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英文翻译原文:(一)BORINGANDBORINGMACHINESAscarriedoutonalathe,boringproducescircularinternalprofilesinhollowwork-piecesoronaholemadebydrillingoranotherprocess,Boringisdonewithcuttingtoolsthataresimilartothoseusedinturning.Becausetheboringbarhastoreachthefulllengthofthebore,tooldeflectionand,therefore,maintainanceofdimensionalaccuracycanbeasignificantproblem.Theboringbarmustbesufficientlystiffthatis,madeofamaterialwithhighelasticmodulus,suchastungstencarbidetominimizedeflectionandavoidvibrationandchatter.Boringbarshavebeendesignedwithcapabilitiesfordampingvibration.Althoughboringoperationsonrelativelysmallwork-pieces.Canbecarriedoutonalathe,boringmillsareusedforlargework-pieces.Thesemachinesareeitherverticalorhorizontal,andarecapableofperformingoperationssuchasturning,facing,grooving,andchamfering.Averticalboringmachineissimilartoalathebuthasaverticalaxisofwork-piecerotation.Thecuttingtool(usuallyasinglepointmadeofM-2andM-3high-speedsteelandC-7andC-8carbide)ismountedonthetoolhead,whichiscapableofverticalmovement(forboringandturning)andradialmovement(forfacing),guidedbythecross-rail.Theheadcanbeswiveledtoproduceconical(tapered)surfaces.Inhorizontalboringmachine,thework-pieceismountedonatablethatcanmovehorizontallyinboththeaxialandradialdirections.Thecuttingtoolismountedonaspindlethatrotatesintheheadstock,whichiscapableofbothverticalandlongitudinalmovements.Drills,reamer,taps,andmillingcutterscanalsobemountedonthemachinespindle.Boringmachineareavailablewithavarietyoffeatures.Althoughwork-piecediametersaregenerally1m-4m(3ft-12ft),work-pieceaslargeas20m(60ft)canbemachinedinsomeverticalboringmachines.Machinecapacitiesrangeupto150kw(200hp).thesemachinesarealsoavailablewithcomputernumericalcontrols,whichallowallmovementstobeprogrammed.Withsuchcontrols,littleoperarorinvolvementisrequiredandconsistencyandproductivityareimproved.Cuttingspeedsandfeedsforboringaresimilartothoseforturning.(Forcapabilitiesofboringoperations)Jigborersareverticalboringmachineswithhighprecisionbearings.Althoughtheyareavailableinvarioussizesandusedintoolroomsformakingjigsandfixtures,theyarenowbeingreplacedbymoreversatilenumericalcontrolmachines.Designconsiderationsforboring.Guidelinesforefficientandeconomicalboringoperationsaresimilartothoseforturning.Additionally,thefollowingfactorsshouldbeconsidered:a.Wheneverpossible,throughholesratherthanblindholesshouldbespecified.(Thetermblindholereferstoaholethatdoesnotgothoughthethicknessofthework-piece)b.Thegreaterthelengthtobore-diameterratio,themoredifficultitistoholddimensionsbecauseofthedeflectionsoftheboringbarduetocuttingforces.c.Interruptedinternalsurfacesshouldbeavoided.(2)FundamentalsofMachineToolsInmanycasesproductsformtheprimaryformingprocessesmustundergofurtherrefinementsinsizeandsurfacefinishtomeettheirdesignspecifications.Tomeetsuchprecisetolerancestheremovalofsmallamountsofmaterialisneeded.Usuallymachinetoolsareusedforsuchoperation.IntheUnitedStatesmaterialremovalisabigbusiness-inexcessof$peryear,includingmaterial,labor,overhead,andmachine-toolshipments,isspent.Since60percentofthemechanicalandindustrialengineeringandtechnologygraduateshavesomethingconnectionwiththemachiningindustryeitherthroughsale,design,oroperationofmachineshops,orworkinginrelatedindustry,itiswiseforanengineeringstudenttodevotesometimeinhiscurriculumtostudyingmaterialremovalandmachinetools.Amachinetoolprovidesthemeansforcuttingtoolstoshapeaworkpiecetorequireddimensions;themachinesupportsthetoolandtheworkpieceinacontrolledrelationshipthroughthefunctioningofitsbasicmembers,whichareasfollow:(a)Bed,StructureorFrame.Thisisthemainmemberwhichprovidesabasisfor,andaconnectionbetween,thespindlesandslides;thedistortionandvibrationunderloadmustbekepttoaminimum.(b)SlidesandSideways.Thetranslationofamachineelement(e.g.theslide)isnormallyachievedbystraight-linemotionundertheconstraintofaccurateguidingsurfaces(theslideway).