injection molding process

1TheCompleteInjectionMoldingProcessIntroductionThischapterprovidesanintroductionandoverviewoftheinjectionmoldingmachine(IMM)process.Itprovidestextwithpictorialreviews.Detailsontheimportantinforma-tionpertainingtoIMMandreviewedinthischapterareprovidedintheotherchapters.Figure1-1providesanoverviewthatbasi-callysummarizeswhatshouldbeconsideredtoensurethatthemoldedproductmeetsper-formancerequirementsandprovidesagoodreturnoninvestmenttoproducealltypesandshapesofproductsforalltypesofmarkets.Injectionmoldingisamajorpartoftheplasticsindustryandisabigbusinessworld-wide,consumingapproximately32wt%ofallplastics.Itisinsecondplacetoextrusion,whichconsumesapproximately36wt%(1,3,7).11:theUnitedStatesalonethereareabout80,000IMMsandabout18,000extrud-ersoperatingtoprocessallthemanydiffer-enttypesofplastics.IntheindustryanIMMisnotregardedasanextruder;however,itisbasicallyanoncontinuousextruderandinsomeoperationsisevenoperatedcontinu-ously(Chap.15).IMMshaveascrewplas-ticator,alsocalledascrewextruder,thatpre-paresthemelt(3).AssummarizedinFig.1-2,injectionmold-ingisanimportantplasticprocessingmethod.Thefigureshowsthenecessarycomponentsfortheinjectionmoldertobesuccessfulandprofitable.Recognizethatthefirsttomarketwithanewproductcaptures80%ofmar-ketshare.Theyoungtreecannotgrowifitisintheshadowofanothertreeorifitdoesnotkeepupwithcompetition.Youneedtobeatthetopofthetreelookingovertheothertrees.Factorssuchasgoodengineer-ingandprocesscontrolareveryimportantbutonlyrepresentpiecesofthepie.Withoutpropermarketinghalesyouareliterallyoutofbusiness.Thisdiagramisbasicallyaphilo-sophicalapproachtotheoverallindustryinthatitprovidesexamplesofallaspectsofthetechnologyandbusinessthatrangefromlocaltoglobalcompetition.Theoldadageaboutthebettermousetrapisnolongercom-pletelytrue,sinceyouneedfactorssuchasthesupportservicesfromthe“tree”toachievecommercialsuccessandmeetproductdesignrequirements(Chap.5)(1,499).TherearemanydifferenttypesofIMMsthatpermitmoldingmanydifferentprod-ucts,basedonfactorssuchasquantities,sizes,shapes,productperformance,oreco-nomics.ThesedifferenttypesofIMMsare121TheCompleteInjectionMoldingProcess~ICOMPLETECONTROLforMANAGEMENTIIndividualCONTROLforeachaperatton,fromsorimretohardware-mSOFTWARE---ANALYSISapproachtomeetpsiiormanooFALLOFollowALLOpportunitiesIIYSOFTWAREIIntegratea11indindualoperationsI.OPERATION-MOLDEDPARTdryer,SecandawISetUPTESTINQIQUALITYCONTROL!Immediatelyafierpartisinproduction--nextstepIMPORTANTSTEP--istoproduceparttomeetsamerequirementsbutproducedatalowercostUseFALLOapproach.Reevaluateallparametersusedfrompartdesign(uselessplastic),uselowercostplasticwithsimiliarprocess-ingcost(orplasticwithhighercost,butfasterprocess,resultsinlowertotalcost),checkhardwareperformance,&otherpara-metersdescribedintheIMHANDBOOK.ACharacterizeproperties,mechanical,physical,chemical,thermal,etcIt-SetuppracticaliusefulTROUBLESHOOTINGpotentialfaults.C/GUIDEbasedoncauses&remediesofIII!D.V.1Fig.1-1TheFALLOapproach:FollowALLOpportunities.reviewedthroughoutthisbook,particularlyinChap.15.Small-andlarge-sizeIMMsbothhavetheiradvantages.Forexample,ifsev-eralsmallmachinesareusedratherthanonelargeone,amachinebreakdownorshutdownforroutinemaintenancewillhavelesseffectonproductionrates.However,thelargerma-chineisusuallymuchmoreprofitablewhileitisrunning.Becausetherearefewercavitiesinmoldsforthesmallmachines,theymayper-mitclosercontrolofthemoldingvariablesintheindividualcavities.ThetwomostpopularkindsofIMMarethesingle-stageandthetwo-stage;therearealsomoldingunitswiththreeormorestages.Thesingle-stageIMMisalsoknownasthereciprocating-screwIMM.Thetwo-stageIMMalsohasothernames,suchasthepiggy-backIMM.Itiscomparableinsomewaystoacontinuousextruder.TheIMMhasthreebasiccomponents:theinjectionunit,themold,andtheclampingsystem.Theinjectionunit,alsocalledtheplasticator,preparestheproperplasticmeltandviatheinjectionunittransfersthemeltintothenextcomponentthatisthemold.Theclampingsystemclosesandopensthemold.Thesemachinesallperformcertainessen-tialfunctions:(1)plasticizing:heatingandmeltingoftheplasticintheplasticator,(2)injection:injectingfromtheplasticatorunderpressureacontrolled-volumeshotofmeltintoaclosedmold,withsolidificationoftheplasticsbeginningonthemold'scavitywall,(3)afterjiilling:maintainingtheinjectedmaterialunderpressureforaspecifiedtimetopreventbackflowofmeltandtocompen-sateforthedecreaseinvolumeofmeltduringsolidification,(4)cooling:coolingthether-moplastic(TP)moldedpartinthemolduntilitissufficientlyrigidtobeejected,orheat-ing:heatingthethermoset(TS)moldedpartinthemolduntilitissufficientlyrigidtobeejected,and(5)molded-partrelease:openingthemold,ejectingthepart,andclosingthemoldsoitisreadytostartthenextcyclewithashotofmelt.1TheCompleteInjectionMoldingProcess3SelectingMaterialProceCompressionReinforcedPlasticsDEvaluateIDetractors-ConstraintsCostAnalysisrRheologyProperlles,CompoundingAlloyshBlendstLEADSIEtc.Firsttomarketwithanewproductcaptures80%ofmarketshare.Theyoungtreecannotgrowifitisintheshadowofanothertreeorifitdoesnotkeepupwiththecompetition.Youneedtobeat