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D3CAVITYSHAPEANDSHRINKAGETHESHAPEOFTHECAVITYISESSENTIALLYTHE“NEGATIVE”OFTHESHAPEOFTHEDESIREDPRODUCT,WITHDIMENSIONALALLOWANCEADDEDTOALLOWFORSHRINKINGOFTHEPLASTICTHESHAPEOFTHECAVITYISUSUALLYCREATEDWITHCHIPREMOVINGMACHINETOOLS,ORWITHELECTRICDISCHARGEMACHINING,WITHCHEMICALETCHING,ORBYANYNEWMETHODTHATMAYBEAVAILABLETOREMOVEMETALORBUILDITUP,SUCHASGALVANICPROCESSESITMAYALSOBECREATEDBYCASTINGCERTAINMETALSINPLASTERMOLDSCREATEDFROMMODELSOFTHEPRODUCTTOBEMADE,ORBYCASTINGSOMESUITABLEHARDPLASTICSTHECAVITYSHAPECANBEEITHERCUTDIRECTLYINTOTHEMOLDPLATESORFORMEDBYPUTTINGINSERTSINTOTHEPLATESCCAVITYANDCOREBYCONVENTION,THEHOLLOWPORTIONOFTHECAVITYSPACEISCALLEDTHECAVITYTHEMATCHING,OFTENRAISEDPORTIONOFTHECAVITYSPACEISCALLEDTHECOREMOSTPLASTICPRODUCTSARECUPSHAPEDTHISDOESNOTMEANTHATTHEYLOOKLIKEACUP,BUTTHEYDOHAVEANINSIDEANDANOUTSIDETHEOUTSIDEOFTHEPRODUCTISFORMEDBYTHECAVITY,THEINSIDEBYTHECORETHEALTERNATIVETOTHECUPSHAPEISTHEFLATSHAPEINTHISCASE,THEREISNOSPECIFICCONVEXPORTION,ANDSOMETIMES,THECORELOOKSLIKEAMIRRORIMAGEOFTHECAVITYTYPICALEXAMPLESFORTHISAREPLASTICKNIVES,GAMECHIPS,ORROUNDDISKSSUCHASRECORDSWHILETHESEITEMSARESIMPLEINAPPEARANCE,THEYOFTENPRESENTSERIOUSMOLDINGPROBLEMSFOREJECTIONOFTHEPRODUCTTHEREASONFORTHISISTHATALLINJECTIONMOLDINGMACHINESPROVIDEANEJECTIONMECHANISMONTHEMOVINGPLATENANDTHEPRODUCTSTENDTOSHRINKONTOANDCLINGTOTHECORE,FROMWHERETHEYARETHENEJECTEDMOSTINJECTIONMOLDINGMACHINESDONOTPROVIDEEJECTIONMECHANISMSONTHEINJECTIONSIDEPOLYMERPROCESSINGPOLYMERPROCESSING,INITSMOSTGENERALCONTEXT,INVOLVESTHETRANSFORMATIONOFASOLIDSOMETIMESLIQUIDPOLYMERICRESIN,WHICHISINARANDOMFORMEG,POWDER,PELLETS,BEADS,TOASOLIDPLASTICSPRODUCTOFSPECIFIEDSHAPE,DIMENSIONS,ANDPROPERTIESTHISISACHIEVEDBYMEANSOFATRANSFORMATIONPROCESSEXTRUSION,MOLDING,CALENDARING,COATING,THERMOFORMING,ETCTHEPROCESS,INORDERTOACHIEVETHEABOVEOBJECTIVE,USUALLYINVOLVESTHEFOLLOWINGOPERATIONSSOLIDTRANSPORT,COMPRESSION,HEATING,MELTING,MIXING,SHAPING,COOLING,SOLIDIFICATION,ANDFINISHINGOBVIOUSLY,THESEOPERATIONSDONOTNECESSARILYOCCURINSEQUENCE,ANDMANYOFTHEMTAKEPLACESIMULTANEOUSLYSHAPINGISREQUIREDINORDERTOIMPARTTOTHEMATERIALTHEDESIREDGEOMETRYANDDIMENSIONSITINVOLVESCOMBINATIONSOFVISCOELASTICDEFORMATIONSANDHEATTRANSFER,WHICHAREGENERALLYASSOCIATEDWITHSOLIDIFICATIONOFTHEPRODUCTFROMTHEMELTSHAPINGINCLUDESTWODIMENSIONALOPERATIONS,EGDIEFORMING,CALENDARINGANDCOATINGTHREEDIMENSIONALMOLDINGANDFORMINGOPERATIONSTWODIMENSIONALPROCESSESAREEITHEROFTHECONTINUOUS,STEADYSTATETYPEEGFILMANDSHEETEXTRUSION,WIRECOATING,PAPERANDSHEETCOATING,CALENDARING,FIBERSPINNING,PIPEANDPROFILEEXTRUSION,ETCORINTERMITTENTASINTHECASEOFEXTRUSIONSASSOCIATEDWITHINTERMITTENTEXTRUSIONBLOWMOLDINGGENERALLY,MOLDINGOPERATIONSAREINTERMITTENT,AND,THUS,THEYTENDTOINVOLVEUNSTEADYSTATECONDITIONSTHERMOFORMING,VACUUMFORMING,ANDSIMILARPROCESSESMAYBECONSIDEREDASSECONDARYSHAPINGOPERATIONS,SINCETHEYUSUALLYINVOLVETHERESHAPINGOFANALREADYSHAPEDFORMINSOMECASES,LIKEBLOWMOLDING,THEPROCESSINVOLVESPRIMARYSHAPINGPAIRSONFORMATIONANDSECONDARYSHAPINGPAIRSONINFLATIONSHAPINGOPERATIONSINVOLVESIMULTANEOUSORSTAGGEREDFLUIDFLOWANDHEATTRANSFERINTWODIMENSIONALPROCESSES,SOLIDIFICATIONUSUALLYFOLLOWSTHESHAPINGPROCESS,WHEREASSOLIDIFICATIONANDSHAPINGTENDTOTAKEPLACESIMULTANEOUSLYINSIDETHEMOLDINTHREEDIMENSIONALPROCESSESFLOWREGIMES,DEPENDINGONTHENATUREOFTHEMATERIAL,THEEQUIPMENT,ANDTHEPROCESSINGCONDITIONS,USUALLYINVOLVECOMBINATIONSOFSHEAR,EXTENSIONAL,ANDSQUEEZINGFLOWSINCONJUNCTIONWITHENCLOSEDCONTAINEDORFREESURFACEFLOWSTHETHERMOMECHANICALHISTORYEXPERIENCEDBYTHEPOLYMERDURINGFLOWANDSOLIDIFICATIONRESULTSINTHEDEVELOPMENTOFMICROSTRUCTUREMORPHOLOGY,CRYSTALLINITY,ANDORIENTATIONDISTRIBUTIONSINTHEMANUFACTUREDARTICLETHEULTIMATEPROPERTIESOFTHEARTICLEARECLOSELYRELATEDTOTHEMICROSTRUCTURETHEREFORE,THECONTROLOFTHEPROCESSANDPRODUCTQUALITYMUSTBEBASEDONANUNDERSTANDINGOFTHEINTERACTIONSBETWEENRESINPROPERTIES,EQUIPMENTDESIGN,OPERATINGCONDITIONS,THERMOMECHANICALHISTORY,MICROSTRUCTURE,ANDULTIMATEPRODUCTPROPERTIESMATHEMATICALMODELINGANDCOMPUTERSIMULATIONHAVEBEENEMPLOYEDTOOBTAINANUNDERSTANDINGOFTHESEINTERACTIONSSUCHANAPPROACHHASGAINEDMOREIMPORTANCEINVIEWOFTHEEXPANDINGUTILIZATIONOFCOMPUTERDESIGN/COMPUTERASSISTEDMANUFACTURING/COMPUTERAIDEDENGINEERINGCAD/CAM/CAESYSTEMSINCONJUNCTIONWITHPLASTICSPROCESSINGITWILLEMPHASIZERECENTDEVELOPMENTSRELATINGTOTHEANALYSISANDSIMULATIONOFSOMEIMPORTANTCOMMERCIALPROCESS,WITHDUECONSIDERATIONTOELUCIDATIONOFBOTHTHERMOMECHANICALHISTORYANDMICROSTRUCTUREDEVELOPMENTASMENTIONEDABOVE,SHAPINGOPERATIONSINVOLVECOMBINATIONSOFFLUIDFLOWANDHEATTRANSFER,WITHPHASECHANGE,OFAVISCOELASTICPOLYMERMELTBOTHSTEADYANDUNSTEADYSTATEPROCESSESAREENCOUNTEREDASCIENTIFICANALYSISOFOPERATIONSOFTHISTYPEREQUIRESSOLVINGTHERELEVANTEQUATIONSOFCONTINUITY,MOTION,ANDENERGYIECONSERVATIONEQUATIONSINJECTIONMOLDINGMANYDIFFERENTPROCESSESAREUSEDTOTRANSFORMPLASTICGRANULES,POWDERS,ANDLIQUIDSINTOFINALPRODUCTTHEPLASTICMATERIALISINMOLDABLEFORM,ANDISADAPTABLETOVARIOUSFORMINGMETHODSINMOSTCASESTHERMOPLASTICMATERIALSARESUITABLEFORCERTAINPROCESSESWHILETHERMOSETTINGMATERIALSREQUIREOTHERMETHODSOFFORMINGTHISISRECOGNIZEDBYTHEFACTTHATTHERMOPLASTICSAREUS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