外文翻译--机床加工.doc
一外文文献MachineToolAmachinetoolisamachineforshapingormachiningmetalorotherrigidmaterials,usuallybycutting,boring,grinding,shearingorotherformsofdeformation.Machinetoolsemploysomesortoftoolthatdoesthecuttingorshaping.Allmachinetoolshavesomemeansofconstrainingtheworkpieceandprovideaguidedmovementofthepartsofthemachine.Thustherelativemovementbetweentheworkpieceandthecuttingtool(whichiscalledthetoolpath)iscontrolledorconstrainedbythemachinetoatleastsomeextent,ratherthanbeingentirely"offhand"or"freehand".Theprecisedefinitionofthetermmachinetoolvariesamongusers,asdetailedinthe"Nomenclatureandkeyconcepts"section.Itissafetosaythatallmachinetoolsare"machinesthathelppeopletomakethings",althoughnotallfactorymachinesaremachinetools.Todaymachinetoolsaretypicallypoweredotherthanbyhumanmuscle(e.g.,electrically,hydraulically,orvialineshaft),usedtomakemanufacturedparts(components)invariouswaysthatincludecuttingorcertainotherkindsofdeformation.Manyhistoriansoftechnologyconsiderthattruemachinetoolswerebornwhenthetoolpathfirstbecameguidedbythemachineitselfinsomeway,atleasttosomeextent,sothatdirect,freehandhumanguidanceofthetoolpath(withhands,feet,ormouth)wasnolongertheonlyguidanceusedinthecuttingorformingprocess.Inthisviewofthedefinition,theterm,arisingatatimewhenalltoolsuptillthenhadbeenhandtools,simplyprovidedalabelfor"toolsthatweremachinesinsteadofhandtools".Earlylathes,thosepriortothelatemedievalperiod,andmodernwoodworkinglathesandpotterswheelsmayormaynotfallunderthisdefinition,dependingonhowoneviewstheheadstockspindleitself;buttheearliestlathewithdirectmechanicalcontrolofthecuttingtoolspathwasascrew-cuttinglathedatingtoabout1483.1Thislathe"producedscrewthreadsoutofwoodandemployedatruecompoundsliderest".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).Thelatteraspectofmachinetoolsisoftenreferredtobyhistoriansoftechnologyas"buildingtheskillintothetool",incontrasttothetoolpath-constrainingskillbeinginthepersonwhowieldsthetool.Asanexample,itisphysicallypossibletomakeinterchangeablescrews,bolts,andnutsentirelywithfreehandtoolpaths.Butitiseconomicallypracticaltomakethemonlywithmachinetools.Inthe1930s,theU.S.NationalBureauofEconomicResearch(NBER)referencedthedefinitionofamachinetoolas"anymachineoperatingbyotherthanhandpowerwhichemploysatooltoworkonmetal".2Thenarrowestcolloquialsenseofthetermreservesitonlyformachinesthatperformmetalcuttinginotherwords,themanykindsofconventionalmachiningandgrinding.Theseprocessesareatypeofdeformationthatproducesswirls.However,economistsuseaslightlybroadersensethatalsoincludesmetaldeformationofothertypesthatsqueezethemetalintoshapewithoutcuttingoffscarf,suchasrolling,stampingwithdies,shearing,swaging,riveting,andothers.Thuspressesareusuallyincludedintheeconomicdefinitionofmachinetools.Forexample,thisisthebreadthofdefinitionusedbyMaxHollandinhishistoryofBurgomasterandLoudhailer,whichisalsoahistoryofthemachinetoolindustryingeneralfromthe1940sthroughthe1980s;hewasreflectingthesenseofthetermusedbyHoltvilleitselfandotherfirmsintheindustry.Manyreportsonmachinetoolexportandimportandsimilareconomictopicsusethisbroaderdefinition.Thecolloquialsenseimplyingconventionalmetalcuttingisalsogrowingobsoletebecauseofchangingtechnologyoverthedecades.Themanymorerecentlydevelopedprocesseslabeled"machining",suchaselectricaldischargemachining,electrochemicalmachining,electronbeammachining,photochemicalmachining,andultrasonicmachining,orevenplasmacuttingandwaterjetcutting,areoftenperformedbymachinesthatcouldmostlogicallybecalledmachinetools.Inaddition,someofthenewlydevelopedadditivemanufacturingprocesses,whicharenotaboutcuttingawaymaterialbutratheraboutaddingit,aredonebymachinesthatarelikelytoenduplabeled,insomecases,asmachinetools.Thenaturallanguageuseofthetermsvaries,withsubtleconnotativeboundaries.Manyspeakersresistusingtheterm"machinetool"torefertowoodworkingmachinery(joiners,tablesaws,routingstations,andsoon),butitisdifficulttomaintainanytruelogicaldividingline,andthereforemanyspeakersarefinewithabroaddefinition.Itiscommontohearmachinistsrefertotheirmachinetoolssimplyas"machines".Usuallythemassnoun"machinery"encompassesthem,butsometimesitisusedtoimplyonlythosemachinesthatarebeingexcludedfromthedefinitionof"machinetool".Thisiswhythemachinesinafood-processingplant,suchasconveyors,mixers,vessels,dividers,andsoon,maybelabeled"machinery",whilethemachinesinthefactorystoolanddiedepartmentareinsteadcalled"machinetools"incontradistinction.Asforthe1930sNBERdefinitionquotedabove,onecouldarguethatitsspecificitytometalisobsolete,asitisquitecommontodayforparticularlathes,millingmachines,andmachiningcenters(definitelymachinetools)toworkexclusivelyonplasticcuttingjobsthroughouttheirwholeworkinglifespan.ThustheNBERdefinitionabovecouldbeexpandedtosay"whichemploysatooltoworkonmetalorothermaterialsofhighhardness".Anditsspecificityto"operatingbyotherthanhandpower"isalsoproblematic,asmachinetoolscanbepoweredbypeopleifappropriatelysetup,suchaswithatreadle(foralathe)orahandlever(forashaper).Hand-poweredshapersareclearly"thesamethingasshaperswithelectricmotorsexceptsmaller",anditistrivialtopoweramicrolathewithahand-crankedbeltpulleyinsteadofanelectricmotor.Thusonecanquestionwhetherpowersourceistrulyakeydistinguishingconcept;butforeconomicspurposes,theNybergsdefinitionmadesense,becausemostofthecommercialvalueoftheexistenceofmachinetoolscomesaboutviathosethatarepoweredbyelectricity,hydraulics,andsoon.Sucharethevagariesofnaturallanguageandcontrolledvocabulary,bothofwhichhavetheirplacesinthebusinessworld.AutomaticcontrolMachinetoolscanbeoperatedmanually,orunderautomaticcontrol.Earlymachinesusedflywheelstostabilizetheirmotionandhadcomplexsystemsofgearsandleverstocontrolthemachineandthepiecebeingworkedon.SoonafterWorldWarII,thenumericalcontrol(NC)machinewasdeveloped.NCmachinesusedaseriesofnumberspunchedonpapertapeorpunchedcardstocontroltheirmotion.Inthe1960s,computerswereaddedtogiveevenmoreflexibilitytotheprocess.Suchmachinesbecameknownascomputerizednumericalcontrol(CNC)machines.NCandCNCmachinescouldpreciselyrepeatsequencesoverandover,andcouldproducemuchmorecomplexpiecesthaneventhemostskilledtooloperators.Beforelong,themachinescouldautomaticallychangethespecificcuttingandshapingtoolsthatwerebeingused.Forexample,adrillmachinemightcontainamagazinewithavarietyofdrillbitsforproducingholesofvarioussizes.Previously,eithermachineoperatorswouldusuallyhavetomanuallychangethebitormovetheworkpiecetoanotherstationtoperformthesedifferentoperations.Thenextlogicalstepwastocombineseveraldifferentmachinetoolstogether,allundercomputercontrol.Theseareknownasmachiningcenters,andhavedramaticallychangedthewaypartsaremade.Fromthesimplesttothemostcomplex,mostmachinetoolsarecapableofatleastpartialself-replication,andproducemachinepartsastheirprimaryfunction