模具專業(yè)英語Unit2課件

Unit2BlangkingTechnique陳顯冰

Overview2.1Cutting(Shearing)Operations

Thecuttingofmetalbetweendiecomponentsisashearingprocessinwhichthemetalisstressedinshearbetweentwocuttingedgestothepointoffracture,orbeyonditsultimatestrength.金屬材料早沖裁模具間的沖裁切斷時(shí)剪切應(yīng)力達(dá)到斷裂點(diǎn)或超出材料強(qiáng)度極限的一種剪切過程。Themetalissubjectedtobothtensileandcompressivestresses;stretchingbeyondtheelasticlimitedoccurs,thenplasticdeformation,reductioninarea,andfinally,fracturingstartsthroughcleavageplanesinthereducedareaandbecomescomplete.金屬承受拉應(yīng)力和壓應(yīng)力。在超出彈性極限時(shí)發(fā)生伸長(zhǎng)，然后進(jìn)入塑性變形，斷面減小，最終裂紋沿不斷減小的斷面上的撕裂帶擴(kuò)展，從而實(shí)現(xiàn)完全分離。

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

圖2.1描述了沖裁和剪切的基本過程。處于金屬上部的凸模施壓使金屬變形并進(jìn)入凹模入口。當(dāng)繼續(xù)加載超出材料的彈性極限時(shí)，金屬的一部分將被壓入凹模入口，在材料下表面形成壓痕，上表面也相應(yīng)地發(fā)生變形，如圖2.1a所示。當(dāng)載荷繼續(xù)增加時(shí)，凸模將把金屬壓入到某一個(gè)深度，直至壓入凹模的深度等于金屬的厚度，如圖2.1b所示。這個(gè)壓入過程發(fā)生在剪切引起的斷裂開始和金屬橫截面減小之前，在上、下剪切刃處縮小的斷面上均出現(xiàn)裂紋，如圖2.1c所示。對(duì)于被剪切的材料，若間隙適當(dāng)，則裂紋將相向擴(kuò)展并最終相遇，從而引起材料的完全分離。凸模繼續(xù)下行將沖下的部分通過料架推入凹模的漏料孔。1)CenterofPressureIfthecontourtobeblankedisirregularlyshaped,thesummationofshearingforcesononesideofthecenteroftherammaygreatlyexceedtheforcesontheotherside.Suchirregularlyresultsinabendingmomentinthepressram,andundesirableandmisalignment.Itisthereforenecessarytofindapointaboutwhichthesummationofshearingforceswillbesymmetrical.Thispointiscalledthecenterofpressure,andisthecenterofgravityofthelinethatistheperimeteroftheblank.Itisnotthecenterofgravityofthearea.Thepresstoolwillbedesignedsothatthecenterofpressurewillbeontheaxisofthepressramwhenthetoolismountedinthepress.如果所沖裁的零件輪廓是不規(guī)則形狀，滑塊一側(cè)的剪切力的總和將遠(yuǎn)遠(yuǎn)超過另一側(cè)的剪切力。這種不規(guī)則形狀將導(dǎo)致壓力機(jī)滑塊處在彎曲力矩的作用下，產(chǎn)生偏斜和變形。因此，尋找一個(gè)能使剪切力的總和對(duì)稱（平衡）的點(diǎn)是很有必要的，這個(gè)點(diǎn)就稱之為壓力中心，它是沖裁輪廓線的重心，而非（封閉區(qū)域內(nèi)）面積的重心。2)ClearancesClearanceisthespacebetweenthematingmembersofadieset.Properclearancebetweencuttingedgesenablethefracturestomeet.Thefracturedportionoftheshearededgewillhaveacleanappearance.Foroptimumfinishofacutedge,properclearanceisnecessaryandisafunctionofthetype,thickness,andtemperoftheworkmaterial.間隙是一副模具凸、凹模之間的配合空間。剪切刃之間的合理間隙可以確保裂紋匯合。剪切刃的撕裂部分將形成一條光亮帶。為了保證剪切刃的最佳精度，合理的間隙是必要的餓，其大小取決于所沖壓成形材料的種類、厚度、韌度（硬度）。3)CuttingForcesTheforcerequiredtocut(shear)theworkmaterialcanbecalculatedbyusingthefollowingformulas:剪切工件材料所需的沖裁（剪切）力可以使用如下公式進(jìn)行計(jì)算：4)StrippingForcesTheforcerequiredtostriptheworkmaterialoffpunchescanbecalculatedbyusingthefollowingformulas:(forcontours)(forroundholes)Where—Cuttingforceinpounds;—Thicknessofmaterialininches—Cuttingforceintons;—Diameterininches.—Strippingforceinpounds;—Strippingforceintons;—Shearstrengthinpoundspersquareinch;—Lengthofcutininches;;

