外文翻译--机床加工.doc -- 5 元

一外文文献MachineToolAmachinetoolisamachineforshapingormachiningmetalorotherrigidmaterials,usuallybycutting,boring,grinding,shearingorotherformsofdeformation.Machinetoolsemploysomesortoftoolthatdoesthecuttingorshaping.Allmachinetoolshavesomemeansofconstrainingtheworkpieceandprovideaguidedmovementofthepartsofthemachine.Thustherelativemovementbetweentheworkpieceandthecuttingtoolwhichiscalledthetoolpathiscontrolledorconstrainedbythemachinetoatleastsomeextent,ratherthanbeingentirelyoffhandorfreehand.Theprecisedefinitionofthetermmachinetoolvariesamongusers,asdetailedintheNomenclatureandkeyconceptssection.Itissafetosaythatallmachinetoolsaremachinesthathelppeopletomakethings,althoughnotallfactorymachinesaremachinetools.Todaymachinetoolsaretypicallypoweredotherthanbyhumanmusclee.g.,electrically,hydraulically,orvialineshaft,usedtomakemanufacturedpartscomponentsinvariouswaysthatincludecuttingorcertainotherkindsofdeformation.Manyhistoriansoftechnologyconsiderthattruemachinetoolswerebornwhenthetoolpathfirstbecameguidedbythemachineitselfinsomeway,atleasttosomeextent,sothatdirect,freehandhumanguidanceofthetoolpathwithhands,feet,ormouthwasnolongertheonlyguidanceusedinthecuttingorformingprocess.Inthisviewofthedefinition,theterm,arisingatatimewhenalltoolsuptillthenhadbeenhandtools,simplyprovidedalabelfortoolsthatweremachinesinsteadofhandtools.Earlylathes,thosepriortothelatemedievalperiod,andmodernwoodworkinglathesandpotterswheelsmayormaynotfallunderthisdefinition,dependingonhowoneviewstheheadstockspindleitselfbuttheearliestlathewithdirectmechanicalcontrolofthecuttingtoolspathwasascrewcuttinglathedatingtoabout1483.1Thislatheproducedscrewthreadsoutofwoodandemployedatruecompoundsliderest.ThemechanicaltoolpathguidancegrewoutofanyofvariousrootconceptsFirstisthespindleconceptitself,whichconstraintsworkpieceortoolmovementtorotationaroundafixedaxis.Thisancientconceptpredatesmachinetoolspersetheearliestlathesandpotterswheelsincorporateditfortheworkpiece,butthemovementofthetoolitselfonthesemachineswasentirelyfreehand.Themachineslide,whichhasmanyforms,suchasdovetailways,boxways,orcylindricalcolumnways.Machineslidesconstraintoolorworkpiecemovementlinearly.Ifastopisadded,thelengthofthelinecanalsobeaccuratelycontrolled.Machineslidesareessentiallyasubsetoflinearbearings,althoughthelanguageusedtoclassifythesevariousmachineelementsincludesconnotativeboundariessomeusersinsomecontextswouldcontradistinguishelementsinwaysthatothersmightnot.Tracing,whichinvolvesfollowingthecontoursofamodelortemplateandtransferringtheresultingmotiontothetoolpath.Camoperation,whichisrelatedinprincipletotracingbutcanbeasteportworemovedfromthetracedelementsmatchingthereproducedelementsfinalshape.Forexample,severalcams,nooneofwhichdirectlymatchesthedesiredoutputshape,canactuateseveralvectorsofthetoolpaths.Abstractlyprogrammabletoolpathguidancebeganwithmechanicalsolutions,suchasinmusicalboxcamsandJacquardlooms.Theconvergenceofprogrammablemechanicalcontrolwithmachinetoolpathcontrolwasdelayedmanydecades,inpartbecausetheprogrammablecontrolmethodsofmusicalboxesandloomslackedtherigidityformachinetoolpaths.Later,electromechanicalsolutionssuchasservosandsoonelectronicsolutionsincludingcomputerswereadded,leadingtonumericalcontrolandcomputernumericalcontrol.Whenconsideringthedifferencebetweenfreehandtoolpathsandmachineconstrainedtoolpaths,theconceptsofaccuracyandprecision,efficiency,andproductivitybecomeimportantinunderstandingwhythemachineconstrainedoptionaddsvalue.Afterall,humansaregenerallyquitetalentedintheirfreehandmovementsthedrawings,paintings,andsculpturesofartistssuchasMichelangeloorLeonardoadVinci,andofcountlessothertalentedpeople,showthathumanfreehandtoolpathhasgreatpotential.Thevaluethatmachinetoolsaddedtothesehumantalentsisintheareasofrigidityconstrainingthetoolpathsdespitethousandsofnewtonspoundsofforcefightingagainsttheconstraint,accuracyandprecision,efficiency,andproductivity.Withamachinetool,toolpathsthatnohumanmusclecouldconstraincanbeconstrainedandtoolpathsthataretechnicallypossiblewithfreehandmethods,butwouldrequiretremendoustimeandskilltoexecute,caninsteadbeexecutedquicklyandeasily,evenbypeoplewithlittlefreehandtalentbecausethemachinetakescareofit.Thelatteraspectofmachinetoolsisoftenreferredtobyhistoriansoftechnologyasbuildingtheskillintothetool,incontrasttothetoolpathconstrainingskillbeinginthepersonwhowieldsthetool.Asanexample,itisphysicallypossibletomakeinterchangeablescrews,bolts,andnutsentirelywithfreehandtoolpaths.Butitiseconomicallypracticaltomakethemonlywithmachinetools.Inthe1930s,theU.S.NationalBureauofEconomicResearchNBERreferencedthedefinitionofamachinetoolasanymachineoperatingbyotherthanhandpowerwhichemploysatooltoworkonmetal.2Thenarrowestcolloquialsenseofthetermreservesitonlyformachinesthatperformmetalcuttinginotherwords,themanykindsofconventionalmachiningandgrinding.Theseprocessesareatypeofdeformationthatproducesswirls.However,economistsuseaslightlybroadersensethatalsoincludesmetaldeformationofothertypesthatsqueezethemetalintoshapewithoutcuttingoffscarf,suchasrolling,stampingwithdies,shearing,swaging,riveting,andothers.Thuspressesareusuallyincludedintheeconomicdefinitionofmachinetools.Forexample,thisisthebreadthofdefinitionusedbyMaxHollandinhishistoryofBurgomasterandLoudhailer,whichisalsoahistoryofthemachinetoolindustryingeneralfromthe1940sthroughthe1980shewasreflectingthesenseofthetermusedbyHoltvilleitselfandotherfirmsintheindustry.Manyreportsonmachinetoolexportandimportandsimilareconomictopicsusethisbroaderdefinition.Thecolloquialsenseimplyingconventionalmetalcuttingisalsogrowingobsoletebecauseofchangingtechnologyoverthedecades.Themanymorerecentlydevelopedprocesseslabeledmachining,suchaselectricaldischargemachining,electrochemicalmachining,electronbeammachining,photochemicalmachining,andultrasonicmachining,orevenplasmacuttingandwaterjetcutting,areoftenperformedbymachinesthatcouldmostlogicallybecalledmachinetools.Inaddition,someofthenewlydevelopedadditivemanufacturingprocesses,whicharenotaboutcuttingawaymaterialbutratheraboutaddingit,aredonebymachinesthatarelikelytoenduplabeled,insomecases,asmachinetools.Thenaturallanguageuseofthetermsvaries,withsubtleconnotativeboundaries.Manyspeakersresistusingthetermmachinetooltorefertowoodworkingmachineryjoiners,tablesaws,routingstations,andsoon,butitisdifficulttomaintainanytruelogicaldividingline,andthereforemanyspeakersarefinewithabroaddefinition.Itiscommontohearmachinistsrefertotheirmachinetoolssimplyasmachines.Usuallythemassnounmachineryencompassesthem,butsometimesitisusedtoimplyonlythosemachinesthatarebeingexcludedfromthedefinitionofmachinetool.Thisiswhythemachinesinafoodprocessingplant,suchasconveyors,mixers,vessels,dividers,andsoon,maybelabeledmachinery,whilethemachinesinthefactorystoolanddiedepartmentareinsteadcalledmachinetoolsincontradistinction.Asforthe1930sNBERdefinitionquotedabove,onecouldarguethatitsspecificitytometalisobsolete,asitisquitecommontodayforparticularlathes,millingmachines,andmachiningcentersdefinitelymachinetoolstoworkexclusivelyonplasticcuttingjobsthroughouttheirwholeworkinglifespan.ThustheNBERdefinitionabovecouldbeexpandedtosaywhichemploysatooltoworkonmetalorothermaterialsofhighhardness.Anditsspecificitytooperatingbyotherthanhandpowerisalsoproblematic,asmachinetoolscanbepoweredbypeopleifappropriatelysetup,suchaswithatreadleforalatheorahandleverforashaper.Handpoweredshapersareclearlythesamethingasshaperswithelectricmotorsexceptsmaller,anditistrivialtopoweramicrolathewithahandcrankedbeltpulleyinsteadofanelectricmotor.Thusonecanquestionwhetherpowersourceistrulyakeydistinguishingconceptbutforeconomicspurposes,theNybergsdefinitionmadesense,becausemostofthecommercialvalueoftheexistenceofmachinetoolscomesaboutviathosethatarepoweredbyelectricity,hydraulics,andsoon.Sucharethevagariesofnaturallanguageandcontrolledvocabulary,bothofwhichhavetheirplacesinthebusinessworld.AutomaticcontrolMachinetoolscanbeoperatedmanually,orunderautomaticcontrol.Earlymachinesusedflywheelstostabilizetheirmotionandhadcomplexsystemsofgearsandleverstocontrolthemachineandthepiecebeingworkedon.SoonafterWorldWarII,thenumericalcontrolNCmachinewasdeveloped.NCmachinesusedaseriesofnumberspunchedonpapertapeorpunchedcardstocontroltheirmotion.Inthe1960s,computerswereaddedtogiveevenmoreflexibilitytotheprocess.SuchmachinesbecameknownascomputerizednumericalcontrolCNCmachines.NCandCNCmachinescouldpreciselyrepeatsequencesoverandover,andcouldproducemuchmorecomplexpiecesthaneventhemostskilledtooloperators.Beforelong,themachinescouldautomaticallychangethespecificcuttingandshapingtoolsthatwerebeingused.Forexample,adrillmachinemightcontainamagazinewithavarietyofdrillbitsforproducingholesofvarioussizes.Previously,eithermachineoperatorswouldusuallyhavetomanuallychangethebitormovetheworkpiecetoanotherstationtoperformthesedifferentoperations.Thenextlogicalstepwastocombineseveraldifferentmachinetoolstogether,allundercomputercontrol.Theseareknownasmachiningcenters,andhavedramaticallychangedthewaypartsaremade.Fromthesimplesttothemostcomplex,mostmachinetoolsarecapableofatleastpartialselfreplication,andproducemachinepartsastheirprimaryfunction