后钢板弹簧吊耳831010加工工艺及钻37孔夹具设计

参考文献[1]李旦等.机床专用夹具图册[M].哈尔滨:哈尔滨工业大学出版社,2005.[2]孙已德.机床夹具图册[M].北京:机械工业出版社,1984.[3]何玉林.机械制图[M].重庆:重庆大学出版社,1983.[4]淘济贤等.机床夹具设计[M].北京:机械工业出版社,1986.[5]李洪.机械加工工艺师手册[M].北京:机械工业出版社,1990.[6]PattonW.J.ThePluminaGoldenVase.NewJersey:Printice-Hall,1981[7]东北重型机械学院.机床夹具设计手册[M].上海:上海科学技术出版社,1979.[8]贺光谊等.画法几何及机械制图[M].重庆:重庆大学出版社,1994.[9]丁骏一.典型零件制造工艺[M].北京:机械工业出版社,1989.[10]孙丽媛.机械制造工艺及专用夹具设计指导[M].北京:冶金工业出版社,2002.[11]东北重型机械学院等.机床夹具设计手册[M].上海:上海科学技术出版社,1979.[12]BallandRollerScrews.EngineeringMaterialandDesign.19(12,)1975[13]马贤智.机械加工余量与公差手册[M].北京:中国标准出版社,1994.附录1Lathesaremachinetoolsdesignedprimarilytodoturning,facingandboring,Verylittleturningisdoneonothertypesofmachinetools,andnonecandoitwithequalfacility.Becauselathesalsocandodrillingandreaming,theirversatilitypermitsseveraloperationstobedonewithasinglesetupoftheworkpiece.Consequently,morelathesofvarioustypesareusedinmanufacturingthananyothermachinetool.Theessentialcomponentsofalathearethebed,headstockassembly,tailstockassembly,andtheleadscrewandfeedrod.Thebedisthebackboneofalathe.Itusuallyismadeofwellnormalizedoragedgrayornodularcastironandprovidessheavy,rigidframeonwhichalltheotherbasiccomponentsaremounted.Twosetsofparallel,longitudinalways,innerandouter,arecontainedonthebed,usuallyontheupperside.SomemakersuseaninvertedV-shapeforallfourways,whereasothersutilizeoneinvertedVandoneflatwayinoneorbothsets,Theyareprecision-machinedtoassureaccuracyofalignment.Onmostmodernlathesthewayaresurface-hardenedtoresistwearandabrasion,butprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Theheadstockismountedinafoxedpositionontheinnerways,usuallyattheleftendofthebed.Itprovidesapoweredmeansofrotatingthewordatvariousspeeds.Essentially,itconsistsofahollowspindle,mountedinaccuratebearings,andasetoftransmissiongears-similartoatrucktransmission—throughwhichthespindlecanberotatedatanumberofspeeds.Mostlathesprovidefrom8to18speeds,usuallyinageometricratio,andonmodernlathesallthespeedscanbeobtainedmerelybymovingfromtwotofourlevers.Anincreasingtrendistoprovideacontinuouslyvariablespeedrangethroughelectricalormechanicaldrives.Becausetheaccuracyofalatheisgreatlydependentonthespindle,itisofheavyconstructionandmountedinheavybearings,usuallypreloadedtaperedrollerorballtypes.Thespindlehasaholeextendingthroughitslength,throughwhichlongbarstockcanbefed.Thesizeofmaximumsizeofbarstockthatcanbemachinedwhenthematerialmustbefedthroughspindle.Thetailsticdassemblyconsists,essentially,ofthreeparts.Alowercastingfitsontheinnerwaysofthebedandcanslidelongitudinallythereon,withameansforclampingtheentireassemblyinanydesiredlocation,Anuppercastingfitsontheloweroneandcanbemovedtransverselyuponit,onsometypeofkeyedways,topermitaligningtheassemblyisthetailstockquill.Thisisahollowsteelcylinder,usuallyabout51to76mm(2to3inches)indiameter,thatcanbemovedseveralincheslongitudinallyinandoutoftheuppercastingbymeansofahandwheelandscrew.Thesizeofalatheisdesignatedbytwodimensions.Thefirstisknownastheswing.Thisisthemaximumdiameterofworkthatcanberotatedonalathe.Itisapproximatelytwicethedistancebetweenthelineconnectingthelathecentersandthenearestpointontheways,Thesecondsizedimensionisthemaximumdistancebetweencenters.Theswingthusindicatesthemaximumworkpiecediameterthatcanbeturnedinthelathe,whilethedistancebetweencentersindicatesthemaximumlengthofworkpiecethatcanbemountedbetweencenters.Enginelathesarethetypemostfrequentlyusedinmanufacturing.Theyareheavy-dutymachinetoolswithallthecomponentsdescribedpreviouslyandhavepowerdriveforalltoolmovementsexceptonthecompoundrest.Theycommonlyrangeinsizefrom305to610mm(12to24inches)swingandfrom610to1219mm(24to48inches)centerdistances,butswingsupto1270mm(50inches)andcenterdistancesupto3658mm(12feet)arenotuncommon.Mosthavechippansandabuilt-incoolantcirculatingsystem.Smallerenginelathes-withswingsusuallynotover330mm(13inches)–alsoareavailableinbenchtype,designedforthebedtobemountedonabenchonabenchorcabinet.Althoughenginelathesareversatileandveryuseful,becauseofthetimerequiredforchangingandsettingtoolsandformakingmeasurementsontheworkpiece,thyarenotsuitableforquantityproduction.Oftentheactualchip-productiontineislessthan30%ofthetotalcycletime.Inaddition,askilledmachinistisrequiredforalltheoperations,andsuchpersonsarecostlyandofteninshortsupply.However,muchoftheoperator’stimeisconsumedbysimple,repetitiousadjustmentsandinwatchingchipsbeingmade.Consequently,toreduceoreliminatetheamountofskilledlaborthatisrequired,turretlathes,screwmachines,andothertypesofsemiautomaticandautomaticlatheshavebeenhighlydevelopedandarewidelyusedinmanufacturing.Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).PriortotheadventofNC,allmachinetoolseremanuallyoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanthelimitationofoperatorskills.Withmanualcontrol,thequalityoftheproductisdirectlyrelatedtoandlimitedtotheskillsoftheoperator.Numericalcontrolrepresentsthefirstmajorstepawayfromhumancontrolofmachinetools.Numericalcontrolmeansthecontrolofmachinetoolsandothermanufacturingsystemsthroughtheuseofprerecorded,writtensymbolicinstructions.Ratherthanoperatingamachinetool,anNCtechnicianwritesaprogramthatissuesoperationalinstructionstothemachinetool.Foramachinetooltobenumericallycontrolled,itmustbeinterfacedwithadeviceforacceptinganddecodingtheprogrammedinstructions,knownasareader.Numericalcontrolwasdevelopedtoovercomethelimitationofhumanoperators,andithasdoneso.Numericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveralotherinnovationsinmanufacturingtechnology:Electricaldischargemachining,Lasercutting,Electronbeamwelding.Numericalcontrolhasalsomademachinetoolsmoreversatilethantheirmanuallyoperatedpredecessors.AnNCmachinetoolcanautomaticallyproduceawideofparts,eachinvolvinganassortmentofwidelyvariedandcomplexmachiningprocesses.Numericalcontrolhasallowedmanufacturerstoundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetollsandprocesses.Likesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirForce.Initsearlieststages,NCmachineswereabletomadestraightcutsefficientlyandeffectively.However,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorterthestraightlinesmakingupthesteps,thesmootheristhecurve,Eachlinesegmentinthestepshadtobecalculated.Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)language.ThisisaspecialprogramminglanguageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentfromthoseusedtoday.Themachineshadhardwiredlogiccircuits.Theinstructionalprogramswerewrittenonpunchedpaper,whichwaslatertobereplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.Together,allofthisrepresentedagiantstepforwardinthecontrolofmachinetools.However,therewereanumberofproblemswithNCatthispointinitsdevelopment.Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapertapecontainingtheprogrammedinstructionstobreakortearduringamachiningprocess.Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtobererunthroughthereader.Ifitwasnecessarytoproduce100copiesofagivenpart,itwasalsonecessarytorunthepapertapethroughthereader100separatetines.Fragilepapertapessimplycouldnotwithstandtherigorsofashopfloorenvironmentandthiskindofrepeateduse.Thisledtothedevelopmentofaspecialmagneticplastictape.Whereasthepapercarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theplastictapecarriedtheinstructionsasaseriesofmagneticdots.Theplastictapewasmuchstrongerthanthepapertape,whichsolvedtheproblemoffrequenttearingandbreakage.However,itstilllefttwootherproblems.Themostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Tomadeeventhemostminoradjustmentsinaprogramofinstructions,itwasnecessarytointerruptmachiningoperationsandmakeanewtape.Itwasalsostillnecessarytorunthetapethroughthereaderasmanytimesastherewerepartstobeproduced.Fortunately,computertechnologybecamearealityandsoonsolvedtheproblemsofNCassociatedwithpunchedpaperandplastictape.Thedevelopmentofaconceptknownasdirectnumericalcontrol(DNC)solvedthepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputer.Programsforoperatingthemachinetoolsarestoredinthehostcomputerandfedtothemachinetoolanneededviathedatatransmissionlinkage.Directnumericalcontrolrepresentedamajorstepforwardoverpunchedtapeandplastictape.However,itissubjecttothesamelimitationsasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.Theenginelathe,oneoftheoldestmetalremovalmachines,hasanumberofusefulandhighlydesirableattributes.Todaytheselathesareusedprimarilyinsmallshopswheresmallerquantitiesratherthanlargeproductionrunsareencountered.Theenginelathehasbeenreplacedintoday’sproductionshopsbyawidevarietyofautomaticlathessuchasautomaticofsingle-pointtoolingformaximummetalremoval,andtheuseofformtoolsforfinishonaparwiththefastestprocessingequipmentonthescenetoday.Tolerancesfortheenginelathedependprimarilyontheskilloftheoperator.Thedesignengineermustbecarefulinusingtolerancesofanexperimentalpartthathasbeenproducedontheenginelathebyaskilledoperator.Inredesigninganexperimentalpartforproduction,economicaltolerancesshouldbeused.TurretLathesProductionmachiningequipmentmustbeevaluatednow,morethaneverbefore,thiscriterionforestablishingtheproductionqualificationofaspecificmethod,theturretlathemeritsahighrating.Indesigningforlowquantitiessuchas100or200parts,itismosteconomicaltousetheturretlathe.Inachievingtheoptimumtolerancespossibleontheturretslathe,thedesignershouldstriveforaminimumofoperations.AutomaticScrewMachinesGenerally,automaticscrewmachinesfallintoseveralcategories;single-spindleautomatics,multiple-spindleautomaticsandautomaticchuckingmachines.Originallydesignedforrapid,automaticproductionofscrewsandsimilarthreadedparts,theautomaticscrewmachinehaslongsinceexceededtheconfinesofthisnarrowfield,andtodayplaysavitalroleinthemassproductionofavarietyofprecisionparts.Quantitiesplayanimportantpartintheeconomyofthepartsmachinedontheautomaticscrewmachine.Quantitieslessthanontheautomaticscrewmachine.Thecostofthepartsmachinedcanbereducediftheminimumeconomicallotsizeiscalculatedandthepropermachineisselectedforthesequantities.AutomaticTracerLathesSincesurfaceroughnessdependsgreatlyonmaterialturned,tooling,andfeedsandspeedsemployed,minimumtolerancesthatcanbeheldonautomatictracerlathesarenotnecessarilythemosteconomicaltolerances.Insomecases,tolerancesof0.05mmareheldincontinuousproductionusingbutonecut.groovewidthcanbeheldto0.125mmonsomeparts.Boresandsingle-pointfinishescanbeheldto0.0125mm.Onhigh-productionrunswheremaximumoutputisdesirable,aminimumtoleranceof0.125mmiseconomicalonbothdiameterandlengthofturn.About40%ofballbearingfailuresarecausedbycontaminationfromdust,dirt,shavings,andcorrosion.Contaminationalsocausestorqueandnoiseproblems,andisoftentheresultofimproperhandlingortheapplicationenvironment．Fortunately,abearingfailurecausedbyenvironmentorhandlingcontaminationispreventable，andasimplevisualexaminationcaneasilyidentifythecause．Conductingapostmortemil1ustrateswhattolookforonafailedorfailingbearing．