模具专业英语Unit4课件

陈显冰

Unit4MoldManufacturing4.1MachiningMethodsModerntoolingmachinesformoldmakinggenerallyfeaturemultiaxialCNCcontrolsandhighlyaccuratepositioningsystems.Theresultishigheraccuracyandgreaterefficiencyagainstrejects.Nowadays,heat-treatedworkpiecesmaybefinishedtofinalstrengthupto2000MPa,bymilling.Variousoperations,e.g.cavitysinkingbyEDM,canbyreplacedbycompletemillingoperationsandtheprocesschainthusshortened.Furthermore,thethermaldamagetotheouterzonethatwouldotherwiseresultfromerosiondoesnotoccur.Hardmillingcanbeusedbothwithconventionalcutting-toolmaterials,suchashardmetals,andwithcubicboronnitride(CBN).Forplasticinjectionmolds,hardmetalsorcoatedhardmetalsshouldprovetobeoptimumcutting-toolmaterials.Machiningfreesexistingresidualstresseswhichcancausedistortioneitherimmediatelyorduringlaterheattreatment.Itisadvisable,therefore,torelievestressesbyannealingafterroughing.Anyoccurringdistortioncanbecompensatedbyensuingfinishing,whichusuallydoesnotgenerateanyfurtherstresses.现代模具制造的加工设备其特征是多轴CNC控制和高精度定位系统，目的是要获得产品的高精度和降低不合格品率。目前，热处理后的工件可通过铣加工，最终强度可以达到2000Mpa。各种工艺，如EDM加工型腔，尽量用铣加工代替，这可以缩短加工工艺链。此外，还可以避免由于腐蚀工艺而导致的外部热损伤。铣加工既可用常规的刀具材料，如硬金属，也可用立方硼氮化合物（CBN）。对于注塑模具，硬金属或镀硬金属是最适合的刀具材料，切削加工释放了残余应力，可能会导致模具立即变形或在后面的热处理中出现变形。因此，明智的做法是在粗加工后进行退火以去除应力。任何变形都可通过后续修整来补偿，且通常不会再产生任何应力。Afterheattreatment,themachinedinsertsarefinished,groundandpolishedtoobtainagoodsurfacequality,becausethesurfaceconditionsofacavityare,intheend,responsibleforthesurfacequalityofaplasticpartanditseaseofrelease.热处理后，模具镶件要经过修整、磨削和抛光以获得良好的表面质量，这是因为型腔表面的质量最终会影响注塑制品的表面质量及脱模。Defectsinthesurfaceofthecavityarereproducedtodifferentextendsdependingonthemoldingmaterialandprocessingconditions.Deviationsfromtheidealgeometricalcontourofthecavitysurface,suchasripplesandroughness,whichincreasethenecessaryreleaseforces.由于注塑制品的材料与注塑工艺的差异，型腔表面的缺陷会不同程度地被复制出来。型腔表面的偏差，如波纹和粗糙不平，需增加脱模力。Competitionhasrecentlydevelopedbetweenhigh-speedcutting(HSC)andsimultaneousfive-axismilling.HSCischaracterizedbyhighcuttingspeedsandhighspindlerotationspeeds.Steelmaterialswithhardnessvaluesofupto62HRCcanalsobemachinedwithcontemporarystandardHSCmillers.Sometimes,HSCmachiningcanbecarriedoutasacompletemachiningsothattheprocessstepsofelectrodemanufacturinganderodingcanbedispensedwithcompletely.Inaddition,bettersurfacequalityisoftenachieved,andthisallowsdrasticreductioninmanualpostmachining.高速加工（HSC）和五轴铣加工艺展开了激烈的竞争，高速加工的特点是高切削速度和高主轴转速。硬度达62HRC的钢材也能用当今标准的HSC铣床加工。有时，HSC可实现完整加工，于是可省去电极制作及腐蚀加工。此外，告诉加工常常还可以得到更好的表面质量，从而可以大大减少后期的手工修正。Fortheproductionofinjectionanddie-castingmolds,acombinationamountofmillingshouldbemaximizedsincethemachiningtimesareshorteronaccountofhigherremovalcapability.Howeververycomplexcontours,filigreegeometriesanddeepcavitiescanbeproducedbysubsequentspark–erosivemachining.Theelectrodecan,inturn,bemadefromgraphiteorcopperbyHSC.对于注射和压铸模具，可综合采用铣削和电火化加工方法来加工。由于铣削加工去除材料的能力更大，所以为了缩短加工时间，应使铣削量达到最大。然而，对于复杂的轮廓、薄细形体和深腔要用后续的电火花加工完成，可用HSC切削石墨或铜而得到电极。WhenmachiningtheprogramfromapartdrawingtooperatetheCNCmachinetool,firstpreparetheprogram,thenoperatetheCNCmachinebyusingtheprogram.当用CNC机床加工零件时，首先要编写程序，然后用程序操作CNC机床。

TheprogramistobereadintotheCNCsystem.Then,mounttheworkpiecesandtoolsthemachine,andoperatethetoolsaccordingtotheprogramming.Finally,executethemachiningactually.程序被读进CNC系统中，然后，在机床上安装工件和刀，并且根据程序运行刀具，最后进行加工。Beforetheactualprogramming,makethemachiningplanforhowtomachinethepart.Itincludes:1)Determinationofworkpiecesmachiningrange.2)Methodofmountingworkpiecesonthemachinetool.3)Machiningsequenceineverymachiningprocess.4)Machiningtoolsandmachining.在实际编程前，应制定如何加工零件的加工计划，包括：1）确定工件加工的范围。2）在机床上安装工件的方法。3）每个加工过程的加工顺序。4）刀具和加工。

ACNCmachinetoolisprovidedwithfixedposition.Normally,toolchangeandprogrammingofabsolutezeropointasdescribelaterareperformedatthisposition.ThispositioniscalledthereferencepositionasshowninFig.4.1.一台数控机床设定一个特定的位置。通常，在这个位置进行换刀和设定编程的绝对零点。这个位置称为参考位置（点），如图4.1所示。

Thetoolcanbemovedothereferencepositionintwoways:1)Manualreferencepositionreturn.Automaticreferencepositionreturn.把刀具移动到参考点，有以下两种方法：1）手动返回参考点。2）自动返回参考点。Thefollowingtwocoordinatesystemsarespecifiedatdifferentlocations:1) Coordinatesystemonpartdrawing.Thecoordinatesystemiswrittenonthepartdrawing.Astheprogramdata,thecoordinatevaluesonthiscoordinatesystemareused.2) CoordinatesystemspecifiedbytheCNC.Thecoordinatesystemispreparedontheactualmachinetooltable.ThiscanbeachievedbyprogrammingthedistancefromthecurrentpositionofthetooltothezeropointofthecoordinatesystemtobesetasshowninFig.4.2.

下面两个坐标系被指定在不同位置：1）零件图样上的坐标系。在零件图样上设定坐标系，该坐标系上的坐标值用作编程数据。2）由CNC设定的坐标系。该坐标系在实际机床工作台上设定。用程序编制从刀具的当前位置到要设定坐标系的零点的距离设定该坐标系，如图4.2所示。Thepositionrelationbetweenthesetwocoordinatesystemsisdeterminedwhenaworkpieceissetonthetable.

当工作安装在工作台上后，就决定了这两个坐标系的位置关系。ThetoolmovesonthecoordinatesystemspecifiedbytheCNCinaccordancewiththecommandprogramgeneratedwithrespecttothecoordinatesystemonthepartdrawing,andcutsaworkpieceintoashapeonthedrawing,thetwocoordinatesystemsmustbesetatthesameposition.按照零件图样坐标系编制的程序指令，刀具在CNC设定的坐标系中移动，把工件加工成图样指定的形状。因此，为了正确地把工件加工成图样指定的形状，两个坐标系必须设在同一位置。Commandformovingthetoolcanbeindicatedbyabsolutecommandorincrementalcommand.Thetoolmovestoapointat“thedistancefromzeropointofthecoordinatesystem”thatistothepositionofthecoordinatevalues.Incrementalcommandspecifiesthedistancefromtheprevioustoolpositiontothenexttoolposition.如图4.3所示，移动刀具的指令可以用绝对值或增量值表示。绝对值指令是刀具移动到“距坐标系零点某一距离”的点，即刀具移动到坐标值的位置。增量值

指令是刀具移动到下一个位置的位移量。

Thesystemofthetoolwithrespecttotheworkpiecewhentheworkpieceiscutiscalledthecuttingspeed.AsfortheCNC,thecuttingspeedcanbespecifiedbythespindlespeed.切削工件时刀具相对于工件的速度称为切削速度。对于CNC，切削速度可用主轴速度指令。Whendrilling,tapping,boring,millingorthelike,isperformed,itisnecessarytoselectasuitabletool.Whenanumberisassignedtoeachtoolandthenumberisspecifiedintheprogram,thecorrespondingtoolisselected.Forexample,whenthetoolisstoredatlocation01intheATCmagazine,thetoolcanbeselectedbyspecifyingT01.ThisiscalledthetoolfunctionasshowninFigure4.4.当进行钻孔、攻丝、镗孔、铣削等加工时，必须选择适当的刀具。给没把刀具赋给一个编号，在程序中指令不同的编号时，应选择相应的刀具。例如，把01号赋给钻头，当这把刀具放在ATC的01号位时，通过指令T01可以选择这把刀具。该功能称为刀具功能。如图4.4所示。

Whenmachiningisactuallystarted,itisnecessarytorotatethespindle,andfeedcoolant.Forthispurpose,on-offoperationsofspindlemotorandcoolantvalveshouldbecontrolled.Thefunctionofspecifyingtheon-offofthemachineiscalledthemiscellaneousfunction.Ingeneral,thefunctionisspecifiedbyanMcode.Forexample,whenM03isspecified,thespindleisrotatedclockwiseatthespecifiedspindlespeed.当开始实际加工时，需要旋转主轴并供给切削液。为此需要控制主轴电机和冷却泵的启动停止操作。指令机床部件的启停操作的功能称为辅助功能。通常，该功能用M代码指令。例如，当指令MO3时，主轴以指令的主轴速度按顺时针方向旋转。ThetoolpathinFigure4.4canbeprogrammedasfollow:1)InabsoluteprogrammingG92X200.0Y40.0Z0;G90G03X140.0Y100.0R60.0F300.;G02X120.0Y60.0R50.0;OrG92X200.0Y40.0Z0;G90G03X140.0Y100.0I-60.0F300.;G02X120.0Y60.0I-50.0;2) InincrementalprogrammingG91G03X-60.0Y60.0R60.0F300.;G02X120.0Y-40.0R50.0;orG91G03X-60.0Y60.0I-60.0F300.;G02X-20.0Y-40.0I50.0;图4.5的刀具轨迹编程如下：1)绝对编程G92X200.0Y40.0Z0;G90G03X140.0Y100.0R60.0F300.;G02X120.0Y60.0R50.0;或G92X200.0Y40.0Z0;G90G03X140.0Y100.0I-60.0F300.;G02X120.0Y60.0I-50.0;2)增量值编程G91G03X-60.0Y60.0R60.0F300.;G02X-20.0Y-40.0R50.0;或G91G03X-60.0Y60.0I-60.0F300.;G02X-20.0Y-40.0I-50.0;Ontheotherhand,sofardeepholedrilling(gundrilling)hasbeenusedmoreandmorewidelyininjectionmolds.Thismethodrequiresaspecialmachineoradeepholedrillingadaptortoanothermachine,suchasamillingmachine.Thedrilloperatesinahorizontalplane.Therearefouressentialdifferencesfromordinarydrillingormillingmachines:1)Thestrokeofthemachine(depthofhole)canbeconsiderablelarge.2)Thedrillissupportedveryclosetotheworkpiece,aswithadrilljig.3)Thecuttingedgeofthedrillisdirectly,pressurelubricated.4)Thedrillworksinonepassthroughsolidmaterial.Itdoesnotrequirepredrilling.