Scientific-Approach-To-Injection-Molding

ScientificApproachtoInjectionMoldingVishuShahConsultekJanuary15,2004WhatisScientificApproachtoInjectionMolding?•UnderstandingScienceofInjectionmolding•Everythingsubstantiatedbyscientificdata•Scientificapproachtoestablishingmoldingvariables•UnderstandingoffourcriticalcomponentsMaterialPartDesignToolingProcessing•EverydecisionMustbebackedbyscientificdataWhyuseScientificapproach?•Becomemoreefficient•CostSavings•QualityImprovementsSeparatingfromOldWaysToNewWaysHowHow&WhyArt(sight,soundandtouch)ScienceMythFactsJetcontainerapproachTDKapproachDecisionsbasedonDATAandDATAonly300TonMachine:MachineHourrate$/Hr35.00CurrentCycleTime:30secondsNewCycletime:29secondsCycletimesavings:2secondsperminuteCycletimesavings:2MinutesperhourCycletimesavings:(5000hrsperyear)10,000Minutesor166hoursTotal$amountsavings:166x35=$5810Total$amountsaved:(10Machineshop)58,100BenjaminFranklinoncesaid“Bewareoflittleexpenses;asmallleakcansinkagreatship.”MaterialsDryingWhydoweneedtodryPlasticsMaterials?AllPlastics,whenexposedtoatmosphere,willpickupmoisturetoacertaindegreedependinguponthehumidityandtypeofthepolymer.HotAirDryerDesiccantDryerAcetalPolyurethanePVC,PolypropylenePolyesterPolyethylenePolycarbonatePolystyreneNylon,ABSNoabsorptionofmoistureintothepellet.Maypickupsurfacemoisture.MoistureisabsorbedintothepelletovertimeuntilequilibriumisreachedPolymerswithverylittleornoaffinityformoisturePolymerswithhighaffinityformoistureNonHygroscopicHygroscopicMaterialDryingIssues…….•Toohighdryingtemperature……Discoloration,Propertybreakdown•Toolongdryingtime(Overdrying)*…..Lossofimpact,propertybreakdown•Residencetimeandprocessingrate•Hydrolysis…Molecularbreakdown•MaterialsthatHydrolyze….Nylon,PC,Polyester,Polyurethane,etc..•Regrindusageanddrying•Ifyoumoldhydrolyzablematerialwet…Mayaswellthrowitaway*RuleofThumb:Resinswhichpickupmoisturefast,alsodryfast!DewPointmeterVs.MoistureAnalyzer•Measuresdryerefficiency•Easytocalibrate•Portable•$800to$1200•Measuresactualmoistureinthematerial•Veryaccuratemeasurement•Labenvironment/verycleanproductionarea•Preprogrammedmaterialdata•$8000andupImportantConsiderations•Checkincomingresintocutdownondryingtime(doyoureallyneed3hours+ofdryingtime?)•Eliminateoverdrying•Areyoupayingforwater?•DryersareworkingfineBUTresiniswet?????MaterialMixing,coloring&Loading•Mixing……Regrindanditsadverseeffect•Lossofadditives•Pelletsizevariations•Fines–Staticcharge–Fastmoisturepickup–cloggedfilters–Fastmelting–Blackspecks,splay,volatiles,burning…..NOHandmixingofregrind….AttachestogrinderColoring•Coloranthavepronouncedeffectonshrinkage•OrganicpigmentshavesignificanteffectsinceittendstointerferewithcrystallizationkineticsandmorphologicalstructureofcoolingpolymerLoadingHandLoadingVacuumLoadersPneumaticLoadersCentralLoadingPressureLoadingAreyoualsoloadingmoisture?L/DandCompressionRatioCompressionRatioGPMaterials3:1PVC1.4:1Acetal4:1Barrier&MixingScrewsNonReturnValveCheckRingRepeatabilityStudyA.SetupmachinetorunstandardpartsB.TurnoffpackandholdtimeandpressureC.Make10FillonlyshotsD.WeighthepartsandrecordweightE.CalculateAcceptablevariationis5%max.NozzleTipTypesAvoidLongReachNozzles&tips•Coldslug•Burning•Splay•PressurelossMoldVentingWhyVent?•Evacuationoflatentairthatisintheclosedmold•AllowevacuationofgasesproducedbylowmolecularweightpolymersandadditivesProblemsassociatedwithpoorventing•Burnmarks•Poormoldfilling•Weakweldlines•Internalbubblesandnon-fillareas•Highstressconcentration•Sinkmarks•Longercycletime•Molddepositbuild-up•Downtime•Decoratingproblems•Adhesionproblems•StresscrackinginpresenceofchemicalVENTTHERUNNER….PERIMETERVENTINGYOUCAN’THAVETOOMUCHVENTING!!!!!VENTINGIfporousmetalpinsgetstoohot&pluggedUseVacuum(LogicSeal)toprovidecoolingPorcerexIIVentPinsVentingproblemswithDelrinacetalresinscanbemademoreobviousbysprayingthemoldwithahydrocarbon(Rustpreventivespray)orKerosene-basedsprayjustbeforeinjection.Ifventingispoor,hydrocarbonwillcauseblackspotwhereairistrapped.MoldFillingSimulationtoOptimizeDesign&solvemoldingproblems•Optimizegatelocationsandnumberofgates•Confidenceoffill•Knitlineandgasentrapmentlocations•filltime•pressuredistribution•TemperaturedistributionMajorProcessVariables•Temperature•FlowRate(Injectionvelocity)•Pressure•Time(Cooling)InterdependenceofVariables……..TemperatureWheredoestheheattomeltthepolymercomefrom?ExternalInternalHeatProfilesettingsRearMiddleFrontAdapter/NozzleAscendingProfile……smallshotsizeinlargebarrelReverseprofile………largeshotsizeinsmallbarrelHeaterbandsScrewTemperatureMelttemperatureaffectscycletimeBTU’s(heat)IN=BTU’s(heat)OUTHeatalwaystravelsfromHOTtoCOLDatagivenratebasedoneachmaterialsrateoftransmissionorthermaldiffusivitySomematerialsgiveoffheatfasterthanothers……PartsMustbecooledbelowHeatDistortionTemperature(HDT)ofthePlasticsinordertoejectitoutofthemoldwithoutwarpageTheHotterthemelt…..LongerthecoolingtimeAvoidtoohighortoolowMelttemperature……..Refertomaterialsupplier’sDatasheetforrecommendedsettingsAnduseitasstartingpointandstartingpointonlyTemperatureWhatisimportant….BarreltemperatureorMelttemperature?OptimumMELTTEM