Then，understandingthemechanismbehindthefailure,suchasbrinellingorfatigue,helpseliminatethesourceoftheproblem.Brinellingisonetypeofbearingfailureeasilyavoidedbyproperhandingandassembly.Itischaracterizedbyindentationsinthebearingracewaycausedbyshockloading－suchaswhenabearingisdropped-orincorrectassembly.Brinellingusuallyoccurswhenloadsexceedthematerialyieldpoint(350,000psiinSAE52100chromesteel)．Itmayalsobecausedbyimproperassembly,Whichplacesaloadacrosstheraces．Racewaydentsalsoproducenoise，vibration，andincreasedtorque.Asimilardefectisapatternofellipticaldentscausedbyballsvibratingbetweenracewayswhilethebearingisnotturning．Thisproblemiscalledfalsebrinelling.Itoccursonequipmentintransitorthatvibrateswhennotinoperation.Inaddition,debriscreatedbyfalsebrinellingactslikeanabrasive,furthercontaminatingthebearing.Unlikebrinelling,falsebinellingisoftenindicatedbyareddishcolorfromfrettingcorrosioninthelubricant.Falsebrinellingispreventedbyeliminatingvibrationsourcesandkeepingthebearingwelllubricated.Isolationpadsontheequipmentoraseparatefoundationmayberequiredtoreduceenvironmentalvibration.Alsoalightpreloadonthebearinghelpskeeptheballsandracewayintightcontact.Preloadingalsohelpspreventfalsebrinellingduringtransit.Seizurescanbecausedbyalackofinternalclearance,improperlubrication,orexcessiveloading.Beforeseizing,excessive,frictionandheatsoftensthebearingsteel.Overheatedbearingsoftenchangecolor，usuallytoblue-blackorstrawcolored．Frictionalsocausesstressintheretainer，whichcanbreakandhastenbearingfailure．Prematurematerialfatigueiscausedbyahighloadorexcessivepreload．Whentheseconditionsareunavoidable，bearinglifeshouldbecarefullycalculatedsothatamaintenanceschemecanbeworkedout．Anothersolutionforfightingprematurefatigueischangingmaterial．Whenstandardbearingmaterials，suchas440CorSAE52100，donotguaranteesufficientlife，specialtymaterialscanberecommended.Inaddition，whentheproblemistracedbacktoexcessiveloading，ahighercapacitybearingordifferentconfigurationmaybeused．Creepislesscommonthanprematurefatigue．Inbearings．itiscausedbyexcessiveclearancebetweenboreandshaftthatallowstheboretorotateontheshaft．Creepcanbeexpensivebecauseitcausesdamagetoothercomponentsinadditiontothebearing．0thermorelikelycreepindicatorsarescratches，scuffmarks，ordiscolorationtoshaftandbore．Topreventcreepdamage，thebearinghousingandshaftfittingsshouldbevisuallychecked．Misalignmentisrelatedtocreepinthatitismountingrelated．Ifracesaremisalignedorcocked．Theballstrackinanoncircumferencialpath．Theproblemisincorrectmountingortolerancing，orinsufficientsquarenessofthebearingmountingsite．Misalignmentofmorethan1/4·cancauseanearlyfailure．Contaminatedlubricantisoftenmoredifficulttodetectthanmisalignmentorcreep．Contaminationshowsasprematurewear．