1、TheInjectionMoldingTheIntroductionofMoldsThemoldisattheceofaplasticmanufacturingprocessbecauseitscavitygivesapartitsshape.Thismakesthemoldatleastascriticalmanycasesmesofthequalityoftheendproductasfexampletheplasticitingu

2、nitothercomponentsoftheprocessingequipment.MoldMaterialDependingontheprocessingparametersfthevariousprocessingmethodsaswellasthelengthoftheproductionrunthenumberoffinishedproductstobeproducedmoldsfplasticsprocessingmusts

3、atisfyagreatvarietyofrequirements.Itistherefenotsurprisingthatmoldscanbemadefromaverybroadspectrumofmaterialsincludingfromatechnicalstpointsuchexoticmaterialsaspapermatchedplaster.Howeverbecausemostprocessesrequirehighpr

4、essuresoftencombinedwithhightemperaturesmetalsstillrepresentbyfarthemostimptantmaterialgroupwithsteelbeingthepredominantmetal.Itisinterestinginthisregardthatinmanycasestheionofthemoldmaterialisnotonlyaquestionofmaterialp

5、ropertiesanoptimumpricetoperfmanceratiobutalsothatthemethodsusedtoproducethemoldthustheentiredesigncanbeinfluenced.Atypicalexamplecanbeseeninthechoicebetweencastmetalmoldswiththeirverydifferentcoolingsystemscomparedtomac

6、hinedmolds.Inadditiontheproductiontechniquecanalsohaveaneffectfinstanceitisoftenreptedthatfthesakeofsimplicityaprototypemoldisfrequentlymachinedfromsolidstockwiththeaidofthelatesttechnologysuchascomputeraided(CAD)compute

7、rintegratedmanufacturing(CIMS).IncontrasttothepreviouslyusedmethodsbasedontheuseofpatternstheuseofCADCAMoftenrepresentsthemeeconomicalsolutiontodaynotonlybecausethisproductioncapabilityisavailablepinhousebutalsobecausewi

8、thanyothertechniqueanderwouldhavetobeplacedwithanoutsidesupplier.Overallalthoughhighgradematerialsareoftenusedasarulestardmaterialsareusedinmoldmaking.Newstateoftheart(highperfmance)materialssuchasceramicsfinstancearealm

9、ostcompletelyabsent.Thismayberelatedtothefactthattheirdesirableacteristicssuchasconstantpropertiesuptoveryhightemperaturesarenotrequiredonmoldswhereastheirnegativeacteristicse.g.lowtensilestrengthpothermalconductivityhav

10、eaclearlyrelatedtoceramicssuchassinteredmaterialisfoundinmildmakingonlytoalimiteddegree.Thisreferslesstothemodernmaterialscomponentsproducedbypowdermetallurgypossiblybyhotisocraticpressingthantosinteredmetalsinthesenseof

11、pousairpermeablematerials.singlecavitymold.Converselytheproductionincreasesinproptiontothenumberofcavities.Amoldwithmecavitiesismeexpensivetobuildthanasinglecavitymoldbutnotnecessarily4timesasmuchasasinglecavitymold.Buti

12、tmayalsorequirealargermachinewithlargerplatenareameclampingcapacitybecauseitwilluse4timestheamountofplasticitmayneedalargeinjectionunitsothemachinehourcostwillbehigherthanfamachinelargeenoughfthesmallermold.3.Cavityshape

13、shrinkageTheshapeofthecavityisessentiallythe“negative”oftheshapeofthedesiredproductwithdimensionalallowanceaddedtoallowfshrinkingoftheplastic.Theshapeofthecavityisusuallycreatedwithchipremovingmachinetoolswithelectricdis

14、gemachiningwithchemicaletchingbyanynewmethodthatmaybeavailabletoremovemetalbuilditupsuchasgalvanicprocesses.Itmayalsobecreatedbycastingcertainmetalsinplastermoldscreatedfrommodelsoftheproducttobemadebycastingsomesuitable

15、hardplastics.Thecavityshapecanbeeithercutdirectlyintothemoldplatesfmedbyputtingsintotheplates.C.CavityceByconventionthehollowptionofthecavityspaceiscalledthecavity.Thematchingoftenraisedptionofthecavityspaceiscalledthece

16、.Mostplasticproductsarecupshaped.Thisdoesnotmeanthattheylooklikeacupbuttheydohaveaninsideanoutside.Theoutsideoftheproductisfmedbythecavitytheinsidebythece.Thealternativetothecupshapeistheflatshape.Inthiscasethereisnospec

17、ificconvexptionsometimesthecelookslikeamirrimageofthecavity.Typicalexamplesfthisareplasticknivesgamechipsrounddiskssuchasrecds.Whiletheseitemsaresimpleinappearancetheyoftenpresentseriousmoldingproblemsfejectionoftheprodu

18、ct.Thereasonfthisisthatallinjectionmoldingmachinesprovideanejectionmechanismonthemovingplatentheproductstendtoshrinkontoclingtothecefromwheretheyarethenejected.Mostinjectionmoldingmachinesdonotprovideejectionmechanismson

19、theinjectionside.PolymerProcessingPolymerprocessinginitsmostgeneralcontextinvolvesthetransfmationofasolid(sometimesliquid)polymericresinwhichisinaromfm(e.g.powderpelletsbeads)toasolidplasticsproductofspecifiedshapedimens

20、ionsproperties.Thisisachievedbymeansofatransfmationprocess:extrusionmoldingcalendaringcoatingthermofmingetc.Theprocessindertoachievetheaboveobjectiveusuallyinvolvesthefollowingoperations:solidtransptcompressionheatingmel