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1、機械加工介紹機械加工介紹1LathesLathesaremachinetoolsdesignedprimarilytodoturningfacingbingVerylittleturningisdoneonothertypesofmachinetoolsnonecandoitwithequalfacility.Becauselathesalsocandodrillingreamingtheirversatilitypermitsseve
2、raloperationstobedonewithasinglesetupofthewkpiece.Consequentlymelathesofvarioustypesareusedinmanufacturingthananyothermachinetool.Theessentialcomponentsofalathearethebedheadstockassemblytailstockassemblytheleadscrewfeedr
3、od.Thebedisthebackboneofalathe.Itusuallyismadeofwellnmalizedagedgraynodularcastironprovidessheavyrigidframeonwhichalltheotherbasiccomponentsaremounted.Twosetsofparallellongitudinalwaysinnerouterarecontainedonthebedusuall
4、yontheupperside.SomemakersuseaninvertedVshapefallfourwayswhereasothersutilizeoneinvertedVoneflatwayinonebothsetsTheyareprecisionmachinedtoassureaccuracyofalignment.Onmostmodernlathesthewayaresurfacehardenedtoresistwearab
5、rasionbutprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Theheadstockismountedinafoxedpositionontheinnerwaysusuallyatthel
6、eftendofthebed.Itprovidesapoweredmeansofrotatingthewdatvariousspeeds.Essentiallyitconsistsofahollowspindlemountedinaccuratebearingsasetoftransmissiongearssimilartoatrucktransmission—throughwhichthespindlecanberotatedatan
7、umberofspeeds.Mostlathesprovidefrom8to18speedsusuallyinageometricratioonmodernlathesallthespeedscanbeobtainedmerelybymovingfromtwotofourlevers.Anincreasingtrendistoprovideacontinuouslyvariablespeedrangethroughelectricalm
8、echanicaldrives.Becausetheaccuracyofalatheisgreatlydependentonthespindleitisofheavyconstructionmountedinheavybearingsusuallypreloadedtaperedrollerballtypes.Thespindlehasaholeextendingthroughitslengththroughwhichlongbarst
9、ockcanbefed.Thesizeofmaximumsizeofbarstockthatcanbemachinedwhenthematerialmustbefedthroughspindle.Thetailsticdassemblyconsistsessentiallyofthreeparts.Alowercastingfitsontheinnerwaysofthebedcanslidelongitudinallythereonwi
10、thameansfclampingtheentireassemblyinanydesiredlocationAnuppercastingfitsontheloweronecanbemovedtransverselyuponitonsometypeofkeyedwaystopermitaligningtheassemblyisthetailstockquill.Thisisahollowsteelcylinderusuallyabout5
11、1to76mm(2to3inches)indiameterthatcanbemovedseveralincheslongitudinallyinoutoftheuppercastingbymeansofahwheelscrew.Thesizeofalatheisdesignatedbytwodimensions.Thefirstisknownastheswing.ThisisthedevelopmentofNCledtothedevel
12、opmentofseveralotherinnovationsinmanufacturingtechnology:ElectricaldisgemachiningLasercuttingElectronbeamwelding.Numericalcontrolhasalsomademachinetoolsmeversatilethantheirmanuallyoperatedpredecesss.AnNCmachinetoolcanaut
13、omaticallyproduceawideofpartseachinvolvinganasstmentofwidelyvariedcomplexmachiningprocesses.Numericalcontrolhasallowedmanufacturerstoundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveus
14、ingmanuallycontrolledmachinetollsprocesses.LikesomanyadvancedtechnologiesNCwasbninthelabatiesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirFce.Initsearlie
15、ststagesNCmachineswereabletomadestraightcutsefficientlyeffectively.Howevercurvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhizontalverticalstepstoproduceacurve.Theshterthestraightlinesmaki
16、ngupthestepsthesmootheristhecurveEachlinesegmentinthestepshadtobecalculated.Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)language.ThisisaspecialprogramminglanguagefNCthatusesstatementssimilar
17、toEnglishlanguagetodefinethepartgeometrydescribethecuttingtoolconfigurationspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajstepfwardinthefurtherdevelopmentfromthoseusedtoday.Themachineshadhardwiredlogicci
18、rcuits.Theinstructionalprogramswerewrittenonpunchedpaperwhichwaslatertobereplacedbymagicplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapefthemachine.Togetherallofthisrepresentedagiantstepfwardinthe
19、controlofmachinetools.HowevertherewereanumberofproblemswithNCatthispointinitsdevelopment.Amajproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonfthepapertapecontainingtheprogrammedinstructionstobreaktearduringa
20、machiningprocess.Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetoolthepapertapecarryingtheprogrammedinstructionshadtobererunthroughthereader.Ifitwasnecessarytoproduce100copiesofagivenp
21、artitwasalsonecessarytorunthepapertapethroughthereader100separatetines.Fragilepapertapessimplycouldnotwithsttherigsofashopfloenvironmentthiskindofrepeateduse.Thisledtothedevelopmentofaspecialmagicplastictape.Whereasthepa
22、percarriedtheprogrammedinstructionsasaseriesofholespunchedinthetapetheplastictapecarriedtheinstructionsasaseriesofmagicdots.Theplastictapewasmuchstrongerthanthepapertapewhichsolvedtheproblemoffrequenttearingbreakage.Howe
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