Solidcontaminantsbecomeanabrasiveinthelubricant．Inaddition。insufficientlubricationbetweenballandretainerwearsandweakenstheretainer．Inthissituation，lubricationiscriticaliftheretainerisafullymachinedtype．Ribbonorcrownretainers，incontrast，allowlubricantstomoreeasilyreachallsurfaces．Rustisaformofmoisturecontaminationandoftenindicatesthewrongmaterialfortheapplication．Ifthematerialchecksoutforthejob，theeasiestwaytopreventrustistokeepbearingsintheirpackaging，untiljustbeforeinstallation．Thebestwaytohandlebearingfailuresistoavoidthem．Thiscanbedoneintheselectionprocessbyrecognizingcriticalperformancecharacteristics．Theseincludenoise，startingandrunningtorque，stiffness，nonrepetitiverunout，andradialandaxialplay．Insomeapplications,theseitemsaresocriticalthatspecifyinganABEClevelaloneisnotsufficient．Torquerequirementsaredeterminedbythelubricant，retainer，racewayquality(roundnesscrosscurvatureandsurfacefinish)，andwhethersealsorshieldsareused．Lubricantviscositymustbeselectedcarefullybecauseinappropriatelubricant，especiallyinminiaturebearings，causesexcessivetorque．Also，differentlubricantshavevaryingnoisecharacteristicsthatshouldbematchedtotheapplication.Forexample，greasesproducemorenoisethanoil．Nonrepetitiverunout(NRR)occursduringrotationasarandomeccentricitybetweentheinnerandouterraces，muchlikeacamaction．NRRcanbecausedbyretainertoleranceoreccentricitiesoftheracewaysandballs．Unlikerepetitiverunout,nocompensationcanbemadeforNRR.NRRisreflectedinthecostofthebearing．Itiscommonintheindustrytoprovidedifferentbearingtypesandgradesforspecificapplications．Forexample，abearingwithanNRRoflessthan0.3umisusedwhenminimalrunoutisneeded，suchasindisk—drivespindlemotors．Similarly，machine—toolspindlestolerateonlyminimaldeflectionstomaintainprecisioncuts．Consequently,bearingsaremanufacturedwithlowNRRjustformachine-toolapplications．Contaminationisunavoidableinmanyindustrialproducts，andshieldsandsealsarecommonlyusedtoprotectbearingsfromdustanddirt．However，aperfectbearingsealisnotpossiblebecauseofthemovementbetweeninnerandouterraces．Consequently，lubricationmigrationandcontaminationarealwaysproblems．Onceabearingiscontaminated,itslubricantdeterioratesandoperationbecomesnoisier．Ifitoverheats，thebearingcanseize．Attheveryleast，contaminationcauseswearasitworksbetweenballsandtheraceway，becomingimbeddedintheracesandactingasanabrasivebetweenmetalsurfaces．Fendingoffdirtwithsealsandshieldsillustratessomemethodsforcontrollingcontamination．Noiseisasanindicatorofbearingquality．Variousnoisegradeshavebeendevelopedtoclassifybearingperformancecapabilities．