另一方面，目前在注塑模具制造中广泛应用深孔钻削（枪钻），这种方法需要一个特别的机床或用其他机床连接深孔钻削装置，如铣床。钻削在水平面内操作，与普通的钻床或铣床有以下四个重要的不同：1)机床钻孔的深度能够相当大。4)钻头钻通固体材料，不需预钻。2)钻头支撑可非常接近工件，如同钻削夹具。3)钻头的切削刃直接受到压力润滑和冷却。Therearetwotypeofdrill,featuringeitherinternalorexternalchipremoval.Theexternalchipremovalmethodismostlyused.有两种钻头，区别是内部去屑或外部去屑，外部去屑方法是最常用的。4.2SparkmachiningSparkmachiningisaprocessinwhichsteelorothermetalscanbemachinedbytheapplicationofanelectricaldischargespark.Thesparkislocalizedandmetalisprogressivelyremovedinsmallquantitiesoveraperiodoftime.电火花加工是指通过电极放电来加工钢件或其他金属材料的工艺方法。电火花的放电位置是固定的，而被加工金属材料是在一定时间内以很小的去除率逐渐加工完成的。Firstconsiderthesparkerosionmachine.ThisisillustrateddiagrammaticallyinFigure4.5.Theworkpiece,whichinourcaseisamouldinsertblank,ismountedonaplatenandsubmergedinatankcontainingadielectricfluid(normallyparaffin).Thetankismountedonthemachinebase.Thetool,whichhastherequiredcomplementaryformofthecavity(i.e.similartoahob),ismountedinachuckwhichisattachedtoaverticalrack.Aservomotor(notshown)actuatestherackviathepinion.Thusthetoolcanbemovedintheverticaldirectionwithrespecttotheworkpiece.Boththetoolandtheworkpieceareconnectedtoanelectricalsupply,andthetoolbecomesanegativeelectrodeandtheworkpieceapositiveelectrode.首先考虑电火花加工机床，如图4.6所示。在我们所研究的情况中，工件是模具拼块坯料，坯料装在台板上，浸入盛有电介液（通常为石蜡）的电介槽中，电介槽安装在机床机座上。电极安装在立式齿条的夹盘中，其形状与模具型腔相符（与挤压头类似）。伺服电机（图中没有表示）通过小齿轮驱动齿条运动，由此，电极就实现了在垂直方向上与工件的相对运动。工件和电极均与电源相连接，当然，电极作为负极，工件作为正极。4.3CuttingbySparkErosionwithTraveling-WireElectrodesThisisaveryeconomicalprocessforcuttingthrough-holeofarbitrarygeometryinworkpieces.Thewallsoftheopeningsmaybeinclinedtotheconsiderableefficiencyofthisprocess,somecavitiesareincreasinglybeingcutdirectlyintomoldplatesasshowninFig.4.7.对于任意形状通孔的加工，线切割是相当经济的方法。开敞的型腔壁可以先倾斜，然后进行线切割加工。线切割加工效率很高，在模板上可直接加工型腔，如图4.7所示。Themetalisremovedbyanelectricaldischargewithoutcontactormechanicalactionbetweentheworkpieceandathinwireelectrode.Theelectrodeisnumericallycontrolledandmovedthroughthemetallikeajigorbandsaw.Deionizedwateristhedielectricfluid,andisfedtothecuttingareathroughcoaxialnozzles.Itissubsequentlycleanedandregeneratedinseparateequipment.Modernequipmenthas5-axisCNCcontrolwithhigh-precisionpositioningsystems.工件的金属材料在与细丝电极之间在没有接触和机械作用的情况下被切割，电极在数控下像带锯一样穿过金属，去离子水是绝缘体，通过同轴喷管流入切割区，随后被清理并在分离设备中回收，现代线切割设备已具有5轴CNC高精度定位系统。Deionizedwaterhasseveraladvantagesoverhydrocarbons.Itcreatesawidersparkgap,whichimprovesflushingandthewholeprocess.Thedebrisislower.Therearenosoliddecompositionproductsandnoarcisgeneratedthatwouldinevitablyresultinawirebreak.去离子水比碳氢化合物的优点更多。