机械设计外文翻译车床和铣床.docx

机械设计外文翻译车床和铣床.docx

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机械设计外文翻译车床和铣床

中文4285字

附录1

LATHES&MILLING

Ashopthatisequippedwithamillingmachineandanenginelathecanmachinealmostanytypeofproductofsuitablesize.

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

Lathesinvariousformshaveexistedformorethantwothousandyears.Modernlathesdatefromabout1797，whenHenryMaudsleydevelopedonewithaleadscrew.Itprovidedcontrolled，mechanicalfeedofthetool.ThisingeniousEnglishmanalsodevelopedachangegearsystemthatcouldconnectthemotionsofthespindleandleadscrewandthusenablethreadstobecut.

LatheConstruction.Theessentialcomponentsofalathearedepictedintheblockdiagramofpicture.Thesearethebed，headstockassembly，tailstockassembly，carriageassembly，quick-changegearbox，andtheleadscrewandfeedrod.

Thebedisthebackboneofalathe.Itusuallyismadeofwell-normalizedoragedgrayornodularcastironandprovidesaheavy，rigidframeonwhichalltheotherbasiccomponentsaremounted.Twosetsofparallel，longitudinalways，innerandouter，arecontainedonthebed，usuallyontheupperside.SomemakersuseaninvertedV-shapeforallfourways，whereasothersutilizeoneinvertedVandoneflatwayinoneorbothsets.Becauseseveralothercomponentsaremountedand/ormoveonthewaystheymustbemadewithprecisiontoassureaccuracyofalignment.Similarly，properprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Thewaysonmostmodernlathesaresurfacehardenedtooffergreaterresistancetowearandabrasion.

Theheadstockismountedinafixedpositionontheinnerwaysatoneendofthelathebed.Itprovidesapoweredmeansofrotatingtheworkatvariousspeeds.Itconsists，essentially，ofahollowspindle，mountedinaccuratebearings，andasetoftransmissiongears——similartoatrucktransmission——throughwhichthespindlecanberotatedatanumberofspeeds.Mostlathesprovidefromeighttoeighteenspeeds，usuallyinageometricratio，andonmodernlathesallthespeedscanbeobtainedmerelybymovingfromtwotofourlevers.Anincreasingtrendistoprovideacontinuouslyvariablespeedrangethroughelectricalormechanicaldrives.

Becausetheaccuracyofalatheisgreatlydependentonthespindle，itisofheavyconstructionandmountedinheavybearings，usuallypreloadedtaperedrollerorballtypes.A

long-itudinalholeextendsthroughthespindlesothatlongbarstockcanbefedthroughit.Thesizeofthisholeisanimportantsizedimensionofalathebecauseitdeterminesthemaximumsizeofbarstockthatcanbemachinedwhenthematerialmustbefedthroughthespindle.

Theinnerendofthespindleprotrudesfromthegearboxandcontainsameansformountingvarioustypesofchucks，faceplates，anddogplatesonit.Whereassmalllathesoftenemployathreadedsectiontowhichthechucksarescrewed，mostlargelathesutilizeeithercam-lockorkey-drivetapernoses.Theseprovidealarge-diametertaperthatassurestheaccuratealignmentofthechuck，andamechanismthatpermitsthechuckorfaceplatetobelockedorunlockedinpositionwithoutthenecessityofhavingtorotatetheseheavyattachments.

PowerissuppliedtothespindlebymeansofanelectricmotorthroughaV-beltorsilent-chaindrive.Mostmodernlatheshavemotorsoffrom5to15horsepowertoprovideadequatepowerforcarbideandceramictoolsattheirhighcuttingspeeds.

Thetailstockassemblyconsists，essentially，ofthreeparts.Alowercastingfitsontheinnerwaysofthebedandcanslidelongitudinallythereon，withameansforclampingtheentireassemblyinanydesiredlocation.Anuppercastingfitsontheloweroneandcanbemovedtransverselyuponitonsometypeofkeyedways.Thistransversemotionpermitsaligningthetailstockandheadstockspindlesandprovidesamethodofturningtapers.Thethirdmajorcomponentoftheassemblyisthetailstockquill.Thisisahollowsteelcylinder，usuallyabout2to3inchesindiameter，thatcanbemovedseveralincheslongitudinallyinandoutoftheuppercastingbymeansofahandwheelandscrew.TheopenendofthequillholeterminatesinaMorsetaperinwhichalathecenter，orvarioustoolssuchasdrills，canbeheld.Agraduatedscale，severalinchesinlength，usuallyisengravedontheoutsideofthequilltoaidincontrollingitsmotioninandoutoftheuppercasting.Alockingdevicepermitsclampingthequillinanydesiredposition.

Thecarriageassemblyprovidesthemeansformountingandmovingcuttingtools.ThecarriageisarelativelyflatH-shapedcastingthatrestsandmovesontheoutersetofwaysonthebed.Thetransversebarofthecarriagecontainswaysonwhichthecrossslideismountedandcanbemovedbymeansofafeedscrewthatiscontrolledbyasmallhandwheelandagraduateddial.Throughthecrossslideameansisprovidedformovingthelathetoolinthedirectionnormaltotheaxisofrotationofthework.

Onmostlathesthetoolpostactuallyismountedonacompoundrest.Thisconsistsofabase，whichismountedonthecrossslidesothatitcanbepivotedaboutaverticalaxis，andanuppercasting.Theuppercastingismountedonwaysonthisbasesothatitcanbemovedbackandforthandcontrolledbymeansofashortleadscrewoperatedbyahandwheelandacalibrateddial.

Manualandpoweredmotionforthecarriage，andpoweredmotionforthecrossslide，isprovidedbymechanismswithintheapron，attachedtothefrontofthecarriage.Manualmovementofthecarriagealongthebediseffectedbyturningahandwheelonthefrontoftheapron，whichisgearedtoapiniononthebackside.Thispinionengagesarackthatisattachedbeneaththeupperfrontedgeofthebedinaninvertedposition.

Toimpartpoweredmovementtothecarriageandcrossslide，arotatingfeedrodisprovided.Thefeedrod，whichcontainsakeywaythroughoutmostofitslength，passesthroughthetworeversingbevelpinionsandiskeyedtothem.Eitherpinioncambebroughtintomeshwitha

matingbevelgearbymeansofthereversingleveronthefrontoftheapronandthusprovide“forward”or“reverse”powertothecarriage.Suitableclutchesconnecteithertherackpinionor

thecross-slidescrewtoprovidelongitudinalmotionofthecarriageortransversemotionofcrossslide.

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

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

Millingisabasicmachiningprocessinwhichthesurfaceisgeneratedbytheprogressiveformationandremovalofchipsofmaterialfromtheworkpieceasitisfedtoarotatingcutterinadirectionperpendiculartotheaxisofthecutter..Insomecasestheworkpieceisstationaryandthecutterisfedtothework.Inmostinstancesamultiple-toothcutterisusedsothatthemetalremovalrateishigh，andfrequentlythedesiredsurfaceisobtainedinasinglepassofthework.

Thetoolusedinmillingisknownasamillingcutter.Itusuallyconsistsofacylindricalbodywhichrotatesonitsaxisandcontainsequallyspacedperipheralteeththatintermittentlyengageandcuttheworkpiece.Insomecasestheteethextendpartwayacrossoneorbothendsofthecylinder.

Becausethemillingprincipleprovidesrapidmetalremovalandcanproducegoodsurfacefinish，itisparticularlywell-suitedformass-productionwork，andexcellentmillingmachineshavebeendevelopedforthispurpose.However，veryaccurateandversatilemillingmachinesofageneral-purposenaturealsohavebeendevelopedthatarewidelyusedinjob-shopandtoolanddiework.Ashopthatisequippedwithamillingmachineandanenginelathecanmachinealmostanytypeofproductofsuitablesize.

TypesofMillingOperations.Millingoperationscanbeclassifiedintotwobroadcategories，eachofwhichhasseveralvariations：

1.Inperipheralmillingasurfaceisgeneratedbyteethlocatedintheperipheryofthec