数字控制 外文文献 外文翻译 英文文献.docx

数字控制 外文文献 外文翻译 英文文献.docx

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数字控制外文文献外文翻译英文文献

NCandCNC

NumericalControl（NC）isanymachiningprocessinwhichtheoperationsareexecutedautomaticallyinsequencesasspecifiedbytheprogramthatcontainstheinformationforthetoolmovements.WhenNCisperformedundercomputersupervision,itiscalledComputerNumericalControl（CNC）.ForbothNCandCNCsystems,workprinciplesarethesame.Onlythewayinwhichtheexecutioniscontrolledisdifferent.Normally,newsystemsarefaster,morepowerful,andmoreversatile.

1.MachinesUsingNC

Earlymachinetoolswereoperatedbycraftsmenwhodecidedmanyvariablessuchasspeeds,feeds,anddepthofcut,etc.Withthedevelopmentofscienceandtechnology,anewterm,NumericalControl（NC）appeared.ControllingamachinetoolusingapunchedtapeorstoredprogramisknownasNumericalControl.NChasbeendefinedbytheElectronicIndustriesAssociation（EIA）as“Asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.Thesystemmustautomaticallyinterpretatleastsomeportionofthisdata.”

Inthepast,machinetoolswerekeptassimpleaspossibleinordertokeeptheircostsdown.Becauseoftheever-risingcostoflabor,bettermachinetools,completewithelectroniccontrols,weredevelopedsothatindustrycouldproducemoreandbetterproductsatpricesthatwerecompetitivewiththoseoffshoreindustries.

NCisbeingusedonalltypesofmachinetoolsfromthesimplesttothemostcomplex.Themostcommonmachinetoolsarethesingle-spindledrillingmachine,lathe,millingmachine,turningcenter,andmachiningcenter.

1.1.Single-SpindleDrillingMachine

Oneofthesimplestnumericallycontrolledmachinetoolsisthesingle-spindledrillingmachine.Mostdrillingmachinesareprogrammedonthreeaxes:

a.TheX-axiscontrolsthetablemovementtotherightorleft.

b.TheY-axiscontrolsthetablemovementtowardorawayfromthecolumn.

c.TheZ-axiscontrolstheupordownmovementofthespindletodrillholestodepth.

1.2.Lathe

Theenginelathe,oneofthemostproductivemachinetools,hasbeenaveryefficientmeansofproducingroundparts.Mostlathesareprogrammedontwoaxes:

a.TheX-axiscontrolsthecrossmotion（inorout）ofthecuttingtool.

b.TheZ-axiscontrolsthecarriagetraveltowardorawayfromtheheadstock.

1.3.MillingMachine

Themillingmachinehasalwaysbeenoneofthemostversatilemachinetoolsusedinindustry.Operationssuchasmilling,contouring,gearcutting,drilling,boringandreamingareonlyafewofthemanyoperationsthatcanbeperformedonamillingmachine.Themillingmachinecanbeprogrammedonthreeaxes:

a.TheX-axiscontrolsthetablemovementtotherightorleft.

b.TheY-axiscontrolsthetablemovementtowardorawayfromthecolumn.

c.TheZ-axiscontrolsthevertical（upanddown）movementofthekneeorspindle.

1.4.TurningCenter

TurningCentersweredevelopedinthemid-1960safterstudiesshowedthatabout40percentofallmetalcuttingoperationswereperformedonlathes.Thesenumericallycontrolledmachinesarecapableofgreateraccuracyandhigherproductionratesthantheenginelathe.Thebasicturningcenteroperatesononlytwoaxes:

a.TheX-axiscontrolsthecrossmotionoftheturrethead.

b.TheZ-axiscontrolsthelengthwisetravel（towardorawayfromtheheadstock）oftheturrethead.

1.5.MachiningCenter

Machiningcentersweredevelopedinthe1960ssothatapartdidnothavetobemovedfrommachinetomachineinordertoperformvariousoperations.Thesemachinesgreatlyincreasedproductionratesbecausemoreoperationscouldbeperformedonawork-pieceinonesetup.Therearetwomaintypesofmachiningcenters,thehorizontalandtheverticalspindletypes.

a.Thehorizontalspindle-machiningcenteroperatesonthreeaxes:

（a）TheX-axiscontrolsthetablemovementtotherightorleft.

（b）TheY-axiscontrolstheverticalmovement（upanddown）ofthespindle.

（c）TheZ-axiscontrolsthehorizontalmovement（inorout）ofthespindle.

b.Theverticalspindle-machiningcenteroperatesonthreeaxes:

（a）TheX-axiscontrolsthetablemovementtotherightorleft.

（b）TheY-axiscontrolsthetablemovementtowardorawayfromthecolumn.

（c）TheZ-axiscontrolstheverticalmovement（upanddown）ofthespindle.

2.ProgrammingforNC

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

Theprogramcontainsinstructionsandcommands.Geometricinstructionspertaintorelativemovementsbetweenthetoolandthework-piece.Processinginstructionspertaintospindlespeeds,feeds,tools,andsoon.Travelinstructionspertaintothetypeofinterpolationandsloworrapidmovementsofthetoolsorworktables.Switchingcommandspertaintoon/offpositionforcoolantsupplies,spindlerotation,directionofspindlerotation,toolchanges,work-piecefeeding,clampingandsoon.

1.Manualprogramming.Manualpartprogrammingconsistsoffirstcalculatingdimensionalrelationshipsofthetool,work-pieceandworktablebasedontheengineeringdrawingsofthepart,andmanufacturingoperationstobeperformedandtheirsequence.Aprogramsheetisthenprepared,whichconsistsofthenecessaryinformationtocarryouttheoperation,suchascuttingtools,spindletools,feeds,depthofcut,cuttingfluids,power,andtoolorwork-piecerelativepositionsandmovements.Basedonthisinformation,thepartprogramisprepared.Usuallyapapertapeisfirstpreparedfortypingoutanddebuggingtheprogram.Dependingonhowoftenitistobeused,thetapemaybemadeofmoredurablemylar.

Someoneknowledgeableabouttheparticularprocessandabletounderstand,read,andchangepartprogramscandomanualprogramming.Becausetheyarefamiliarwithmachinetoolsandprocesscapabilities,skilledmachinistscandomanualprogrammingwithsometraininginprogramming,however,theworkistedious,timeconsuming,anduneconomicalandisusedmostlyinsimplepoint-to-pointapplications.

2.Computer-aidedProgramming.Computer-aidedpartprogramminginvolvesspecialsymbolicprogramminglanguagesthatdeterminethecoordinatepointsofcorners,edges,andsurfacesofthepart.Becausenumericalcontrolinvolvestheinsertionofdataconcerningwork-piecematerialsandprocessingparameters,programmingmustbedonebyoperatorsorprogrammerswhoareknowledgeableabouttherelevantaspectsofthemanufacturingprocessesbeingused.Beforeproductionbegins,programsshouldbeverified,eitherbyviewingasimulationoftheprocessiononaCRTscreenorbymakingthepartfromaninexpensivematerial,suchasaluminum,wood,orplastic,ratherthanthematerialspecifiedforthefinishedparts.3.CNC

WhenNumericalControlisperformedundercomputersupervision,itiscalledComputerNumericalControl（CNC）.ComputersarethecontrolunitsofCNCmachines.Theyarebuiltinorlinkedtothemachinesviacommunicationschannels.Whenaprogrammerinputssomeinformationintheprogrambytapeandsoon,thecomputercalculatesallnecessarydatatogetthejobdone.

Today’ssystemshavecomputerscontroldata,sotheyarecalledComputerNumericallyControlledMachines.ForbothNCandCNCsystems,workprinciplesarethesame.Onlythewayinwhichtheexecutioniscontrolledisdifferent.Normally,newsystemsarefaster,morepowerful,andmoreversatileunit.

TheConstructionofCNCMachines

CNCmachinetoolsarecomplexassemblies.However,ingeneral,anyCNCmachinetoolconsistsofthefollowingunits:

computers,controlsystems,drivemotorsandtoolchangers.

AccordingtotheconstructionofCNCmachinetools,CNCmachinesworkinthefollowingmanner:

（1）TheCNCmachinelanguage,whichisaprogramminglanguageofbinarynotationusedoncomputers,isnotusedonCNCmachines.

（2）Whentheoperatorstartstheexecutioncycle,thecomputertranslatesbinarycodesintoelectronicpulsesthatareautomaticallysenttothemachine’spowerunits.Thecontrolunitscomparethenumberofpulsessentandreceived.

（3）Whenthemotorsreceiveeachpulse,theyautomaticallytransformthepulsesintorotationsthatdrivethespindleandleadscrew,causingthespindlerotationandslideortablemovement.Thepartonthemillingmachinetableorthetoolinthelatheturretisdriventothepositionspecifiedbytheprogram.

CNCmachineshavemanyadvantagesoverconventionalmachines,someofthemare:

（1）Thereisapossibilityofperformingmultipleoperationsonthesamemachineinsomesetup.

（2）ThescraprateissignificantlyreducedbecauseoftheprecisionoftheCNCmachineandlesseroperatorimpact.

（3）ItiseasytoincorporatepartdesignchangeswhenCAD/CAMsystemareused.

（4）Productionissignificantlyincreased.

（5）Itiseasiertoperformqualityassurancebyaspot-checkinsteadofcheckingallparts.

（6）Becauseofthepossibilityofsimultaneousmuti-axistoolmovement,specialprofiletoolsarenotnecessarytocutunusualpartshapes.

3.1.Computers

Aswithallcomputers,theCNCmachinecomputerworksonbinaryprincipleusingonlytwocharacters1and0,forinformationprocessingprecisetimeimpulsesfromthecircuit.Therearetwostates,astatewithvoltage,1,andastatewithoutvoltage,0.Seriesofonesandzeroesaretheonlystatesthatthecomputerdistinguishesarecalledmachinelanguage,anditistheonlylanguagethecomputerunderstands.Whencreatingtheprogram,theprogramm