模具专业英语Unit2课件

Unit2BlangkingTechnique陈显冰

Overview2.1Cutting(Shearing)Operations

Thecuttingofmetalbetweendiecomponentsisashearingprocessinwhichthemetalisstressedinshearbetweentwocuttingedgestothepointoffracture,orbeyonditsultimatestrength.金属材料早冲裁模具间的冲裁切断时剪切应力达到断裂点或超出材料强度极限的一种剪切过程。Themetalissubjectedtobothtensileandcompressivestresses;stretchingbeyondtheelasticlimitedoccurs,thenplasticdeformation,reductioninarea,andfinally,fracturingstartsthroughcleavageplanesinthereducedareaandbecomescomplete.金属承受拉应力和压应力。在超出弹性极限时发生伸长，然后进入塑性变形，断面减小，最终裂纹沿不断减小的断面上的撕裂带扩展，从而实现完全分离。

ThefundamentalstepsinshearingorcuttingareshowninFigure2.1.Thepressureappliedbythepunchonthemetaltendstodeformitintothedieopening.Whentheelasticlimitisexceededbyfurtherloading,aportionofthemetalwillbeforcedintothedieopeningintheformofanembossedpadonthelowerfaceofthematerial.Acorrespondingdepressionresultsontheupperface,asindicatedatFigure2.1a.Astheloadisfurtherincreased,thepunchwillpenetratethemetaltoacertaindepthandforceanequalportionofmetalthicknessintothedie,asindicatedatFigure2.1b.Thispenetrationoccursbeforefracturingstartsandreducesthecross-sectionalareaofmetalthroughwhichthecutisbeingmade.Fracturewillstartinthereducedareaatbothupperandlowercuttingedges,asindicatedatFigure2.1c.Iftheclearanceissuitableforthematerialbeingcut,thesefractureswillspreadtowardeachotherandeventuallymeet,causingcompleteseparation.Furthertravelofthepunchwillcarrythecutportionthroughthestockandintothedieopening.

图2.1描述了冲裁和剪切的基本过程。处于金属上部的凸模施压使金属变形并进入凹模入口。当继续加载超出材料的弹性极限时，金属的一部分将被压入凹模入口，在材料下表面形成压痕，上表面也相应地发生变形，如图2.1a所示。当载荷继续增加时，凸模将把金属压入到某一个深度，直至压入凹模的深度等于金属的厚度，如图2.1b所示。这个压入过程发生在剪切引起的断裂开始和金属横截面减小之前，在上、下剪切刃处缩小的断面上均出现裂纹，如图2.1c所示。对于被剪切的材料，若间隙适当，则裂纹将相向扩展并最终相遇，从而引起材料的完全分离。凸模继续下行将冲下的部分通过料架推入凹模的漏料孔。1)CenterofPressureIfthecontourtobeblankedisirregularlyshaped,thesummationofshearingforcesononesideofthecenteroftherammaygreatlyexceedtheforcesontheotherside.Suchirregularlyresultsinabendingmomentinthepressram,andundesirableandmisalignment.Itisthereforenecessarytofindapointaboutwhichthesummationofshearingforceswillbesymmetrical.Thispointiscalledthecenterofpressure,andisthecenterofgravityofthelinethatistheperimeteroftheblank.Itisnotthecenterofgravityofthearea.Thepresstoolwillbedesignedsothatthecenterofpressurewillbeontheaxisofthepressramwhenthetoolismountedinthepress.如果所冲裁的零件轮廓是不规则形状，滑块一侧的剪切力的总和将远远超过另一侧的剪切力。这种不规则形状将导致压力机滑块处在弯曲力矩的作用下，产生偏斜和变形。因此，寻找一个能使剪切力的总和对称（平衡）的点是很有必要的，这个点就称之为压力中心，它是冲裁轮廓线的重心，而非（封闭区域内）面积的重心。2)ClearancesClearanceisthespacebetweenthematingmembersofadieset.Properclearancebetweencuttingedgesenablethefracturestomeet.Thefracturedportionoftheshearededgewillhaveacleanappearance.Foroptimumfinishofacutedge,properclearanceisnecessaryandisafunctionofthetype,thickness,andtemperoftheworkmaterial.间隙是一副模具凸、凹模之间的配合空间。剪切刃之间的合理间隙可以确保裂纹汇合。剪切刃的撕裂部分将形成一条光亮带。为了保证剪切刃的最佳精度，合理的间隙是必要的饿，其大小取决于所冲压成形材料的种类、厚度、韧度（硬度）。3)CuttingForcesTheforcerequiredtocut(shear)theworkmaterialcanbecalculatedbyusingthefollowingformulas:剪切工件材料所需的冲裁（剪切）力可以使用如下公式进行计算：4)StrippingForcesTheforcerequiredtostriptheworkmaterialoffpunchescanbecalculatedbyusingthefollowingformulas:(forcontours)(forroundholes)Where—Cuttingforceinpounds;—Thicknessofmaterialininches—Cuttingforceintons;—Diameterininches.—Strippingforceinpounds;—Strippingforceintons;—Shearstrengthinpoundspersquareinch;—Lengthofcutininches;;

