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机械设计制造及其自动化专业英语翻译Unit1Metals金属Theuseofmetalshasalwaysbeenakeyfactorinthedevelopmentofthesocialsystemsofman.Oftheroughly100basicelementsofwhichallmatteriscomposedabouthalfareclassifiedasmetals.Thedistinctionbetweenametalandanonmetalisnotalwaysclear-cut.Themostbasicdefinitioncentersaroundthetypeofbondingexistingbetweentheatomsoftheelementandaroundthecharacteristicsofcertainoftheelectronsassociatedwiththeseatoms.Inamorepracticalwayhoweverametalcanbedefinedasanelementwhichhasaparticularpackageofproperties.Metalsarecrystallinewheninthesolidstateandwithfewexceptionse.g.mercuryaresolidatambienttemperatures.Theyaregoodconductorsofheatandelectricityandareopaquetolight.Theyusuallyhaveacomparativelyhighdensity.Manymetalsareductile-thatistheirshapecanbechangedpermanentlybytheapplicationofaforcewithoutbreaking.Theforcesrequiredtocausethisdeformationandthoserequiredtobreakorfractureametalarecomparativelyhighalthoughthefractureforcesisnotnearlyashighaswouldbeexpectedfromsimpleconsiderationoftheforcesrequiredtotearaparttheatomsofthemetal.Oneofthemoresignificantofthesecharacteristicsfromourpointofviewisthatofcrystallinity.Acrystallinesolidisoneinwhichtheconstituentatomsarelocatedinaregularthree-dimensionalarrayasiftheywerelocatedatthecornersofthesquaresofathree-dimensionalchessboard.Thespacingoftheatomsinthearrayisofthesameorderasthesizeoftheatomstheactualspacingbeingacharacteristicoftheparticularmetal.Thedirectionsoftheaxesofthearraydefinetheorientationofthecrystalinspace.Themetalscommonlyusedinengineeringpracticearecomposedofalargenumberofsuchcrystalscalledgrains.Inthemostgeneralcasethecrystalsofthevariousgrainsarerandomlyorientedinspace.Thegrainsareeverywhereinintimatecontactwithoneanotherandjoinedtogetheronanatomicscale.Theregionatwhichtheyjoinisknownasagrainboundary.Anabsolutelypuremetali.e.onecomposedofonlyonetypeofatomhasneverbeenproduced.Engineerswouldnotbeparticularlyinterestedinsuchametalevenifitweretobeproducedbecauseitwouldbesoftandweak.Themetalsusedcommerciallyinevitablycontainsmallamountsofoneormoreforeignelementseithermetallicornonmetallic.Theseforeignelementsmaybedetrimentaltheymaybebeneficialortheymayhavenoinfluenceatallonaparticularproperty.Ifdisadvantageoustheforeignelementstendtobeknownasimpurities.Ifadvantageoustheytendtobeknownasalloyingelements.Alloyingelementsarecommonlyaddeddeliberatelyinsubstantialamountsinengineeringmaterials.Theresultisknownasanalloy.Thedistinctionbetweenthedescriptors“metal”and“alloy”isnotclear-cut.Theterm“metal”maybeusedtoencompassbothacommerciallypuremetalanditsalloys.Perhapsitcanbesaidthatthemoredeliberatelyanalloyingadditionhasbeenmadeandthelargertheamountoftheadditionthemorelikelyitisthattheproductwillspecificallybecalledanalloy.Inanyeventthechemicalcompositionofametaloranalloymustbeknownandcontrolledwithincertainlimitsifconsistentperformanceistobeachievedinservice.Thuschemicalcompositionhastobetakenintoaccountwhendevelopinganunderstandingofthefactorswhichdeterminethepropertiesofmetalsandtheiralloys.Ofthe50orsometallicelementsonlyafewareproducedandusedinlargequantitiesinengineeringpractice.Themostimportantbyfarisirononwhicharebasedtheubiquitoussteelsandcastironsbasicallyalloysofironandcarbon.Theyaccountforabout98%byweightofallmetalsproduced.Nextinimportanceforstructuralusesthatisforstructuresthatareexpectedtocarryloadsarealuminumcoppernickelandtitanium.Aluminumaccountsforabout
0.8%byweightofallmetalsproducedandcopperabout
0.7%leavingonly