NoiseanalysisisdonewithanAnderonmeter,whichisusedforqualitycontrolinbearingproductionandalsowhenfailedbearingsarereturnedforanalysis.Atransducerisattachedtotheouterringandtheinnerraceisturnedat1,800rpmonanairspindle.Noiseismeasuredinandirons,whichrepresentballdisplacementinμm/rad.Withexperience,inspectorscanidentifythesmallestflawfromtheirsound.Dust,forexample,makesanirregularcrackling.Ballscratchesmakeaconsistentpoppingandarethemostdifficulttoidentify.Inner-racedamageisnormallyaconstanthigh-pitchednoise,whileadamagedouterracemakesanintermittentsoundasitrotates.Bearingdefectsarefurtheridentifiedbytheirfrequencies.Generally,defectsareseparatedintolow,medium,andhighwavelengths.Defectsarealsoreferencedtothenumberofirregularitiesperrevolution.Low-bandnoiseistheeffectoflong-wavelengthirregularitiesthatoccurabout1.6to10timesperrevolution.Thesearecausedbyavarietyofinconsistencies,suchaspocketsintherace.Detectablepocketsaremanufacturingflawsandresultwhentheraceismountedtootightlyinmultiplejawchucks.Medium-handnoiseischaracterizedbyirregularitiesthatoccur10to60timesperrevolution.Itiscausedbyvibrationinthegrindingoperationthatproducesballsandraceways.High-handirregularitiesoccurat60to300timesperrevolutionandindicatecloselyspacedchattermarksorwidelyspaced,roughirregularities.ClassifyingbearingsbytheirnoisecharacteristicsallowsuserstospecifyanoisegradeinadditiontotheABECstandardsusedbymostmanufacturers.ABECdefinesphysicaltolerancessuchasbore,outerdiameter,andrunout.AstheABECclassnumberincrease(from3to9),tolerancesaretightened.ABECclass,however,doesnotspecifyotherbearingcharacteristicssuchasracewayquality,finish,ornoise.Hence,anoiseclassificationhelpsimproveontheindustrystandard.附录2车床主要是为了进行车外圆、车端面和镗孔等项工作而设计的机床。车削很少在其他种类的机床上进行，而且任何一种其他机床都不能像车床那样方便地进行车削加工。由于车床还可以用来钻孔和铰孔，车床的多功能性可以使工件在一次安装中完成几种加工。因此，在生产中使用的各种车床比任何其他种类的机床都多。车床的基本部件有：床身、主轴箱组件、尾座组件、溜板组件、丝杠和光杠。床身是车床的基础件。它能常是由经过充分正火或时效处理的灰铸铁或者球墨铁制成。它是一个坚固的刚性框架，所有其他基本部件都安装在床身上。通常在床身上有内外两组平行的导轨。有些制造厂对全部四条导轨都采用导轨尖朝上的三角形导轨（即山形导轨），而有的制造厂则在一组中或者两组中都采用一个三角形导轨和一个矩形导轨。导轨要经过精密加工以保证其直线度精度。为了抵抗磨损和擦伤，大多数现代机床的导轨是经过表面淬硬的，但是在操作时还应该小心，以避免损伤导轨。导轨上的任何误差，常常意味着整个机床的精度遭到破坏。主轴箱安装在内侧导轨的固定位置上，一般在床身的左端。它提供动力，并可使工件在各种速度下回转。它基本上由一个安装在精密轴承中的空心主轴和一系列变速齿轮(类似于卡车变速箱)所组成。通过变速齿轮，主轴可以在许多种转速下旋转。大多数车床有8~12种转速，一般按等比级数排列。而且在现代机床上只需扳动2~4个手柄，就能得到全部转速。一种正在不断增长的趋势是通过电气的或者机械的装置进行无级变速。由于机床的精度在很大程度上取决于主轴，因此，主轴的结构尺寸较大，通常安装在预紧后的重型圆锥滚子轴承或球轴承中。主轴中有一个贯穿全长的通孔，长棒料可以通过该孔送料。主轴孔的大小是车床的一个重要尺寸，因此当工件必须通过主轴孔供料时，它确定了能够加工的棒料毛坯的最大尺寸。尾座组件主要由三部分组成。底板与床身的内侧导轨配合，并可以在导轨上作纵向移动。底板上有一个可以使整个尾座组件夹紧在任意位置上的装置。尾座体安装在底板上，可以沿某种类型的键槽在底板上横向移动，使尾座能与主轴箱中的主轴对正。尾座的第三个组成部分是尾座套筒。它是一个直径通常大约在51~76mm（2~3英寸）车床的规格用两个尺寸表示。第一个称为车床的床面上最大加工直径。这是在车床上能够旋转的工件的最大直径。它大约是两顶尖连线与导轨上最近点之间距离的两倍。第二个规格尺寸是两顶尖之间的最大距离。车床床面上最大加工直径表示在车床上能够车削的最大工件直径，而两顶尖之间的最大距离则表示在两个顶尖之间能够安装的工件的最大长度。普通车床是生产中最经常使用的车床种类。它们是具有前面所叙的所有那些部件的重载机床，并且除了小刀架之外，全部刀具的运动都有机动进给。它们的规格通常是：车床床面上最大加工直径为305~610mm（12~24英寸）；但是，床面上最大加工直径达到1270mm（50英寸）和两顶尖之间距离达到3658mm的车床也并不少见。