從凸模上卸下材料的力可以使用如下公式進(jìn)行計(jì)算：

式中P____剪切力（1b）

TN____沖裁力（t）

Ps____卸料力（1b）

TNs____卸料力（t）

S____材料抗剪強(qiáng)度（lb/in）

L____剪切輪廓線長(zhǎng)度（in）

T____材料厚度（in）

D____凸模直徑（in）5)PressTonnageThisisatotalofforcesrequiredtocutandformthepartwitha30%safetyfactoradded.Inmanycases,youwillhavetoaddstrippingforceifstrippingisbeingdonewithaspring-loadedstripper,becausethepresshastocompressthespringswhilecuttingthematerial.Likewise,anyspringpressureforforming,drawpads,andthelike,willhavetobeadded.壓力機(jī)噸位是剪切和成形零件所需要的力加上考慮30%的安全因素的力的總和。在很多情況下，如果使用彈簧驅(qū)動(dòng)的卸料裝置，還必須加上卸料力，因?yàn)樵跊_剪材料時(shí)的壓力機(jī)必須有壓縮彈簧。相應(yīng)地，對(duì)于任何利用彈簧力成形、拉深凸緣（防皺）及類似的用途都應(yīng)加上彈簧力。2.2BlankingTechnique1)BendingdiesBendingistheuniformstrainingofmaterial(usuallyflatsheetorstripmetal)aroundastraightaxiswhichliesintheneutralplaneandnormaltothelengthwisedirectionofthesheetorstrip.Metalflowtakesplacewithintheplasticrangeofthemetal,sothatthebendretainsapermanentsetafterremovaloftheappliedstress.Theinnersurfaceofabendisincompression;theoutersurfaceisintension.Apurebendingactiondoesnotreproducetheexactshapeofthepunchanddieinthemetal;suchareproductionisoneofforming.Theneutralaxisistheplaneareainbendmetalwhereallstrainiszero.彎曲是指材料（通常是板料或條料）圍繞位于中性面上的縱向方向的直線軸產(chǎn)生均勻變形的沖壓工藝。因?yàn)椋◤澢鷷r(shí)）金屬流動(dòng)發(fā)生在金屬塑性變形范圍內(nèi)，所以去除施加的外力后，彎曲將保持永久的變形。彎曲件的內(nèi)表面處于壓縮狀態(tài)，外表面處于拉深狀態(tài)。單一的彎曲工序并不能使金屬材料呈現(xiàn)出與模具的凸模或凹模完全一致的形狀，這種復(fù)制工藝也是一種成型方法。在受到彎曲作用的金屬中，中性面是彎曲金屬上張力為零的平面區(qū)域。Metalsheetorstrip,supportedbyaVblock,isforcedbyawedge-shapedpunchintotheblock.ThismethodtermedVbending(Figure2.2),producesabendhavinganincludedanglewhichmaybeacute,obtuse,orof90°.Frictionbetweenaspring-loadedknurledpinintheveeofadieandthepartwillpreventorreducesidecreepofthepartduringitsbending.OthermethodsareZ-bending(Figure2.3),edgebendingandU-bending,etc.

放置在V形支撐塊的板料或條料在楔形沖頭的作用下壓入V形凹模，這類彎曲方式稱為V形彎曲（圖2.2）。V形彎曲能夠生產(chǎn)帶有鈍角、銳角或直角的彎曲件。V形模具內(nèi)的彈簧加載壓銷和零件之間的摩擦力將阻止或減少?gòu)澢鷷r(shí)零件邊緣的移動(dòng)。其他彎曲方式有Z形彎曲（圖2.3）、側(cè)邊彎曲和U形彎曲等。2)DrawingdiesDrawingisaprocessofchangingaflat,precutmetalblankintoahollowvesselwithoutexcessivewrinkling,thinning,orfracturing.Thevariousformsproducedmaybecylindricalorbox-shapedwithstraightortaperedsidesoracombinationofstraight,tapered,orcurvedsides.Thesizeofthepartsmayvaryfrom0.25mmdiameterorsmallertoaircraftorautomotivepartslargeenoughtorequiretheuseofmechanicalhandingequipment.

