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外文翻译--基本的加工工序—切削,镗削和铣削.doc

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外文翻译--基本的加工工序—切削,镗削和铣削.doc

1英文原文BasicMachiningOperationsMachiningtoolshaveevolvedfromtheearlyfoot–poweredlatheEgyptiansandJohnWilkinsonsboringmill.Theyaredesignedtoproviderigidsupportforboththeworkpieceandthecuttingtoolandcuttingtoolandcanpreciselycontroltheirrelativepositionsandthevelocityofthetoolwithrespecttotheworkpiece.Basically,inmetalcutting,asharpenedwedgeshapedtoolremovesarathernarrowstripofmetalfromthesurfaceofaductileworkpieceinthefromofaseverelydeformedchip.Thechipiswasteproductthatisworkpieceinthefromofaseverelydeformedchipisawasteproductthatisconsiderablyshorterthantheworkpiecefromwhichitcamebutwithacorrespondingincreaseinthicknessoftheuncutchip.Thegeometricalshapeofthemachinesurfacedependsontheshapeofthetoolanditspathduringthemachiningopration.Mostmachineoperationsproducepartsofdifferinggeometry.Ifaroughcylindricalworkpiecerevolvesaboutacentralaxisandtoolpenetratesbeneathitssurfaceandtravelsparalleltothecenterofrotation,asurfaceofrevolutionisproduced,andtheoperationiscalledturning.Ifahollowtubeisonthemachinedontheinsideinasimilarmanner,theoperationiscalledboring.Producinganexternalconicalsurfaceofuniformlyvaryingdiameteriscalledtaperturning.Ifthetoolpointtravelsinapathofvaryingradius,acontouredsurfacelikethatofbowlingpincanbeproducedor,ifthepieceisshortenoughandthesupportissufficientlyrigid,acontouredsurfacecouldbeproducedbyfeedingashapedtoolnormaltotheaxisofrotation.Shorttaperedorcylindricalsurfacescouldalsobecontourformed.Flatorplanesurfacearefrequentlyrequired.Theycanbegeneratedbyradialturningorfacing,inwhichthetoolpointmovesnormaltotheaxisofrotation.Inothercases,itismoreconvenienttoholetheworkpiecesteadyandreciprocatethetoolacross,itisseriesofstraightlinecutswithacrosswisefeedincrementbeforeeachcuttingstroke.Thisoperationiscalledplanningandiscarriedoutonashaper.Forlargerpiecesitiseasiertokeepthetoolstationaryanddrawtheworkpieceunderitasinplanning.Thetoolisfedateachreciprocation.Contouredsurfacescanbeproducedbyusingshapedtools.Multipleedgedtoolscanalsobeused.Drillingusesatwinedgedflutedtoolforholeswithdepthsupto5to10timesthedrilldiameter.Whetherthedrillturnsortheworkpiecerotates,relativemotionbetweenthecuttingedgeandtheworkpieceistheimportantfactor.Inmillingoperationsarotarycutterwithanumberofcuttingedgesengagestheworkpiece,whichmovesslowlywithrespecttothecutter.Planeorcontouredsurfacesmaybeproduced,dependingonthegeometryofthecutterandthetypeoffeed.Horizontalorverticalaxesofrotationmaybeused,andthefeedoftheworkpiecemaybeinanyofthethreecoordinatedirections.BasicMachineToolsMachinetoolsareusedtopartofaspecifiedgeometetricalshapeandprecisesizebyremovingmetalfromaductilematerialintheformchips.Thelatterareawasteproductandvaryfromlongcontinuousribbonsofadisposalpointofview,toeasilyhandedwellbrokenchipsresultingfromcastiron.Machinetoolsperformfivebasicmetalremoveprocessesturning,planning,drilling,milling,andgrinding.Allothermetalremovalprocessesaremodificationsofthesefivebasicprocesses.Forexample,boringisinternalturningreaming,tapping,andcounterboringmollifydrilledholesandarerelatedtodrillinghobblingandgearcuttingarefundamentallymillingoperationshacksawingandbroachingareafromofplanningandhoninglapping,superfinishing,polishing,andbuffingarevariantsofgrindingorabrasiveremovaloperations.Therefore,thereareonlyfourtypesofbasicmachinetools,whichusecuttingtoolsofspecificcontrollablegeometry.Thegrindingprocessformschips,butthegeometryoftheabrasivegrainisuncontrollable.Theamountandrateofmaterialremovedbythevariousmachiningprocessesmaybelarge,asinheavyturningoperations,orextremelysmall,asinlappingorsuperfinishingoperationswhereonlythehighspotsofasurfaceareremoved.Amachiningtoolperformsthreemajorfunctions1.itrigidlysupportstheworkpiceoritsholderandthecuttingtool2.itprovidesrelativemotionbetweentheworkpiceandthecuttingtool3.itprovidesarangeoffeedsandspeedsusuallyrangingfrom4to32choicesineachcase.2SpeedandFeedsinMachiningSpeeds,feeds,anddepthpfcutarethethreemajorvariablesforeconomicalmachining.Othervariablesaretheworkandtoolmaterials,coolantandgeometryofthecuttingtool.Therateofmetalremovalandpowerrequiredformachiningdependuponthesevariables.Thedepthsofcut,feed,andcuttingspeedaremachinesettingthatmustbeestablishedinanymetalcuttingoperation.Theyallaffecttheforces,thepower,andtherateofmetalremoval.Theycanbedefinedbycomparingthemtotheneedleandrecordofaphonograph.ThecuttingspeedVisrepresentedbythevelocityoftherecordsurfacerelativetotheneedleinthetonearmatanyinstant.Feedisrepresentedbytheadvanceoftheneedleradiallyinwardperrevolution,oristhedifferenceinpositionbetweentwoadjacentgrooves.Thedepthofcutisthepenetrationoftheneedleintotherecordorthedepthofthegrooves.TurningonlathecentersThebasicoperationsoperationsperformedonanenginelatheareillustratedinfig.113.thoseoperationsperformedonexternalsurfaceswithasinglepointcuttingtoolarecalledturning.Exceptfordrilling,reaming,andtapping,theoperationsoninternalsurfacesarealsoperformedbyasinglepointcuttingtool.Allmachiningoperate,includingturningandboring,canbeclassifiedasroughing,finishing,orsemifinishing.Theobjectiveofaroughingoperationistoremovethebulkofthematerialasrapidlyandasefficientlyaspossible,whileleavingasmallamountofmaterialontheworkpieceforthefinishingoperation.Finishingoperationsareperformedtoobtainthefinalsize,shape,andsurfacefinishontheworkpiece.Sometimesasemifinishingoperationwillprecedethefinishingoperationtoleaveasmallpredeterminedanduniformamountofstockontheworkpiecetoberemovedbythefinishingoperation.Generally,longerworkpiecesareturnedwhilesupportedononeortwolathecenters.Coneshapedholes,calledcenterholes,whichfitthelathecentersaredrilledintheendoftheworkpieceusuallyalongtheaxisofthecylindricalpart.Theendoftheworkpieceadjacenttothetailstockisalwayssupportedbyatailstockcenter,whileendneartheheadstockmaybesupportedbyaheadstockcenterorheldinachuck.Theheadstockendoftheworkpiecemaybeheldinafourjawchuck,orinacollettypechuck.Thismethodholdstheworkpiecefirmlyandtransfersthepowertotheworkpiecesmoothlytheadditionalsupporttotheworkpieceprovidedbythechucklessensthetendencyforchattertooccurwhencutting.Preciseresultcanbeobtainedwiththismethodifcareistakentoholdtheworkpieceaccuratelyinthechuck.Verypreciseresultscanbeobtainedbysupportingtheworkpiecebetweentwocenters.Alathedogisclampedtotheworkpiecetogethertheyaredrivenbythedriverplatemountedonthespindlenose.Oneendoftheworkpieceismachinedthentheworkpiececanbeturnedaroundinthelathetomachinetootherend.Thecenterholesintheworkpieceserveaspreciselocatingsurfacesaswellasbearingsurfacestocarrytheweightoftheworkpieceandtoresistthecuttingforces.Aftertheworkpiecehasbeenremovefromthelatheforanyreason,thecenterholeswillaccuratelyaligntheworkpiecebackinthelatheorinanotherlathe,orinacylindricalgrindingmachine.Theworkpiecemustneverbeheldattheheadstockendbybothachuckandalathecenter.Whileatfirstthoughtthisseemslikeaquickmethodofaligningtheworkpieceinthechuck,thismustnotbedonebecauseitisnotpossibletopressevenlywiththejawsagainsttheworkpiecewhileitisalsosupportedbythecenter.Thealignmentprovidedbythecenterwillnotbemaintainedandthepressureofthejawsmaydamagethecenterhole,thelathecenter,andperhapseventhelathespindle.Compensatingorfloatingjawchucksusedalmostexclusivelyonhighproductionworkprovideanexceptiontothestatementsmadeabove.Thesechucksarereallyworkdriversandcannotbeusedforthesamepurposeasordinarythreeorfourjawchicks.Whileverylargediameterworkpiecearesometimesmountedontwocenters,theyarepreferablyheldattheheadstockendbyfaceplatejawstoobtainthesmoothpowertransmissionmoreover,largelathedogsthatareadequatetotransmitthepowernotgenerallyavailable,althoughtheycanbemadeasaspecial.Faceplatejawsarelikechuckjawsexceptthattheyaremountedonafaceplate,whichhaslessoverhangfromthespindlebearingsthanalargechuckwouldhave.BoringTheobjectiveofboringaholeinalatheis31、Toenlargethehole2、Tomachinetheholetothedesireddiameter3、Toaccuratelylocatethepositionofthehole4、ToobtainasmoothsurfacefinishintheholeThemotionoftheboringtoolisparalleltotheaxisofthelathewhenthecarriageismovedinthelongitudinaldirectionandtheworkpiecerevolvesabouttheaxisofthelathe.Whenthesetwomotionsarecombinedtoboreahole,itwillbeconcentricwiththeaxisofrotationofthelathe.Thepositionoftheholecanbeaccuratelylocatedbyholdingtheworkpieceinthelathesothattheaxisaboutwhichtheholeistobemachinedcoincideswiththeaxisofrotationofthelathe.Whentheboringoperationisdoneinthesamesetupoftheworkthatisusedtoturnandfaceit,practicallyperfectconcentricityandperpendicularitycanbeachieved.Theboringtoolisheldinaboringbarwhichisfedthroughtheholebycarriage.Variationsofthisdesignareused,dependingonthejobtobedone.Theleadangleused,ifany,shouldalwaysbesmall.Also,thenoseradiusoftheboringtoolmustnotbetoolarge.Thecuttingspeedusedforboringcanbeequaltothespeedforturning.However,whenthespindlespeedofthelatheiscalculated,thefinished,orlargest,borediametershouldbeused.Thefeedrateforboringisusuallysomewhatlessthanforturningtocompensatefortherigidityoftheboringbar.Theboringoperationisgenerallyperformedintwostepsnamely,roughboringandfinishboring.Theobjectiveoftheroughboringoperationistoremovetheexcessmetalrapidlyandefficiently,andtheobjectiveofthefinishboringoperationistoobtainthedesiredsize,surfacefinish,andlocationofthehole.Thesizeoftheholeisobtainedbyusingthetrialcutprocedure.