这些车床大部分都有切屑盘和一个安装在内部的冷却液循环系统。小型的普通车床—车床床面最大加工直径一般不超过330mm（虽然普通车床有很多用途，是很有用的机床，但是更换和调整刀具以及测量工件花费很多时间，所以它们不适合在大量生产中应用。通常，它们的实际加工时间少于其总加工时间的30%。此外，需要技术熟练的工人来操作普通车床，这种工人的工资高而且很难雇到。然而，操作工人的大部分时间却花费在简单的重复调整和观察切屑过程上。因此，为了减少或者完全不雇用这类熟练工人，六角车床、螺纹加工车床和其他类型的半自动和自动车床已经很好地研制出来，并已经在生产中得到广泛应用。先进制造技术中的一个基本的概念是数字控制（NC）。在数控技术出现之前，所有的机床都是由人工操纵和控制的。在与人工控制的机床有关的很多局限性中，操作者的技能大概是最突出的问题。采用人工控制是，产品的质量直接与操作者的技能有关。数字控制代表了从人工控制机床走出来的第一步。数字控制意味着采用预先录制的、存储的符号指令来控制机床和其他制造系统。一个数控技师的工作不是去操纵机床，而是编写能够发出机床操纵指令的程序。对于一台数控机床，其上必须安有一个被称为阅读机的界面装置，用来接受和解译出编程指令。发展数控技术是为了克服人类操作者的局限性，而且它确实完成了这项工作。数字控制的机器比人工操纵的机器精度更高、生产出零件的一致性更好、生产速度更快、而且长期的工艺装备成本更低。数控技术的发展导致了制造工艺中其他几项新发明的产生：电火花加工技术、激光切割、电子束焊接数字控制还使得机床比它们采用有人工操的前辈们的用途更为广泛。一台数控机床可以自动生产很多类的零件，每一个零件都可以有不同的和复杂的加工过程。数控可以使生产厂家承担那些对于采用人工控制的机床和工艺来说，在经济上是不划算的产品生产任务。同许多先进技术一样，数控诞生于麻省理工学院的实验室中。数控这个概念是50年代初在美国空军的资助下提出来的。在其最初的价段，数控机床可以经济和有效地进行直线切割。然而，曲线轨迹成为机床加工的一个问题，在编程时应该采用一系列的水平与竖直的台阶来生成曲线。构成台阶的每一个线段越短，曲线就越光滑。台阶中的每一个线段都必须经过计算。在这个问题促使下，于1959年诞生了自动编程工具（APT）语言。这是一个专门适用于数控的编程语言，使用类似于英语的语句来定义零件的几何形状，描述切削刀具的形状和规定必要的运动。APT语言的研究和发展是在数控技术进一步发展过程中的一大进步。最初的数控系统下今天应用的数控系统是有很大差别的。在那时的机床中，只有硬线逻辑电路。指令程序写在穿孔纸带上（它后来被塑料带所取代），采用带阅读机将写在纸带或磁带上的指令给机器翻译出来。所有这些共同构成了机床数字控制方面的巨大进步。然而，在数控发展的这个阶段中还存在着许多问题。一个主要问题是穿孔纸带的易损坏性。在机械加工过程中，载有编程指令信息的纸带断裂和被撕坏是常见的事情。在机床上每加工一个零件，都需要将载有编程指令的纸带放入阅读机中重新运行一次。因此，这个问题变得很严重。如果需要制造100个某种零件，则应该将纸带分别通过阅读机100次。易损坏的纸带显然不能承受严配的车间环境和这种重复使用。这就导致了一种专门的塑料磁带的研制。在纸带上通过采用一系列的小孔来载有编程指令，而在塑料带上通过采用一系列的磁点眯载有编程指令。塑料带的强度比纸带的强度要高很多，这就可以解决常见的撕坏和断裂问题。然而，它仍然存在着两个问题。其中最重要的一个问题是，对输入到带中指令进行修改是非常困难的，或者是根本不可能的。即使对指令程序进行最微小的调整，也必须中断加工，制作一条新带。而且带通过阅读机的次数还必须与需要加工的零件的个数相同。幸运的是，计算机技术的实际应用很快解决了数控技术中与穿孔纸带和塑料带有关的问题。在形成了直接数字控制（DNC）这个概念之后，可以不再采用纸带或塑料带作为编程指令的载体，这样就解决了与之有关的问题。在直接数字控制中，几台机床通过数据传输线路联接到一台主计算机上。操纵这些机床所需要的程序都存储在这台主计算机中。当需要时，通过数据传输线路提供给每台机床。直接数字控制是在穿孔纸带和塑料带基础上的一大进步。然而，它敢有着同其他信赖于主计算机技术一样的局限性。当主计算机出现故障时，由其控制的所有机床都将停止工作。这个问题促使了计算机数字控制技术的产生。微处理器的发展为可编程逻辑控制器和微型计算机的发展做好了准备。这两种技术为计算机数控（CNC）的发打下了基础。采用CNC技术后，每台机床上都有一个可编程逻辑控制器或者微机对其进行数字控制。这可以使得程序被输入和存储在每台机床内部。它还可以在机床以外编制程序，并将其下载到每台机床中。计算机数控解决了主计算机发生故障所带来的问题，但是它产生了另一个被称为数据管理的问题。同一个程序可能要分别装入十个相互之间没有通讯联系的微机中。这个问题目前正在解决之中，它是通过采用局部区域网络将各个微机联接起来，以得于更好地进行数据管理。普通车床作为最早的金属切削机床的一种，目前仍然有许多有用的和为人要的特性和为人们所需的特性。现在，这些机床主要用在规模较小的工厂中，进行小批量的生产，而不是进行大批量的和产。在现代的生产车间中，普通车床已经被种类繁多的自动车床所取代，诸如自动仿形车床，六角车床和自动螺丝车床。现在，设计人员已经熟知先利用单刃刀具去除大量的金属余量，然后利用成型刀具获得表面光洁度和精度这种加工方法的优点。这种加工方法的生产速度与现在工厂中使用的最快的加工设备的速度相等。普通车床的加偏差主要信赖于操作者的技术熟练程度。设计工程师应该认真地确定由熟练工人在普通车床上加工的试验件的公差。在把试验伯重新设计为生产零件时，应该选用经济的公差。六角车床对生产加工设备来说，目前比过去更注重评价其是否具有精确的和快速的重复加工能力。应用这个标准来评价具体的加工方法，六角车床可以获得较高的质量评定。在为小批量的零件（100~200件）设计加工方法时，采用六角车床是最经济的。为了在六角车床上获得尽可能小的公差值，设计人员应该尽量将加工工序的数目减至最少。自动螺丝车床自动螺丝车床通被分为以下几种类型：单轴自动、多轴自动和自动夹紧车床。自动螺丝车床最初是被用来对螺钉和类似的带有螺纹的零件进行自动化和快速加工的。但是，这种车床的用途早就超过了这个