外文翻译--机床加工.doc

一外文文献MachineToolAmachinetoolisamachineforshapingormachiningmetalorotherrigidmaterials,usuallybycutting,boring,grinding,shearingorotherformsofdeformation.Machinetoolsemploysomesortoftoolthatdoesthecuttingorshaping.Allmachinetoolshavesomemeansofconstrainingtheworkpieceandprovideaguidedmovementofthepartsofthemachine.Thustherelativemovementbetweentheworkpieceandthecuttingtool(whichiscalledthetoolpath)iscontrolledorconstrainedbythemachinetoatleastsomeextent,ratherthanbeingentirelyoffhandorfreehand.Theprecisedefinitionofthetermmachinetoolvariesamongusers,asdetailedintheNomenclatureandkeyconceptssection.Itissafetosaythatallmachinetoolsaremachinesthathelppeopletomakethings,althoughnotallfactorymachinesaremachinetools.Todaymachinetoolsaretypicallypoweredotherthanbyhumanmuscle(e.g.,electrically,hydraulically,orvialineshaft),usedtomakemanufacturedparts(components)invariouswaysthatincludecuttingorcertainotherkindsofdeformation.Manyhistoriansoftechnologyconsiderthattruemachinetoolswerebornwhenthetoolpathfirstbecameguidedbythemachineitselfinsomeway,atleasttosomeextent,sothatdirect,freehandhumanguidanceofthetoolpath(withhands,feet,ormouth)wasnolongertheonlyguidanceusedinthecuttingorformingprocess.Inthisviewofthedefinition,theterm,arisingatatimewhenalltoolsuptillthenhadbeenhandtools,simplyprovidedalabelfortoolsthatweremachinesinsteadofhandtools.Earlylathes,thosepriortothelatemedievalperiod,andmodernwoodworkinglathesandpotterswheelsmayormaynotfallunderthisdefinition,dependingonhowoneviewstheheadstockspindleitself；buttheearliestlathewithdirectmechanicalcontrolofthecuttingtoolspathwasascrew-cuttinglathedatingtoabout1483.1Thislatheproducedscrewthreadsoutofwoodandemployedatruecompoundsliderest.Themechanicaltoolpathguidancegrewoutofanyofvariousrootconcepts:Firstisthespindleconceptitself,whichconstraintsworkpieceortoolmovementtorotationaroundafixedaxis.Thisancientconceptpredatesmachinetoolsperse；theearliestlathesandpotterswheelsincorporateditfortheworkpiece,butthemovementofthetoolitselfonthesemachineswasentirelyfreehand.Themachineslide,whichhasmanyforms,suchasdovetailways,boxways,orcylindricalcolumnways.Machineslidesconstraintoolorworkpiecemovementlinearly.Ifastopisadded,thelengthofthelinecanalsobeaccuratelycontrolled.(Machineslidesareessentiallyasubsetoflinearbearings,althoughthelanguageusedtoclassifythesevariousmachineelementsincludesconnotativeboundaries；someusersinsomecontextswouldcontradistinguishelementsinwaysthatothersmightnot.)Tracing,whichinvolvesfollowingthecontoursofamodelortemplateandtransferringtheresultingmotiontothetoolpath.Camoperation,whichisrelatedinprincipletotracingbutcanbeasteportworemovedfromthetracedelementsmatchingthereproducedelementsfinalshape.Forexample,severalcams,nooneofwhichdirectlymatchesthedesiredoutputshape,canactuateseveralvectorsofthetoolpaths.Abstractlyprogrammabletoolpathguidancebeganwithmechanicalsolutions,suchasinmusicalboxcamsandJacquardlooms.Theconvergenceofprogrammablemechanicalcontrolwithmachinetoolpathcontrolwasdelayedmanydecades,inpartbecausetheprogrammablecontrolmethodsofmusicalboxesandloomslackedtherigidityformachinetoolpaths.Later,electromechanicalsolutions(suchasservos)andsoonelectronicsolutions(includingcomputers)wereadded,leadingtonumericalcontrolandcomputernumericalcontrol.Whenconsideringthedifferencebetweenfreehandtoolpathsandmachine-constrainedtoolpaths,theconceptsofaccuracyandprecision,efficiency,andproductivitybecomeimportantinunderstandingwhythemachine-constrainedoptionaddsvalue.Afterall,humansaregenerallyquitetalentedintheirfreehandmovements；thedrawings,paintings,andsculpturesofartistssuchasMichelangeloorLeonardoadVinci,andofcountlessothertalentedpeople,showthathumanfreehandtoolpathhasgreatpotential.Thevaluethatmachinetoolsaddedtothesehumantalentsisintheareasofrigidity(constrainingthetoolpathsdespitethousandsofnewtons(pounds)offorcefightingagainsttheconstraint),accuracyandprecision,efficiency,andproductivity.Withamachinetool,toolpathsthatnohumanmusclecouldconstraincanbeconstrained；andtoolpathsthataretechnicallypossiblewithfreehandmethods,butwouldrequiretremendoustimeandskilltoexecute,caninsteadbeexecutedquicklyandeasily,evenbypeoplewithlittlefreehandtalent(becausethemachinetakescareofit).Thelatteraspectofmachinetoolsisoftenreferredtobyhistoriansoftechnologyasbuildingtheskillintothetool,incontrasttothetoolpath-constrainingskillbeinginthepersonwhowieldsthetool.Asanexample,itisphysicallypossibletomakeinterchangeablescrews,bolts,andnutsentirelywithfreehandtoolpaths.Butitiseconomicallypracticaltomakethemonlywithmachinetools.Inthe1930s,theU.S.NationalBureauofEconomicResearch(NBER)referencedthedefinitionofamachinetoolasanymachineoperatingbyotherthanhandpowerwhichemploysatooltoworkonmetal.2Thenarrowestcolloquialsenseofthetermreservesitonlyformachinesthatperformmetalcuttinginotherwords,themanykindsofconventionalmachiningandgrinding.Theseprocessesareatypeofdeformationthatproducesswirls.However,economistsuseaslightlybroadersensethatalsoincludesmetaldeformationofothertypesthatsqueezethemetalintoshapewithoutcuttingoffscarf,suchasrolling,stampingwithdies,shearing,swaging,riveting,andothers.Thuspressesareusuallyincludedintheeconomicdefinitionofmachinetools.Forexample,thisisthebreadthofdefinitionusedbyMaxHollandinhishistoryofBurgomasterandLoudhailer,whichisalsoahistoryofthemachinetoolindustryingeneralfromthe1940sthroughthe1980s；hewasreflectingthesenseofthetermusedbyHoltvilleitselfandotherfirmsintheindustry.Manyreportsonmachinetoolexportandimportandsimilareconomictopicsusethisbroaderdefinition.Thecolloquialsenseimplyingconventionalmetalcuttingisalsogrowingobsoletebecauseofchangingtechnologyoverthedecades.Themanymorerecentlydevelopedprocesseslabeledmachining,suchaselectricaldischargemachining,electrochemicalmachining,electronbeammachining,photochemicalmachining,andultrasonicmachining,orevenplasmacuttingandwaterjetcutting,areoftenperformedbymachinesthatcouldmostlogicallybecalledmachinetools.Inaddition,someofthenewlydevelopedadditivemanufacturingprocesses,whicharenotaboutcuttingawaymaterialbutratheraboutaddingit,aredonebymachinesthatarelikelytoenduplabeled,insomecases,asmachinetools.Thenaturallanguageuseofthetermsvaries,withsubtleconnotativeboundaries.Manyspeakersresistusingthetermmachinetooltorefertowoodworkingmachinery(joiners,tablesaws,routingstations,andsoon),butitisdifficulttomaintainanytruelogicaldividingline,andthereforemanyspeakersarefinewithabroaddefinition.Itiscommontohearmachinistsrefertotheirmachinetoolssimplyasmachines.Usuallythemassnounmachineryencompassesthem,butsometimesitisusedtoimplyonlythosemachinesthatarebeingexcludedfromthedefinitionofmachinetool.Thisiswhythemachinesinafood-processingplant,suchasconveyors,mixers,vessels,dividers,andsoon,maybelabeledmachinery,whilethemachinesinthefactorystoolanddiedepartmentareinsteadcalledmachinetoolsincontradistinction.Asforthe1930sNBERdefinitionquotedabove,onecouldarguethatitsspecificitytometalisobsolete,asitisquitecommontodayforparticularlathes,millingmachines,andmachiningcenters(definitelymachinetools)toworkexclusivelyonplasticcuttingjobsthroughouttheirwholeworkinglifespan.ThustheNBERdefinitionabovecouldbeexpandedtosaywhichemploysatooltoworkonmetalorothermaterialsofhighhardness.Anditsspecificitytooperatingbyotherthanhandpowerisalsoproblematic,asmachinetoolscanbepoweredbypeopleifappropriatelysetup,suchaswithatreadle(foralathe)orahandlever(forashaper).Hand-poweredshapersareclearlythesamethingasshaperswithelectricmotorsexceptsmaller,anditistrivialtopoweramicrolathewithahand-crankedbeltpulleyinsteadofanelectricmotor.Thusonecanquestionwhetherpowersourceistrulyakeydistinguishingconcept；butforeconomicspurposes,theNybergsdefinitionmadesense,becausemostofthecommercialvalueoftheexistenceofmachinetoolscomesaboutviathosethatarepoweredbyelectricity,hydraulics,andsoon.Sucharethevagariesofnaturallanguageandcontrolledvocabulary,bothofwhichhavetheirplacesinthebusinessworld.AutomaticcontrolMachinetoolscanbeoperatedmanually,orunderautomaticcontrol.Earlymachinesusedflywheelstostabilizetheirmotionandhadcomplexsystemsofgearsandleverstocontrolthemachineandthepiecebeingworkedon.SoonafterWorldWarII,thenumericalcontrol(NC)machinewasdeveloped.NCmachinesusedaseriesofnumberspunchedonpapertapeorpunchedcardstocontrolth