(c)SpindlesandBearings.Angulardisplacementstakeplaceaboutanaxisofrotation;thepositionofthisaxismustbeconstantwithinextremelyfinelimitsinmachinetools,andisensuredbytheprovisionofprecisionspindlesandbearings.(d)PowerUnit.Theelectricmotoristheuniversallyadoptedpowerunitformachinetools.Bysuitablypositioningindividualmotors,beltandgeartransmissionsarereducedtoaminimum.(e)TransmissionLinkage.Linkageisthegeneraltermusedtodenotethemechanical,hydraulic,pneumaticorelectricmechanismswhichconnectangularandlineardisplacementsindefinedrelationship.Therearetwobroaddivisionsofmachiningoperations:(a)Roughing,forwhichthemetalremovalrate,andconsequentlythecuttingforce,ishigh,buttherequireddimensionalaccuracyrelativelylow.(b)Finishing,forwhichthemetalremovalrate,andconsequentlythecuttingforce,islow,buttherequireddimensionalaccuracyandsurfacefinishrelativelyhigh.Itfollowsthatstaticloadsanddynamicloads,suchasresultformanunbalancedgrindingwheel,aremoresignificantinfinishingoperationsthaninroughingoperations,Thedegreeofprecisionachievedinanymachiningprocesswillusuallybeinfluencedbythemagnitudeofthedeflections,whichoccurasaresultoftheforceacting.Machinetoolframesaregenerallymadeincastiron,althoughsomemaybesteelcastingormild-steelfabrications.Castironischosenbecauseofitscheapness,rigidity,compressivestrengthandcapacityfordampingthevibrationsset-upinmachineoperations,Toavoidmassivesectionsincastings,carefullydesignedsystemsofribbingareusedtoofferthemaximumresistancetobendingandtorsionalstresses.Twobasictypesofribbingareboxanddiagonal.Theboxformationisconvenienttoproduce,aperturesinwallspermittingthepositioningandextractionofcores.Diagonalribbingprovidesgreatertorsionalstiffnessandyetpermitsswarftofallbetweenthesections;itisfrequentlyusedforlathebeds.Theslidesandslidewaysofamachinetoollocateandguidememberswhichmoverelativetoeachother,usuallychangingthepositionofthetoolrelativetoworkpiece.Themovementgenerallytakestheformoftranslationinastraightline,butissometimesangularrotation,e.g.tiltingthewheel-headofauniversalthread-grindingmachinetoananglecorrespondingwhichthehelixangleoftheworkpiecethread.Thebasicgeometricelementsofslidesareflat,vee,dovetailandcylinder.Theseelementsmaybeusedseparatelyorcombinedinvariouswaysaccordingtotheapplications.Featuresofslidewaysareasfollows:(a)AccuracyofMovement.Whereaslideistobedisplacedinastraightline,thislinemustlieintwomutuallyperpendicularplanesandtheremustbenosliderotation.Thegeneraltoleranceforstraightnessofmachinetoolslidewaysis00.02mmper1000mm;onhorizontalsurfacesthistolerancemaybedisposedsothataconvexsurfaceresults,thuscounteringtheeffectofsagoftheslideway.(b)MeansofAdjustment.Tofacilitateassembly,maintainaccuracyandeliminateplaybetweenslidingmembersafterwearhastakenplace,astripissometimesinsertedinslides.Thisiscalledagibstrip.Usually,thegibisretainedbysocket-headscrewspassingthroughelongatedslots;andisadjustedbygrub-screwssecuredbylocknuts.(c)Lubrication.Slidewaysmaybelubricatedbyeitherofthefollowingsystems:1)Intermittentlythroughgreaseoroilnipples,amethodsuitablewheremovementsareinfrequentandspeedlow2)Continuouslye.g.bypumpingthroughameteringvalveandpipe-worktothepointofapplication;thefilmofoilintroducedbetweensurfacesbythesemeansmustbeextremelythintoavoidtheslide“floating”Ifslidingsurfaceswereopticallyflatoilwouldbesqueezedout,resultinginthesurfacessticking.HenceinpracticeslideSillfacesareeithergrourldusingtheedgeofacupwheel,orscraped.Bothprocessesprodueeminultesurfacedepressions,whichretainpocket”ofoil,andcompleteseparationofthepartsmaynotoccuratallpoints.(d)ProtectionTomaintainslidewaysingoodorder,thefollowingconditionsmustbemet:1)Ingressofforeignmatter,egswarf,mustbeprevented.Wherethisisnopossible,itisdesirabletohaveaformofslideway,whichdoesnotretainswarf,e.g.theinvertedvee.2)LubricatingoilmustberetainedTheadhesivepropertyofoilforuseonverticalorincline
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