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.Thislathehascamlocktypeofspindlenosewhichpermitsittotakeacutwhenrotatingineitherdirection.Normalturningcutsaretakenwiththespindlerotatingcounterclockwise.Theboringcutistakenwiththespindlerevolvinginaclockwisedirection,orbackwards.Thispermittheboringcuttobetakenonthebacksideoftheborewhichiseasiertoseefromtheoperatorspositionfrontofthelathe.Thisshouldnotbedoneonlatheshavingathreadedspindlenosebecausethecuttingforcewilltendtounscrewthechuck.MillingMillingisamachiningprocessforremovingmaterialbyrelativemotionbetweenaworkpieceandarotatingcutterhavingmultiplecuttingedges.Insomeapplications,theworkpieceisheldstationarywhiletherotatingcutterismovedpastitandagivenfeedratetraversed.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.Themajormillingmethodsareperipheralandfacemillinginaddition,anumberofrelatedmethodsexistthatarevariationsofthesetwomethods,dependinguponthetypeofworkpieceorcutter.PeripheralMillingOnperipheralmilling,sometimescalledslabmilling,themilledsurfacegeneratedbyteethorinsertslocatedintheperipheryofthecutterbodyisgenerallyinaplaneparalleltothecutteraxis.Millingoperationswithformrelievedandformedprofilecuttersareincludedinthisclass.Thecrosssectionofthemilledsurfacecorrespondstotheoutlineorcontourofthemillingcutterorcombinationofcuttersused.Peripheralmillingoperationsareusuallyperformedonmillingmachineswiththespindlepositionedhorizontally,however,theycanalsobeperformedwithendmillsonvertiaslspindlemachines.Themillingcuttersaremountedonanarborwhichisgenerallysupportedattheouterendforincreasedrigidity,particularlywhen,becauseoftheconditionsofthesetup,thecutterorcuttersarelocatedatsomedistancefromthenoseofthespindle.Peripheralmillingshouldgenerallynotbedoneiftheperipheralmillingshouldgenerallynotbedoneifthepartcanbefacemilled.FaceMillingFacemillingisdoneonbothhorizontalandverticalmillingmachines.Themilledsurfaceresultingfromthecombinedactionofcuttingedgeslocatedontheperipheryandfaceofthecutterisgenerallyatrightanglestothecutteraxis.Themilledsurfaceisflat,withnorelationtothecontouroftheteeth,exceptwhenmillingisdonetoashoulder.Generally,facemillingshouldbeappliedwhereverandwheneverpossible.Chipthicknessinconventionalupfacemillingvariesfromaminimumattheentranceandexitofthecuttertoothtoamaximumalongthehorizontaldiameter.Themilledsurfaceischaracterizedbytoothandrevolutionmarks,asinthecaseofperipheralmillingcutters.Theprominenceofthesemarksiscontrolledbytheaccuracyofgrindingthefacecuttingedgeoftheteeth,orbytheaccuracyofthebody/insertcombinationinindexablecuttersandofmountingthecuttersothatitrunstrueonthemachinespindle.Itisalsocontrolledbytherigidityofthemachineandworkpieceitself.Whenthelengthofthefacecuttingedgeislessthanthefeedperrevolutionortheamounttheworkhasmovedinonerevolutionofthecutter,aseriesofroughlycirculargroovesorridgesresultsonthemilledsurface.Similarmarkingisproducedbythetrailingteethdragonthemilledsurfaceofthework.Thisisknownasheeldrag.Infacemilling,itisimportanttoselectacutterwithadiametersuitedtotheproposedwidthofcutifbestresultsaretobeobtained.Cutsequalinwidthtothefullcutterdiametershouldbeavoided,ifpossible,sincethethinchipsectionatentryoftheteethresultsinacceleratedtoothwearabrasionplusatendencyforthechiptoweldorsticktothetoothorinsertandbecarriedaroundandrecut.Thisisdetrimentaltosurfacefinish.Agoodratioofcutterdiametertothewidthoftheworkpieceorproposedpathofcutis53.

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