0.5%forallothermetals.Asmightbeexpectedtheremaindersareallusedinratherspecialapplications.Forexamplenickelalloysareusedprincipallyincorrosion-andheat-resistantapplicationswhiletitaniumisusedextensivelyintheaerospaceindustrybecauseitsalloyshavegoodcombinationsofhighstrengthandlowdensity.Bothnickelandtitaniumareusedinhigh-costhigh-qualityapplicationsandindeeditistheirhighcostthattendstorestricttheirapplication.Wecannotdiscussthesemoreesotericpropertieshere.Sufficeittosaythatawholecomplexofpropertiesinadditiontostructuralstrengthisrequiredofanalloybeforeitwillbeacceptedintoandsurviveinengineeringpractice.Itmayforexamplehavetobestrongandyethavereasonablecorrosionresistance;itmayhavetobeabletobefabricatedbyaparticularprocesssuchasdeepdrawingmachiningorwelding;itmayhavetobereadilyrecyclable;anditscostandavailabilitymaybeofcriticalimportance.在人类社会的发展中,金属的应用起着关键性的作用构成物质的大约100种基本元素中,大约有一半为金属金属和非金属之间的区别不是特别明显最基本的定义集中在元素原子间存在的连接形式和与这些原子相关联的电子的某些特性然而,在实际应用中,可以将具有某些特性集合金属定义为某种元素除了少数例外金属在常温下是固态的它们是热和电的良导体,不透光它们往往具有较高的密度许多金属具有延展性,也就是说,在不被破坏的情况下它们的形状在外力的作用下可以发生变化引起永久变形所需的力和最终使金属断裂所需的力相当大,尽管发生断裂所需的力远没有像所预期的撕开金属原子所需的力那么大从我们的观点来看,在所有的特性中结晶性是最重要的结晶体是这样一种结构,组成它的原子定位在规则的三维排列中,仿佛位于三维棋盘的方格的角上原子间距随着原子大小呈规律性变化,原子间距是金属的一种特性三维排列的轴线决定了晶体在空间中的方向在工程实践中应用的金属由大量的晶体组成,这些晶体称之为晶粒在大多数情况下,晶粒在空间中是自由排列的在原子范围内,晶粒之间相互接触紧密结合晶粒之间连接区域被称为晶界绝对纯净的金属从来也没有被生产出来过即使绝对纯净的金属可以生产出来,工程师们对它们也并不会特别感兴趣,因为它们很柔软、脆弱实际应用中的金属往往都包含着一定数量的一种或多种外来金属或非金属元素,这些外来元素可能是有害的也可能是有益的或者它们对某种特定的属性没有影响如果是有害的,这些外来元素被认为是杂质如果是有益的,它们被认为是合金元素在工程材料中往往被特意地加入一定数量的合金元素得到的物质被叫做合金金属和合金区别不大金属这个词可以包括工业用纯金属和它的合金也许可以这样说,合金元素越故意的被添加,被添加的合金元素的量越大,那么生产出来的产品越倾向于被称之为合金不管怎样,如果想使一种金属或合金在使用中表现出稳定一致的特性,在其中添加何种化学成分,它的量多大都应该在控制范围之内因此,当想了解决定金属和合金性质的因素时,应充分考虑它们的化学组成在50种左右的金属元素里,工程实践中只有少数金属被大量生产和使用到目前为止最重要的是铁,以它为基础构成了处处可见的钢和铸铁(主要由铁和碳构成的合金)它们的重量占所有生产出来的金属重量的98%在结构应用(也就是说,可以承受载荷的结构)中居于其次位置的是铝、铜、镍和钛在所有的金属产量中,铝占
0.8%,铜占
0.7%,剩下的占
0.5%剩下的金属用于相对特殊的用途例如,镍合金主要用于抗磨损和耐高温的用途,由于钛合金具有高强度和低密度的综合特性,钛被广泛应用于航空工业中镍合钛有高成本和高质量的使用特性,事实上,它们高的成本限制了它们的应用我们不能在这里讨论这些深奥的特性在合金材料被采用和应用于工程实际之前,掌握其结构强度和它的综合性质就够了举例来说,它可以强度很高,并且有好的耐磨性;它可以被例如拉伸加工,机械加工,或焊接等特殊工艺来加工出来;它可以被循环利用;它的成本和实用性是首要的Unit2SelectionofConstructionMaterials工程材料的选择Thereisnotagreatdifferencebetween“this”steeland“that”steel;allareverysimilarinmechanicalproperties.Selectionmustbemadeonfactorssuchashardenabilitypriceandavailabilityandnotwiththeideathat“this”steelcandosomethingnoothercandobecauseitcontains2percentinsteadof1percentofacertainalloyingelementorbecauseithasamysterious神秘的,不可思议的name.Atremendousrangeofpropertiesisavailableinanysteelafterheattreatment;thisisparticularlytrueofalloysteels.在钢之间没有太大的区别;所有的钢在机械性能方面都是近似的它们的选取标准是诸如脆硬性,价格,和可用性等不仅仅是因为这种钢含有2%的合金元素另一种钢含有1%而使前者具有了后者没有的某些能力,或者是某种钢具有神奇的名字经过热处理后,任何一种钢都具有大范围的特性;这种性质同样在合金钢中存在Considerationsinfabrication制造Thepropertiesofthefinalparthardnessstrengthandmachinabilityratherthanpropertiesrequiredbyforginggoverntheselectionofmaterial.Thepropertiesrequiredforforginghaveverylittlerelationtothefinalpropertiesofthematerial;thereforenotmuchcanbedonetoimproveitsforgeability.Higher-carbonsteelisdifficulttoforge.Largegrainsizeisbestifsubsequentheattreatmentwillrefinethegrainsize.关于加工的考虑最后零件的特性(硬度、强度和可加工性)而不是锻造特性决定了材料的选择可锻性与材料的最后特性联系不大;因此,提高金属的可锻造性价值不大高碳钢很难锻造如果在随后的热处理过程进行细化,大尺寸晶粒是最好的Low-carbonnickel-chromium铬steelsarejustaboutasplasticathightemperatureunderasingle520-ft·lb1ft·lb=
1.35582Jblowasplainsteelsofsimilarcarboncontent.Nickeldecreasesforgeabilityofmedium-carbonsteelsbuthaslittleeffectonlow-carbonsteels.Chromiumseemstohardensteelatforgingtemperaturesbutvanadium钒hasnodiscernible可辨别的effect;neitherhasthemethodofmanufactureanyeffectonhigh-carbonsteel.在高温下低碳,镍铬合金钢在受到520-ft·lb的冲击下表现出与相同碳含量普通钢几乎同样的塑性镍减少了中碳钢的可锻性,但对低碳钢影响不大铬在锻造温度下时使钢硬化,但钒没有明显的效果;两种加工方法对高碳钢没有影响FormabilityThecold-formabilityofsteelisafunction功能ofitstensilestrengthcombinedwithductility.Thetensilestrengthandyieldpointmustnotbehighortoomuchworkwillberequiredinbending(弯曲);likewise(同样地)thesteelmusthavesufficient(充足的)ductilitytoflowtotherequiredshapewithoutcracking.Theforcerequireddependsontheyieldpointbecausedeformationstartsintheplasticrangeabovetheyieldpointofsteel.Work-hardeningalsooccurshereprogressively(日益增多地)stiffening(使变硬)themetalandcausingdifficultyparticularly(独特的,显著的)inthelow-carbonsteels.