数控技术数控编程外文翻译中英文翻译外文文献翻译Word文档格式.docx

数控技术数控编程外文翻译中英文翻译外文文献翻译Word文档格式.docx

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NumericalControl（NC）isanymachiningprocessinwhichtheoperationsareexecutedautomaticallyinsequencesasspecifiedbytheprogramthatcontainstheinformationforthetoolmovements.TheNCconceptwasproposedinthelate1940sbyJohnParsonsofTraverseCity,Michigan.Parsonsrecommendedamethodofautomaticmachinecontrolthatwouldguideamillingcuttertoproducea"

thru-axiscurve"

inordertogeneratesmoothprofilesonworkpieces.

In1949,TheU.S.AirForceawardedParsonsacontracttodevelopanewtypeofmachinetoolthatwouldbeabletospeedupproductionmethods.ParsonscommissionedtheMassachusettsInstituteofTechnology（M.I.T.）todevelopapracticalimplementationofhisconcept.ScientistsandengineersatM.I.T.builtacontrolsystemforatwo-axismillingmachinethatusedaperforatedpapertapeastheinputmedia.Inashortperiodoftime,allmajormachinetoolmanufacturerswereproducingsomemachineswithNC,butitwasnotuntilthelate1970sthatcomputer-basedNCbecamewidelyused.NCmaturedasanautomationtechnologywheninexpensiveandpowerfulmicroprocessorsreplacedhard-wirelogic-makingcomputer-basedNCsystems.

WhenNumericalControlisperformedundercomputersupervision,itiscalledComputerNumericalControl（CNC）.ComputersarethecontrolunitsofCNCmachines,theyarebuiltinorlinkedtothemachinesviacommunicationschannels.Whenaprogrammerinputsomeinformationintheprogrambytapeandsoon,thecomputercalculatesallnecessarydatatogetthejobdone.

OnthefirstNumericallyControlled（NC）machineswerecontrolledbytape,and

becauseofthat,theNCsystemswereknownastape-controlledmachines.Theywereabletocontrolasingleoperationenteredintothemachinebypunchedormagnetictape.Therewasnopossibilityofeditingtheprogramonthemachine.Tochangetheprogram,anewtapehadtobemade.

Today'

ssystemshavecomputerstocontroldata;

theyarecalledComputerNumericallyControlled（CNC）machines.ForbothNCandCNCsystems,workprinciplesarethesame.Onlythewayinwhichtheexecutioniscontrolledisdifferent.Normally,newsystemsarefaster,morepowerful,andmoreversatile

TheApplicationsofNC/CNC

Sinceitsintroduction,NCtechnologyhasfoundmanyapplications,includinglathesandturningCenters,millingmachinesandmachiningcenters,punches,electricaldischargmachines（EDM）Flamecutters,grinders,andinspectionequipment.themostcomplexCNCmachinetoolsaretheturningcenter,showninFig.4-1（Amodernturningcenterwithaten-stationturretthatacceptsquick-changtools.EachtoolcanbepositionedinSecondswiththepressofabutton）.AndthemachinecentershowninFig.4-2（Verticalmachiningcenter,thetoolmagazineisonthemachine.thecontrolpanelontherightcanbeswiveledbytheoperator）andFig.4-3（horizontalmachiningcenter,equippedwithanautomatictoolchanger.toolmagazinescanstore200cttingtools.

Whenpreparingaprogamforaparticularoperation,theprommermustselectallcuttingdatausingrecommendationsforconventionalmachining.thisincludesproper

Selectionofcuttingspeeds,feedrate,toolsandtoolgeometry,andsoon.whentheprogrammerhaschosenallofthenecessaryinformationproperly,theoperatorloadstheprogrammeintothemachineandpressesabuttontostartthecuttingcrycle.theCNCmachinemovesautomaticallyfromonemachingoperationtoanother,changingthecuttingtolsandapplyingthecoolent.inasurprisinglyshorttime,theworkpieceis

Machinedaccordingtothehighestqualitystangards.Butthatisnotall.nomatterhowbigtheworkseriesis,allofthepartswillbealmostidenticalinsizeandsurfacefinishing.Atthistimeofadvancedtechnology,withitshighdemandsforsurfacefinishingandtolerancesofcomponentsin,forexample,aerospace,nuclear,andmedicalequipmentmanufacturing,onlyCNCmachinesprovidesuccessfulresults.

Numericalcontrol（NC）isaformofprogrammableautomationinwhichtheprocessingequipmentiscontrolledbymeansofnumbers,letters,andothersymbols.Thenumbers,letters,andsymbolsarecodedinanappropriateformattodefineaprogramofinstructionsforaparticularworkpartorjob.Theinstructionsareprovidedbyeitherofthetwobinarycodeddecimalsystems:

theElectronicIndustriesAssociation（EIA）code,ortheAmericanStandardCodeforInformationInterchange（ASCII）.ASCII-codedmachinecontrolunitswillnotaccept.EIAcodedinstructionsandviceversa.Increasingly,however,controlunitsarebeingmadetoacceptinstructionsineithercode.121AutomationoperationbyNCisreadilyadaptabletothe

operationofallmetalworkingmachines.Lathes,millingmachines,drillpresses,boringmachines,grindingmachines,turretpunches,flameorwire-cuttingandweldingmachines,andevenpipebendersareavailablewithnumericalcontrols.

