文献翻译车床和车削Word格式.docx
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TheLatheandItsConstruction
Alatheisamachinetoolusedprimarilyforproducingsurfacesofrevolutionflatedges.Basedontheirpurpose,construction,numberoftoolsthatcansimultaneouslybemounted,anddegreeofautomation,lathesor,moreaccurately,lathe-typemachinetoolscanbeclassifiedasfollows:
(1)Enginelathes
(2)Toolroomlathes
(3)Turretlathes
(4)Verticalturningandboringmills
(5)Automaticlathes
(6)Special-purposelathes
Inspiteofthatdiversityoflathe-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,thatholehasataperedsurfacetoallowmountingaplainlathecenter.Theoutersurfaceofthespindleisthreadedtoallowmountingofachuck,afaceplate,orthelike.
Tallstock.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.
LatheCuttingTools
Theshapeandgeometryofthelathetoolsdependuponthepurposeforwhichtheyareemployed.Turningtoolscanbeclassifiedintotowmaingroups,namely,externalcuttingtoolsandinternalcuttingtools,Eachofthesegroupsincludethefollowingtypesoftools:
Turningtools.Turingtoolscanbeeitherfinishingorroughturningtools.Roughturningtoolshavesmallnoseradiiandareusedforobtainingthefinalrequireddimensionswithgoodsurfacefinishbymarkingslightdepthofcut.Roughturningtoolscanberight–handorleft-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.11.2indicatesanarrangementofthislattertype,whichincludesthecarbidetip,thechipbreaker,thepad,theclampingscrew(withawasherandanut),andtheshank..Asthenamesuggests,thefunctionofthechipbreakeristobreaklongchipseverynowandthen,thuspreventingtheformationofverylongtwistedribbonsthatmaycauseproblemsduringthemachiningoperations.Thecarbidetips(orceramictips)canhavedifferentshapes,dependinguponthemachiningoperationsforwhichtheyaretobeemployed.Thetipscaneitherbesolidorwithacentralthroughhole,dependingonwhetherbrazingormechanicalclampingisemployedformountingthetipontheshank.
LatheOperations
Inthefollowingsection,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,smallerdepthofcut(lessthan0.05in.,or0.4mm),andhighcuttingspeedsarepreferredforfinishingcuts.
Facing.Theresultofafacingoperationisaflatsurfacethatiseitherthewholeendsurfaceoftheworkpieceoranannularintermediatesurfacelikeashoulder.Duringafacingoperation,feedisprovidedbythecrossslide,whereasthedepthofcutiscontrolledbythecarriageorcompoundrest.Facingcanbecarriedouteitherfromtheperipheryinwardorfromthecenteroftheworkpieceoutward.Itisobviousthatthemachiningmarksinbothcasestacktheformofaspiral.Usually,itispreferredtoclampthecarriageduringafacingoperation,sincethecuttingforcetendstopushthetool(and,ofcourse,thewholecarriage)awayfromtheworkpiece.Inmostfacingoperations,theworkpieceisheldinachuckoronafaceplate.
Groovecutting.Incut-offandgroove-cuttingoperations,onlycrossfeedofthetoolisemployed.Thecut-offandgroovingtools,whichwerepreviouslydiscussed,areemployed.
Boringandinternalturning.Boringandinternalareperformedontheinternalsurfacesbyaboringbarorsuitableinternalworkpieceissolid,adrillingoperationmustbeperformedfirst.Thedrillingtoolisheldinthetailstock,andlatteristhenfedagainsttheworkpiece.
Taperturning.Taperturningisachievedbydrivingthetoolinadirectionthatisnotparalledtothelatheaxisbutinclinedtoitwithananglethatisequaltothedesiredangleofthetaper.