成形钢的冷成形是它的拉伸强度和延展性相结合的结果拉伸强度和屈服点不能太高否则在发生弯曲时需要做很多工作;与之相类似,钢应该有高延展性,使其在没有断裂的情况下成形加工力的大小取决于屈服点,因为钢在屈服点之上才开始变形与此同时,加工硬化也同时发生,金属变得越来越硬,增加加工难度,尤其在低碳钢中容易发生Itisquiteinterestinginthisconnection(关于这一点,就此而论)todiscoverthatdeepdrawscansometimesbemadeinonerapidoperationthatcouldnotpossiblybedoneleisurely(缓慢地,从容不迫地)intwoorthree.Ifadrawishalfmadeandthenstoppeditmaybenecessarytoanneal(退火)beforeproceedingthatis(换句话说)ifthepieceisgiventimetowork-harden.Thismaynotbeascientificstatementbutitisactuallywhatseemstohappen.在这方面,相当有趣的是你将发现有时可通过一次快速加载完成大拉伸,但以缓慢的方式两三次加载却不能实现如果拉伸进行了一半就停止了,那么在再加工之前应先退火,也就是说工件是否有时间进行加工硬化这不是一种科学的叙述方法,但确实是发生了InternalstressesColdformingisdoneabovetheyieldpointinthework-hardeningrangesointernalstressescanbebuiltupeasily.Evidenceofthisisthespringback(回弹)astheworkleavestheformingoperationandthewarpage(翘曲,扭曲)inany(任何一种)subsequentheattreatment.Evenasimplewashermightbyvirtueof依靠theinternalstressesresultingfrompunching(冲压)andthenflattening(整平)warp(弯曲)severely(严格地,激烈地)duringheattreating.(virtuen.德行美德贞操优点功效效力英勇believedinthevirtueofprayer.相信祈祷的力量内应力在高于屈服点的加工硬化区进行冷加工很容易产生内应力例如工件停止成型加工后会发生回弹,在随后的热处理后,工件会发生翘曲即使是一个简单的垫圈,由于打孔和随后的平整加工中产生内应力,也会在热处理中呈现严重的翘曲Whendoubtexistsasto(关于)whetherinternalstresseswillcausewarpageapiececanbecheckedbyheatingittoabout1100andthenlettingitcool.Ifthereareinternalstressesthepieceislikelyto(可能)deform.Piecesthatwillwarpseverelywhilebeingheatedhavebeenseenyet(然而)theheat-treaterwasexpectedtoputthemthroughandbringthemoutbetterthantheywereinthefirstplace.当是否内应力会引起翘曲的怀疑存在时,可以通过将工件加工至1100然后进行冷却来验证如果存在内应力,工件会发生变形经过热处理的工件像我们看到的那样会发生严重的翘曲,但是我们仍然希望工件被扔到热处理炉中被处理,这样好过它存在内应力的状态WeldingThemaximumcarboncontentofplaincarbonsteelsafeforweldingwithoutpreheatingorsubsequentheattreatmentis
0.3%.higher-carbonsteelisweldedeverydaybutonlywithproperpreheating.Therearetwoimportantfactors:theamountofheatsthatisputin;therateatwhichitisremoved.焊接不需要预热或之后进行热处理就能安全焊接的最高碳含量为
0.3%高碳钢通过合适的预热通常也可焊接有两点值得注意吸收热量的多少;移除速度Weldingataslowerrateputsinmoreheatandheatsalargevolumeofmetalsothecoolingrateduetolossofheattothebasemetalisdecreased减少.Apreheatwilldothesamething.Forexamplesae4150steelpreheatedto600or800canbeweldedreadily(容易地).Whentheflameorarcistakenawayfromtheweldthecoolingrateisnotsogreatowingtothehighertemperatureofthesurroundingmetalandslowercoolingresults.Eventhemostrapidair-hardening(风硬钢)steelsareweldableifpreheatedandweldedataslowrate.低速焊接带来了更多的热量,这对金属的大量体积进行了加热,所以冷却速度降低预热可以取得与之相当的效果例如当被预热至或时可以很好的焊接由于周围金属的较高温度,当焊接弧移开焊接点后,冷却速度不会太快,产生了低速冷却的结果即使是冷作硬化速度最快的金属也可以通过预热和慢速焊接达到良好的焊接效果MachinabilityMachinability(机械加工性能)meansseveralthings.Toproductionmenitgenerallymeansbeingabletoremovemetalatthefastestrateleavethebestpossiblefinishandobtainthelongestpossibletoollife.Machinabilityappliesto(应用于)thetool-work(工具,零件)combination.可加工性可加工性意味着几件事情对于加工者来说,它意味着可以快速的移除金属,取得最好的加工效果,得到最长的刀具寿命可加工性是刀具和零件的结合Itisnotdeterminedbyhardness(硬度)alonebutbythetoughness(韧性)microstructurechemicalcomposition(成分)andtendency(倾向)ofametaltohardenundercoldwork.Inthemisleadingexpression“toohardtomachine”theword“hard”isusuallymeanttobesynonymous(同义的)with“difficult”.Manytimesamaterialisactuallytoosofttomachinereadily.Softnessandtoughnessmaycausethemetaltotear(撕裂)andflowaheadofthecuttingtoolratherthancutcleanly.Metalthatareinherently(天性地,固有地)softandtougharesometimesalloyedtoimprovetheirmachinabilityatsomesacrifice(牺牲)inductility.Examplesareuseoflead(铅)inbrass(黄铜)andofsulfur(硫磺)insteel.加工性不仅仅只由硬度决定,它还由韧性,微观结构,化学成分和在冷加工下金属所呈现的硬化特性所决定在容易混淆的表示“难加工”中,“hard”与“difficult”同义许多时候,因为材料过软而难于稳定加工材料柔软性和韧性能够产生金属撕裂,使金属在完成切削前流动至刀具前端柔软的金属往往会被加入合金从而牺牲它的延展性来提高加工性能如黄铜中加入铅钢中加入硫磺Machinabilityisatermusedtoindicatetherelative(比较的)ease(不费力)withwhichamaterialcanbemachinedbysharpcuttingtoolsinoperationssuchasturning(车)drilling(钻)milling(铣)broaching(拉削)andreaming(铰).机械加工性能是在指对工件材料使用刀具进行诸如车、钻、铣、拉削、铰加工时的难易程度Inthemachiningofmetalthemetalbeingcutthecuttingtoolthecoolanttheprocessandtypeofmachinetool(机床)andthecuttingconditionsallinfluencetheresults.Bychanginganyoneofthesefactorsdifferentresultswillbeobtained.Thecriterion(标准)uponwhichtheratings(等级)listedarebased等级评定的标准istherelativevolumeofvarious(不同种)materialsthatmayberemovedbyturningunderfixedconditionstoproduceanarbitrary(任意的)fixedamountoftoolwear.在对金属进行加工时,被切削的金属,切削刀具,冷却液,使用的机床的种类,切削条件均影响着切削效果改变任何一种均会产生不同的切削效果切削效果评定的准则是车削时在固定的切削条件下产生一定量的刀具磨损时,被加工试件相应的材料去除量淬透性指在规定条件下,决定钢材淬硬深度和硬度分布的特性即钢淬火时得到淬硬层深度大小的能力,它表示钢接受淬火的能力钢材淬透性好与差,常用淬硬层深度来表示淬硬层深度越大,则钢的淬透性越好钢的淬透性是钢材本身所固有的属性,它只取决于其本身的内部因素,而与外部因素无关钢的淬透性主要取决于它的化学成分,特别是含增大淬透性的合金元素及晶粒度,加热温度和保温时间等因素有关淬透性好的钢材,可使钢件整个截面获得均匀一致的力学性能以及可选用钢件淬火应力小的淬火剂,以减少变形和开裂 淬透性主要取决于其临界冷却速度的大小,而临界冷却速度则主要取决于过冷奥氏体的稳定性,影响奥氏体的稳定性主要是
