第6次课-UNIT-4-Forging-Processes

第6次课ForgingProcesses锻造工艺Unit4ForgingProcesses1.IntroductionofForging2.CommonForgingProcesses3.DieDesignConsideration4.Tolerances1.IntroductionofForgingForgingisanimportanthot-formingprocess.Itisusedinproducingcomponentsofallshapesandsizes,fromquitesmallitemstolargeunitsweighingseveraltons.锻造是一种重要的热成型工艺。它能用于生产各种形状和尺寸、从很小到重量数吨的零件。1.IntroductionofForgingForgingistheprocessbywhichmetalisheatedandisshapedbyplasticdeformationbysuitablyapplyingcompressiveforce.Usuallythecompressiveforceisintheformofhammerblowsusingapowerhammerorapress,asshowninFig.4.1.在锻造过程中先将金属加热，然后施加合适的压力使其塑性变形。通常压力都是以由如图4.1所示的动力锤或压力机提供的锤击形式出现。1.IntroductionofForgingHandforgingtoolscomprisevariouslyshapedhammers.Thebaseonwhichtheworkissupportedduringforgingistheanvil(铁砧).手工锻造工具包括各种不同形状的锤子。在锻造中用于支撑工件的基础是铁砧。1.IntroductionofForgingForthesemimechanizedforgingofsmalltomedium-sizedcomponents,forginghammerspoweredbyvariousmeansareemployed.Thefeaturecommontoallofthemisthat,likethehandforginghammer,theyutilizetheenergyofafallingweighttodevelopthepressureneededforshapingthemetal.对小到中等尺寸零件的半机械化锻造而言，锻锤可采用多种动力。就其一般特性而言，都象手工锻锤一样，它们均利用落重能量来产生金属成型所需的压力。1.IntroductionofForgingLargercomponentsareforgedbymeansof(借助，用到)forgingpressesoperatedbysteamorcompressedairorbyhydraulicorelectricpower.Largelyautomaticforgingmachinesareusedforthequantityproductionofengineeringparts.锻造大零件则要用到蒸汽、压缩空气、液力或电力驱动的锻压机。大型的自动化锻机用于工程零件的批量生产。1.IntroductionofForgingAdistinctionmaybemadebetweenopen-die(开模，冲模)forging,usuallyintheformofhammerforging,andclosed-dieforging.Inhammerforging,thecomponentisshapedbyhammerblowsaidedbyrelativelysimpletools.Thesemayincludeopendiesi.e.,diesthatdonotcompletelyenclosethemetaltobeshaped.锤锻中常用的开式模锻与闭式模锻是有区别的。在锤锻中零件通过锤击辅之以相对简单的工具成型。其中包括开式锻模，就是不完全封闭被成型金属的模具。1.IntroductionofForgingOneofthebasicoperationsofhammerforgingistheelongationofapieceofmetalbystretchingwithhammerblows,causingittobecomethinnerandlonger.Inhandforgingthework-pieceisusuallyturned90°aftereachblow,inordertoforgeitthoroughlyandpreventitslateralexpansion.锤锻的基本操作之一就是通过锤击使金属伸长，促成其变细变长。手工锻造时一般在每次锤击后都转过90°以充分锻打工件并防止横向膨胀。1.IntroductionofForgingTheoppositeofelongationisupsetting,whichproducescompressiveshortening.Forexample,thediameterofabarcanbeincreasedbyheatingandhammeringaxially.与伸长相反的是镦粗，即产生压缩性缩短。例如，棒料的直径可以通过加热和轴向锤击而增大。1.IntroductionofForgingMoreimportantisclosed-dieforging,verywidelyusedformassproductioninindustry,inwhichthemetalisshapedbypressingbetweenapairofforgingdies.Theupperdieisusuallyattachedtotheramofaforgingpressoraforginghammer,whilethelowerdieisstationary.