英语论文翻译毕业设计论文.docx

英语论文翻译毕业设计论文.docx

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英语论文翻译毕业设计论文

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未经允许切勿外传

LATHES

Thebasicmachinesthataredesignedprimarilytodoturning,facingandboringarecalledlathes.Verylittleturningisdoneonothertypesofmachinetools,andninecandoitwithequalfacility.Becauselathecandoboring,facing,drilling,andreaminginadditiontoturning,theirversatilitypermitsseveraloperationstobeperformedwithasinglesetupoftheworkpiece.Thisaccountsforthefactthatlathesofvarioustypesaremorewidelyusedinmanufacturingthananyothermachinetool.

Lathesinvariousformstwothousandyears.Modemlathesdatefromabout1797,whenHenryMaudsleydevelopedonewithaleadscrew.Itprovidedcontrolled,mechanicalfeedofthetool.ThisingeniousEnglishmanalsodevelopedachange-gearsystemthatcouldconnectthemotionsofthespindleandleadscrewandthusenablethreadstobecut.

LatheConstruction.TheessentialcomponentsofalathearedepictedintheblockdiagramofFig.15-1.Thesearethebed,andprovidesawhichalltheotherbasiccomponentsaremounted.Twosetsofparallel,longitudinalways,innerandouter,arecontainedonthebed,usuallyontheupperside.SomemakersuseaninvertedV-shapeforallfourways,whereasothersutilizeoneinvertedVandoneflatwayinoneorbothsets.Becauseseveralothercomponentsaremountedandormoveonthewaystheymustbemadewithprecisiontoassureaccuracyofalignment.Similarly,properprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Thewaysonmostmodernlathesaresurface.

Theafixedpositionontheinnerwaysatoneendofthelathebed.Itprovidesapoweredmeansofrotatingtheworkatvariousspeeds.Itconsists,essentially,ofaaccuratebearings,andasetoftransmissiongears---similartoatrucktransmission---throughwhichthespindlecanberotatedatanumberofspeeds.Mostlathesprovidefromeighttoeighteenspeeds,usuallyinageometricratio,andonmodernlathesallthespeedscanbeobtainedmerelybymovingfromtwotofourlevers.Anincreasingtrendistoprovideacontinuouslyvariablespeedrangethroughelectricalormechanicaldrives.

Becausetheaccuracyofalatheisgreatlydependentonthespindle,itisofandmountedinbefedthroughit.Thesizeofthisimportantsizedimensionofalathebecauseitdeterminesthemaximumsizeofbarstockthatcanbemachinedwhenthematerialmustbefedthroughthespindle.

Theinnerendofthespindleprotrudesfromthegearboxandcontainsameansformountingvarioustypesofchucks,faceplates,anddogplatesonit.Whereassmalllathesoftenemployathreadedsectiontowhichthechucksarescrewed,mostlargelathesutilizeeithercam-lockorkey-drivetapernoses.Theseprovidealarge-diametertaperthatassurestheaccuratealignmentofthechuck,andamechanismthatpermitsthechuckorfaceplatetobelockedorunlockedinpositionwithoutthenecessityofelectricmotorthroughaV-beltorsilent-chaindrive.Mostmodernlathestheinnerwaysofthebedandcanslidelongitudinallythereon,withameansforclampingtheentireassemblyinanydesiredlocation.Anuppercastingfitsontheloweroneandcanbemovedtransverselyuponitonsometypeofkeyedways.Thistransversemotionpermitsaligningthetailstockanddiameter,thatcanbemovedseveralincheslongitudinallyinandoutoftheuppercastingbymeansofaendofthequillaMorsetaperinwhichalathecenter,orvarioustoolssuchasdrills,canbelength,usuallyisengravedontheoutsideofthequilltoaidincontrollingitsmotioninandoutoftheuppercasting.Alockingdevicepermitsclampingthequillinanydesiredposition.

Thecarriageassemblyprovidesthemeansformountingandmovingcuttingtools.ThecarriageisarelativelyflatH-shapedcastingthatrestsandmovesontheoutersetofwaysonthebed.Thetransversebarofthecarriagecontainswaysonwhichthecrossslideismountedandcanbemovedbymeansofafeedscrewthatiscontrolledbyasmallthedirectionnormaltotheaxisofrotationofthework.

Onmostlathesthetoolpostactuallyismountedonacompoundrest.Thisconsistsofabase,whichismountedonthecrossslidesothatitcanbepivotedaboutaverticalaxis,andanuppercasting.Theuppercastingismountedonwaysonthisbasesothatitcanbemovedbackandforthandcontrolledbymeansofashortleadscrewoperatedbyaforthecarriage,andpoweredmotionforthecrossslide,isprovidedbymechanismswithintheapron,attachedtothefrontofthecarriage.Manualmovementofthecarriagealongthebediseffectedbyturningathefrontoftheapron,whichisgearedtoapiniononthebackside.Thispinionengagesarackthatisattachedbeneaththeupperfrontedgeofthebedinaninvertedposition.

