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JournalofMaterialsProcessingTechnology187188(2007)690693AdaptivesystemforelectricallydriventhermoregulationofmouldsforinjectionmouldingB.Nardina,B.Zagara,A.Glojeka,D.KriajbzaTECOS,ToolandDieDevelopmentCentreofSlovenia,KidrievaCesta25,3000Celje,SloveniacbFacultyofElectricalEngineering,Ljubljana,SloveniaAbstractOneofthebasicproblemsinthedevelopmentandproductionprocessofmouldsforinjectionmouldingisthecontroloftemperaturecon-ditionsinthemould.Precisestudyofthermodynamicprocessesinmouldsshowed,thatheatexchangecanbemanipulatedbythermoelectricalmeans.Suchsystemupgradesconventionalcoolingsystemswithinthemouldorcanbeastandaloneapplicationforheatmanipulationwithinit.Inthepaper,theauthorswillpresentresultsoftheresearchproject,whichwascarriedoutinthreephasesanditsresultsarepatentedinA6862006patent.Thetestingstage,theprototypestageandtheindustrializationphasewillbepresented.Themainresultsoftheprojectweretotalandrapidon-linethermoregulationofthemouldoverthecycletimeandoverallinuenceonqualityofplasticproductwithemphasisondeformationcontrol.Presentedapplicationcanpresentamilestoneintheeldofmouldtemperatureandproductqualitycontrolduringtheinjectionmouldingprocess.2006ElsevierB.V.Allrightsreserved.Keywords:Injectionmoulding；Mouldcooling；Thermoelectricmodules；FEMsimulations1.Introduction,denitionofproblemDevelopmentoftechnologyofcoolingmouldsviathermo-electrical(TEM)meansderivesoutoftheindustrialpraxisandproblems,i.e.atdesign,toolmakingandexploitationoftools.Currentcoolingtechnologieshavetechnologicallimitations.Theirlimitationscanbelocatedandpredictedinadvancewithniteelementanalyses(FEA)simulationpackagesbutnotcom-pletelyavoided.Resultsofadiversestateoftheartanalysesrevealedthatallexistingcoolingsystemsdonotprovidecon-trollableheattransfercapabilitiesadequatetotintodemand-ingtechnologicalwindowsofcurrentpolymerprocessingtechnologies.Polymerprocessingisnowadayslimited(intermofshort-eningtheproductioncycletimeandwithinthatreducingcosts)onlywithheatcapacitymanipulationcapabilities.Otherproduc-tionoptimizationcapabilitiesarealreadydriventomechanicalandpolymerprocessinglimitations3.1.1.ThermalprocessesininjectionmouldingplasticprocessingPlasticprocessingisbasedonheattransferbetweenplasticmaterialandmouldcavity.Withincalculationofheattransferoneshouldconsidertwomajorfacts:rstisallusedenergywhichisbasedonrstlawofthermodynamicslawofenergyconservation1,secondisvelocityofheattransfer.Basictaskatheattransferanalysesistemperaturecalculationovertimeanditsdistributioninsidestudiedsystem.Thatlastdependsonvelocityofheattransferbetweenthesystemandsurroundingsandvelocityofheattransferinsidethesystem.Heattransfercanbebasedasheatconduction,convectionandradiation1.1.2.CoolingtimeCompleteinjectionmouldingprocesscyclecomprisesofmouldclosingphase,injectionofmeltintocavity,packingpres-surephaseforcompensatingshrinkageeffect,coolingphase,mouldopeningphaseandpartejectionphase.Inmostcases,thelongesttimeofallphasesdescribedaboveiscoolingtime.Coolingtimeininjectionmouldingprocessisdenedastimeneededtocooldowntheplasticpartdowntoejectiontemperature1.Correspondingauthors.Tel.:+3863490920；fax:+38634264612.E-mailaddress:Blaz.Nardintecos.si(B.Nardin).0924-0136/$seefrontmatter2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.jmatprotec.2006.11.052B.Nardinetal./JournalofMaterialsProcessingTechnology187188(2007)690693691Fig.1.Mouldtemperaturevariationacrossonecycle2.Fig.2.TEMblockdiagram.Themainaimofacoolingprocessistoloweradditionalcoolingtimewhichistheoreticallyneedless；inpraxis,itextendsfrom45upto67%ofthewholecycletime1,4.Fromliteratureandexperiments1,4,itcanbeseen,thatthemouldtemperaturehasenormousinuenceontheejectiontimeandthereforethecoolingtime(costs).InjectionmouldingprocessisacyclicprocesswheremouldtemperaturevariesasshowninFig.1wheretemperaturevariesfromaveragevaluethroughwholecycletime.2.CoolingtechnologyforplasticinjectionmouldsAsitwasalreadydescribed,therearealreadyseveraldiffer-enttechnologies,enablingtheuserstocoolthemoulds5.Themostconventionalisthemethodwiththedrillingtechnology,ducingholesinthemould.Throughtheseholes(coolinglines),thecoolingmediaisowing,removingthegeneratedandaccumulatedheatfromthemould1,2.Itisalsoveryconvenienttobuildindifferentmaterials,withdifferentthermalconductiv-itywiththeaimtoenhancecontrolovertemperatureconditionsinthemould.Suchapproachesaresocalledpassiveapproachestowardsthemouldtemperaturecontrol.Thechallengingtaskistomakeanactivesystem,whichcanalterthethermalconditions,regardingtothedesiredaspects,likeproductqualityorcyclestime.Oneofsuchapproachesisintegratingthermalelectricalmodules(TEM),whichcanalterthethermalconditionsinthemould,regardingthedesiredprop-erties.Withsuchapproach,theonecancontroltheheattransferwiththetimeandspacevariable,whatmeans,thatthetemper-aturecanberegulatedthroughouttheinjectionmouldingcycle,independentofthepositioninthemould.Theheatcontrolisdonebythecontrolunit,wheretheinputvariablesarereceivedfromthemanualinputortheinputfromtheinjectionmouldingsimulation.Withtheoutputvalues,thecontrolunitmonitorstheTEMmodulebehaviour.2.1.Thermoelectricodules(TEM)Fortheneedsofthethermalmanipulation,theTEMmodulewasintegratedintomould.Interactionbetweentheheatandelec-tricalvariablesforheatexchangeisbasedonthePeltiereffect.ThephenomenonofPeltiereffectiswellknown,butitwasuntilnowneverusedintheinjectionmouldingapplications.TEMmodule(seeFig.2)isadevicecomposedofproperlyarrangedpairsofPandNtypesemiconductorsthatarepositionedbetweentwoceramicplatesformingthehotandthecoldthermoelectriccoolersites.Powerofaheattransfercanbeeasilycontrolledthroughthemagnitudeandthepolarityofthesuppliedelectriccurrent.2.2.ApplicationformouldcoolingThemainideaoftheapplicationisinsertingTEMmoduleintowallsofthemouldcavityservingasaprimaryheattransferunit.SuchbasicassemblycanbeseeninFig.3.Secondaryheattransferisrealizedviaconventionaluidcoolingsystemthatallowsheatowsinandoutfrommouldcavitythermodynamicsystem.DevicepresentedinFig.3comprisesofthermoelectricmodules(A)thatenableprimarilyheattransferfromortotem-peraturecontrollablesurfaceofmouldcavity(B).Secondaryheattransferisenabledviacoolingchannels(C)thatdeliverconstanttemperatureconditionsinsidethemould.Thermoelec-tricmodules(A)operateasheatpumpandassuchmanipulatewithheatderivedtoorfromthemouldbyuidcoolingsys-tem(C).Systemforsecondaryheatmanipulationwithcoolingchannelsworkasheatexchanger.Toreduceheatcapacityofcontrollableareathermalinsulation(D)isinstalledbetweenthemouldcavity(F)andthemouldstructureplates(E).Fig.3.StructureofTEMcoolingassembly.692B.Nardinetal./JournalofMaterialsProcessingTechnology187188(2007)690693Fig.4.Structurefortemperaturedetectionandregulation.ThewholeapplicationconsistsofTEMmodules,atemper-aturesensorandanelectronicunitthatcontrolsthecompletesystem.ThesystemisdescribedinFig.4andcomprisesofaninputunit(inputinterface)andasupplyunit(unitforelectronicandpowerelectronicsupplyHbridgeunit).Theinputandsupplyunitswiththetemperaturesensorloopinformationareattachedtoacontrolunitthatactsasanexe-cutionunittryingtoimposepredenedtemperate/time/positionrelations.UsingthePeltiereffect,theunitcanbeusedforheatingorcoolingpurposes.ThesecondaryheatremovalisrealizedviauidcoolingmediaseenasheatexchangerinFig.4.Thatunitisbasedoncurrentcoolingtechnologiesandservesasasinkorasourceofaheat.Thisenablescompletecontrolofprocessesintermsoftemperature,timeandpositionthroughthewholecycle.Furthermore,itallowsvarioustemperature/time/positionpro-leswithinthecyclealsoforstartingandendingprocedures.Describedtechnologycanbeusedforvariousindustrialandresearchpurposeswhereprecisetemperature/time/positioncon-trolisrequired.ThepresentedsystemsinFigs.3and4wereanalysedfromthetheoretical,aswellasthepracticalpointofview.ThetheoreticalaspectwasanalysedbytheFEMsimulations,whilethepracticalonebythedevelopmentandtheimplementationoftheprototypeintorealapplicationtesting.3.FEManalysisofmouldcoolingCurrentdevelopmentofdesigningmouldsforinjectionmouldingcomprisesofseveralphases3.Amongthemisalsodesignandoptimizationofacoolingsystem.Thisisnowa-daysperformedbysimulationsusingcustomizedFEMpackages(Moldow4)thatcanpredictcoolingsystemcapabilitiesandespeciallyitsinuenceonplastic.Withsuchsimulations,moulddesignersgatherinformationonproductrheologyanddeforma-tionduetoshrinkageasellasproductiontimecycleinformation.Thisthermalinformationisusuallyaccuratebutcanstillbeunreliableincasesofinsufcientrheologicalmaterialinforma-tion.ForthehighqualityinputforthethermalregulationofTEM,itisneededtogetapictureaboutthetemperaturedistri-butionduringthecycletimeandthroughoutthemouldsurfaceandthroughoutthemouldthickness.Therefore,differentprocesssimulationsareneeded.Fig.5.Cross-sectionofaprototypeinFEMenvironment.3.1.Physicalmodel,FEManalysisImplementationofFEManalysesintodevelopmentprojectwasdoneduetoauthorslongexperienceswithsuchpackages4andpossibilitytoperformdifferenttestinthevirtualenvi-ronment.WholeprototypecoolingsystemwasdesignedinFEMenvironment(seeFig.5)throughwhichtemperaturedistributionineachpartofprototypecoolingsystemandcontactsbetweenthemwereexplored.Forsimulatingphysicalpropertiesinsideadevelopedprototype,asimulationmodelwasconstructedusingCOMSOLMultiphysicssoftware.ResultwasaFEMmodelidenticaltorealprototype(seeFig.7)throughwhichitwaspossibletocompareandevaluateresults.FEMmodelwasexploredintermofheattransferphysicstakingintoaccounttwoheatsources:awaterexchangerwithuidphysicsandathermoelectricmodulewithheattransferphysics(onlyconductionandconvectionwasanalysed,radiationwasignoredduetolowrelativetemperatureandthereforelowimpactontemperature).BoundaryconditionsforFEManalysesweresetwiththegoaltoachieveidenticalworkingconditionsasinrealtest-ing.Surroundingairandthewaterexchangerweresetatstabletemperatureof20C.Fig.6.TemperaturedistributionaccordingtoFEManalysis.B.Nardinetal./JournalofMaterialsProcessingTechnology187188(2007)690693693Fig.7.Prototypeinrealenvironment.ResultsoftheFEManalysiscanbeseeninFig.6,i.e.temper-aturedistributionthroughthesimulationareashowninFig.5.Fig.6representssteadystateanalysiswhichwasveryaccurateincomparisontoprototypetests.Inordertosimulatethetimeresponsealsothetransientsimulationwasperformed,showingverypositiveresultsforfuturework.Itwaspossibletoachieveatemperaturedifferenceof200Cinashortperiodoftime(5s),whatcouldcauseseveralproblemsintheTEMstructure.Thoseproblemsweresolvedbyseveralsolutions,suchasadequatemounting,choosingappropriateTEMmaterialandapplyingintelligentelectronicregulation.3.2.LaboratorytestngAsitwasalreadydescribed,theprototypewasproducedandtested(seeFig.7).Theresultsareshowing,thatthesetassump-tionswereconrmed.WiththeTEMmoduleitispossibletocontrolthetemperaturedistributionondifferentpartsofthemouldthroughoutthecycletime.Withthelaboratorytests,itwasproven,thattheheatmanipulationcanbepracticallyregu-latedwithTEMmodules.Thetestweremadeinthelaboratory,simulatingtherealindustrialenvironment,withtheinjectionmouldingmachineKraussMaffeiKM60C,temperaturesen-sors,infraredcamerasandtheprototypeTEMmodules.Thetemperatureresponsein1.8svariedform+5upto80C,whatrepresentsawideareafortheheatcontrolwithintheinjectionmouldingcycle.4.ConclusionsUseofthermoelectricmodulewithitsstraightforwardcon-nectionbetweentheinputandoutputrelationsrepresentsamilestoneincoolingapplications.Itsintroductionintomouldsforinjectionmouldingwithitsproblematiccoolingconstructionandproblematicprocessingofpreciseandhighqualityplasticpartsrepresentshighexpectations.TheauthorswereassumingthattheuseofthePeltiereffectcanbeusedforthetemperaturecontrolinmouldsforinjectionmoulding.Withtheapproachbasedonthesimulationworkandtherealproductionoflaboratoryequipmentproved,theassump-tionswereconrmed.SimulationresultsshowedawideareaofpossibleapplicationofTEMmoduleintheinjectionmouldingprocess.Withmentionedfunctionalityofatemperatureproleacrosscycletime,injectionmouldingprocesscanbefullycontrolled.Industrialproblems,suchasuniformcoolingofproblematicAclasssurfacesanditsconsequenceofplasticpartappear-ancecanbesolved.Problemsofllingthinlongwallscanbesolvedwithoverheatingsomesurfacesatinjectiontime.Further-more,withsuchapplicationcontroloverrheologicalpropertiesofplasticmaterialscanbegained.WiththeproperthermalregulationofTEMitwaspos