英文翻譯原文:(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