从凸模上卸下材料的力可以使用如下公式进行计算：

式中P____剪切力（1b）

TN____冲裁力（t）

Ps____卸料力（1b）

TNs____卸料力（t）

S____材料抗剪强度（lb/in）

L____剪切轮廓线长度（in）

T____材料厚度（in）

D____凸模直径（in）5)PressTonnageThisisatotalofforcesrequiredtocutandformthepartwitha30%safetyfactoradded.Inmanycases,youwillhavetoaddstrippingforceifstrippingisbeingdonewithaspring-loadedstripper,becausethepresshastocompressthespringswhilecuttingthematerial.Likewise,anyspringpressureforforming,drawpads,andthelike,willhavetobeadded.压力机吨位是剪切和成形零件所需要的力加上考虑30%的安全因素的力的总和。在很多情况下，如果使用弹簧驱动的卸料装置，还必须加上卸料力，因为在冲剪材料时的压力机必须有压缩弹簧。相应地，对于任何利用弹簧力成形、拉深凸缘（防皱）及类似的用途都应加上弹簧力。2.2BlankingTechnique1)BendingdiesBendingistheuniformstrainingofmaterial(usuallyflatsheetorstripmetal)aroundastraightaxiswhichliesintheneutralplaneandnormaltothelengthwisedirectionofthesheetorstrip.Metalflowtakesplacewithintheplasticrangeofthemetal,sothatthebendretainsapermanentsetafterremovaloftheappliedstress.Theinnersurfaceofabendisincompression;theoutersurfaceisintension.Apurebendingactiondoesnotreproducetheexactshapeofthepunchanddieinthemetal;suchareproductionisoneofforming.Theneutralaxisistheplaneareainbendmetalwhereallstrainiszero.弯曲是指材料（通常是板料或条料）围绕位于中性面上的纵向方向的直线轴产生均匀变形的冲压工艺。因为（弯曲时）金属流动发生在金属塑性变形范围内，所以去除施加的外力后，弯曲将保持永久的变形。弯曲件的内表面处于压缩状态，外表面处于拉深状态。单一的弯曲工序并不能使金属材料呈现出与模具的凸模或凹模完全一致的形状，这种复制工艺也是一种成型方法。在受到弯曲作用的金属中，中性面是弯曲金属上张力为零的平面区域。Metalsheetorstrip,supportedbyaVblock,isforcedbyawedge-shapedpunchintotheblock.ThismethodtermedVbending(Figure2.2),producesabendhavinganincludedanglewhichmaybeacute,obtuse,orof90°.Frictionbetweenaspring-loadedknurledpinintheveeofadieandthepartwillpreventorreducesidecreepofthepartduringitsbending.OthermethodsareZ-bending(Figure2.3),edgebendingandU-bending,etc.

放置在V形支撑块的板料或条料在楔形冲头的作用下压入V形凹模，这类弯曲方式称为V形弯曲（图2.2）。V形弯曲能够生产带有钝角、锐角或直角的弯曲件。V形模具内的弹簧加载压销和零件之间的摩擦力将阻止或减少弯曲时零件边缘的移动。其他弯曲方式有Z形弯曲（图2.3）、侧边弯曲和U形弯曲等。2)DrawingdiesDrawingisaprocessofchangingaflat,precutmetalblankintoahollowvesselwithoutexcessivewrinkling,thinning,orfracturing.Thevariousformsproducedmaybecylindricalorbox-shapedwithstraightortaperedsidesoracombinationofstraight,tapered,orcurvedsides.Thesizeofthepartsmayvaryfrom0.25mmdiameterorsmallertoaircraftorautomotivepartslargeenoughtorequiretheuseofmechanicalhandingequipment.

