英語翻譯FormingFormingcanbedefinedasaprocessinwhichthedesiredsizeandshapeareobtainedthroughtheplasticdeformationsofamaterial.Thestressesinducedduringtheprocessaregreaterthantheyieldstrength,butlessthanthefracturestrength,ofthematerial.Thetypeofloadingmaybetensile,compressive,bending,orshearing,oracombinationofthese.Thisisaveryeconomicalprocessasthedesiredshape,size,andfinishcanbeobtainedwithoutanysignificantlossofmaterial.Moreover,apartoftheinputenergyisfruitfullyutilizedinimprovingthestrengthoftheproductthroughstrainhardening.Theformingprocessescanbegroupedundertwobroadcategories,namely,coldforming,andhotforming.Iftheworkingtemperatureishigherthantherecrystallizationtemperatureofthematerial,thentheprocessiscalledhotforming.Otherwisetheprocessistermedascoldforming.Theflowstressbehaviorofamaterialisentirelydifferentaboveandbelowitsrecrystallizationtemperature.Duringhotworking,alargeamountofplasticdeformationcanbeimpartedwithoutsignificantstrainhardening.Thisisimportantbecausealargeamountofstrainhardeningrendersthematerialbrittle.Thefrictionalcharacteristicsofthetwoformingprocessesarealsoentirelydifferent.Forexample,thecoefficientoffrictionincoldformingisgenerallyoftheorderof0.1,whereasthatinhotformingcanbeashighas0.6.Further,hotforminglowersdownthematerialstrengthsothatamachinewithareasonablecapacitycanbeusedevenforaproducthavinglargedimensions.Thetypicalformingprocessesarerolling,forging,drawing,deepdrawing,bending,andextrusion.Forabetterunderstandingofthemechanicsofvariousformingoperations,weshallbrieflydiscusseachoftheseprocesses.RollingInthisprocess,thejobisdrawnbymeansoffrictionthrougharegulatedopeningbetweentwopower-drivenroll.Theshapeandsizeoftheproductaredecidedbythegapbetweentherollsandtheircontours.Thisisaveryusefulprocessfortheproductionofsheetmetalandvariouscommonsections,e.g.,rail,channel,angle,andround.ForgingInforging,thematerialissqueezedbetweentwoormorediestoalteritsshapeandsize.Dependingonthesituation,thediesmaybeopenorclosed.DrawingInthisprocess,thecross-sectionofawireorthatofabarortubeisreducedbypullingtheworkpiecethroughtheconicalorificeofadie.Whenhighreductionisrequired,itmaybenecessarytoperformtheoperationinseveralpasses.DeepDrawingIndeepdrawing,acup-shapedproductisobtainedfromaflatsheetmetalwiththehelpofapunchandadie.Thesheetmetalisheldoverthediebymeansofablankholdertoavoiddefectsintheproduct.BendingAsthenameimplies,thisisaprocessofbendingametalsheetplasticallytoobtainthedesiredshape.Thisisachievedbyasetofsuitablydesignedpunchanddie.ExtrusionThisisaprocessbasicallysimilartothecloseddieforming.Butinthisoperation,theworkpieceiscompressedinaclosedspace,forcingthematerialtoflowoutthroughasuitableopening,calledadie.Inthisprocess,onlytheshapeswithconstantcross-sections(dieoutletcross-section)canbeproduced.AdvantagesandDisadvantagesofHotandColdFormingNowthatwehavecoveredthevarioustypesofmetalworkingoperations,itwouldonlybeappropriatethatweprovideanoverallevaluationofthehotandcoldworkingprocesses.Suchadiscussionwillhelpinchoosingtheproperworkingconditionsforagivensituation.Duringhotworking,apropercontrolofthegrainsizeispossiblesinceactivegraingrowthtakesplaceintherangeoftheworkingtemperature.Asaresult,thereisnostrainhardening,andthereforethereisnoneedofexpensiveandtime-consumingintermediateannealing.Ofcourse,strainhardeningisadvisableduringsomeoperations(viz.,drawing)toachieveanimprovedstrength；insuchcases,hotworkingislessadvantageous.Apartfromthis,strainhardeningmaybeessentialforasuccessfulcompletionofsomeprocesses(e.g.,indeepdrawing,strainhardeningpreventstheruptureofthematerialaroundthebottomcircumferencewherethestressismaximum).Largeproductsandhighstrengthmaterialscanbeworkeduponunderhotconditionssincetheelevatedtemperaturelowersdownthestrengthand,consequently,theworkload.Moreover,formostmaterials,theductilityincreaseswithtemperatureand,asaresult,brittlecanalsobeworkeduponbythehotworkingoperation.Itshould,however,berememberedthattherearecertainmaterials(viz.,steelscontainingsulphur)whichbecomemorebrittleatelevatedtemperatures.Whenaveryaccuratedimensionalcontrolisrequired,hotworkingisnotadvisedbecauseofshrinkageandlossofsurfacemetalduetoscaling.Moreover,surfacefinishispoorduetooxideformationandscaling.Themajoradvantagesofcoldworkingarethatitiseconomical,quicker,andeasiertohandlebecauseherenoextraarrangementsforheatingandhandlingarenecessary.Further,themechanicalpropertiesnormallygetimprovedduringtheprocessduetostrainhardening.Whatismore,thecontrolofgrainflowdirectionsaddstothestrengthcharacteristicsoftheproduct.However,apartfromotherlimitationsofcoldworking(viz.,difficultywithhighstrengthandbrittlematerialsandlargeproductsizes),theinabilityoftheprocesstopreventthesignificantreductionbroughtaboutincorrosionresistanceisanundesirablefeature.成形成形可以定義為一種通過材料的塑性變形獲得所需尺寸和形狀的工藝。在此工藝中引起的應力大于材料的屈服強度，但小于材料的斷裂強度。加載的類型可以是拉應力、壓應力、彎曲應力或剪應力，或者是這些類型的組合。這是個很經(jīng)濟的方法，因為可以獲得所需的形狀、尺寸和光潔度而無需使材料有任何大的損失。此外，一部分輸入的能量在通過應變硬化提高產(chǎn)品的強度上得到了卓有成效的利用。成形工藝可以分為以下兩個大類，即冷成形和熱成形。如果加工溫度高于材料的再結晶溫度，那么這一過程就叫熱變形，否則，這一個過程就被稱為冷變形。材料的流動應力在再結晶溫度之上或之下全然不同。在熱加工過程中，可以產(chǎn)生大的塑性變形而無大的冷作硬化。這一點很重要，因為大的冷作硬化會使材料變脆。兩種成形方法的摩擦特性也完全不同。例如，冷成形的摩擦系數(shù)一般為0.1左右，而熱變形的摩擦系數(shù)可以高達0.6。此外，熱變形降低了材料的強度，結果甚至可以使用具有一定容量的機器加工很大尺寸的產(chǎn)品。典型的成形方法有軋制、鍛造、拉延、拉深、彎曲和擠壓。為了更好地理解各種成形操作地機械學原理，我們將簡要討論每一種方法。軋制在這一工藝中，通過一個調整過的位于兩個動力驅動的軋輥之間的孔利用摩擦來拉伸工件。產(chǎn)品的形狀和尺寸由軋輥及其輪廓之間的間隙來決定。這是一種很有用途的工藝，用于生產(chǎn)金屬薄板和各種常用端面，如鐵軌、槽鋼、角鋼和圓鋼。鍛造鍛造時，材料在兩個和多個磨具間受到擠壓以改變其形狀和尺寸。根據(jù)情況不同，磨具可以是開式或閉式。拉延在這一工藝中，金屬絲的截面或者是條鋼或鋼管的截面由于工件被拉過磨具的錐形孔而減小。當截面需要減小很多時，也許有必要通過幾個階段來完成此操作。拉深在拉深中，杯形產(chǎn)品是在一個凸模和一個凹模的幫助下由一塊金屬板獲得的。金屬薄板被放在磨具上利用一個坯料壓板來避免產(chǎn)品缺陷。彎曲如其名所示，這是一道塑性彎曲一塊金屬薄板以獲得所需形狀的工藝。這道工藝由一套設計適當?shù)耐鼓：桶寄硗瓿?。擠壓這是一道基本上類似于閉式磨具鍛造的工藝。但是在該工序中，工件被壓進一個封閉空間迫使材料通過一個被稱為磨具的適當