更重要的是闭式模锻，在工业上广泛用于规模生产。闭式模锻中金属在一对锻模之间挤压成型。顶模通常放在锻压机的撞头或锻锤上，而底模则是固定的。1.IntroductionofForgingTogethertheyformacloseddie.Closed-dieforgingcanproducecomponentsofgreatercomplexityandaccuracy,withabettersurfacefinishthanthemoretraditionalmethodsnotusingcloseddies.Thediesaremadeofspecialheat-resistantandwear-resistanttoolsteels.两者合在一起形成闭式锻模。闭式模锻能生产高度复杂和精确的零件，而且表面光洁度要比不用闭式锻模的更传统方法好。闭式锻模采用特殊的耐热、耐磨工具钢制成。1.IntroductionofForgingApieceofhotmetalsufficienttoslightlyoverfillthedieshapeisplacedinthebottomdie,andthetopdieisforcedagainstit,sothatthemetaltakestheinternalshapeofthedie.将一块大小足以充填模腔并能稍有溢出的加热金属放入底模，并将顶模加压合拢，这块金属便获得该模腔的形状。1.IntroductionofForgingClosed-dieforgingisusedfortherapidproductionoflargenumbersoffairlysmallpartsandalsoforverylargecomponents.Forthelatter,e.g.,modernjet-aircraftcomponents,gianthydraulicallyoperatedpressesareused,whichcandevelopforcesof50,000tonsandmore.闭式模锻用于相当小的零件大批量快速生产，也可用于很大的零件。对后者而言，例如现代喷气飞机零件，使用能产生50,000吨以上压力的巨型液力锻压机。1.IntroductionofForgingOnevaluablefeatureofforgingisthatitimprovesthestrengthofthemetalbyrefiningthestructureandmakingituniform;soforheavyforgings,suchasmarinepropellershafts,animmenselypowerfulhydraulicpresssqueezesthemetalwithaforcesometimesasgreatas10,000tones.锻造有价值的特性之一是它通过使金属组织均匀而改善强度，因此对诸如船舶螺旋桨轴之类的重型锻件，要用能达10,000吨压力的庞大而有力的液压机来挤压金属。1.IntroductionofForgingAlthoughthehydraulicforgingpressisamoreexpensivepieceofequipmentthanadrop-forge,ithasadvantagesbesidethoseofgivinggreaterstrengthandmoreuniformstructuretolargecomponents.Onaccountofthehighpressureandsqueezingaction,itoperateswithlessnoiseandvibrationthanadrop-forge.虽然这种液压锻机比落锤锻造要昂贵得多，但它除了能给予大零件较高的强度和更均匀的组织外还有其它优点。由于较高的压力和挤压作用，它比落锤锻造噪声及振动都小得多。1.IntroductionofForgingAsingots（锻钢胚，钢锭）ofsteelweighing30tonnesormoreareforgedinthisway,manualoperationisimpossibleanditisessentialthatallthemanipulationoftheingotisdonemechanically.由于这种情况下被锻钢坯重量大于30吨，人工操作是不可能的，钢坯的所有操作都必须是机械化的。1.IntroductionofForgingForgingrefinesthegrainstructureandimprovesphysicalpropertiesofthemetal.Withproperdesign,thegrainflowcanbeorientedinthedirectionofprincipalstressesencounteredinactualuse.铸造细化金属的晶粒组织、改善其物理性能。通过适当的设计，可以使晶粒流动方向与实际使用时的主应力方向一致。1.IntroductionofForgingAsshowninFig.4.2,grainflowisthedirectionofthepatternthatthecrystalstakeduringplasticdeformation.Physicalproperties(suchasstrength,ductilityandtoughness)aremuchbetterinaforgingthaninthebasemetal,whichhascrystalsrandomlyoriented.如图4.2所示，晶粒流动的方向就是在塑性变形期间结晶排列的方向。锻件的物理性能(如强度、延展性和韧性)远好于基础金属，因