外文翻译--节省模具材料费用细则.doc

-1-1-CostSavingsforMoldMaterials:ConsidertheDetailsWaystoreducecoststhatarenotrelatedtothepriceperpoundofthemoldmaterial.ByPatriciaMillerChoosingtherighttoolingmaterialforplasticmoldingisbecomingevermoredifficult.Inlightofintensecompetition,aswellasthecostofrawmaterials,whichisdrivingthepriceofmaterialsformoldsup,itbecomesincreasinglymoreimportanttobeselectiveinthechoiceofmoldmaterials.Therearethingsthatcanbedonetohelpthemoldmakermakethebestselectionsfortheapplicationathand,andthesethingsarenotsimplylookingatthepriceperpound.Butinordertodothis,themoldmakermustconsiderotherfactors.Thisstartsatthebeginningofthemoldmakingcycle,astheparttobemanufacturedisbeingproposed.Themajorareastobeconsideredinamolddesigninclude:SizeandcomplexityofthepartormoldProductionquantityrequiredTypeofplasticmoldingmaterialrequiredanditsimpactonthemoldingenvironmentMechanicalrequirementsforthemoldPhysicalpropertyrequirementsforthemold(thermalconductivity,stiffness,thermalexpansion)StabilityrequirementofmoldduringoperationAssemblyissues(matingmaterialcriteria,coatability)Designfeatures(sharpcorners,thinsections,sealingmethods)Surfaceconditionrequirements(polishing,texturingdemands)Manufacturingmethods(electrodis-chargemachining,hardmilling)Costsavingscanoccurinalltheseareas,butforthisdiscussionfourareasofalloyswillbeaddressed:1.Newhighhardnessmatrixalloys2.Thermallyconductivealloys3.Corrosionresistantmaterials4.PrehardenedalloysIneachcase,thecostofthemoldmaterialissignificantlyoutweighedbythebenefitsthesealloysbring.-2-2-Figure1.Amoldforplasticinjectionmoldedelectricmotorrotors,madeof30percentglass-filledPolyamide.Moldmaterialhas,todate,increasedthelifeofthemoldover20percent,eliminatingmoldrepairsandrefurbishment.FigurescourtesyofBohler-UddeholmCorporation.1.HighHardnessMatrixAlloysInanexcitingdevelopmentformoldmaterials,therearenowtoolsteelgradesavailablethatcanreplaceS7,H13andwithcoatingreplaceA2,D2andM2typeswherewearresistanceisrequired.Buttheadvantagethatthesegradesbringisthattheycanbeusedfrom50HRCupto62HRC,andareweldable,polishabletohighlevels,texturableandarecoatablewhenevenhigherwearresistanceisrequired.Figure2.Therelationshipofhighlyconductivealloys,thermalconductivityversushardness.ThenewCu-Nialloy,havinghardnesslevelslikethatofP20,hashigherthermalconductivitythanothercopperalloysandaluminum.Verytoughgrades,thesematerialsalsoprovideanaddedadvantagethatthermalconductivityexceedsthatofH13,hencecycletimescanbereduced.Thesegradesreplacepastcoldworkgradesthatcouldonlyachievetheirmechanicalpropertiesbylowtemperaturetempers,whichdidnotpermitgoodweldability,nitridingorPVDcoatingabove400oF.Theirhighpolishabilityandtexturabilityisduetotheexcellentuniformityofthematrixfromtheuseofhightechnologyremeltingprocesses.AnexampleofthisisshowninFigure1.AninjectionmoldinsertmadeofPolyamideplus30percentglassfiber,wasmanufacturedfromachromium-molybdenum-vanadiumalloyedtoolsteel.At54-56HRC,ithasbeenrunningforover7,700piecesandisstillrunningwell.PremiumH13at50-52HRCbegantowearandplasticallydeformat6,000pieces.2.ThermallyConductiveAlloysCopperalloyshavebeenavailableforseveralyearstoaddresstheneedforcycletimereductionandpartreproducibility,andhavebeenusedparticularlyforcoreswhereplasticresidingtimesarehighest.Copper-berylliumalloysareavailableinhardnessrangesof30-40HRC.Inaddition,thereisacopper-nickelalloythatcanachievehardnessof30HRC,whichisintherangeofatypicalP20.Theadvantagethisgradebringsisthatitsthermalconductivityexceedsthatofothercopperalloysinthishardnessrange,andalsothatof-3-3-aluminum.Thisgradealsoisantigallingandcorrosionresistant(seeFigure2).Figure3.Roughmillingofthecavity；premiumH13,45HRC.3.DesignandStainlessAlloysItistimetoreconsiderstainlessalloys.Therearenewstainlessalloyswhosebenefitsareclear:highpolishability,withtoughnesslevelsintherangeofPremiumH13,upto50-52HRC.Thefactthatthesealloyswillmaintaintheircorrosionresistancewithminimalneedforreworkorrepolishingoverthelifeofthemold,andstillprovideadurable,highmechanicalstrengthmold,isworthcarefulconsideration.Figure4.Drillingofcoolingchannels；premiumH13,45HRCOneareawhichhaslimitedthelifeofstainlessmoldsinthepasthasbeentheuseoftaperedpipeplugs.Heattreatmentlimitations,machiningissueswithdevel-opingthethreads,stressesgeneratedinthethreadsfollowingtorquing,alongwiththecorrosiveconditionsofdeadzoneswhichcreatepittingattackonthestainlesscanleadtocrackingintheseregions.Newstainlessalloyscanminimizesusceptibilitytothisalongwithplugdesignsthatareavailabletohandlehydraulicsealingissueswithoutmachiningthreadsintothemoldmaterial.4.PrehardenedMoldMaterialsLookingawayfromthesteelcosttomanufacturingtechnique,wenowseethedevelopmentofmachiningpractices,whichpermitthecustomertousegradesthatareprehardenedtohigherhardnessranges.ItisnowpossibletomachinegradeslikeH13athardnesslevelsintherangeof44-46HRC,andinmanycasesevenharder.Theadvantagethisbringsisthatthesteelcanbeprehardened,inamethodthatgivesexcellentpropertiesbecausethecoolingratescanbefasterwhenlessdetailisinthemold,andcrackingsusceptibilityisless.Theintegrityofthesteelincreases,whiletheneedforroughmachining,stressrelievingandprefinishmachiningiseliminated.Thissavestimeandmoney,whenusuallyatthestagewhenheattreatmentisperformed,timeconstraintsarehigh.Withthesetimeconstraints,cornersgetcutandheattreatmentisnotalwaysdonetooptimizethepropertyofthesteel.Tempersmaynotallgetdone,andcoolingratesaresloweddowntopermitlessstocktobelefton,becausethemoldmakerhaslesstimetoremovetheextrastock-4-4-neededforthemovementthatwilltakeplacefromagood,rapidquench.Figure5.Finishingmillingofcavity；premiumH13,45HRC.SomeexamplesofhowtomachineahardenedH13aregiveninFigures3,4and5.ConclusionTherearemanywaystoreducecostthatarenotrelatedtothepriceperpoundofthemoldmaterial.Withtheultimategoaltoprovidethecustomerwhattheyneedintermsofpartintegrityandreliability,manufacturingamoldthatwillprovideallofthesethingsinareasonablewayrequiresathoroughreviewofthedesigncriteria,manufacturingprocessesandproductiondemands.Newmaterialsandmethodsareavailablethatwerenottherethelasttimethemoldwasmade,thatcanhelpminimizetheoverallcostofthemold.