机械加工外文翻译.docx
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机械加工外文翻译.docx
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机械加工外文翻译
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英文原文
BasicMachiningOperationsandCuttingTechnology
BasicMachiningOperations
Machinetoolshaveevolvedfromtheearlyfoot-poweredlathesoftheEgyptiansandJohnWilkinson'sboringmill.Theyaredesignedtoproviderigidsupportforboththeworkpieceandthecuttingtoolandcanpreciselycontroltheirrelativepositionsandthevelocityofthetoolwithrespecttotheworkpiece.Basically,inmetalcutting,asharpenedwedge-shapedtoolremovesarathernarrowstripofmetalfromthesurfaceofaductileworkpieceintheformofaseverelydeformedchip.Thechipisawasteproductthatisconsiderablyshorterthantheworkpiecefromwhichitcamebutwithacorrespondingincreaseinthicknessoftheuncutchip.Thegeometricalshapeofworkpiecedependsontheshapeofthetoolanditspathduringthemachiningoperation.
Mostmachiningoperationsproducepartsofdifferinggeometry.Ifaroughcylindricalworkpiecerevolvesaboutacentralaxisandthetoolpenetratesbeneathitssurfaceandtravelsparalleltothecenterofrotation,asurfaceofrevolutionisproduced,andtheoperationiscalledturning.Ifahollowtubeismachinedontheinsideinasimilarmanner,theoperationiscalledboring.Producinganexternalconicalsurfaceuniformlyvaryingdiameteriscalledtaperturning,ifthetoolpointtravelsinapathofvaryingradius,acontouredsurfacelikethatofabowlingpincanbeproduced;or,ifthepieceisshortenoughandthesupportissufficientlyrigid,acontouredsurfacecouldbeproducedbyfeedingashapedtoolnormaltotheaxisofrotation.Shorttaperedorcylindricalsurfacescouldalsobecontourformed.
Flatorplanesurfacesarefrequentlyrequired.Theycanbegeneratedbyradialturningorfacing,inwhichthetoolpointmovesnormaltotheaxisofrotation.Inothercases,itismoreconvenienttoholdtheworkpiecesteadyandreciprocatethetoolacrossitinaseriesofstraight-linecutswithacrosswisefeedincrementbeforeeachcuttingstroke.Thisoperationiscalledplanningandiscarriedoutonashaper.Forlargerpiecesitiseasiertokeepthetoolstationaryanddrawtheworkpieceunderitasinplanning.Thetoolisfedateachreciprocation.Contouredsurfacescanbeproducedbyusingshapedtools.
Multiple-edgedtoolscanalsobeused.Drillingusesatwin-edgedflutedtoolforholeswithdepthsupto5to10timesthedrilldiameter.Whetherthe
drillturnsortheworkpiecerotates,relativemotionbetweenthecuttingedgeandtheworkpieceistheimportantfactor.Inmillingoperationsarotarycutterwithanumberofcuttingedgesengagestheworkpiece.Whichmovesslowlywithrespecttothecutter.Planeorcontouredsurfacesmaybeproduced,dependingonthegeometryofthecutterandthetypeoffeed.Horizontalorverticalaxesofrotationmaybeused,andthefeedoftheworkpiecemaybeinanyofthethreecoordinatedirections.
BasicMachineTools
MachinetoolsareusedtoproduceapartofaspecifiedgeometricalshapeandpreciseIsizebyremovingmetalfromaductilematerialintheformofchips.Thelatterareawasteproductandvaryfromlongcontinuousribbonsofaductilematerialsuchassteel,whichareundesirablefromadisposalpointofview,toeasilyhandledwell-brokenchipsresultingfromcastiron.Machinetoolsperformfivebasicmetal-removalprocesses:
Iturning,planning,drilling,milling,andgrinding.Allothermetal-removalprocessesaremodificationsofthesefivebasicprocesses.Forexample,boringisinternalturning;reaming,tapping,andcounterboringmodifydrilledholesandarerelatedtodrilling;bobbingandgearcuttingarefundamentallymillingoperations;hacksawingandbroachingareaformofplanningandhoning;lapping,superfinishing.Polishingandbuffingarevariantsofgrindingorabrasiveremovaloperations.Therefore,thereareonlyfourtypesofbasicmachinetools,whichusecuttingtoolsofspecificcontrollablegeometry:
1.lathes,2.planers,3.drillingmachines,and4.millingmachines.Thegrindingprocessformschips,butthegeometryoftheabrasivegrainisuncontrollable.
TheamountandrateofmaterialremovedbythevariousmachiningprocessesmaybeIlarge,asinheavyturningoperations,orextremelysmall,asinlappingorsuperfinishingoperationswhereonlythehighspotsofasurfaceareremoved.
Amachinetoolperformsthreemajorfunctions:
1.itrigidlysupportstheworkpieceoritsholderandthecuttingtool;2.itprovidesrelativemotionbetweentheworkpieceandthecuttingtool;3.itprovidesarangeoffeedsandspeedsusuallyrangingfrom4to32choicesineachcase.