能产生更宽的火花间隙，从而改善冲洗及整个工艺，淬屑更少，无固体分解物体并且不会产生电弧，从而不容易把线弄断。Standardequipmentcanhandlecomplicatedopeningsanddifficultcontourswithcuttingheightsupto600mm.Thewidthofthegapdependsonthediameterofthewireadiameterof0.03to0.3mm.Thewireisconstantlyreplacedbywindingfromareel.Abrasionandtensionwouldotherwisecausethewiretobreak.Furthermore,thecutswouldnotbeaccurateasthewirediameterwouldbecomeprogressivelyshorter.标准的线切割设备可以切割厚度到600mm的敞开的复杂工件。间隙的宽度取决于线电极的直径，其值从0.03~0.3mm，经常做成卷轴线圈。磨损和拉紧会将电极线拉断，而且随着电极线的直径的减小，会影响切割精度。4.4ElectrochemicalMaterialRemoval-EtchingFordecorativeorfunctionalpurpose,asurfaceisveryoftentextured.Thisiseitherdoneforcosmeticreasons,forobtainingamorescratchandwearresistantsurface(e.g.leatherorwoodgrain)orabetterhand.Flowmarksandweldlinescanbehidden,too.由于需要装饰或增加某些功能，经常需要在模具表面加工出纹理，或是出于包装的原因，或是使注塑制品表面抗刮伤的抗磨损（例如羽毛或木材纹理）或是增加舒适的手感，模具纹理也用于掩饰留痕和溶接痕。Thebasisofthisprocessisthesolubilityofmetalsinacidsandsaltsolutions.Metallicdissolveasaresultofpotentialdifferencesbetweenmicroregionsofthematerialorbetweenmaterialandetchingagent.Themetalatomsemitelectronsandaredischargedasionsfromthemetallattice.Thefreeionsareusedupbyreducingprocesseswithcationsandanionspresentintheetchingagent.Theremovedmetalcombineswithanionstoformaninsolublemetalsalt,whichhastobrremovedfromtheetchingagentbyfilteringorcentrifuging.电化学腐蚀工艺的基础是金属在酸和盐溶液中的溶解性。金属材料的溶解是材料的微观区域之间或材料与蚀刻介质之间的电压势差的结果。金属原子释放出电子并从金属点阵中以离子的形式逸出，自由的离子在蚀刻介质中，被阳离子和阴离子中和。腐蚀下来的金属和阴离子相结合生成不能溶解的金属盐，然后通过过滤或离心分离从蚀刻介质中除掉。Almostallsteels,withoutrestrictionontheamountofalloyingelementssuchasnickelorchromiumincludingstainlesssteel,canbechemicallymachinedortextured.Besidessteelmolds,thosemadeofnonferrousmetalscanalsobechemicallytreated.几乎所有的金属，若没有某些合金元素，如镍或铬的限制，包括不锈钢都可以用化学方法加工或产生纹理。除了钢模具，不含铁的金属模具也可以用化学方法处理。Thesurfacefinishthatcanbeachievedbychemicalmaterialremovedoretchingdependsmostlyonthematerialanditssurfaceconditionsand,ofcourse,ontheetchingagent,Uniformremovalisonlyachievedwithmaterialsthathaveahomogeneouscompositionandstructure.Thefinerthegrainofthestructure,thesmootherandbettertheetchedsurfacewillturnout.Thereforemoldsarefrequentlyheat-treatedbeforeetching.Thedepthofheattreatmentshouldalwaysbegreaterthanthedepthofetching.Ifthisisnotthecase,theheat-treatedlayermaybepenetrated.Thiswouldresultinveryirregularetching.Adequatelayersareobtainedbyhardening.通过化学方法去除材料或蚀刻的模具表面质量主要取决于模具材料、表面状况和腐蚀介质。均衡的去除只能在具有均匀的成分和结构的材料中实现。结构的颗粒越好，腐蚀产生的表面越光滑。因此模具在腐蚀前经常要热处理，热处理的深度应该腐蚀的深度大。否则，热处理层会穿透，从而导致不规则腐蚀。通过表面硬化能得到足够厚的表层。Theinitialroughnessofthemoldplaysanimportantroleasregardsthesurfacefinishafteretching.Non-permissibletracesfrommachiningarenotcoveredupbutremainhazilyvisible.Beforeetching,thesurfaceshouldbewellplannedwithanabrasive.Thepermissibledepthofetchingdependsontheinjectionmoldingprocessingconditions.Thespeedofmaterialremovalisdeterminedbytheetchingagent,thetemperatureandthetypeofmaterial.Itincreaseswithrisingtemperature.