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Unit11.2FerrousMetalsandAlloysByvirtueoftheirwiderangeofmechanical,physical,andchemicalproperties,ferrousmetalsandalloysareamongthemostusefulofallmetals.Ferrousmetalsandalloyscontainironastheirbasemetal:thegeneralcategoriesarecastirons,carbonandalloysteels,stainlesssteels,toolanddiesteels.1.2黑色金属及其合金：由于它们的一系列广泛的机械物理和化学的特征，黑色金属及其合金是所有金属中最有用的铁是黑色金属及其合金中的基本元素主要种类有铸铁，碳钢，合金钢，不锈钢，工具钢和磨具钢Thetermcastironreferstoafamilyofferrousalloyscomposedofiron,carbon(rangingfrom2.11%toabout4.5%),andsilicon(uptoabout3.5%).Castironsareusuallyclassifiedasfollows:1.Graycastiron,orgrayiron;2.Ductilecastiron,nodularcastiron,orsphericalgraphitecastiron;3.Whitecastiron;4.Malleableiron;5.Compactedgraphiteiron。（），它包含铁碳（2.5%—4.5%）和硅（3.5%）铸铁的分类如下1.灰铸铁2.球墨铸铁3.白口铸铁4.可锻铸铁5.如墨铸铁TheequilibriumphasediagramrelevanttocastironsisshowninFig.1.1,inwhichtherightboundaryis100%carbon,thatispuregraphite.Theeutectictemperatureis1154hC(2109hF),andsocastironsarecompletelyliquidattemperatureslowerthanthoserequiredforliquidsteels.Consequently,ironwithhighcarboncontentcanbecastatlowertemperaturesthancansteels.有关铸铁的平衡相图如图1.1所示其右边界是100%的碳那是纯石墨，其共晶温度是1154℃因此铸铁可以在比那些熔化钢更低的温度下完全液化所以含碳量较高的铸铁的浇注温度比钢低。Carbonsteelsaregenerallyclassifiedbytheirproportion(byweight)ofcarboncontent.1.Low-carbonsteel,alsocalledmildsteel,haslessthan1.30%carbon.Itisgenerallyusedforcommonindustrialproducts,suchasbolts,nuts,sheet,plate,andtubes,andformachinecomponentsthatdonotrequirehighstrength.3.碳钢：碳铜大体上是按碳含量的臂力来分类的1）低碳钢又叫做软钢其碳含量小于0.30%它用于普遍的工业产品，例如螺栓，螺母。钢板，港片钢管和那些强度要求不高的机器零件Unit55.1IntroductionConventionalmachiningisthegroupofmachiningoperationsthatusesingle-ormulti-pointtoolstoremovematerialintheformofchips.Metalcuttinginvolvesremovingmetalthroughmachiningoperations.Machiningtraditionallytakesplaceonlathes,drillpresses,andmillingmachineswiththeuseofvariouscuttingtools.Mostmachininghasverylowset-upcostcomparedwithforming,molding,andcastingprocesses.However,machiningismuchmoreexpensiveforhighvolumes.Machiningisnecessarywheretighttolerancesondimensionsandfinishesarerequired.传统机加工是利用单刃或多刃刀具以切削形式去除材料的（一组）加工方法。金属切削就是利用机加工的方法去除材料，传统机加工都是利用不用的刀具在车床，钻床和铣床上进行的，与成型加工，模压制件和铸造工艺相比，机加工的准备成本还是比较低的。然而，如果是大批量生产，其成本要高得多，当对零件的光洁度和尺寸公差要求较高时，机加工是必须的。5.2TurningandLatheTurningisoneofthemostcommonofmetalcuttingoperations.Inturning,aworkpieceisrotatedaboutitsaxisassingle-pointcuttingtoolsarefedintoit,shearingawayexcessmaterialandcreatingthedesiredcylindricalsurface.Turningcanoccuronbothexternalandinternalsurfacestoproduceanaxially-symmetricalcontouredpart.Partsrangingfrompocketwatchcomponentstolargediametermarinepropellershaftscanbeturnedonalathe.5.1车削与车床车削是金属切削加工中最常用的方法之一。