外文翻译--基本的加工工序—切削，镗削和铣削.doc

1英文原文BasicMachiningOperationsMachiningtoolshaveevolvedfromtheearlyfootpoweredlatheEgyptiansandJohnWilkinsonsboringmill.Theyaredesignedtoproviderigidsupportforboththeworkpieceandthecuttingtoolandcuttingtoolandcanpreciselycontroltheirrelativepositionsandthevelocityofthetoolwithrespecttotheworkpiece.Basically,inmetalcutting,asharpenedwedge-shapedtoolremovesarathernarrowstripofmetalfromthesurfaceofaductileworkpieceinthefromofaseverelydeformedchip.Thechipiswasteproductthatisworkpieceinthefromofaseverelydeformedchipisawasteproductthatisconsiderablyshorterthantheworkpiecefromwhichitcamebutwithacorrespondingincreaseinthicknessoftheuncutchip.Thegeometricalshapeofthemachinesurfacedependsontheshapeofthetoolanditspathduringthemachiningopration.Mostmachineoperationsproducepartsofdifferinggeometry.Ifaroughcylindricalworkpiecerevolvesaboutacentralaxisandtoolpenetratesbeneathitssurfaceandtravelsparalleltothecenterofrotation,asurfaceofrevolutionisproduced,andtheoperationiscalledturning.Ifahollowtubeisonthemachinedontheinsideinasimilarmanner,theoperationiscalledboring.Producinganexternalconicalsurfaceofuniformlyvaryingdiameteriscalledtaperturning.Ifthetoolpointtravelsinapathofvaryingradius,acontouredsurfacelikethatofbowlingpincanbeproduced；or,ifthepieceisshortenoughandthesupportissufficientlyrigid,acontouredsurfacecouldbeproducedbyfeedingashapedtoolnormaltotheaxisofrotation.Shorttaperedorcylindricalsurfacescouldalsobecontourformed.Flatorplanesurfacearefrequentlyrequired.Theycanbegeneratedbyradialturningorfacing,inwhichthetoolpointmovesnormaltotheaxisofrotation.Inothercases,itismoreconvenienttoholetheworkpiecesteadyandreciprocatethetoolacross,itisseriesofstraight-linecutswithacrosswisefeedincrementbeforeeachcuttingstroke.Thisoperationiscalledplanningandiscarriedoutonashaper.Forlargerpiecesitiseasiertokeepthetoolstationaryanddrawtheworkpieceunderitasinplanning.Thetoolisfedateachreciprocation.Contouredsurfacescanbeproducedbyusingshapedtools.Multiple-edgedtoolscanalsobeused.Drillingusesatwin-edgedflutedtoolforholeswithdepthsupto5to10timesthedrilldiameter.Whetherthedrillturnsortheworkpiecerotates,relativemotionbetweenthecuttingedgeandtheworkpieceistheimportantfactor.Inmillingoperationsarotarycutterwithanumberofcuttingedgesengagestheworkpiece,whichmovesslowlywithrespecttothecutter.Planeorcontouredsurfacesmaybeproduced,dependingonthegeometryofthecutterandthetypeoffeed.Horizontalorverticalaxesofrotationmaybeused,andthefeedoftheworkpiecemaybeinanyofthethreecoordinatedirections.BasicMachineToolsMachinetoolsareusedtopartofaspecifiedgeometetricalshapeandprecisesizebyremovingmetalfromaductilematerialintheformchips.Thelatterareawasteproductandvaryfromlongcontinuousribbonsofadisposalpointofview,toeasilyhandedwell-brokenchipsresultingfromcastiron.Machinetoolsperformfivebasicmetal-removeprocesses:turning,planning,drilling,milling,andgrinding.Allothermetal-removalprocessesaremodificationsofthesefivebasicprocesses.Forexample,boringisinternalturning；reaming,tapping,andcounterboringmollifydrilledholesandarerelatedtodrilling；hobblingandgearcuttingarefundamentallymillingoperations；hacksawingandbroachingareafromofplanningandhoning；lapping,superfinishing,polishing,andbuffingarevariantsofgrindingorabrasiveremovaloperations.Therefore,thereareonlyfourtypesofbasicmachinetools,whichusecuttingtoolsofspecificcontrollablegeometry.Thegrindingprocessformschips,butthegeometryoftheabrasivegrainisuncontrollable.Theamountandrateofmaterialremovedbythevariousmachiningprocessesmaybelarge,asinheavyturningoperations,orextremelysmall,asinlappingorsuperfinishingoperationswhereonlythehighspotsofasurfaceareremoved.Amachiningtoolperformsthreemajorfunctions:1.itrigidlysupportstheworkpiceoritsholderandthecuttingtool；2.itprovidesrelativemotionbetweentheworkpiceandthecuttingtool；3.itprovidesarangeoffeedsandspeedsusuallyrangingfrom4to32choicesineachcase.2SpeedandFeedsinMachiningSpeeds,feeds,anddepthpfcutarethethreemajorvariablesforeconomicalmachining.Othervariablesaretheworkandtoolmaterials,coolantandgeometryofthecuttingtool.Therateofmetalremovalandpowerrequiredformachiningdependuponthesevariables.Thedepthsofcut,feed,andcuttingspeedaremachinesettingthatmustbeestablishedinanymetal-cuttingoperation.Theyallaffecttheforces,thepower,andtherateofmetalremoval.Theycanbedefinedbycomparingthemtotheneedleandrecordofaphonograph.Thecuttingspeed(V)isrepresentedbythevelocityoftherecordsurfacerelativetotheneedleinthetonearmatanyinstant.Feedisrepresentedbytheadvanceoftheneedleradiallyinwardperrevolution,oristhedifferenceinpositionbetweentwoadjacentgrooves.Thedepthofcutisthepenetrationoftheneedleintotherecordorthedepthofthegrooves.TurningonlathecentersThebasicoperationsoperationsperformedonanenginelatheareillustratedinfig.11-3.thoseoperationsperformedonexternalsurfaceswithasinglepointcuttingtoolarecalledturning.Exceptfordrilling,reaming,andtapping,theoperationsoninternalsurfacesarealsoperformedbyasinglepointcuttingtool.Allmachiningoperate,includingturningandboring,canbeclassifiedasroughing,finishing,orsemi-finishing.Theobjectiveofaroughingoperationistoremovethebulkofthematerialasrapidlyandasefficientlyaspossible,whileleavingasmallamountofmaterialonthework-pieceforthefinishingoperation.Finishingoperationsareperformedtoobtainthefinalsize,shape,andsurfacefinishontheworkpiece.Sometimesasemi-finishingoperationwillprecedethefinishingoperationtoleaveasmallpredeterminedanduniformamountofstockonthework-piecetoberemovedbythefinishingoperation.Generally,longerworkpiecesareturnedwhilesupportedononeortwolathecenters.Coneshapedholes,calledcenterholes,whichfitthelathecentersaredrilledintheendoftheworkpiece-usuallyalongtheaxisofthecylindricalpart.Theendoftheworkpieceadjacenttothetailstockisalwayssupportedbyatailstockcenter,whileendneartheheadstockmaybesupportedbyaheadstockcenterorheldinachuck.Theheadstockendoftheworkpiecemaybeheldinafour-jawchuck,orinacollettypechuck.Thismethodholdstheworkpiecefirmlyandtransfersthepowertotheworkpiecesmoothly；theadditionalsupporttotheworkpieceprovidedbythechucklessensthetendencyforchattertooccurwhencutting.Preciseresultcanbeobtainedwiththismethodifcareistakentoholdtheworkpieceaccuratelyinthechuck.Verypreciseresultscanbeobtainedbysupportingtheworkpiecebetweentwocenters.Alathedogisclampedtotheworkpiece；togethertheyaredrivenbythedriverplatemountedonthespindlenose.Oneendoftheworkpieceismachined；thentheworkpiececanbeturnedaroundinthelathetomachinetootherend.Thecenterholesintheworkpieceserveaspreciselocatingsurfacesaswellasbearingsurfacestocarrytheweightoftheworkpieceandtoresistthecuttingforces.Aftertheworkpiecehasbeenremovefromthelatheforanyreason,thecenterholeswillaccuratelyaligntheworkpiecebackinthelatheorinanotherlathe,orinacylindricalgrindingmachine.Theworkpiecemustneverbeheldattheheadstockendbybothachuckandalathecenter.Whileatfirstthoughtthisseemslikeaquickmethodofaligningtheworkpieceinthechuck,thismustnotbedonebecauseitisnotpossibletopressevenlywiththejawsagainsttheworkpiecewhileitisalsosupportedbythecenter.Thealignmentprovidedbythecenterwillnotbemaintainedandthepressureofthejawsmaydamagethecenterhole,thelathecenter,andperhapseventhelathespindle.Compensatingorfloatingjawchucksusedalmostexclusivelyonhighproductionworkprovideanexceptiontothestatementsmadeabove.Thesechucksarereallyworkdriversandcannotbeusedforthesamepurposeasordinarythreeorfour-jawchicks.Whileverylargediameterworkpiecearesometimesmountedontwocenters,theyarepreferablyheldattheheadstockendbyfaceplatejawstoobtainthesmoothpowertransmission；moreover,largelathedogsthatareadequatetotransmitthepowernotgenerallyavailable,althoughtheycanbemadeasaspecial.Faceplatejawsarelikechuckjawsexceptthattheyaremountedonafaceplate,whichhaslessoverhangfromthespindlebearingsthanalargechuckwouldhave.BoringTheobjectiveofboringaholeinalatheis:31、Toenlargethehole2、Tomachinetheholetothedesireddiameter3、Toaccuratelylocatethepositionofthehole4、ToobtainasmoothsurfacefinishintheholeThemotionoftheboringtoolisparalleltotheaxisofthelathewhenthecarriageismovedinthelongitudinaldirectionandtheworkpiecerevolvesabouttheaxisofthelathe.Whenthesetwomotionsarecombinedtoboreahole,itwillbeconcentricwiththeaxisofrotationofthelathe.Thepositionoftheholecanbeaccuratelylocatedbyholdingtheworkpieceinthelathesothattheaxisaboutwhichtheholeistobemachinedcoincideswiththeaxisofrotationofthelathe.Whentheboringoperationisdoneinthesamesetupoftheworkthatisusedtoturnandfaceit,practicallyperfectconcentricityandperpendicularitycanbeachieved.Theboringtoolisheldinaboringbarwhichisfedthroughtheholebycarriage.Variationsofthisdesignareused,dependingonthejobtobedone.Theleadangleused,ifany,shouldalwaysbesmall.Also,thenoseradiusoftheboringtoolmustnotbetoolarge.Thecuttingspeedusedforboringcanbeequaltothespeedforturning.However,whenthespindlespeedofthelatheiscalculated,thefinished,orlargest,borediametershouldbeused.Thefeedrateforboringisusuallysomewhatlessthanforturningtocompensatefortherigidityoftheboringbar.Theboringoperationisgenerallyperformedintwosteps；namely,roughboringandfinishboring.Theobjectiveoftherough-boringoperationistoremovetheexcessmetalrapidlyandefficiently,andtheobjectiveofthefinish-boringoperationistoobtainthedesiredsize,surfacefinish,andlocationofthehole.Thesizeoftheholeisobtainedbyusingthetrial-cutprocedure.Thediameteroftheholecanbemeasuredwithinsidecalipersandoutsidemicrometercalipers.BasicMeasuringInstrument,orinsidemicrometercaliperscanbeusedtomeasurethediameterdirectly.Coredholesanddrilledholesaresometimeseccentricwithrespecttotherotationofthelathe.Whentheboringtoolentersthework,theboringbarwilltakeadeepercutononesideoftheholethanontheother,andwilldeflectmorewhentakingthisdeepercut,withtheresultthattheboredholewillnotbeconcentricwiththerotationofthework.Thiseffectiscorrectedbytakingseveralcutsthroughtheholeusingashallowdepthofcut.Eachsucceedingshallowcutcausestheresultingholetobemoreconcentricthanitwaswiththepreviouscut.Beforethefinale,finishcutistaken,theholeshouldbeconcentricwiththerotationoftheworkinordertomakecertainthatthefinishedholewillbeaccuratelylocated.Shoulders,grooves,contours,tapers,andthreadsarealsoboredinsideofholes.Internalgroovesarecutusingatoolthatissimilartoexternalgroovingtool.Theprocedureforboringinternalshoulderisverysimilartotheprocedureforturningshoulders.Largershouldersarefacedwiththeboringtoolpositionedwiththenoseleading,andusingthecrossslidetofeedthetool.Internalcontourscanbemachinedusingatracingattachmentonalathe.Thetracingattachmentismountedonthecrossslideandthestylusfollowstheoutlineofthemasterprofileplate.Thiscausesthecuttingtooltomoveinapathcorrespondingtotheprofileoftheprofileplate.Thus,theprofileonthemasterprofileplateisreproducedinsidethebore.Themasterprofileplateisaccuratelymountedonaspecialslidewhichcanbepreciselyintwodirections,inordertoalignthecuttingtoolinthecorrectrelationshiptothework.Thislathehascam-locktypeofspindlenosewhichpermitsittotakeacutwhenrotatingineitherdirection.Normalturningcutsaretakenwiththespindlerotatingcounterclockwise.Theboringcutistakenwiththespindlerevolvinginaclockwisedirection,or“backwards”.Thispermittheboringcuttobetakenonthe“backside”oftheborewhichiseasiertoseefromtheoperatorspositionfrontofthelathe.Thisshouldnotbedoneonlatheshavingathreadedspindlenosebecausethecuttingforcewilltendtounscrewthechuck.MillingMillingisamachiningprocessforremovingmaterialbyrelativemotionbetweenaworkpieceandarotatingcutterhavingmultiplecuttingedges.Insomeapplications,theworkpieceisheldstationarywhiletherotatingcutterismovedpastitandagivenfeedrate(traversed).Inotherapplications,boththeworkpieceand4cutteraremovedinrelationtoeachotherandinrelationtothemillingmachine.Morefrequently,however,theworkpieceisadvancedatarelativelylowrateofmovementorfeedtoamillingcutterrotatingatacomparativelyhighspeed,withthecuteraxisremaininginafixedposition,acharacteristicfeatureofthemillingprocessisthateachmillingcuttertoothtakesitsshareofthestockintheformofsmallindividualchips.Millingoperationsareperformedonmanydifferentmachines.Sinceboththeworkpieceandcuttercanbemovedrelativetooneanother,independentlyorincombination,awidevarietyofoperationscanbeperformedbymilling.Applicationsincludetheproductionofflatorcontouredsurfaces,slots,grooves,recesses,threads,andotherconfigurations.Millingisoneofthemostuniversal,yetcomplicatedmachiningmethods.Theprocesshasmorevariationsinthekindsofmachinesused,workpiecemovements,andtypesoftoolingthananyotherbasicmachiningmethod.Importantadvantagesofremovingmaterialbymeansofmillingincludehighstockremovalrates,thecapabilityofproducingrelativelysmoothsurfacefinishes,andthewidevarietyifcuttingtoolsthatareavailable.Cuttingedgesofthetoolscanbeshapedtoformanycomplexsurface.Themajormillingmethodsareperipheralandfacemilling；inaddition,anumberofrelatedmethodsexistthatarevariationsofthesetwomethods,dependinguponthetypeofworkpieceorcutter.PeripheralMillingOnperipheralmilling,sometimescalledslabmilling,themilledsurfacegeneratedbyteethorinsertslocatedintheperipheryofthecutterbodyisgenerallyinaplaneparalleltothecutteraxis.Millingoperationswithform-relievedandformedprofilecuttersareincludedinthisclass.Thecrosssectionofthemilledsurfacecorrespondstotheoutlineorcontourofthemillingcutterorcombinationofcuttersused.Peripheralmillingoperationsareusuallyperformedonmillingmachineswiththespindlepositionedhorizontally,however,theycanalsobeperformedwithendmillsonvertiasl-spindlemachines.Themillingcuttersaremountedonanarborwhichisgenerallysupportedattheouterendforincreasedrigidity,particularlywhen,becauseoftheconditionsofthesetup,thecutterorcuttersarelocatedatsomedistancefromthenoseofthespindle.Peripheralmillingshouldgenerallynotbedoneiftheperipheralmillingshouldgenerallynotbedoneifthepartcanbefacemilled.FaceMillingFacemillingisdoneonbothhorizontalandverticalmillingmachines.Themilledsurfaceresultingfromthecombinedactionofcuttingedgeslocatedontheperipheryandfaceofthecutterisgenerallyatrightanglestothecutteraxis.Themilledsurfaceisflat,withnorelationtothecontouroftheteeth,exceptwhenmillingisdonetoashoulder.Generally,facemillingshouldbeappliedwhereverandwheneverpossible.Chipthicknessinconventional(up)facemillingvariesfromaminimumattheentranceandexitofthecuttertoothtoamaximumalongthehorizontaldiameter.Themilledsurfaceischaracterizedbytoothandrevolutionmarks,asinthecaseofperipheralmillingcutters.Theprominenceofthesemarksiscontrolledbytheaccuracyofgrindingthefacecuttingedgeoftheteeth,orbytheaccuracyofthebody/insertcombinationinindexablecuttersandofmountingthecuttersothatitrunstrueonthemachinespindle.Itisalsocontrolledbytherigidityofthemachineandworkpieceitself.Whenthelengthofthefacecuttingedgeislessthanthefeedperrevolution(ortheamounttheworkhasmovedinonerevolutionofthecutter),aseriesofroughlycirculargroovesorridgesresultsonthemilledsurface.Similarmarkingisproducedbythetrailingteethdragonthemilledsurfaceofthework.Thisisknownasheeldrag.Infacemilling,itisimportanttoselectacutterwithadiametersuitedtotheproposedwidthofcutifbestresultsaretobeobtained.Cutsequalinwidthtothefullcutterdiametershouldbeavoided,ifpossible,sincethethinchipsectionatentryoftheteethresultsinacceleratedtoothwearabrasionplusatendencyforthechiptoweldorsticktothetoothorinsertandbecarriedaroundandrecut.Thisisdetrimentaltosurfacefinish.Agoodratioofcutterdiametertothewidthoftheworkpieceorproposedpathofcutis5:3.