1.化学成分的影响碳的影响是主要的,当C%小于
1.2%时,随着奥氏体中碳浓度的提高,显著降低临界冷却速度,C曲线右移,钢的淬透性增大;当C%大于时,钢的冷却速度反而升高,C曲线左移,淬透性下降其次是合金元素的影响,除钴外,绝大多数合金元素溶入奥氏体后,均使C曲线右移,降低临界冷却速度,从而提高钢的淬透性
2.奥氏体晶粒大小的影响奥氏体的实际晶粒度对钢的淬透性有较大的影响,粗大的奥氏体晶粒能使C曲线右移,降低了钢的临界冷却速度但晶粒粗大将增大钢的变形、开裂倾向和降低韧性
3.奥氏体均匀程度的影响在相同冷度条件下,奥氏体成分越均匀,珠光体的形核率就越低,转变的孕育期增长,C曲线右移,临界冷却速度减慢,钢的淬透性越高
4.钢的原始组织的影响钢的原始组织的粗细和分布对奥氏体的成分将有重大影响
5.部分元素,例如Mn,Si等元素对提高淬透性能起到一定作用,但同时也会对钢材带来其他不利的影响可锻性forgeability金属具有热塑性,在加热状态各种金属要求温度不同,可以进行压力加工,称为具有可锻性可锻性指金属材料在压力加工时,能改变形状而不产生裂纹的性能它包括在热态或冷态下能够进行锤锻,轧制,拉伸,挤压等加工可锻性的好坏主要与金属材料的化学成分有关[讨论]元素在钢中的形成物对可锻性的影响1C与Fe形成渗碳体Fe3C,与其它合金元素形成合金渗碳体FeM3C或合金碳化物所有碳化物都有硬度高、塑性低、熔点高的特点,但渗碳体型碳化物在加热到锻造温度时经适当保温可大部分或全部溶入固溶体中,而合金碳化物较难溶入固溶体中,对钢的可锻性影响最大一般高合金工具钢含碳高,故具有变形抗力大,塑性差,碳化物不易被粉碎等特点2Mn在钢中形成MnS以代替FeS因MnS熔点高(1620℃),且呈断续分布,不像FeS熔点988℃,呈网状分布在晶界,所以可减少热脆锰对钢的过热性(粗晶)很敏感,钢锭加热温度过高,易生粗晶,使锻造困难锰对珠光体钢的可锻性影响较小,奥氏体锰钢临界点将降低3Ni炼钢时有Ni极易吸收氢形成大量气泡,锻造时引起开裂Ni与Mn的作用相反,它促使硫化物成网状分布于晶界,使锻造时开裂,所以不宜在含硫的炉气中加热珠光体Ni钢在锻造时易形成片状破裂和带状组织为了消除这种组织可采用镦粗和拔长交错进行,或在1000~1100℃下长时期扩散退火4Cr铬在钢中形成较稳定的碳化物,提高碳化物在钢中的溶解温度,减慢溶解速度铬能促进使铸锭生成大晶粒,冷却时沿晶界形成内裂高铬钢在空气中冷却即能淬火,常在表面生裂,所以不易锻造5V与碳形成稳定碳化物V能使钢生成细晶组织,阻止过热,适当加入对锻性有利6Mo钼的熔点高,能降低钢的过热倾向它和Ni一样,使硫化物以网状分布在晶界含有
0.7%C,2~5%Mo的钼钢,锻造时无特殊困难这些钢在空冷时间淬火,要防止冷裂Mo提高钢的热强性,提高变形抗力7W与碳形成稳定的碳化物提高钢的热强性,增大变形抗力8Cu铜在钢中可溶于铁素体中,也可沿晶界析出游离铜铜中含
0.15%Cu时,加热不当,表面易生裂纹,高温轧制时易产生热脆9B硼能细化晶粒,能溶解在γ和α固溶体中,与Fe化合成Fe2B钢中含B>
0.007%时,锻造易裂10S在钢中形成硫化物或共晶体,如FeS、Fe的熔点为985℃,且成网状布于晶界显著降低可锻性(红脆)11P促成偏析,使晶粒粗大,容易引起锻件表面龟裂降低可锻性Unit3MechanicalPropertiesofMaterialsThematerialpropertiescanbeclassifiedintothreemajorheadings:iPhysicaliiChemicaliiiMechanical.PhysicalpropertiesDensityorspecificgravitymoisturecontentetc.canbeclassifiedunderthiscategory.ChemicalpropertiesManychemicalpropertiescomeunderthiscategory.Theseincludeacidityoralkalinityreactivityandcorrosion.Themostimportantoftheseiscorrosionwhichcanbeexplainedinlayman’stermsastheresistanceofthematerialtodecaywhileincontinuoususeinaparticularatmosphere.MechanicalpropertiesMechanicalpropertiesincludethestrengthpropertiesliketensilecompressionsheartorsionimpactfatigueandcreep.Thetensilestrengthofamaterialisobtainedbydividingthemaximumloadwhichthespecimenbearsbytheareaofcross-sectionofthespecimen.ThisisacurveplottedbetweenthestressalongtheY-axisordinateandthestrainalongtheX-axisabscissainatensiletest.Amaterialtendstochangeorchangesitsdimensionswhenitisloadeddependinguponthemagnitudeoftheload.Whentheloadisremoveditcanbeseenthatthedeformationdisappears.Formanymaterialsthisoccursuptoacertainvalueofthestresscalledtheelasticlimit.Thisisdepictedbythestraightlinerelationshipandasmalldeviationthereafterinthestress-straincurve.Withintheelasticrangethelimitingvalueofthestressuptowhichthestressandstrainareproportionaliscalledthelimitofproportionality.InthisregionthemetalobeysHooke’slawwhichstatesthatthestressisproportionaltostrainintheelasticrangeofloadingthematerialcompletelyregainsitsoriginaldimensionsaftertheloadisremoved.Intheactualplottingofthecurvetheproportionalitylimitisobtainedataslightlylowervalueoftheloadthantheelasticlimit.Thismaybeattributedtothetime-lagintheregainingoftheoriginaldimensionsofthematerial.Thiseffectisveryfrequentlynoticedinsomeno-ferrousmetals.Whileironandnickelexhibitclearrangesofelasticitycopperzinc(锌)tin(锡)etcarefoundtobeimperfectlyelasticevenatrelatively(相当地)lowvaluesofstresses.Actuallytheelasticlimitisdistinguishable(可区分的)fromtheproportionality(比例性)limitmoreclearlydependinguponthesensitivity(灵敏性)ofthemeasuringinstrument.Whentheloadisincreasedbeyondtheelasticlimitplasticdeformationstarts.Simultaneouslythespecimengetswork-hardened.Apointisreachedwhen(这时)thedeformationstartstooccurmorerapidlythantheincreasingload.ThispointiscalledtheyieldpointQ.themetalwhichwasresistingtheloadtillthenstartstodeformsomewhatrapidlyi.e.yield.Theyieldstressiscalledyieldlimit.TheelongationofthespecimencontinuesformQtoSandthentoT.thestess-strainrelationinthisplasticflowperiodisindicatedbytheportionQRSTofthecurve.AtTthespecimenbreaksandthisloadiscalledthebreakingload.ThevalueofthemaximumloadSdividedbytheoriginalcross-sectionalareaofthespecimenisreferredtoastheultimatetensilestrengthofthemetalorsimplythetensilestrength.Logicallyspeakingoncetheelasticlimitisexceededthemetalshouldstartstoyieldandfinallybreakwithoutanyincreaseinthevalueofstress.Butthecurverecordsanincreasedstressevenaftertheelasticlimitisexceeded.Tworeasonscanbegivenforthisbehavior:thestrainhardeningofthematerial;thediminishingcross-sectionalareaofthespecimensufferedonaccountoftheplasticdeformation.Themoreplasticdeformationthemetalundergoestheharderitbecomesduetowork-hardening.Themorethemetalgetselongatedthemoreitsdiameterandhencecross-sectionalareaisdecreased.ThiscontinuesuntilthepointSisreached.AfterStherateatwhichtheredutioninareatakesplaceexceedstherateatwhichthestressincreases.Strainbecomessohighthattheredutioninareabeginstoproducealocalizedeffectatsomepoint.Thisiscalledneching.Reductionincross-sectionalareatakesplaceveryrapidly;sorapidlythattheloadvalueactullydrops.ThisisindicatedbyST.FailureoccursatthispointT.Thenpercentageelongationandreductioninareaindicatetheductilityorplasticityofthematerial:Whereandaretheoriginalandthefinallengthofthespecimen;andaretheoriginalandthefinalcross-sectionalarea.材料特性主要分为三类i物理特性,ii化学特性,iii力学性能物理特性密度或特定的重力,湿度等都属于此范畴化学特性许多化学特性都归入到这个范畴其中包括酸性或碱性,活性和耐腐蚀性而在这其中最重要的是耐腐蚀性,通俗的解释是材料在特定大气中长期使用时,抵抗腐蚀的能力力学特性力学特性包括诸如拉伸,压缩,剪切,扭转,冲击,疲劳和蠕变等强度特性一种材料的拉伸强度由试件承载的最大载荷除以试件的横截面积得到如图所示为在拉伸试验中沿着X轴(横轴)的应变和沿着Y轴(纵轴)的应力之间的关系曲线材料在加载时,随着载荷大小的变化,尺寸会发生改变当卸载时,变形消失对于许多材料来说,上述情况发生的应力极限值称为弹性极限在应力-应变曲线中,直线关系和随后的小小的弯曲描述了上述的加载和卸载在弹性范围内,应力应变成比例的应力极限值称为比例极限在这个区域中,金属服从胡克定律—阐述了在加载的弹性范围内,应力和应变成比例关系(材料在卸载后,能够完全回复它原来的尺寸)在曲线的实际绘制中,比例极限值要稍微比弹性极限值低这可能是由于材料回复原尺寸需要的时间延迟这种现象在一些有色金属中常常出现铁和镍存在明显的弹性范围,铜,锌,锡等即使在相当低的应力值下弹性也表现得不是很充分实际上依靠测试仪器的精确性可以使比例极限和弹性极限区分得更清晰当在弹性极限之上增大载荷时会产生塑性变形同时,试件发生加工硬化到达某点后变形的速度快于载荷增加的速度这一点叫做屈服极限点一开始一直在抵抗载荷的金属在这一点后开始迅速地发生形变,也就是,屈服屈服应力叫做屈服极限试件从Q到S在到T不断地延长在这个塑性流动期间的应力-应变关系表示为曲线上的QRST段在T点试件断裂,此时的载荷称为断裂载荷最大荷载值S除以试件的横截面积为金属的最大拉伸强度或简单地称为拉伸强度逻辑上来说,一旦超过弹性极限,金属应该就会屈服直至最后断裂,在应力值上应该没有增加但是实际的曲线却记录了在超过弹性极限后的增加了的应力这种现象的发生可能有两种原因材料的应变强化;由于塑性变形引起的试件横截面积的缩小(ForChristwasGodandsufferedonaccountofusbeinghimselftheFatherthathemightbeabletosaveus.因为基督就是上帝,为我们受苦,他自己身为父,好叫祂也能救赎我们)由于加工硬化,金属在发生塑性变形时会变得越来越硬金属拉伸越长它的直径越小这种现象一直持续到曲线上的S点超过S点后,面积减少的速度超过了应力增加的速度应变变得很大,面积的减少在某些点产生了局部效应叫做颈缩横截面积减小的速度非常快;以至于实际上载荷降低伸长率和面积减少率表示了材料的延展性Unit6ManufacturingProcess1生产过程
(1)
一、Newwordsandexpressions
二、TranslationComputer-AidedManufacturing计算机辅助制造
1、Thescientificstudyofmetal-cuttingandautomationtechniquesisproductsofthetwentiethcentury.金属切削和自动化技术的科学研究时二十世纪的产物automation自动化techniques技术技巧手法TwopioneersofthesetechniqueswereFrederickTaylorandHenryFord.FrederickTaylor和HenryFord是这些技术的两个先驱pioneer先驱开拓者先锋Duringtheearly1900stheimprovingU.S.standardoflivingbroughtanewhighinpersonalwealth.在十九世纪的早期,美国日益提高的生活水平将个人财富带到了一个新的高度improve改善改进提高standard标准水平规范bring(brought)带来产生促进personal个人wealth财富Themajorresultwastheincreaseddemandfordurablegoods.这种现象主要影响就是对耐用消费品的需求的增长demand需求需要durable耐用经久结实durablegood耐用消费品Thisincreaseddemandmeantthatmanufacturingcouldnotlongerbetreatedasablacksmithtradeandtheuseofscientificstudywasemployedinmanufacturinganalysis.日益增长的需求意味着制造业不再是简单的手工作坊式的行业,而应该在制造业中引入科学化的研究手段mean意味着meanttreat处理对待blacksmith铁匠锻工trade商业交易营业行业Taylorpioneeredstudiesinscientificmanagementinwhichmethodsforproductionbybothmenandmachineswerestudied.Taylor开创了有关“科学管理”的研究,科学管理是涉及生产中人与设备间关系的研究pioneer先驱开拓者先锋pioneered首创率先开创了scientificmanagement科学管理method方法办法模式production生产作业TayloralsoconductedmetalcuttingexperimentsattheMidvaleSteelCompanythatlasted26yearsandproduced400tonsofmetalchips.Taylor还领导了在MidvaleSteelCompany进行的金属切削实验,该实验持续了26年,产生了400吨金属切削件conduct进行办理引导指挥conduction传导experiment试验chip芯片切削TheresultofTaylorsmetal-cuttingexperimentswasthedevelopmentoftheTaylortool-lifeequationthatisstillusedinindustrytoday.Taylor的金属切削实验最终导致了Taylor刀具寿命公式的发现,该公式目前仍然被工业界所采用equation方程等式公式Thistool-lifeequationisstillthebasisofdeterminingeconomicmetalcuttingandhasbeenusedinadaptivecontrolledmachining.该刀具寿命公式仍然是决定低成本金属切削的基础所在,同时,该刀具寿命公式还被用于自适应控制加工determine确定判定adaptive自适应(adapt适应改编)adaptivecontrolledmachining自适应控制加工