拉深是指把一定形狀的金屬平板制成空心零件而不發(fā)生起皺、變薄或開裂現(xiàn)象的沖壓工序。不同形狀的拉深可得到側(cè)壁不同的圓柱形或盒形制件，這些側(cè)壁的形式有：直壁、錐形壁、直壁和錐形的混合側(cè)壁以及曲面壁。拉深件的尺寸相差很大，從直徑為0.25mm或更小的拉深件，到足以覆蓋機(jī)械設(shè)備的航天器或汽車覆蓋件。Thesimplesttypeofdrawdiesisonewithonlyapunchanddie.Onetypeofdrawingdieforuseinasingle-actionpressisshowninFigure2.4.Thisdieisplainsingle-actiontypewherethepunchpushesthemetalblankintothedie,usingaspring-loadedpressurepadtocontrolthemetalflow.Thepunchhasanairventtoeliminatesuctionwhichwouldholdthecuponthepunchanddamagethecupwhenitisstrippedfromthepunchbythepressurepad.Thesketchshowsthepressurepadfittingthestoppin,whichactsasaspacerthatanevenandproperpressureisexertedontheblankatalltimes.Ifthespringpressurepadisusedwithoutthestoppin,themorethespringsaredepressedthegreaterthepressureexertedontheblank,therebylimitingthedepthofdraw.Becauseoflimitedpressuresobtainable,thistypeofdieshouldbeusedwithlight-gagestockandshallowdepths.最簡(jiǎn)單的拉深模只帶有一對(duì)凸模和凹模，圖2.4所示為單次拉深的一種拉深模結(jié)構(gòu)。這種結(jié)構(gòu)是簡(jiǎn)單的單次拉深類型，沖頭把金屬坯料壓入凹模，利用彈壓板控制金屬流動(dòng)。沖頭上開設(shè)的排氣孔能夠消除推出（拉深件）時(shí)產(chǎn)生的真空吸力，這種真空現(xiàn)象能使杯形拉深件包緊在沖頭上，若由壓料板強(qiáng)制脫模，（則）會(huì)損壞杯形件。圖中所示的模具裝有壓料板（壓料板上帶有限位螺釘），壓料板起壓料作用，沖壓時(shí)能為沖頭外的坯料提供均勻而合適的壓力。如果彈壓板沒有安裝限位螺釘，那么彈簧壓縮量越多，板料承受的壓力就越大，這將限制拉深的程度。由于有效壓力有限，這種拉深模適用于所需沖壓力較小及深度較淺的沖壓件。3)CompoundDiesAcompounddieperformsonlycuttingoperations(usuallyblankingandpiercing)whicharecompletedduringasinglepressstroke.Acharacteristicofcompounddiesistheinvertedpositionoftheblankingdieandblankingpunchwhichalsofunctionsasthepiercingdie.AsshowninFigure2.5,thedieisfastenedtotheuppershoeandtheblankingpunchhavingataperedholeinitandinthelowershoeforslugdisposalismountedonthelowershoe.

（落料沖孔）復(fù)合模是指在一次沖壓行程中完成（兩種）沖裁工序（通常包括落料和沖孔）的模具。復(fù)合模的特點(diǎn)是能夠調(diào)轉(zhuǎn)落料模和沖孔模（凸模和凹模）的位置，即落料模也可以作為沖孔模。如圖2.5所示，沖頭和內(nèi)部帶有錐孔的落料凸模被固定在上模座上，下模座上開有推桿放置孔。Theguidepinsorpostsaremountedinthelowershoe.Theuppershoecontainsbushingwhichslideontheguidepins.Theassemblyoftheloweranduppershoeswithguidepinsandbushingisadieset.Diesetsinmanysizesanddesignsarecommerciallyavailable.導(dǎo)料銷或?qū)е惭b在下模座上。導(dǎo)套裝在上模座上且可以沿導(dǎo)柱滑動(dòng)。上、下模座（帶有導(dǎo)柱和導(dǎo)套）組合成模架。模架在市場(chǎng)上可以買到，且有許多種尺寸和結(jié)構(gòu)供選擇。Ontheupstrokeofthepressslide,theknockoutrodofthepressstrikestheejectorplate,forcingtheejectortierodandshedderdownward,thuspushingthefinishedworkpieceoutoftheblankingdie.Fourspecialshoulderscrews(stripperboltscommerciallyavailable),guidethestripperinitstravelandretainitagainstthepreloadofitssprings.Theblankingdieaswellasthepunchpadisscrewedanddoweledtotheuppershoe.在沖壓機(jī)滑塊的向上行程中，沖壓機(jī)的打料桿接觸到推板，作用在連接推桿上的力使卸料裝置下移，將沖壓件從落料凹模中推出。四個(gè)特殊的帶肩螺釘（卸料螺釘，在市場(chǎng)上可以買到）引導(dǎo)卸料裝置移動(dòng)，并使其抵抗彈簧的預(yù)壓。與（沖孔）凸模一樣，落料凹模也用螺栓和銷子安裝在上模座上。

