数控外文翻译.doc
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数控外文翻译.doc
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NumericalControl
Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).PriortotheadventofNC,allmachinetoolsweremanualoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanthelimitationofoperatorskills.Withmanualcontrol,thequalityoftheproductisdirectlyrelatedtoandlimitedtotheskillsoftheoperator.Numericalcontrolrepresentsthefirstmajorstepawayfromhumancontrolofmachinetools.
Numericalcontrolmeansthecontrolofmachinetoolsandothermanufacturingsystemsthoughtheuseofprerecorded,writtensymbolicinstructions.Ratherthanoperatingamachinetool,anNCtechnicianwritesaprogramthatissuesoperationalinstructionstothemachinetool,Foramachinetooltobenumericallycontrolled,itmustbeinterfacedwithadeviceforacceptinganddecodingthep2ogrammedinstructions,knownasareader.
Numericalcontrolwasdevelopedtoovercomethelimitationofhumanoperator,andithasdoneso.Numericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveralotherinnovationsinmanufacturingtechnology:
1.Electricaldischargemachining.
2.Lasercutting.
3.Electronbeamwelding.
Numericalcontrolhasalsomademachinetoolsmoreversatilethantheirmanuallyoperatedpredecessors.AnNCmachinetoolcanautomaticallyproduceawidevarietyofpar4s,eachinvolvinganassortmentofundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetoolsandprocesses.
Likesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.SAirForce.Initsearlieststages,NCmachineswereabletomakestraightcutsefficientlyandeffectively.
However,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorteristhestraightlinesmakingupthestep,thesmootheris4hecurve.Eachlinesegmentinthestepshadtobecalculated.
Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)languageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.TheoriginalNCsystemwerevastlydifferentfromthoseusedpunchedpaper,whichwaslatertoreplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.Together,all/fthisrepresentedgiantstepforwardinthecontrolofmachinetools.However,therewereanumberofproblemswithNCatthispointinitsdevelopment.
Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapercontainingtheprogrammedinstructionstobreakortearduringamachiningprocess,Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtorerunthoughtthereader.Ifitwasnecessarytoproduce100copiesofagivenpart,itwasalsonecessarytorunthepapertapethoughtthereader100separatetimes.Fragilepapertapessimplycouldnotwithstandtherigorsofshopfloorenvironmentandthiskindofrepeateduse.
Thisledtothedevelopmentofaspecialmagnetictape.Whereasthepapertapecarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theThismostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Tomakeeventhemostminoradjustmentsinaprogramofinstructions,itwasnecessarytointerruptmachiningoperationsandmakeanewtape.Itwasalsostillnecessarytorunthetapethoughtthereaderasmanytimesastherewerepartstobeproduced.Fortunately,computertechnologybecomearealityandsoonsolvedtheproblemsofNC,associatedwithpunchedpaperandplastictape.
Thedevelopmentofaconceptknownasnumericalcontrol(DNC)solvethepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputerandfedtothemachinetoolasneededviathedatatransmissionlinkage.Directnumericalcontrolrepresentedamajorstepforwardoverpunchedtapeandplastictape.Ho
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