注塑件成型与设计

InjectionMoldingandDesign注塑成型与设计InjectionMoldingProcessOverview PartandToolDesignTerminologyCommonMoldingDefectsMoldedPartDesignBestPracticesInjectionMoldingProcessOverview InjectionMoldingProcessOverview Injectionmoldingisusedtoproducemostofourcomplexplasticparts.Injectionmoldingisaprocesswhichinvolvesforcingmoltenplasticintoamachinedmoldcavityunderhighpressure.InjectionMoldingPressTheinjectionmoldingpressoperationincludesameansto:Openandcloseandclamptheinjectionmold.Measure,melt,andinjecttheplasticresin.Coolthemoltenplasticinthemold.Ejectthefinishedpartfromthemold.Computercontrolsystem.InjectionMoldTheinjectionmoldformsboththeshow(A)sideandtheback(B)sideofthepart.Theshowsideofthepartisgenerallythecavitysideofthetool,andthebacksideisthecoreside.Theinterfacebetweenthecavityandcoreisthepartingline.Thenumberofcavitiesisthenumberofpartsproducedpercycle.InjectionMoldComponentsCavityCoreClampPlatesEjectorPlate&PinsLiftersSlidesWaterLinesGatesandSpruesHotRunnerSystem,etcHotRunnerManifold&MultipleValveGatesThemanifoldinalargemoldheatsanddeliversthehotplasticfromthemoldingmachinetothegatelocationsonthepart.Lifters-FormDie-LockedFeaturesLiftersaremechanismswhichmoveapproximatelyinthedirectionofthemoldopening(dieangle).Theyareusuallyactivatedbylifterrodsoperatedbytheejectorplate.Liftersoftenmoveonanangletothepartduringmoldopeningandejectiontounlockadie-lockedfeature.MoldOpenMoldClosedDieDirection(moldopeningangle)LifterCoreSlides-FormDie-LockedFeaturesAcoreslideisamechanismonthecorewhichmovesnormal(90°)todieangledirectiontoformdie-lockfeaturesorundercutsinthepartdesign.Theslideisactuatedbypins,cams,orhydraulicorpneumaticcylindersduringandafterthemoldcavityopens.SimpleCoreSlideandEjectionPlasticPartEjectionPinCoreWithSlideCavityWithHornPin*Actually,thecavityisstationary,andthecoresidemovestoopenthetoolwhenmountedinthemoldingmachine.AcceleratingEjectionPinInjectionSprueEjectionwithLifterCavityandCorewithLifterandPinPlasticPartEjectionPinCorewithlifterCavityTravelingAngledLifterFormsribwithflangeInjectionSprueCamOperatedCorePinFormsholeinflange*Actually,thecavityisstationary,andthecoresidemovestoopenthetoolwhenmountedinthemoldingmachine.CamDesignTerminologyPartandToolDesignTerminologyPartandToolDesignTerminology-DieAngles&DraftAngles,拔模角-ASurface,BSurface,etc.A面,B面-PartingLines,LifterLines,分模线-Doghouses,Ribs,Flanges安装支座,加强筋,翻边-TrueHoles,MoldedHoles,注塑孔-ToolingConsiderations,注塑模考虑DieAngle&PartingLineDieAngle(DieVector)

MoldopeningdirectionPartingLine–

wherethecore,cavity,andpartmeettogether.Part(2cavity)CoreCavityDraftAnglesPartsmusthaveopendraftanglesinthepartgeometrydesign.Partdraftangleismeasuredrelativetothedieopeningangle.Ifthereisnodraftangle,thepartwillcoolandshrinkontothetoolandwillbedifficultorimpossibletoremovewithoutdamage.Wegenerallyuseminimum3degreesdraftperside.Moredraftisneededforgrainedsurfaces.Cavity'A'surfacevs.Core'B'surfaceOriginalPart,tooledwrong,core/cavity.Ejectionpinsonshowsurface(Asurface).RevisedPart,eliminatepinsonAsurfaceDoyouknowthedifference?Doesyoursupplierandtoolshop?Didyouindicateitclearlyinyourmathdatafile?Oops!MoldingIssuesandCommonDefectsMoldingIssuesandCommonDefectsMoldExpansion/PartShrinkageThermoplasticsshrinkastheycool

andsolidifyduringthemoldingprocessandafterpartejection.Themoldcavityismachinedlargerthanthefinaldesiredpartsizeinordertocompensateforpartshrinkageasthepartcools.Moldshrinkagedataforthespecificplasticmaterialcanbeusedtocalculatetheamountofmoldexpansionneeded.Moldshrinkageunitsareexpressedaslength-perunit-length,orasapercentage,andiscalculatedusingthefollowingformula:

