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