostcases,thelongesttimeofallphasesdescribedaboveiscoolingtime.Coolingtimeininjectionmouldingprocessisdefinedastimeneededtocooldowntheplasticpartdowntoejectiontemperature1.∗Correspondingauthors.Tel.3863490920fax38634264612.EmailaddressBlaz.Nardintecos.siB.Nardin.09240136/–seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi10.1016/j.jmatprotec.2006.11.052B.Nardinetal./JournalofMaterialsProcessingTechnology187–1882007690–693691Fig.1.Mouldtemperaturevariationacrossonecycle2.Fig.2.TEMblockdiagram.Themainaimofacoolingprocessistoloweradditionalcoolingtimewhichistheoreticallyneedlessinpraxis,itextendsfrom45upto67ofthewholecycletime1,4.Fromliteratureandexperiments1,4,itcanbeseen,thatthemouldtemperaturehasenormousinfluenceontheejectiontimeandthereforethecoolingtimecosts.InjectionmouldingprocessisacyclicprocesswheremouldtemperaturevariesasshowninFig.1wheretemperaturevariesfromaveragevaluethroughwholecycletime.2.CoolingtechnologyforplasticinjectionmouldsAsitwasalreadydescribed,therearealreadyseveraldifferenttechnologies,enablingtheuserstocoolthemoulds5.Themostconventionalisthemethodwiththedrillingtechnology,i.e.producingholesinthemould.Throughtheseholescoolinglines,thecoolingmediaisflowing,removingthegeneratedandaccumulatedheatfromthemould1,2.Itisalsoveryconvenienttobuildindifferentmaterials,withdifferentthermalconductivitywiththeaimtoenhancecontrolovertemperatureconditionsinthemould.Suchapproachesaresocalledpassiveapproachestowardsthemouldtemperaturecontrol.Thechallengingtaskistomakeanactivesystem,whichcanalterthethermalconditions,regardingtothedesiredaspects,likeproductqualityorcyclestime.OneofsuchapproachesisintegratingthermalelectricalmodulesTEM,whichcanalterthethermalconditionsinthemould,regardingthedesiredproperties.Withsuchapproach,theonecancontroltheheattransferwiththetimeandspacevariable,whatmeans,thatthetemperaturecanberegulatedthroughouttheinjectionmouldingcycle,independentofthepositioninthemould.Theheatcontrolisdonebythecontrolunit,wheretheinputvariablesarereceivedfromthemanualinputortheinputfromtheinjectionmouldingsimulation.Withtheoutputvalues,thecontrolunitmonitorstheTEMmodulebehaviour.2.1.ThermoelectricodulesTEMFortheneedsofthethermalmanipulation,theTEMmodulewasintegratedintomould.InteractionbetweentheheatandelectricalvariablesforheatexchangeisbasedonthePeltiereffect.ThephenomenonofPeltiereffectiswellknown,butitwasuntilnowneverusedintheinjectionmouldingapplications.TEMmoduleseeFig.2isadevicecomposedofproperlyarrangedpairsofPandNtypesemiconductorsthatarepositionedbetweentwoceramicplatesformingthehotandthecoldthermoelectriccoolersites.Powerofaheattransfercanbeeasilycontrolledthroughthemagnitudeandthepolarityofthesuppliedelectriccurrent.2.2.ApplicationformouldcoolingThemainideaoftheapplicationisinsertingTEMmoduleintowallsofthemouldcavityservingasaprimaryheattransferunit.SuchbasicassemblycanbeseeninFig.3.Secondaryheattransferisrealizedviaconventionalfluidcoolingsystemthatallowsheatflowsinandoutfrommouldcavitythermodynamicsystem.DevicepresentedinFig.3comprisesofthermoelectricmodulesAthatenableprimarilyheattransferfromortotemperaturecontrollablesurfaceofmouldcavityB.SecondaryheattransferisenabledviacoolingchannelsCthatdeliverconstanttemperatureconditionsinsidethemould.ThermoelectricmodulesAoperateasheatpumpandassuchmanipulatewithheatderivedtoorfromthemouldbyfluidcoolingsystemC.Systemforsecondaryheatmanipulationwithcoolingchannelsworkasheatexchanger.ToreduceheatcapacityofcontrollableareathermalinsulationDisinstalledbetweenthemouldcavityFandthemouldstructureplatesE.Fig.3.StructureofTEMcoolingassembly.692B.Nardinetal./JournalofMaterialsProcessingTechnology187–1882007690–693Fig.4.Structurefortemperaturedetectionandregulation.ThewholeapplicationconsistsofTEMmodules,atemperaturesensorandanelectronicunitthatcontrolsthecompletesystem.ThesystemisdescribedinFig.4andcomprisesofaninputunitinputinterfaceandasupplyunitunitforelectronicandpowerelectronicsupplyHbridgeunit.Theinputandsupplyunitswiththetemperaturesensorloopinformationareattachedtoacontrolunitthatactsasanexecutionunittryingtoimposepredefinedtemperate/time/positionrelations.UsingthePeltiereffect,theunitcanbeusedforheatingorcoolingpurposes.ThesecondaryheatremovalisrealizedviafluidcoolingmediaseenasheatexchangerinFig.4.Thatunitisbasedoncurrentcoolingtechnologiesandservesasasinkorasourceofaheat.Thisenablescompletecontrolofprocessesintermsoftemperature,timeandpositionthroughthewholecycle.Furthermore,itallowsvarioustemperature/time/positionprofileswithinthecyclealsoforstartingandendingprocedures.Describedtechnologycanbeusedforvariousindustrialandresearchpurposeswhereprecisetemperature/time/positioncontrolisrequired.ThepresentedsystemsinFigs.3and4wereanalysedfromthetheoretical,aswellasthepracticalpointofview.ThetheoreticalaspectwasanalysedbytheFEMsimulations,whilethepracticalonebythedevelopmentandtheimplementationoftheprototypeintorealapplicationtesting.3.FEManalysisofmouldcoolingCurrentdevelopmentofdesigningmouldsforinjectionmouldingcomprisesofseveralphases3.Amongthemisalsodesignandoptimizationofacoolingsystem.ThisisnowadaysperformedbysimulationsusingcustomizedFEMpackagesMoldflow4thatcanpredictcoolingsystemcapabilitiesandespeciallyitsinfluenceonplastic.Withsuchsimulations,moulddesignersgatherinformationonproductrheologyanddeformationduetoshrinkageasellasproductiontimecycleinformation.Thisthermalinformationisusuallyaccuratebutcanstillbeunreliableincasesofinsufficientrheologicalmaterialinformation.ForthehighqualityinputforthethermalregulationofTEM,itisneededtogetapictureaboutthetemperaturedistributionduringthecycletimeandthroughoutthemouldsurfaceandthroughoutthemouldthickness.Therefore,differentprocesssimulationsareneeded.Fig.5.CrosssectionofaprototypeinFEMenvironment.3.1.Physicalmodel,FEManalysisImplementationofFEManalysesintodevelopmentprojectwasdoneduetoauthorslongexperienceswithsuchpackages4andpossibilitytoperformdifferenttestinthevirtualenvironment.WholeprototypecoolingsystemwasdesignedinFEMenvironmentseeFig.5throughwhichtemperaturedistributionineachpartofprototypecoolingsystemandcontactsbetweenthemwereexplored.Forsimulatingphysicalpropertiesinsideadevelopedprototype,asimulationmodelwasconstructedusingCOMSOLMultiphysicssoftware.ResultwasaFEMmodelidenticaltorealprototypeseeFig.7throughwhichitwaspossibletocompareandevaluateresults.FEMmodelwasexploredintermofheattransferphysicstakingintoaccounttwoheatsourcesawaterexchangerwithfluidphysicsandathermoelectricmodulewithheattransferphysicsonlyconductionandconvectionwasanalysed,radiationwasignoredduetolowrelativetemperatureandthereforelowimpactontemperature.BoundaryconditionsforFEManalysesweresetwiththegoaltoachieveidenticalworkingconditionsasinrealtesting.Surroundingairandthewaterexchangerweresetatstabletemperatureof20◦C.Fig.6.TemperaturedistributionaccordingtoFEManalysis.B.Nardinetal./JournalofMaterialsProcessingTechnology187–1882007690–693693Fig.7.Prototypeinrealenvironment.ResultsoftheFEManalysiscanbeseeninFig.6,i.e.temperaturedistributionthroughthesimulationareashowninFig.5.Fig.6representssteadystateanalysiswhichwasveryaccurateincomparisontoprototypetests.Inordertosimulatethetimeresponsealsothetransientsimulationwasperformed,showingverypositiveresultsforfuturework.Itwaspossibletoachieveatemperaturedifferenceof200◦Cinashortperiodoftime5s,whatcouldcauseseveralproblemsintheTEMstructure.Thoseproblemsweresolvedbyseveralsolutions,suchasadequatemounting,choosingappropriateTEMmaterialandapplyingintelligentelectronicregulation.3.2.LaboratorytestngAsitwasalreadydescribed,theprototypewasproducedandtestedseeFig.7.Theresultsareshowing,thatthesetassumptionswereconfirmed.WiththeTEMmoduleitispossibletocontrolthetemperaturedistributionondifferentpartsofthemouldthroughoutthecycletime.Withthelaboratorytests,itwasproven,thattheheatmanipulationcanbepracticallyregulatedwithTEMmodules.Thetestweremadeinthelaboratory,simulatingtherealindustrialenvironment,withtheinjectionmouldingmachineKraussMaffeiKM60C,temperaturesensors,infraredcamerasandtheprototypeTEMmodules.Thetemperatureresponsein1.8svariedform5upto80◦C,whatrepresentsawideareafortheheatcontrolwithintheinjectionmouldingcycle.4.ConclusionsUseofthermoelectricmodulewithitsstraightforwardconnectionbetweentheinputandoutputrelationsrepresentsamilestoneincoolingapplications.Itsintroductionintomouldsforinjectionmouldingwithitsproblematiccoolingconstructionandproblematicprocessingofpreciseandhighqualityplasticpartsrepresentshighexpectations.TheauthorswereassumingthattheuseofthePeltiereffectcanbeusedforthetemperaturecontrolinmouldsforinjectionmoulding.Withtheapproachbasedonthesimulationworkandtherealproductionoflaboratoryequipmentproved,theassumptionswereconfirmed.SimulationresultsshowedawideareaofpossibleapplicationofTEMmoduleintheinjectionmouldingprocess.Withmentionedfunctionalityofatemperatureprofileacrosscycletime,injectionmouldingprocesscanbefullycontrolled.Industrialproblems,suchasuniformcoolingofproblematicAclasssurfacesanditsconsequenceofplasticpartappearancecanbesolved.Problemsoffillingthinlongwallscanbesolvedwithoverheatingsomesurfacesatinjectiontime.Furthermore,withsuchapplicationcontroloverrheologicalpropertiesofplasticmaterialscanbegained.WiththeproperthermalregulationofTEMitwaspossibleeventocontrolthemeltflowinthemould,duringthefillingstageofthemouldcavity.Thisisdonewiththeappropriatetemperaturedistributionofthemouldhighertemperatureonthethinwalledpartsoftheproduct.WiththeapplicationofTEMmodule,itispossibletosignificantlyreducethecycletimeintheinjectionmouldingprocess.Thelimitsofpossibletimereductionliesintheframeof10–25ofadditionalcoolingtime,describeinSection1.2.WiththeapplicationofTEMmoduleitispossibletoactivelycontrolthewarpingoftheproductandtoregulatetheamountofproductwarpageinthewaytoachieverequiredproducttolerances.ThepresentedTEMmodulecoolingapplicationforinjectionmouldingprocessisamatterofprioritynoteforthepatent,heldandownedbyTECOS.Referencesˇc1I.Cati´,Izmjenatoplineukalupimazainjekcijskopreˇanjeplastomera,sDruˇtvoplastiˇaraigumaraca,Zagreb,1985.scˇc2I.Cati´,F.Johannaber,Injekcijskopreˇanjepolimeraiostalihmateriala,sDruˇtvozaplastikuigumu,Bibliotekapolimerstvo,Zagreb,2004.s3B.Nardin,K.Kuzman,Z.Kampuˇ,Injectionmouldingsimulationresultssasaninputtotheinjectionmouldingprocess,inAFDM2002TheSecondInternationalConferenceonAdvancedFormingandDieManufacturingTechnology,Pusan,Korea,2002.4TECOS,SlovenianToolandDieDevelopmentCentre,MoldflowSimulationProjects1996–2006.5S.C.Chen,etal.,Rapidmoldsurfaceheating/coolingusingelectromagneticinductiontechnologyANTEC2004,ConferenceCDROM,Chicago,Illinois,16–20May,2004.