模具的初始粗糙度对于腐蚀后表面的质量具有重要的影响机加工的痕迹可能未被覆盖并隐约可见，因此，在腐蚀模具表面应该用研磨剂来磨平。允许的腐蚀深度取决于注塑条件。去除材料的速度取决于腐蚀介质、温度和材料的类型，随着温度的升高而增加。Basicallytherearetwoproceduresemployedforetching,namelydipetchingandsprayetching.Bothhaveadvantagesanddisadvantages.Withdipetchingmoldsofalmostanysizecanbrtreatedinsimple,cost-effectiveequipment.Differentarisefromtheneedfordisposingofthereactionproductsandconstantlyexchangingtheetchingagentnearthepartsurface.Itiseasiertoremovethereactionproductsinsprayetchingandmaintainasteadyexchangeoftheagentonthepartsurface.Theprocessitself,however,takesconsiderablymoreeffortandequipmentismoreexpensive.Theetchingagentispressurizedandsprayedthroughnozzlesagainstthesurfacetobeetched.Anymasksforareasnottobeetchedmustnotbedestroyedwhenhitbythespray,orlifted,permittingtheagenttoactunderneath.通常有两种腐蚀方法，浸渍蚀刻和喷射腐蚀，这两种方法既有优点又有缺点。对于蚀刻，任何尺寸大小的模具都可以在简单的低成本的设备中处理。但在处理反应产物和持续交换接近零件表面的腐蚀介质时出现困难。在喷射腐蚀中，反应产物更容易被移走且能稳定交换零件表面的介质腐蚀，但工艺本身费时费钱。腐蚀介质被加压并从喷嘴喷射到模具表面上，当喷嘴喷射时一定不能将其覆盖非腐蚀区域的覆盖物损坏，或者提起覆盖物，使介质在其下产生反应。4.5RapidToolingTimeandcostarebecomingmoreandmoreimportantfactorsinthedevelopmentofnewproducts.Itisthereforeextremelyimportantfortheinjectionmoldingindustrytoproduceprototypesthatcangointoproductionasquicklyaspossible.Tobesure,rapidprototypingisbeingemployedmoreandmoreoftenbutmuchprototypesfrequentlycannotfullymatchtheimposedrequirements.Wherethereisaneedformoldsthatareasclosetogoingintoproductionaspossible,RT(rapidtooling)istheonlyprocessbywhichthemoldscanbemadethatwillenabletheproductionofinjectionmoldedprototypesfromthesamematerialthatwilleventullybeusedforthemassproducedpart.Suchproximitytoseriousproduction,however,alsoentailsgreateroutlayontimeandcostsforthisreason.RTwillonlybeusedwherethespecificationsrequireit.在开发新产品过程中，时间和成本越来越重要。因此对注塑工业来说，制造能尽快投入生产的样模往往不能完全满足特定要求。在需要模具尽可能快地投入生产的场合，RT（快速制模）是制造模具的唯一办法，该方法能使用最终批量生产所用的相同材料生产注塑样件。然而，这种接近于连续生产的方式在时间和费用上的代价也是很大的。基于这种原因，快速成形只用于有特殊要求的场合。Thematerialadditiveprocessesleadfastesttomoldingandarethereforethemostpromising.ThesealsoincludenewandfurtherdevelopmentinRP.Examplesofsuchtechniquesarelasersintering,laser-generatedRPandstereolithography,whichenablemoldinsertstobemadedirectlyfromathere-dimensionalCADmodelofthedesiredmold.RTalsocoversmetalspraying,whichhasbeenusedfordecadesinmoldmaking.材料叠加工艺使成型过程最快，因此是最有前途的快速原型制造方法。其中包括RP（快速原型制造）领域的新技术，如激光烧结、激光生成RP和立体平版印刷，它们都能从三维CAD模型直接制造出模具镶件来。RT也包括金属喷涂工艺，该技术已在模具制造中涌来几十年。MastermoldingtechniqueslikeprecisionandresincastingmaybeconsideredasbelongingtoRT.TheseprocesschainsbecomerapidtoolingtechniqueswhenanRPtechniqueisusedtoproducethenecessarymastermold.像精密树脂成型等母模成型技术也认为属于RT技术，当采用RP技术生产母模是，这些工艺过程便成为快速制模方法。Whereas,inthetechniquesmentionedsofar,theprototypemoldisproducedeitherdirectlybymeansofamaterialadditivemethodorinseveralprocessingstages,thesocalledhybridtechniquesintegrateseveralsuchstagesinoneitemofequipment.Theseprocessingstagesareacombinationofprocessesfromtheotherthreegroups(conventional,master-molding,andmaterialadditivetechniques).Becausebybridadditivetechniquescombinesequentialprocessesinunit,theycanbejustasfastasthematerialadditivetechniques.在目前提到的这些技术中，原模型由材料叠加方法制造，或者由将几种工艺阶段进行组合，即用所谓的混成技术的设备来制造，这种工艺是其他三组工艺的结合（传统加工、母模成型和材料叠加技术）。由于混合技术将几种有序的技术结合成一个单元，因此它们能像材料叠加技术一样快。EXERCISEQuestions1.Whatisthedifferencebetweenabsolutecommandandincrementalcommand?2.WhatisthePrincipleofmachinecontrolforelectric-dischargebandsawingwithwireelectrodes?3.Whataretheadvantagesanddisadvantagesofdipetchingandsprayetching?4.Whyisrapidtoolingtheonlyprocessbywhichthemoldscanbemadethatwillenabletheproductionofinjectionmoldedprototypesfromthesamematerialthatwilleventullybeusedforthemassproducedpart?ReadingMaterial:DieLifeandDieFailure

Properselectionofdiematerialandofthediemanufacturingtechniquedetermines,toalargeextent,theusefullifeofformingdies.Diesmayhavetobereplacedforanumberofreasons,suchaschangesindimensionsduetowearorplasticdeformation,deteriorationofthesurfacefinish,andcrackingorbreakage.Inhotimpressiondieforging,theprincipalmodesofdiefailureareerosion,thermalfatigue,mechanicalfatigueandplasticdeformation.正确选用模具材料和模具制造技术，在很大程度上决定了成形模具的使用寿命。在以下情况发生时需要更换模具，如磨损和塑性变形导致模具尺寸发生变化，模具表面粗糙度下降，或模具发生破裂或破坏。对热锻成形而言，模具的主要失效形式为：模具腐蚀、热疲劳、机械疲劳和塑性变形。Inerosion,alsocommonlycalleddiewear,materialisactuallyremovedfromthediesurfacebypressureandslidingofthedeformedmaterial,wearresistanceofthediematerial,diesurfacetemperature,relativeslidingspeedatthedie/materialinterfaceandthenatureoftheinterfacearethemostsignificantfactorsinfluencingabrasivediewear.Thermalfatigueoccursonthesurfaceofdieimpressioninhotformingandresultsin“heatchecking”.Thermalfatigueresultsformcyclicyieldingofthediesurfaceduetocontactwiththehotformingmaterial.Thiscontactcausesthesurfacelayerstoexpand,and,becauseoftheverysteeptemperaturegradients,thesurfacelayersaresubjecttocompressivestressed.Atsufficienthightemperatures,thesecompressivestressedmaycausethesurfacelayerstodeform.Whenthediesurfacecools,astressreversalmayoccurandthesurfacelayerswillthenbeintension.Afterrepeatedcyclinginthismanner,fatiguewillcauseformationofacrackpatternthatisrecognizedasheatchecking.Diebreakageorcrackingisduetomechanicalfatigueandoccursincaseswherethediesareoverloadedandlocalstressesarehigh.Thediesaresubjectedtoalternatingstressesduetoloadingandunloadingduringthedeformationprocess,andthiscausecrackignitionandeventualfailure.模具腐蚀，通常称为模具磨损，实际上