机械毕业英语论文翻译车床Word文档下载推荐.docx
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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。
2NumericalControl
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。
Indirectnumer
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