拉深是指把一定形状的金属平板制成空心零件而不发生起皱、变薄或开裂现象的冲压工序。不同形状的拉深可得到侧壁不同的圆柱形或盒形制件，这些侧壁的形式有：直壁、锥形壁、直壁和锥形的混合侧壁以及曲面壁。拉深件的尺寸相差很大，从直径为0.25mm或更小的拉深件，到足以覆盖机械设备的航天器或汽车覆盖件。Thesimplesttypeofdrawdiesisonewithonlyapunchanddie.Onetypeofdrawingdieforuseinasingle-actionpressisshowninFigure2.4.Thisdieisplainsingle-actiontypewherethepunchpushesthemetalblankintothedie,usingaspring-loadedpressurepadtocontrolthemetalflow.Thepunchhasanairventtoeliminatesuctionwhichwouldholdthecuponthepunchanddamagethecupwhenitisstrippedfromthepunchbythepressurepad.Thesketchshowsthepressurepadfittingthestoppin,whichactsasaspacerthatanevenandproperpressureisexertedontheblankatalltimes.Ifthespringpressurepadisusedwithoutthestoppin,themorethespringsaredepressedthegreaterthepressureexertedontheblank,therebylimitingthedepthofdraw.Becauseoflimitedpressuresobtainable,thistypeofdieshouldbeusedwithlight-gagestockandshallowdepths.最简单的拉深模只带有一对凸模和凹模，图2.4所示为单次拉深的一种拉深模结构。这种结构是简单的单次拉深类型，冲头把金属坯料压入凹模，利用弹压板控制金属流动。冲头上开设的排气孔能够消除推出（拉深件）时产生的真空吸力，这种真空现象能使杯形拉深件包紧在冲头上，若由压料板强制脱模，（则）会损坏杯形件。图中所示的模具装有压料板（压料板上带有限位螺钉），压料板起压料作用，冲压时能为冲头外的坯料提供均匀而合适的压力。如果弹压板没有安装限位螺钉，那么弹簧压缩量越多，板料承受的压力就越大，这将限制拉深的程度。由于有效压力有限，这种拉深模适用于所需冲压力较小及深度较浅的冲压件。3)CompoundDiesAcompounddieperformsonlycuttingoperations(usuallyblankingandpiercing)whicharecompletedduringasinglepressstroke.Acharacteristicofcompounddiesistheinvertedpositionoftheblankingdieandblankingpunchwhichalsofunctionsasthepiercingdie.AsshowninFigure2.5,thedieisfastenedtotheuppershoeandtheblankingpunchhavingataperedholeinitandinthelowershoeforslugdisposalismountedonthelowershoe.

（落料冲孔）复合模是指在一次冲压行程中完成（两种）冲裁工序（通常包括落料和冲孔）的模具。复合模的特点是能够调转落料模和冲孔模（凸模和凹模）的位置，即落料模也可以作为冲孔模。如图2.5所示，冲头和内部带有锥孔的落料凸模被固定在上模座上，下模座上开有推杆放置孔。Theguidepinsorpostsaremountedinthelowershoe.Theuppershoecontainsbushingwhichslideontheguidepins.Theassemblyoftheloweranduppershoeswithguidepinsandbushingisadieset.Diesetsinmanysizesanddesignsarecommerciallyavailable.导料销或导柱安装在下模座上。导套装在上模座上且可以沿导柱滑动。上、下模座（带有导柱和导套）组合成模架。模架在市场上可以买到，且有许多种尺寸和结构供选择。Ontheupstrokeofthepressslide,theknockoutrodofthepressstrikestheejectorplate,forcingtheejectortierodandshedderdownward,thuspushingthefinishedworkpieceoutoftheblankingdie.Fourspecialshoulderscrews(stripperboltscommerciallyavailable),guidethestripperinitstravelandretainitagainstthepreloadofitssprings.Theblankingdieaswellasthepunchpadisscrewedanddoweledtotheuppershoe.在冲压机滑块的向上行程中，冲压机的打料杆接触到推板，作用在连接推杆上的力使卸料装置下移，将冲压件从落料凹模中推出。四个特殊的带肩螺钉（卸料螺钉，在市场上可以买到）引导卸料装置移动，并使其抵抗弹簧的预压。与（冲孔）凸模一样，落料凹模也用螺栓和销子安装在上模座上。