BasicComponentsofNC

Anumericalcontrolsystemconsistsofthefollowingthreebasiccomponents:

（1）Programinstructions

（2）Machinecontrolunit

（3）Processingequipment

Theprograminstructionsarethedetailedstepbystepcommandsthatdirecttheprocessingequipment.[31Initsmostcommonform,thecommandsrefertopositionsofamachinetoolspindlewithrespecttotheworktableonwhichthepartisfixtured.Moreadvancedinstructionsincludeselectionofspindlespeeds,cuttingtools,andotherfunctions.

Themachinecontrolunit（MCU）consistsoftheelectronicsandcontrolhardwarethatreadsandinterpretstheprogramofinstructionsandconvertitintomechanicalactionsofthemachinetoolorotherprocessingequipment.

Theprocessingequipmentisthecomponentthatperformsmetalprocess.Inthemostcommonexampleofnumericalcontrol,itisusedtoperformmachiningoperations.Theprocess-ingequipmentconsistsoftheworktableandspindleaswellasthemotorsandcontrolsneededtodrivethem.

TypesofNC

Therearetwobasictypesofnumericalcontrolsystems:

pointtopointandcontouring.

Pointtopointcontrolsystem,alsocalledpositioning,issimplerthancontouringcontrolsystem.Itsprimarypurposeistomoveatoolorworkpiecefromoneprogrammedpointtoanother.Usuallythemachinefunction,suchasadrillingoperation,isalsoactivatedateachpointbycommandfromtheNCprogram.Pointtopointsystemsaresuitableforholemachiningoperationssuchasdrilling,countersinking,couterbofing,reaming,boringandtapping.Holepunchingmachines,spotweldingmachines,andassemblymachinesalsousepointtopointNCsystems.

Contouringsystem,alsoknownasthecontinuouspathsystem,positioningandcuttingoperationsarebothalongcontrolledpathsbutatdifferentvelocities.Becausethetoolcutsasittravelsalongaprescribedpath,accuratecontrolandsynchronizationofvelocitiesandmovementsareimportant.Thecontouringsystemisusedonlathes,millingmachines,grinders,incrementally,byoneofseveralbasicmethods.ThereareanumberofinterpolationschemesthathavebeendevelopedtodealwiththevariousproblemsthatareencounteredingeneratingasmoothcontinuouspathwithacontouringtypeNCsystem.Theyincludelinearinterpolation,circularinterpolation,helicalinterpolation,parabolicinterpolationandcubicinterpolation.Inallinterpolations,thepathcontrolledisthatofthecenterofrotationofthetool.Compensationfordifferenttools,differentdiametertools,ortoolswearduringmachining,canbemadeintheNC.

ProgrammingforNC

AprogramfornumericalcontrolconsistsofasequenceofdirectionsthatcausesanNCmachinetocarryoutacertainoperation,machiningbeingthemostcommonlyusedprocess.ProgrammingforNCmaybedonebyaninternalprogrammingdepartment,ontheshopfloor,orpurchasedfromanoutsidesource.Also,programmingmaybedonemanuallyorwithcomputerassistance.

Theprogramcontainsinstructionsandcommands.Geometricinstructionspertaintorelativemovementsbetweenthetoolandtheworkpiece.Processinginstructionspertaintospindlespeeds,feeds,tools,andsoon.Travelinstructionspertaintothetypeofinterpolationandsloworrapidmovementsofthetoolorworktable.Switchingcommandspertaintoon/offpositionforcoolantsupplies,spindlerotation,directionofspindlerotation,toolchanges,workpiecefeeding,clamping,andsoon.ThefirstNCprogramminglanguagewasdevelopedbyMITdevelopmentalworkonNCprogrammingsystemsinthelate1950sandcalledAPT（AutomaticallyProgrammedTools）.

DNCandCNC

Thedevelopmentofnumericalcontrolwasasignificantachievementinbatchandjobshopmanufacturing,frombothatechnologicalandacommercialviewpoint.TherehavebeentwoenhancementsandextensionsofNCtechnology,including:

（1）Directnumericalcontrol

（2）Computernumericalcontrol

Directnumericalcontrolcanbedefinedasamanufacturingsysteminwhichanumberofmachinesarecontrolledbyacomputerthroughdirectconnectionandinrealtime.ThetapereaderisomittedinDNC,thusrelievingthesystemofitsleastreliablecomponent.Insteadofusingthetapereader,thepartprogramistransmittedtothemachinetooldirectlyfromthecomputermemory.Inprinciple,onecomputercanbeusedtocontrolmorethan100separatemachines.（OnecommercialDNCsystemduringthe1970sboastedacontrolcapabilityofupto256machinetools.）TheDNCcomputerisdesignedtoprovideinstructionstoeachmachinetoolondemand.Whenthemachineneedscontrolcommands,theyarecommunicatedtoitimmediately.

SincetheintroductionofDNC,therehavebeendramaticadvancesincomputertechnology.Thephysicalsizeandcostofadigitalcomputerhasbeensignificantlyreducedatth