2、HenrvFord’scontributionstookadifferentturnfromTaylor’s.HenrvFord的贡献与Taylor不同contribution贡献功绩tookadifferentturnfrom采取了不同的方式(次序轮次)Fordrefinedanddevelopedtheuseofassemblylinesforthemajorcomponentmanufacturerofhisautomobile.Ford优化和开发了流水线的应用,这种流水线应用于他的大部分汽车部件的生产厂assembly装配部件总成assemblyline流水线major主要成年大多数少校component原件部件构建组成manufacturer生产厂家制造业者automobile汽车FordfeltthateveryAmericanfamilyshouldhaveanautomobileandiftheycouldbemanufacturedinexpensivelyenoughtheneveryfamilywouldbuyone.Ford认为,每个美国家庭都应该有一部汽车,如果他们能够制造出足够便宜的汽车的话,那么,每个家庭都会买一辆的feltfeel的过去式觉得认为感觉SeveralmechanismsweredevelopedatFordtoaccommodateassemblylines.Ford公司开发了一些设备以适应装配线mechanism机制机构机理机械accommodate容纳迁就和解TheautomationthatForddevelopedwasbuiltintothehardwareandFordrealizedthatsignificantdemandwasnecessarytooffsettheinitialdevelopmentandproductioncostsofsuchsystems.Ford开发的自动化被植入了生产线中,而且,Ford还意识到,为了弥补系统的早期开发和制造成本,必须有非常大的产品需求automation自动化realize明白意识到significant显著重大demand需求necessary必要offset抵消initial初始开始
3、Althoughmanufacturingindustriescontinuedtoevolveitwasnotuntilthe1950sthatthenextmajordevelopmentoccurred.虽然制造业的研发一直持续不断,但新的一轮大发展是在1950年代出现的evolve发展演变wasnotuntil直到Forsometimestridestoreducehumaninvolvementinmanufacturingwerebeingtaken.长期以来,人们一直致力于减少制造过程中的人为参与Forsometime一段时间以来stride进步步伐reduce减小involvement介入卷入参与manufacturing制造业Specialtymachinesusingcamsandother“hardwired”logiccontrollershadbeendeveloped.已经开发出了采用凸轮和其他“硬布线”逻辑控制器的专用设备TheU.S.AirForcerecognizedthedevelopmenttimerequiredtoproducethisspecialequipmentandthatthetimerequiredtomakeonlysmallsequencechangeswasexcessive.美国空军意识到,用来生产这些专用设备的研发时间和用来仅作程序小改变的时间都是很长的recognize识别认出承认认识sequence序列顺序次序smallsequencechange小序列变化excessive过度过高过分AsaresulttheAirForcecommissionedtheMassachusettsInstituteofTechnologytodemonstrateprogrammableornumericallycontrolledNCmachinesalsoknownassoftwiredmachines.因此,美国空军委托MassachusettsInstituteofTechnology开发可编程的数字化控制器(也称“软布线”设备)commissioned委托demonstrate表明演示示范论证指明Withthisfirstdemonstrationin1952camethebeginningofanewerainmanufacturing.1952年的这次首创开始了制造业的新纪元era时代年代纪元SincethendigitalcomputershavebeenusedtoproduceinputeitherinadirectedmannertomanyNCmachines,directnumericalcontrolDNC,orinamorededicatedcontrolsensecomputernumericalcontrolCNC.从那时起,数字计算机就被用来当做输入设备,它即能以直接方式输入到NC设备中,既直接控制(DNC),也可以用更专用的控制传感,即计算机数字控制(CNC).direct指导直接指挥dedicated专用sense感觉感应TodaymachinecontrollanguagessuchasAPTAutomaticProgrammingToolhavebecomethestandardforcreatingtoolcontrolforNCmachines.今天,机器控制语言,比如APT(自动编程工具)已经成为NC设备的创建工具控制的标准create创建创造制造
4、Itisinterestingtonotethatmuchoftheevolutioninmanufacturinghascomeasaresponsetoparticularchangesduringdifferentperiods.有趣的是制造业的许多发展都对应于不同历史时期的特定的变化evolution进化演化进程发展response响应反应应对period期间时期周期年代Forinstancethetechnologythatevolvesinthenineteenthcenturybroughtwithittheneedforhigher-precisionmachining.例如,十九世纪的技术发展就导致了对较高加工精度的需求evolve发展演变推移nineteenthcentury十九世纪precision精确缜密higher-precisionmachining较高精度的加工Thisresultedinthecreationofmanynewmachinetoolsamorerefinedmachinedesignandnewproductionprocesses.Theearlytwentiethcenturybecameaneraofprosperityandindustrializationthatcreatedthedemandnecessaryformass-productiontechniques.(这也导致了很多新机床的出现,更精细的机械设计和新的加工工艺)二十世纪初期成为一个繁荣的、工业化的年代,这个年代也创造了大规模生产技术所必须的产品需求result导致致使结果效果成功creation创建建立发明machinetool机床refine更好design设计process过程提炼处理era时代年代纪元prosperity繁荣昌盛丰富industrialization工业化(modernization现代化)mass块堆大多数mass-production大规模生产technique技术技巧手法Inthe1950sitwasestimatedthatasthespeedofanaircraftincreasedthecostofmanufacturingtheaircraftbecauseofgeometriccomplexityincreasedproportionatelywiththespeed.在1950年代,人们预测,当一个飞机的速度增加时,这个飞机的制造成本也会以这个速度同样比例的增加(因为其复杂程度是以几何级数增加的)estimate估计预算计量increase提高增加加强放大aircraft航空器飞机geometric几何complexity复杂复杂性proportionately比例TheresultofthiswasthedevelopmentofNCtechnology.也正是这个原因导致了NC技术的发展
