1中文+英文14頁8516字數翻譯部分LatheandTurningTheLatheandItsConstructionAlatheisamachinetoolusedprimarilyforproducingsurfacesofrevolutionflatedges.Basedontheirpurpose,construction,numberoftoolsthatcansimultaneouslybemounted,anddegreeofautomation,lathesor,moreaccurately,lathe-typemachinetoolscanbeclassifiedasfollows:(1)Enginelathes(2)Toolroomlathes(3)Turretlathes(4)Verticalturningandboringmills(5)Automaticlathes(6)Special-purposelathesInspiteofthatdiversityoflathe-typemachinetools,theyallhaveallhavecommonfeatureswithrespecttoconstructionandprincipleofoperation.Thesefeaturescanbestbeillustratedbyconsideringthecommonlyusedrepresentativetype,theenginelathe.Followingisadescriptionofeachofthemainelementsofanenginelathe,whichisshowninFig.11.1.Lathebed.Thelathebedisthemainframe,involvingahorizontalbeamontwoverticalsupporis.Itisusuallymadeofgreyornodularcastirontodampvibrationsandismadebycasting.Ithasguidewaystoallowthecarriagetoslideeasilylengthwise.Theheightofthelathebedshouldbeappropriatetoenablethetechniciantodohisorherjibeasilyandcomfortably.Headstock.Theheadstockisfixedatthelefthandsideofthelathebedandincludesthespindlewhoseaxisisparalleltotheguideways(thesildesurfaceofthebed).Thespindleisdriventhroughthegearbox,whichishousedwithintheheadstock.Thefunctionofthegearboxistoprovideanumberofdifferentspindlespeeds(usually6upto18speeds).Somemodernlatheshaveheadstockswithinfinitelyvariablespindlespeeds,whichemployfrictional,electrical,orhydraulicdrives.Thespindleisalwayshollow,I.e,ithasathroughholeextendinglengthwise.Barstockscanbefedthrougththatholeifcontinousproductionisadopted.Also,thatholehasatapered2surfacetoallowmountingaplainlathecenter.Theoutersurfaceofthespindleisthreadedtoallowmountingofachuck,afaceplate,orthelike.Tailstock.Thetailstockassemblyconsistsbasicallyofthreeparts,itslowerbase,anintermediatepart,andthequill.Thelowerbaseisacastingthatcanslideonthelathebedalongtheguidewayes,andithasaclampingdevicetoenablelockingtheentiretailstockatanydesiredlocation,dependinguponthelengthoftheworkpiece.Theintermediateparteisacastingthatcanbemovedtransverselytoenablealignmentoftheaxisofthethetailstockwiththatoftheheadstock.Thethirdpart,thequill,isahardenedsteeltube,whichcanbemovedlongitudinallyinandoutoftheintermediatepartasrequired.Thisisachievedthroughtheuseofahandwheelandascrew,aroundwhichanutfixedtothequilliscanbelockedatanypointalongitstravelpathbymeansofaclampingdevice.Thecarriage.Themainfunctionofthecarriageismountingofthecuttingtoolsandgeneratinglongitudinaland/orcrossfeeds.ItisactuallyanH-shapedblockthatslidesonthelathebedbetweentheheadstockandtailstockwhilebeingguidedbytheV-shapedguidewaysofthebed.Thecarriagecanbemovedeithermanuallyormechanicallybymeansoftheapronandeitherthefeedrodortheleadscrew.Whencuttingscrewthreads,powerisprovidedtothegearboxoftheapronbytheleadscrew.Inallotherturningoperations,itisthefeedrodthatdrivesthecarriage.Theleadscrewgoesthroughapairohalfnuts,whicharefixedtotherearoftheapron.Whenactuatingacertainlever,thehalfnutsareclampedtogetherandengagewiththerotatingleadscrewasasinglenut,whichisfed,togetherwithcarriage,alongthebed.whentheleverisdisengaged,thehalfnutsarereleasedandthecarriagestops.Ontheotherhand,whenthefeedrodisused,itsuppliespowertotheapronthroughawromgear.Thelatteriskeyedtofeedrodandtravelswiththeapronalongthefeedrod,whichhasakeywayextendingtocoveritswholelength.Amodernlatheusuallyhasaquick-changegearboxlocatedundertheheadstockanddrivenfromthespindlethroughatrainofgears.Itisconnectedtoboththefeedrodandtheleadscrewandenablesselectingavarietyoffeedseasilyandrapidlybysimplyshiftingtheappropriatelevers,thequick-changegearboxisemployedinplainturning,facingandthreadcuttingoperations.Sincethatgearboxislinkedtospindle,thedistancethattheapron(andthecuttingtool)travelsforeachrevolutionofthespindlecanbecontrolledandisreferredtoasthefeed.LatheCuttingToolsTheshapeandgeometryofthelathetoolsdependuponthepurposeforwhichtheyareemployed.Turningtoolscanbeclassifiedintotowmaingroups,namely,externalcuttingtoolsand3internalcuttingtools,Eachofthesegroupsincludethefollowingtypesoftools:Turningtools.Turingtoolscanbeeitherfinishingorroughturningtools.Roughturningtoolshavesmallnoseradiiandareusedforobtainingthefinalrequireddimensionswithgoodsurfacefinishbymarkingslightdepthofcut.Roughturningtoolscanberighthandorleft-handtypes,dependinguponthedirectionoffeed.Theycanhavestraight,bent,oroffsetshanks.Facingtools.Facingtoolsareemployedinfacingoperationsformachiningplanesideorendsurfaces.Therearetoolsformachiningleft-hand-sidesurfacesandtoolsforright-hand-sidesurfaces.Thosesidesurfacesaregeneratedthroughtheuseofthecrossfeed,contrarytoturningoperations,wheretheusuallongitudinalfeedisused.Cutofftools.Cutofftools,whicharesometimescalledpartingtools,servetoseparatetheworkpieceintopartsand/ormachineexternalannualgrooves.Thread-cuttingtools.Thread-cuttingtoolshaveeithertriangular,square,ortranpezoidalcuttingedges,dependinguponthecrosssectionofthedesiredthread.Also,theplaneanglesofthesetoolsmustalwaysbeidenticaltothoseofthethreadforms.Thread-cuttingtoolshavestraightshanksforexternalthreadcuttingandareofthebent-shanktypewhencuttinginternalthreads.Formtools.Formtoolshaveedgesespeciallymanufacturedtotakeacertainform,whichisoppositetothedesiredshapeofthemachinedworkpiece.AnHSStoolsisusuallymadeintheformofasinglepiece,contrarytocementedcarbidesorceramic,whicharemadeintheformoftipes.Thelatterarebrazedormechanicallyfastenedtosteelshanks.Fig.1indicatesanarrangementofthislattertype,whichincludesthecarbidetip,thechipbreaker,thepad,theclampingscrew(withawasherandanut),andtheshank.Asthenamesuggests,thefunctionofthechipbreakeristobreaklongchipseverynowandthen,thuspreventingtheformationofverylongtwistedribbonsthatmaycauseproblemsduringthemachiningoperations.Thecarbidetips(orceramictips)canhavedifferentshapes,dependinguponthemachiningoperationsforwhichtheyaretobeemployed.Thetipscaneitherbesolidorwithacentralthroughhole,dependingonwhetherbrazingormechanicalclampingisemployedformountingthetipontheshank.4Fig.1LatheOperationsInthefollowingsection,wediscussthevariousmachiningoperationsthatcanbeperformedonaconventionalenginelathe.Itmustbeborneinmind,however,thatmoderncomputerizednumericallycontrolledlatheshavemorecapabiblitiesanddootheroperations,suchascontouring,forexample.Followingareconventionallatheoperations.Cylindricalturning.Cylindricalturningisthethesimplestandthemostcommonofalllatheoperations.Asinglefullturnoftheworkpiecegenerateacirclewhosecenterfallsonthelatheaxis；thismotionisthenreproducednumeroustimesasaresultoftheaxialfeedmotionofthetool.Theresultingmachiningmarksare,therefore,ahelixhavingaverysmallpitch,whichisequaltothefeed.Consequently,themachinedsurfaceisalwayscylindrical.Theaxialfeedisprovidedbythecarriageorthecompoundrest,eithermanuallyorautomatically,whereasthedepthsofcutsiscontrolledbythecrossslide.Inroughingcuts,itisrecommendedthatlargedepthsofcuts(upto0.25in.or6mm,dependingupontheworkpiecematerial)andsmallerfeedswouldbeused.Ontheotherhand,veryfinefeeds,smallerd