EXERCISE

Questions1.Whatisthecenterofpressure?2.Describeshearactionindiecuttingoperation.3.Whatisthefundamentalstepsinshearingorcutting?4.Whatisthecharacteristicofcompounddies?ReadingMaterial：FerrousMetalsMetalsaredividedintotwogeneralgroups:ferrousmetalsandnonferrousmetals.Ferrousmetalsarethosemetalswhosemajorelementisiron.Themajortypesofferrousmetalsareirons,carbonsteels,alloysteelsandtoolsteels.金属材料分为两种基本类型：铁类金属和非铁金属。主要合金元素是铁的金属材料是铁类金属。铁类金属主要有铁、碳钢、合金钢和工具钢。1)IronTheironorewhichwefindintheearthisnotpure.Itcontainssomeimpuritieswhichwemustremovebysmelting.Theprocessofsmeltingconsistsofheatingtheoreinablastfurnacewithcokeandlimestone,andreducingittometal.Blastsofhotairenterthefurtherfromthebottomandprovidetheoxygenwhichisnecessaryforthereductionoftheore.Theorebecomesmolten,anditsoxidecombineswithcarbonfromthecoke.Thenon-metallicconstituentsoftheorecombinewiththelimestonetoformaliquidslag.Thisfloatsontopofthemolteniron,andpassesoutofthefurnacethroughatap.Themetalwhichremainsispig-iron,andconsistsofapproximately93percentiron,5percentcarbon,and2percentimpurities.我们在地下找到的铁矿石并不是纯净的，其中含有一些杂质，必须通过冶炼去除。冶炼过程是把铁矿石同焦炭和石灰石装入高炉加热，使它还原成金属。热风从高炉底部吹入高炉内，供给铁矿石进行氧化还原反应所需要的氧气。铁矿石变成熔融状态后，其氧化物便与焦炭中的碳化合。矿石里的非金属成分与石灰石结合形成液态炉渣。炉渣浮在铁液上面，经过出渣口排出炉外。剩下的金属就是生铁，生铁中含有约93%的铁，5%的碳和2%的杂质。Remeltingpigironandscrapironinafurnacetoremovesomeoftheimpuritiesproducescastiron.Thetype,orgrade,ofcastironisdeterminedbytheextentofrefining,theamountsofpigironandscrapiron,andthemethodsusedtocastandcoolthemetal.将生铁和废铁在炉子中重新熔化，除去某些杂质后得到铸铁。铸铁的类型和质量等级决定于精炼的程度、生铁和废铁的比例，以及浇铸方法和冷却方式。Thethreeprimarytypesofcastironaregraycastiron,whilecastiron,andmalleableiron.Graycastironisprimarilyusedforcastframes,automobileengineblocks,handwheel,andcasthousings.Whitecastironishardandwearresistantandisusedforpartssuchastrainwheels.Malleablecastironisatoughmaterialusedfortoolssuchaspipesandwrenches.Generally,castironshaveverygoodcompressivestrength,corrosionresistance,andgoodmachinability.Themaindisadvantageofcastironisitsnaturalbrittleness.铸铁主要分为三种：灰铸铁、白口铸铁和可锻铸铁。灰铸铁主要用于制造支架、汽车发动机气缸、手轮和机架。白口铸铁硬度高、耐磨性好，可以用于制造如火车车轮之类的零件。可锻铸铁是韧性较好，可用来制造如管道和扳手之类的零件。一般来说，铸铁有较好的抗压强度，较好的耐腐蚀性能和良好的机械加工性能，其主要缺点是脆性较大。2)CarbonSteelCarbonsteelismadefrompigironthathasbeenrefinedandcleanedofmostimpurities.Mostoftheoriginalcarboninthemetalisburnedoutduringtherefiningprocess.Measuredamountsofcarbonarethenaddedintothemoltenmetaltoproducetheexactgradeofcartonsteeldesired.Afterthesteelispouredintoingotsandallowedtocool,itisusuallysenttoarollingmilltoberolledandformedintospecificshapes.碳钢是生铁经过精炼后除去大部分杂质后得到的。由于生铁中含有的碳在精炼过程中大部分被烧损，因此需要在金属液中加入一定量的碳，以获得所需等级的碳钢。金属液浇铸到铸型中被冷却后，将其送入*轧轧制成不同的形状。Thethreeprincipaltypesofcartonsteelusedinindustryarelow,medium,andhighcarbonsteel.Thepercentageofcarbonisthemostimportantfactorindeterminingthemechanicalproperitiesofeachtypeofcarbonsteel.工业上使用的碳钢主要有三种：低碳钢、中碳钢和高碳钢。碳含量是影响碳钢力学性能的最主要因素。Lowcarboncontainsbetween0.05%and0.28%carbonandisprimarilyusedforpartsthatdonotrequiregreatsteel.Typicalusesoflowcarbonsteelincludechains,bolts,screws,washers,nuts,pins,wire,shafting,andpipes.Thismetalisalsoknownasmachinesteel,mildsteel,andcold-rolledsteel.Lowcarbonsteelistough,ductilematerialthatiseasilymachinedandwelded.Itisusefulforpartsthatmustbestampedorformed.低碳钢碳含量为0.06%～0.28%，主要用于制造强度要求不高的零件。低碳钢主要用于制造链条、螺钉、螺杆、垫圈、螺母、销钉、电线、轴和管道。低碳钢又称为结构钢、软钢和冷轧钢。其韧性、延展性较好，易于切削加工和焊接，也有利于零件的冲压成形。Containingbetween0.25%and0.55%carb;on,mediumcarbonsteelisusedforpartsthatrequiredgreatstrengththanispossiblewithlowcarbonsteel,suchasgears,crankshafts,machinepartsandaxles.Becausethissteelhashighercarboncontent,itcanbeheat-treatedtoincreasebothhardnessandwearresistance.Mediumcarbonsteelisatough,hardnessmetalthathasgoodmachinabilityandiseasilywelded.中碳钢含碳量为0.25%～0.55%，用于制造强度要求高于低碳钢的零件，如齿轮、曲轴、机器零件和车轴。由于碳含量较高，可以对中碳钢进行热处理来提高其硬度和耐磨性。中碳钢韧性较好，强度较高，机械加工性能和焊接性能好。Containingbetween0.60%and1.03%carbon,highcarbonsteelisusedforpartsthatrequirehardnessandstrength,suchasfiles,knives,drills,razors,andwoodworkingtools.Duetotheirincreasedcarboncontent,highcarbonsteelscanbeheat-treatedtomakethemharderandmorewearresistantthanlowormediumcarbonsteels.Duetotheirgreathardness,highcarbonsteelsareoftenbrittle.