SpeedandFeedsinMachining
Speeds,feeds,anddepthofcutarethethreemajorvariablesforeconomicalmachining.Othervariablesaretheworkandtoolmaterials,coolantandgeometryofthecuttingtool.Therateofmetalremovalandpowerrequiredformachiningdependuponthesevariables.
Thedepthofcut,feed,andcuttingspeedaremachinesettingsthatmustbeestablishedinanymetal-cuttingoperation.Theyallaffecttheforces,thepower,andtherateofmetalremoval.Theycanbedefinedbycomparingthemtotheneedleandrecordofaphonograph.Thecuttingspeed(V)isrepresentedbythevelocityof-therecordsurfacerelativetotheneedleinthetonearmatanyinstant.Feedisrepresentedbytheadvanceoftheneedleradiallyinwardperrevolution,oristhedifferenceinpositionbetweentwoadjacentgrooves.Thedepthofcutisthepenetrationoftheneedleintotherecordorthedepthofthegrooves.
TurningonLatheCenters
Thebasicoperationsperformedonanenginelatheareillustrated.Thoseoperationsperformedonexternalsurfaceswithasinglepointcuttingtoolarecalledturning.Exceptfordrilling,reaming,andlapping,theoperationsoninternalsurfacesarealsoperformedbyasinglepointcuttingtool.
Allmachiningoperations,includingturningandboring,canbeclassifiedasroughing,finishing,orsemi-finishing.Theobjectiveofaroughingoperationistoremovethebulkofthematerialasrapidlyandasefficientlyaspossible,whileleavingasmallamountofmaterialonthework-pieceforthefinishingoperation.Finishingoperationsareperformedtoobtainthefinalsize,shape,andsurfacefinishontheworkpiece.Sometimesasemi-finishingoperationwillprecedethefinishingoperationtoleaveasmallpredeterminedanduniformamountofstockonthework-piecetoberemovedbythefinishingoperation.
Generally,longerworkpiecesareturnedwhilesupportedononeortwolathecenters.Coneshapedholes,calledcenterholes,whichfitthelathecentersaredrilledintheendsoftheworkpiece-usuallyalongtheaxisofthecylindricalpart.Theendoftheworkpieceadjacenttothetailstockisalwayssupportedbyatailstockcenter,whiletheendneartheheadstockmaybesupportedbyaheadstockcenterorheldinachuck.Theheadstockendoftheworkpiecemaybeheldinafour-jawchuck,orinatypechuck.Thismethodholdstheworkpiecefirmlyandtransfersthepowertotheworkpiecesmoothly;theadditionalsupporttotheworkpieceprovidedbythechucklessensthetendencyforchattertooccurwhencutting.Preciseresultscanbeobtainedwiththismethodifcareistakentoholdtheworkpieceaccuratelyinthechuck.
Verypreciseresultscanbeobtainedbysupportingtheworkpiecebetweentwocenters.Alathedogisclampedtotheworkpiece;togethertheyaredrivenbyadriverplatemountedonthespindlenose.OneendoftheWorkpieceismecained;thentheworkpiececanbeturnedaroundinthelathetomachinetheotherend.Thecenterholesintheworkpieceserveaspreciselocatingsurfacesaswellasbearingsurfacestocarrytheweightoftheworkpiece andtoresistthecuttingforces.Aftertheworkpiecehasbeenremovedfromthelatheforanyreason,thecenterholeswillaccuratelyaligntheworkpiecebackinthelatheorinanotherlathe,orinacylindricalgrindingmachine.Theworkpiecemustneverbeheldattheheadstockendbybothachuckandalathecenter.Whileatfirstthoughtthisseemslikeaquickmethodofaligningtheworkpieceinthechuck,thismustnotbedonebecauseitisnotpossibletopressevenlywiththejawsagainsttheworkpiecewhileitisalsosupportedbythecenter.Thealignmentprovidedbythecenterwillnotbemaintainedandthepressureofthejawsmaydamagethecenterhole,thelathecenter,andperhapseventhelathespindle.Compensatingorfloatingjawchucksusedalmostexclusivelyonhighproductionworkprovideanexceptiontothestatementsmadeabove.Thesechucksarereallyworkdriversandcannotbeusedforthesamepurposeasordinarythreeorfour-jawchucks.
Whileverylargediameterworkpiecesaresometimesmountedontwocenters,theyarepreferablyheldattheheadstockendbyfaceplatejawstoobtainthesmoothpowertransmission;moreover,largelathedogsthatareadequatetotransmitthepowernotgenerallyavailable,althoughtheycanbemadeasaspecial.Faceplatejawsarelikechuckjawsexceptthattheyaremountedonafaceplate,whichhaslessoverhangfromthespindlebearingsthanalargechuckwouldhave.
IntroductionofMachining
Machiningasashape-producingmethodisthemostuniversallyusedandthemostimportantofallmanufacturingprocesses.Machiningisashape-producingprocessinwhichapower-drivendevicecausesmaterialtoberemovedinchipform.Mostmachiningisdonewithequipmentthatsupportsboththeworkpieceandcuttingtoolalthoughinsomecasesportableequipmentisusedwithunsupportedworkpiece.
LowsetupcostforsmallQuantities.Machininghastwoapplicationsinmanufacturing.Forcasting,forging,andpressworking,
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