EXERCISE

Questions1.Whatisthecenterofpressure?2.Describeshearactionindiecuttingoperation.3.Whatisthefundamentalstepsinshearingorcutting?4.Whatisthecharacteristicofcompounddies?ReadingMaterial：FerrousMetalsMetalsaredividedintotwogeneralgroups:ferrousmetalsandnonferrousmetals.Ferrousmetalsarethosemetalswhosemajorelementisiron.Themajortypesofferrousmetalsareirons,carbonsteels,alloysteelsandtoolsteels.金屬材料分為兩種基本類型：鐵類金屬和非鐵金屬。主要合金元素是鐵的金屬材料是鐵類金屬。鐵類金屬主要有鐵、碳鋼、合金鋼和工具鋼。1)IronTheironorewhichwefindintheearthisnotpure.Itcontainssomeimpuritieswhichwemustremovebysmelting.Theprocessofsmeltingconsistsofheatingtheoreinablastfurnacewithcokeandlimestone,andreducingittometal.Blastsofhotairenterthefurtherfromthebottomandprovidetheoxygenwhichisnecessaryforthereductionoftheore.Theorebecomesmolten,anditsoxidecombineswithcarbonfromthecoke.Thenon-metallicconstituentsoftheorecombinewiththelimestonetoformaliquidslag.Thisfloatsontopofthemolteniron,andpassesoutofthefurnacethroughatap.Themetalwhichremainsispig-iron,andconsistsofapproximately93percentiron,5percentcarbon,and2percentimpurities.我們?cè)诘叵抡业降蔫F礦石并不是純凈的，其中含有一些雜質(zhì)，必須通過冶煉去除。冶煉過程是把鐵礦石同焦炭和石灰石裝入高爐加熱，使它還原成金屬。熱風(fēng)從高爐底部吹入高爐內(nèi)，供給鐵礦石進(jìn)行氧化還原反應(yīng)所需要的氧氣。鐵礦石變成熔融狀態(tài)后，其氧化物便與焦炭中的碳化合。礦石里的非金屬成分與石灰石結(jié)合形成液態(tài)爐渣。爐渣浮在鐵液上面，經(jīng)過出渣口排出爐外。剩下的金屬就是生鐵，生鐵中含有約93%的鐵，5%的碳和2%的雜質(zhì)。Remeltingpigironandscrapironinafurnacetoremovesomeoftheimpuritiesproducescastiron.Thetype,orgrade,ofcastironisdeterminedbytheextentofrefining,theamountsofpigironandscrapiron,andthemethodsusedtocastandcoolthemetal.將生鐵和廢鐵在爐子中重新熔化，除去某些雜質(zhì)后得到鑄鐵。鑄鐵的類型和質(zhì)量等級(jí)決定于精煉的程度、生鐵和廢鐵的比例，以及澆鑄方法和冷卻方式。Thethreeprimarytypesofcastironaregraycastiron,whilecastiron,andmalleableiron.Graycastironisprimarilyusedforcastframes,automobileengineblocks,handwheel,andcasthousings.Whitecastironishardandwearresistantandisusedforpartssuchastrainwheels.Malleablecastironisatoughmaterialusedfortoolssuchaspipesandwrenches.Generally,castironshaveverygoodcompressivestrength,corrosionresistance,andgoodmachinability.Themaindisadvantageofcastironisitsnaturalbrittleness.鑄鐵主要分為三種：灰鑄鐵、白口鑄鐵和可鍛鑄鐵?；诣T鐵主要用于制造支架、汽車發(fā)動(dòng)機(jī)氣缸、手輪和機(jī)架。白口鑄鐵硬度高、耐磨性好，可以用于制造如火車車輪之類的零件。可鍛鑄鐵是韌性較好，可用來制造如管道和扳手之類的零件。一般來說，鑄鐵有較好的抗壓強(qiáng)度，較好的耐腐蝕性能和良好的機(jī)械加工性能，其主要缺點(diǎn)是脆性較大。2)CarbonSteelCarbonsteelismadefrompigironthathasbeenrefinedandcleanedofmostimpurities.Mostoftheoriginalcarboninthemetalisburnedoutduringtherefiningprocess.Measuredamountsofcarbonarethenaddedintothemoltenmetaltoproducetheexactgradeofcartonsteeldesired.Afterthesteelispouredintoingotsandallowedtocool,itisusuallysenttoarollingmilltoberolledandformedintospecificshapes.碳鋼是生鐵經(jīng)過精煉后除去大部分雜質(zhì)后得到的。由于生鐵中含有的碳在精煉過程中大部分被燒損，因此需要在金屬液中加入一定量的碳，以獲得所需等級(jí)的碳鋼。金屬液澆鑄到鑄型中被冷卻后，將其送入*軋軋制成不同的形狀。Thethreeprincipaltypesofcartonsteelusedinindustryarelow,medium,andhighcarbonsteel.Thepercentageofcarbonisthemostimportantfactorindeterminingthemechanicalproperitiesofeachtypeofcarbonsteel.工業(yè)上使用的碳鋼主要有三種：低碳鋼、中碳鋼和高碳鋼。碳含量是影響碳鋼力學(xué)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.低碳鋼碳含量為0.06%～0.28%，主要用于制造強(qiáng)度要求不高的零件。低碳鋼主要用于制造鏈條、螺釘、螺桿、墊圈、螺母、銷釘、電線、軸和管道。低碳鋼又稱為結(jié)構(gòu)鋼、軟鋼和冷軋鋼。其韌性、延展性較好，易于切削加工和焊接，也有利于零件的沖壓成形。Containingbetween0.25%and0.55%carb;on,mediumcarbonsteelisusedforpartsthatrequiredgreatstrengththanispossiblewithlowcarbonsteel,suchasgears,crankshafts,machinepartsandaxles.Becausethissteelhashighercarboncontent,itcanbeheat-treatedtoincreasebothhardnessandwearresistance.Mediumcarbonsteelisatough,hardnessmetalthathasgoodmachinabilityandiseasilywelded.中碳鋼含碳量為0.25%～0.55%，用于制造強(qiáng)度要求高于低碳鋼的零件，如齒輪、曲軸、機(jī)器零件和車軸。由于碳含量較高，可以對(duì)中碳鋼進(jìn)行熱處理來提高其硬度和耐磨性。中碳鋼韌性較好，強(qiáng)度較高，機(jī)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.