5、Afewtangentialnotesonthishistoryincludethefollowing.tangential切线离题的肤浅的Asthevolumeofpartsmanufacturedincreasestheproductioncostforthepartsdecreasethisisgenerallyknownas“economyofscale”).当零部件的制造数量增加时,那么,这个零件的生产成本会减小(这种现象通常被称之为“经济规模”)Someofthechangeinproductioncostisduetofixedversusvariablecosts.生产成本某些变化是由于固定成本与可变成本的比例改变versus与对战相对于variable变量可变variablecosts可变成本Forinstanceifonlyasinglepartistobeproducedsuchasaspacevehicleallofthefixedcostsforplanninganddesignbothproductandprocessmustbeabsorbedbythesingleitem.例如,如果一个零件仅仅生产一个(诸如太空车),那么,所有固定成本,包括规划、设计(也包含产品和加工)都只能由这个单一项目去承担absorb吸收摄取product产品process过程加工进程Ifhoweverseveralpartsareproducedthefixedchargecanbedistributedoverseveralparts.然而,如果一个零件生产几个,那么,固定成本就可以均摊在几个零件上distributed分布分发散布分配Changesinproductioncost,notreflectedinthissimplefixed-versusvariable-costrelationship,areusuallytheresultofdifferentmanufacturingprocedures-transfer-linetechniquesforhigh-volumeitemsversusjob-shopproceduresforlow-volumeitems.生产成本的变化并不仅仅是简单的固定成本与可变成本间的关系,通常,这是不同制造方法的结果,自动化生产线用于大批量产品,加工车间用于小批量产品reflect反映体现versus与对战相对于variable变量可变variablecosts可变成本procedures-transfer-line程序传输线job-shop车间作业AutomatedManufacturingSystems自动化制造系统
6、Anautomatedmanufacturingsystemconsistsofacollectionofautomaticorsemiautomaticmachineslinkedtogetherbya“intrasystem”material-handlingsystem.自动化制造系统由一系列的自动化机床或半自动化机床,及将他们连接到一起的内部物料传送系统组成intrasystem系统内material-handlingsystem物料传递系统ThesesystemshavebeenaroundsincebeforeHenryFordbegantomanufacturehisModelTonhismovingassemblyline.这种系统大约起始于HenryFord在他的移动装配线上开始生产T型汽车的时候sincebefore起始于aroundsincebefore大约起始于ModelTT型车assembly装配movingassemblyline移动装配线Theseautomatedsystemshavebeenusedtoproducemachinedcomponentsassemblieselectricalcomponentsfoodproductschemicalproductsetc.这些自动化系统被用来生产机器零部件,总成,电器元件,食品,化工产品等Thetotalnumberofproductsproducedonasinglesystemvarieswiththeproductionmethods.单一系统的生产总量是随这个系统的生产方法变化而变化的vary变化变换不等Howevertheprinciplesofdesigningtheproductionsystemsarethesameindependentlyoftheproductbeingmanufactured.然而,不管生产什么产品,设计生产系统的原理是一样的Theworkstationsinaproductionsystemcanbemanual,semiautomaticorfullyautomatic.一个生产系统中的工作站可以是手工的、半自动的或全自动的workstations工作站Theautomaticstationscanbeprogrammableorhardwired.全自动的工作站即可以是可编程的,也可以是硬布线的
7、Thepurposeofanyproductionsystemistoproduceaproductorfamilyofproductsinthemosteconomicalmanner.任何生产系统的目的都是为了以最经济的方式生产一种或一系列产品purpose目的Automatedproductionsystemsarenodifferentfromanyothertypeofmanufacturingsystem.自动化生产系统与任何其它类型的制造系统没有区别Inordertoemployanyformofautomationtheimplementationmustbeeconomicallyjustifiable.无论采用哪种自动化形式,经济上都应该是合理的employ使用雇佣采用implementation履行justifiable合理的(justify辩解)Automationhastraditionallybeenmostappropriateforhigh-valueproducts.自动化通常更适合高价值产品traditionally传统appropriate适当合适适宜Howeverflexibleautomationequipmenthasbroughtautomationtosomerelativelylowvalueproducts.然而,柔性的自动化装备也被用来生产一些低价格产品flexible灵活有弹性伸缩relatively相对比较
1.Unit7ShaperPlanerMillingandGrindingMachines
2.ShapersShapersaremachinetoolsusedprimarilyintheproductionofflat平坦的;扁平的andangular有角的)surfaces.Inadditiontheshaperisusedtomachineirregularshapesandcontours(轮廓)whicharedifficulttoproduceonothermachinetools.Internalaswellasexternalsurfacesandshapescanbeproducedontheshaper.Commonshapesproducedontheshaperareflatangulargroovesdovetails(鸠尾榫头;楔形榫头)T-slotskeywaysslotsserrations(锯齿状)andcontours.Single-pointcuttingtoolssimilartothetypeusedonthelatheareusedinmachiningmostsurfacesontheshaper.Contoursurfacescanbeproducedwitheitherasingle-pointtooloraformedcuttingtool.Whenusingasingle-pointcuttingtoolforcontoursurfacesthedepthofcutmustbeconstantly(不断地)regulatedbythemachineoperatortoachievethepropercontour.Profiling(仿形)attachmentscanbeusedonsomeshaperstoregulatethefeedmotionandprovideduplicationofotherparts.Numericalcontrolunitsalsoenabletheproductionofirregularsurfaceswithconstantregulationofthedepthofcut.Shapersareclassifiedbytheplaneinwhichthecuttingactionoccurseitherhorizontalorvertical.Inadditionthehorizontal-typeshapersarefurtherclassifiedaspushorpullcut.Apush-cutshapercutswhiletheram(滑枕)ispushingthetoolacrosstheworkandapullcutmachineremovesmaterialwhilethetoolispulledtowardthemachine.Verticalshapersuseapushing-typecuttingactionandaresometimesreferredtoasslottersorkeyseaters.PlanersPlanersaresimilartoshapersbecausebothmachinesareprimarilyusedtoproduceflatandangularsurfaces.Howeverplanersarecapableofaccommodatingmuchlargerwork-piecesthantheshaper.Inplaneroperationstheworkpieceismountedonthetablewhichreciprocates(往复运动)inahorizontalplaneprovidingastraight-linecuttingandfeedaction.Single-pointcuttingtoolsaremountedonanoverheadcrossrailandalongtheverticallysupportedcolumns(柱状物).Thecuttingtoolsarefedintoorawayfromtheworkpieceoneitherthehorizontalorverticalplanethusbeingcapableoffourstraight-linefeedmotions.Cuttingspeedsareslowontheplanerbecauseoftheworkpiecesizeandtypeofcuttingtoolbeingused.Inordertoincreasetheproductionoftheplanermultipletoolingstationsareemployed.Twotoolingstationsarelocatedontheoverheadcrossrailswithusuallyonetoolingstationontheverticalsupports.Anothermethodofincreasingproductionontheplaneristomountanumberofworkpiecesonthetableatthesametime.Thismethodisonlyfeasiblewhentheworkpiecesrequirethesamecutandarerelativelysmallinsize.Theplanersizeisdesignated(指定,选定)bythemaximumworkpiececapacityofthemachine.Theheightwidthandlengthoftheworkpiecethatcanbeaccommodatedontheplanersworktablevarieswiththetypeofplaner.MillingMachinesMillingmachinesareprobablythemostversatilemachinetoolsusedinmodernmanufacturingwiththeexceptionofthelathe.Primarilydesignedtoproduceflatandangularsurfacesthemillingmachineisalsousedtomachineirregularshapessurfacesgroovesandslots.Themillingmachinecanalsobeusedfordrillingboringreamingandgear-cuttingoperations.Anumberofdifferenttypesofmillingmachinesaremanufacturedinordertoservethemultitudeofneedsandthediverseapplications.Millingmachinesareclassifiedaccordingtotheirstructureandincludecolumn-kneefixedbedplanerandspecialmachines.GrindingMachinesGrindingmachinesutilizeabrasive(研磨料)grainsbondedintovariousshapesandsizesofwheelsandbeltstobeusedasthecuttingagent(介质).Grindingoperationsareusedtoimpart(给予,传递)ahigh-qualitysurfacefinishontheworkpiece.Inadditionthedimensionalaccuracyoftheworkpieceisimprovedsincetolerancesof
0.00001in.[
0.00025mm]arepossibleingrindingoperations.Bothinternalandexternalsurfacescanbegroundbyusingthevarietyofgrindingmachinesavailable.Relatedoperations—whichuseabrasives(研磨剂)invariousformssuchaspastepowderandgrains—includelapping(研磨)honinganddrumfinishing.Grindingmachinesareclassifiedaccordingtothetypeofsurfaceproduced.Commonsurfacesandclassificationsofgrindingmachinesaresurfacecylindrical[silindrikəl]andspecialmachines.刨床刨床是主要用于加工平面和斜面的加工机床此外,刨床还可用于加工在其它机床上难于加工的不规则形状和外形轮廓内外表面和形状都可以在刨床上加工刨床可以加工的形状通常有平面,斜面,凹槽,燕尾槽,T型槽,键槽,槽,锯齿和外形轮廓与车床上使用的刀具相类似的单点切削刀具在刨床上用来加工大多数表面轮廓面可以用单点的方式或成型的方式切削出来用单点切削刀具加工曲面时,操作人员应不停地连续调整切削深度来加工出合适的轮廓在一些刨床上用仿形附件来复制其它零件的轮廓调整进给运动使用数字控制单元能不断地调整切削深度来完成不规则曲面的加工刨床类型由发生切削的平面来定义,或者是卧式的或者是立式的另外,卧式的还被进一步划分为推刨或拉刨龙门刨床龙门刨床与刨床类似,因为两者都用来加工平面或斜面不同的是龙门刨床适合加工更大尺寸的工件龙门刨床在加工过程中,工件被安装在提供直线切削和进给运动的沿水平往复运动的工作台上刀具被安装在上方的交叉导轨和垂直立柱上刀具在水平方向和垂直方向朝向工件或远离工件做进给运动,因此刀具有四个直线进给运动因为工件尺寸和使用刀具类型的关系,龙门刨床的切削速度比较慢为了提高龙门刨床的生产效率会使用多个动力头来进行切削在上方交叉导轨上会安装两个刀架,在垂直导轨上会安装一个另一种提高龙门刨生产率的方法是在工作台上同时装夹多个零件只有工件具有相同的切削要求和工件尺寸较小时才能使用这种方法龙门刨的规格是由机床所能加工零件的最大尺寸决定的能够加工零件的长、宽、高随着龙门刨型号的不同而不同铣床铣床可能是现代加工中除了车床外最为多样化的一种机床主要设计用来加工平面和斜面,铣床还可以用来加工不规则形状,曲面,槽铣床还可以进行钻,镗,铰和齿轮加工不同种类的铣床被制造出来以适应于不同的需求铣床通过其结构来定义其类型,包括卧式,固定工作台式,龙门式和专用铣床磨床磨床使用磨粒进行切削,磨粒粘接在一起形成不同形状不同尺寸的砂轮和砂带用于切削磨削可以带来高质量的工件表面另外,工件的尺寸精度在磨削过程中以
0.00025的精度得到提高使用不同种类的磨床可以加工工件的内外表面相同的加工方法--使用不同形式的研磨介质诸如粘接剂,粉状颗粒和磨粒--还包括研磨,珩磨和圆形砂轮磨削磨床类型由加工表面类型来定义通常有平面磨,外圆磨内圆磨,和专用磨床等。