(molddimension–partsize)/molddimension=ShrinkFactorMoldingIssuesandCommonDefectsDimensionalSizeErrors(toolong,tooshort,toothin,toothick,etc.)DimensionalWarpage,Distortion,&StressSink&ShrinkMarksLifterLineRead-ThroughFlowLines,Weld(Knit)LinesMetallicFlakeOrientationPorosityNon-isotropicBehavior(differentbehaviorindifferentdirections)FlowLines,MetalFlakeOrientationThissectionofmetallicmolded-in-colorrockermoldingshowappearancedefectscausedbyflowlinesandmetalflakealignmentsformedaroundtheattachingholepins.GateFlowObstructionFlowLine&MetalFlakeOrientationWeldLines(KnitLines)Weld(knit)linesareappearanceandstructuraldefectswhichareformedwhenthemoltenplasticmustdividetogoaroundanobstructionandthenrejoinitself.Weoftenfindthisproblemondoghousesandalsoatattachingholesnearapartedge.SinkMarksSinkMarksformaroundthecenterofthelargermassofmaterialandshrinktowardsthecenterofthemass.Sinkmarksareappearancedefectscausedbypoorpartdesign.Sinksmarksaredifficulttoimprovebytoolingorprocessing.RibsandGussetsRibsandgussetsshouldhaveangledcornerstoavoidtrappingairduringfilling.Squarecornersaremoredifficulttofillcomparedtoangledorradiusedcorners.ChromePlatingConsiderationsChromeplatingisanelectrochemicalprocess,andthedepositionofthemetaltothepartisattractedtosharpoutsideradiiandisrejectedbysharpinsideradii.Non-uniformchromedepositcausessurfaceprofileappearanceproblems.Useradiiandfilletstoeliminatesharpfeaturesandmakethechromedepositionmoreuniform.ChromePlatingConsiderationsStiffenedgesifpossibletoreducedamage.Avoidflatsurfacesduetoriskofnon-uniformchromedepositionandalsoplasticshrinkagesinkmarks.Usecrowned(largeradius,notflat)surfacestomaintainuniformchromethicknessandavoidshrinkmarks.Runner,Gating,FillingMoldingAnalysisDoanalysisbeforeyoudesignandbuildthetool!PartDesignBestPracticesPartDesignBestPracticesDesignForSuccess–FollowaPlanAfteryougatherandunderstandthepartrequirements:Selecttheproperpartconstruction,materialsselection,andprocess.(materialtype,stiffness,weatherable,paintable,moldable,etc.)Studyandunderstandthematerialbehavioranddesignrequirements(minimumwallstockthickness,ribsensitivity,holesensitivity,shrinkage,etc.SeekassistancefromMaterialsEngineers,suppliers,LeadEngineers,colleagues,etcfordesignreviewandadvice.ConductPeerReviewsofyourdesignwithmoldersandtoolshopsasitdevelops.InjectionMaterialFamiliesThermoplastic:Categoryofplasticswhichdeformsandre-meltswhenreheated."recyclable“

CommonFillers:GlassFiber:Short,Long,Continuous,MatMineral:MicaTalcThermoplasticMaterialsThermoplasticscommoninautomotive:TPO,PPABS,ABS+PC,ASA,ASA+PCPC,PC+PBT,PMMAPA6,PA66,Nylon,+mineralorglassfiber

Thermoplasticmaterialsareusuallyhighpressureinjectionmoldedbutsomegradescanalsobeblow-moldedorextrudedorthermoformed.