高碳钢含碳量为0.50%～1.70%，用于制造要求强度和硬度高的零件，如锉刀、刀、钻头、剃刀和木工刀具。由于碳含量高，高碳钢可以通过热处理获得比低碳钢和中碳钢更高的硬度和更好的耐磨性。由于其高硬度，高碳钢通常也很脆。3)AlloySteelsAlloysteelsarebasicallycarbonsteelswithelementsaddedtomodifyofchangethemechanicalpropertiesofthesteel,amixtureofironandcarbon.Toidentifythetwogroups,oneiscalledcarbonorplainsteelandtheotherisreferredtoasalloysteel.合金钢是在碳钢中加入一定的合金元素以改变或提高其力学性能的钢铁材料，任意一种钢铁材料都含有一种以上的元素，因此，所有钢铁材料都是合金，其中包括普通碳钢——铁和碳的合金。为了区分这两类材料，一类称为碳钢或普通钢，另一类称为合金钢。Alloyelementsareaddedtothemolteninmeasuredamounts.Thedesiredendproductdeterminestheelementsandamountsadded.Theprimaryalloyingelementsandtheireffectonthesteelareasfollows:加入熔融钢铁中的合金元素是定量的。添加合金元素种类和数量决定于最终产品的性能要求。钢铁中主要合金元素以及它们的作用如下：Boron—Thehardenabilityofanalloyisincreasedbyboron.Onlyverysmallamountsofboronareneededtoincreasethehardenabilitycharacteristicsoftheotherelementsinthealloy.硼——硼的加入可提高合金的淬透性。只需添加少量的硼元素就能提高合金中其他元素的淬透性。Chromium—Whenusedinsmallamount,chromiumincreasesthedepthhardnessofthemetal.Themorechromiumused,thebetterthealloyresistscorrosion.Chromiumisaprincipleelementinstainlesssteels.铬——添加少量铬元素能提高合金淬硬层深度。添加的铬元素越多，合金的耐腐蚀性能越好。铬是不锈钢的主要合金元素。Cobalt—Cobaltisaddedtoantoanalloytoincreasewearresistanceandincreaseredhardness,whichistheabilityofametaltomaintainacuttingedgeatelevatedtemperature.Cobaltisavaluableadditiontosomehigh-speedtoolsteels.钴——钴用来提高合金的耐磨性和热硬性。热硬性指金属在高温下保持高硬度的能力。钴是一些高速工具钢中重要添加元素。Lead—Byreducingthecuttingfriction,leadimprovesmachinability.Leadedsteelsalsohavegoodweldabilityandformability.铅——铅的加入可减少切削摩擦，提高切削加工性能。添加铅的合金钢可提高焊接性能和锻造性能。Molybdenum—Atoughalloysuitableforawiderangeofhigh-strength