高碳鋼含碳量為0.50%～1.70%，用于制造要求強(qiáng)度和硬度高的零件，如銼刀、刀、鉆頭、剃刀和木工刀具。由于碳含量高，高碳鋼可以通過熱處理獲得比低碳鋼和中碳鋼更高的硬度和更好的耐磨性。由于其高硬度，高碳鋼通常也很脆。3)AlloySteelsAlloysteelsarebasicallycarbonsteelswithelementsaddedtomodifyofchangethemechanicalpropertiesofthesteel,amixtureofironandcarbon.Toidentifythetwogroups,oneiscalledcarbonorplainsteelandtheotherisreferredtoasalloysteel.合金鋼是在碳鋼中加入一定的合金元素以改變或提高其力學(xué)性能的鋼鐵材料，任意一種鋼鐵材料都含有一種以上的元素，因此，所有鋼鐵材料都是合金，其中包括普通碳鋼——鐵和碳的合金。為了區(qū)分這兩類材料，一類稱為碳鋼或普通鋼，另一類稱為合金鋼。Alloyelementsareaddedtothemolteninmeasuredamounts.Thedesiredendproductdeterminestheelementsandamountsadded.Theprimaryalloyingelementsandtheireffectonthesteelareasfollows:加入熔融鋼鐵中的合金元素是定量的。添加合金元素種類和數(shù)量決定于最終產(chǎn)品的性能要求。鋼鐵中主要合金元素以及它們的作用如下：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.鉻——添加少量鉻元素能提高合金淬硬層深度。添加的鉻元素越多，合金的耐腐蝕性能越好。鉻是不銹鋼的主要合金元素。Cobalt—Cobaltisaddedtoantoanalloytoincreasewearresistanceandincreaseredhardness,whichistheabilityofametaltomaintainacuttingedgeatelevatedtemperature.Cobaltisavaluableadditiontosomehigh-speedtoolsteels.鈷——鈷用來提高合金的耐磨性和熱硬性。熱硬性指金屬在高溫下保持高硬度的能力。鈷是一些高速工具鋼中重要添加元素。Lead—Byreducingthecuttingfriction,leadimprovesmachinability.Leadedsteelsalsohavegoodweldabilityandformability.鉛——鉛的加入可減少切削摩擦，提高切削加工性能。添加鉛的合金鋼可提高焊接性能和鍛造性能。Molybdenum—Atoughalloysuitableforawiderangeofhigh-strength