Toimpartpoweredmovementtothecarriageandcrossslide,arotatingfeedrodisprovided.Thefeedrod,whichcontainsakeywaythroughoutmostofitslength,passesthroughthetworeversingbevelpinionsandiskeyedtothem.Eitherpinioncanbebroughtintomeshwithamatingbevelgearbymeansofthereversingleveronthefrontoftheapronandthusprovide“forward”or“reverse”powertothecarriage.Suitableclutchesconnecteithertherackpinionorthecross-slidescrewtoprovidelongitudinalmotionofthecarriageortransversemotionofcrossslide.

Forcuttingthreads,asecondmeansoflongitudinaldriveisprovidedbyaleadscrew.Whereasmotionofthecarriagewhendrivenbythefeed-rodmechanismtakesplacethroughafrictionclutchinwhichslippageispossible,motionthroughtheleadscrewisbyadirect,mechanicalconnectionbetweentheapronandtheleadscrew.Thisisachievedbyasplitnut.Bymeansofaclampingleveronthefrontoftheapron,thesplitnutcanbeclosedaroundtheleadscrew.Withthesplitnutclosed,thecarriageismovedalongtheleadscrewbydirectdrivewithoutpossibilityofslippage.

Modernlathesfromthelathespindlebymeansofsuitablegearing.Theoutputendofthegearboxisconnectedtothefeedrodandleadscrew.Thus,throughthisgeartrain,leadingfromthespindletothequick-changegearbox,thencetotheleadscrewandfeedrod,andthentothecarriage,thecuttingtoolcanbemadetomoveaspecificdistance,eitherlongitudinallyortransversely,foreachrevolutionofthespindle.Atypicallatheprovides,throughthefeedrod,forty-eightfeedsrangingfrom0.002inchto0.118inchperrevolutionofthespindle,and,throughtheleadscrew,leadsforcuttingforty-eightdifferentthreadsfrom1.5to92perinch.Onsomeolderandsomecheaperlathes,oneortwogearsinthegeartrainbetweenthespindleandthechangegearboxmustbechangedinordertoobtainafullrangeofthreadsandfeeds.

CUTTINGTOOL

Shapeofcuttingtools,particularlytheangles,andtoolmaterialareveryimportantfactors.Thepurposeofthisunitistointroducethecuttingtoolgeometryandtoolmaterials.

CuttingToolGeometry

Anglesdeterminegreatlynotonlytoollifebutfinishqualityaswell.Generalprinciplesuponwhichcuttingtoolanglesarebaseddonotdependontheparticulartool.Basically,grindingwheelarebeingdesigned.Since,Fig.14-1,mightbeeasiesttovisualize,itsgeometryisdiscussed.

Toolfeaturesidentifiedbymanynames.Thetechnicalliteratureisfullofconfusingterminology.Thusintheattempttoclearupexistingdisorganizedconceptionsandnomenclature,theAmericanSocietyofMechanicalEngineerspublishedASAStandardAsingle-pointtoolisacuttingtoolFig.14-2areasfollows:

（1）Back-rakeangle,

（2）Side-rakeangle,（3）End-reliefangle（4）End-reliefangle（5）Side-reliefangle（6）End-cutting-edgeangle,（7）Side-cutting-edgeangle,（8）Noseangle,（9）Noseradius.

Toolangle1,onfrontview,istheback-rakeangle.Itistheanglebetweenthetoolfaceandalineparalleltothebaseoftheshankinalongitudinalplaneperpendiculartothetoolbase.Thenthisangleisdownwardfromfronttorearofthecuttingedge,therakeidpositive;whenupwardfromfronttoback,therakeisnegative.Thisangleismostsignificantinthemachiningprocess,becauseitdirectlyaffectsthecuttingforce,finish,andtoollife.

Theside-rakeangle,numbered2,measurestheslopeofthefaceinacrossplaneperpendiculartothetoolbase.It,also,isanimportantangle,becauseitdirectschipflowtothesideofthetoolpostandpermitsthetooltofeedmoreeasilyintothework.

Theend-reliefangleismeasuredbetweenalineperpendiculartothebaseandtheendflankimmediatelybelowtheendcuttingedge;itisnumbered3inthefigure.Itprovidesclearancebetweenworkandtoolsothatitscutsurfacecanflowbywithminimumrubbingagainstthetool.Tosavetime,aportionoftheendflankofthetoolmaysometimesbeleftunground,previouslyforgedtosize.Insuchcase,thisend-clearanceangle,numbered4,measuredtotheendflanksurfacebelowthegroundportion,wouldbelargerthanthereliefangle.

Oftentheendcuttingedgeisobliquetotheflank.Thereliefangleisthenbestmeasuredinaplanenormaltotheendcuttingedgeperpendiculartothebaseofthetool.Thisclearancepermitsthetooltoadvancemoresmoothlyintothework.

Theside-reliefangle,indicatedas5,ismeasuredbetweenthesideflank,justbelowthecuttingedge,andalinethroughthecuttingedgeperpendiculartothebaseofthetool.Thisclearancepermitsthetooltoadvancemoresmoothlyintothework.

Angle6istheend-cutting-edgeanglemeasuredbetweentheendcuttingedgeandalineperpendiculartothesideofthetoolshank.Thisanglepreventsrub