在车削过程中，一个工件绕其轴线回转，单刃车刀沿工件进给，切掉多余的材料，最后形成要求的圆柱型表面，车削可以加工外表面以形成轴对称的成型零件，从怀表的零件到大型螺旋角零件轴都可以在车床上加工。Apartfromturning,severalotheroperationscanalsobeperformedonalathe.除了车削，一些其它的操作也可以在车床上完成。Boringandinternalturning.Boringandinternalturningareperformedontheinternalsurfacesbyaboringbarorsuitableinternalcuttingtools.Iftheinitialworkpieceissolid,adrillingoperationmustbeperformedfirst.Thedrillingtoolisheldinthetailstock,andthelatteristhenfedagainsttheworkpiece.Whenboringisdoneinalathe,theworkusuallyisheldinachuckoronafaceplate.Holesmaybeboredstraight,tapered,ortoirregularcontours.Boringisessentiallyinternalturningwhilefeedingthetoolparalleltotherotationaxisoftheworkpiece.镗削和车内圆：利用镗杆或合适的内圆车刀可以进行镗削和车内圆。工件毛坯如果是实心的，首先要钻孔，钻头安装在尾架上，后者向工件进给，如果在车床上进行镗削，工件一般安装在卡盘活花盘上。镗出的孔可以是盲孔、锥孔或者不规则的轮廓，当工具与回转轴平行进给时，镗削实际上是车削。Unit7Qualityandaccuracyaremajorconsiderationsinmakingpartsorstructures.Interchangeablepartsrequireahighdegreeofaccuracytofittogether.Withincreasingaccuracyorlessvariationinthedimension,thelaborandmachineryrequiredtomanufactureapartismorecostintensive.Anymanufacturershouldhaveathoroughknowledgeofthetolerancestoincreasethequalityandreliabilityofamanufacturedpartwiththeleastexpense.在制造机器零件和结构的过程中，质量和精度是最重要的因素。互换性零件需要有高精度以实现相互配合。随着精度的增加和尺寸变化的减小，制造零件所需的劳动力和机器更趋于成本密集型，制造商应该对公差有全面的了解，并以最小的成本提高加工零件的质量和可靠性。Anengineeringdrawingmustbeproperlydimensionedinordertoconveythedesigner’sintenttotheenduser.Dimensionsofpartsgivenonblueprintsandmanufacturedtothosedimensionsshouldbeexactlyalikeandfitproperly.Unfortunately,itisimpossibletomakethingstoanexactordimension.Mostdimensionshaveavaryingdegreeofaccuracyandameansodspecifyingacceptablelimitationsindimensionalvariancesothatamanufacturedpartwillbeacceptedandstillfunction.Itisnecessarythatthedimensions,shapesandmutualpositionofsurfacesofindividualpartsarekeptwithinacertainaccuracytoachievetheircorrectandreliablefunctioning.Routineprocessesdonotallowmaintenance(ormeasurement)ofthegivengeometricalpropertieswithabsoluteaccuracy.Actualsurfacesoftheproducedpartsthereforedifferfromidealsurfacesprescribedindrawings.Deviationsofactualsurfacesaredividedintofourgroupstoenableassessment,prescriptionandcheckingofthepermittedinaccuracyduringproduction:1:Dimensionaldeviations;2:Shapedeviations;3:Positiondeviations;4:Surfaceroughnessdeviations.一张工程图应有恰当的尺寸标注，来把设计师的想法传递给用户，加工出的零件尺寸应与图纸上所标注的零件尺寸完全一致并匹配，但是加工零件的尺寸不可能是精确的尺寸，大多数的尺寸都有一个加工范围，这是可接受的规定尺寸变化