PartMaterialsUsageMatrixUniformWallStock(thickness)PoorDesignGoodDesignDesigningpartsforuniformwallstock(thickness)isprobablythesinglemostimportantthingyoucandotomakeadesignwhichisrobustformoldingandpainting.Uniformwallstockpartsmoldwithbetterfillingandreducedinternalstresses.Uniformwallstockpartscoolandshrinkmoreuniformly,reducingdimensionaldistortionandwarpage.CornerRadiiMaintainconstantpartthicknessincornerradii.Avoid"Thick-thin-thick"or"Thin-thick-thin"sectiontransitions.Non-uniformthicknesscreatesflow,stress,shrinkage,andwarpageconditionsinthepartastheplasticcoolsandshrinksatdifferentratesduetodifferentthicknesses.Good!ThicknessTransitionsAvoidsuddenorsharpchangesinsectionshape.Suddenchangesaffectflowandfillcharacteristics,andalsocreatehighstressconcentrationsinthepart.Usesmoothtransitionsbetweensections.AvoidSolidMassesPoorDesignGoodDesignThickmassesofsolidplastic.Coolsslowly.Someareasarethinner.Shrinksunevenly.UniformconstantthicknessOffsetRibsOffsetribscanhelphidesinkmarksandmakethemlessvisible.Sinkmarksandshrinkageareeasierto'hide'whentheyoccuronsmallradiussurfaces.Sinkmarksaredifficulttohideonlargeradius(flat)surfaces.Itisgenerallygoodpracticetoplaceanyribsbehindpartsurfacefeaturelines,ratherthanbehindflatsurfaces.RibDesignPracticesAvoidthickribfeatureswhichcancausepartwarpageandsurfacesinkmarks.Avoidtallthinribfeatureswhichcanbuckleorbendunderload.RibDesignGuidelinesRibdesignislargelyaffectedbymaterialselection.ConsultwithResinsuppliersandmoldersforassistance.Generally,wedesignaminimumof3degreesdraftpersideforribsandsurfacesforrobustmoldingandejection.Smallerdraftcansometimesbeusedifyouhaveagreementfromyourmolderandtoolshop.However,largeribsincreasethechanceofsurfacesinkmarks.0.3-0.4TRibWarpageItisalwaysbettertogainstructurethroughsurfaceshapechange,ratherthanaddedribsandgussetsonthebackside.Ribsaddstructurebutcancausewarpageduetocoolingofnon-uniformgeometry.Fillershaveavariedeffectoncoolingandwarpage.Itisdifficulttopredict,analyze,orcontrolwarpagefromplasticribstructure.GlassFilledresinUn-FilledresinMultipleRibsSometimesasinglelargeribcanbereplacedbymultiplesmallerribstoavoidsinkmarks,etc.BossDesignsThisshowsatypicalbossdesignforascreworstudforreferenceDetailsvarydependingonmaterialsandfastenerdesign.Consultfastenerandmaterialsassistance.Theimportantideashownistoreducethewallthicknessofthemoldingatthebottomofthebosstoreducethesinkmarkonthesurfaceduetotheexcessmassofmaterial.BossDesigns‘Open’bossdesignmaintainsuniformthicknessinthepartwall,andavoidsathintoolsteelcondition.BossCoreDepthWillformsinkmarkWillformsinkmarkGood,pincouldbealittlelonger.Pinmaybetoolong.Partmaybetoothin.BasicPartDesignPracticesSomeoilsandcoatingsonfastenersattackPCandABS+PC.UseHi-LotypethreadedscrewsfordirectengagementintoTPO,ASA,andNylonplasticbosses.Usemetalthreadedstudsandinsertsforhighloadattachments.BasicPartDesignPracticesAvoiddesigningvariablecrosssectionareasbecauseitallowsmaterialtoflowfasterinsomeareasthaninothers.Ejectorpinssometimesinterferewithcoolingwatercircuits,andpinsapplyforceonlyinsmallareas.Somepartsejectbetterbycontrollingcoolingratherthanexertingmechanicalforce.BasicPartDesignPracticesDraftangleof3degreesisnormallyusedforpaintedexteriorparts.Moreisaddedforgrainedparts.3+1.5/0.001’’graindeepth

Avoidsharpcornersandstress