数控机床与原理外文翻译文献.docx
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数控机床与原理外文翻译文献.docx
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数控机床与原理外文翻译文献
数控机床与原理外文翻译文献
(文档含中英文对照即英文原文和中文翻译)
FundamentalsNumbercalControlofmachinetools
MachineTools
Machinetoolsaremachinesforcuttingmetals.Themostimportantofmetalusedinindustryarelathes,drillingmachinesandmillingmachines.Otherkindsofmetalworkingmachinesarenotsowidelyusedinmachiningmetalsasthesethree.
Drillingisperfurmedwitharotatingtoolcalledadrill.Mostdrillinginmetaldonewithatwistdrill.Themachineusedfordrillingiscalledadrillpress.Operationssuchasreamingandtapping,arealsoclassifiedasdrilling.Reamingconsistsofremovingasmallamountofmetalfromaholealreadydrilled.
Tappingistheprocessofcuttingathreadinsideaholesothatacapscreworboltmaybethreadedintoit.
Thelatheiscommonlycalledthefatheroftheentiremachinetoolfamily.Forturningoperations,thelatheusedasingle-point-cuttingtool,whichremovemetalasittravelspasttherevolvingworkpiece.Turningoperationsarerequiredtomakemanydifferentcylindricalshapes,suchasaxes,gearblanks,pulleys,andthreadedshafts.
Boringoperationsareperformedtoenlarge,finish,andaccuratelylocateholes.
Milingremovesmetalwitharevolving,multiplecuttingedgetoolscalledmilingcutter.Milingcutteraremadeinmanystylesandsizes.Somehaveasfewastwocuttingedgesandothershave30ormore.Milingcanproduceflatorangledsurfaces,grooves,slots,gearteeth,andotherprofile,dependingontheshapeofthecuttersbeingused.
Shapingandplanningproduceflatsurfaceswithasingle-point-cuttingtool.Inshaping,thecuttingtoolonashaperreciprocatesormovesbackandforthwhiletheworkisfedautomaticallytowardsthetool.Inplanning,theworkpieceisattachedtoaworktablethatreciprocatespastthecuttingtool.Thecuttingtoolisautomaticallyfedintotheworkpieceasmallamountoneachstroke.
Grindingmakesuseofabrasiveparticlestodothecutting.Grindingoperationsmaybeclassifiedasprecisionornon-precision,dependingonthepurpose.Precisiongrindingisconcernedwithgrindingtoclosetolerancesandverysmoothfinish.Non-precisiongrindinginvolvestheremovalofmetalwhereaccuracyisnotimportant.
FundamentalsNumberControl
Controllingamachinetoolbymeansofapreparedprogramisknownasnumericalcontrol,orNC.NCequipmenthasbeendefinedtheElectronicIndustriesAssociation(EIA)as“Asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.Thesystemmustautomaticallyinterpretatleastsomeportionofthisdata.”
InatypicalNCsystemthenumericaldatawhichisrequiredforproducingapartismaintainedonapunchedtapeandiscalledthepartprogram.Thepartprogramisarrangedintheformofblockofinformation,whereeachblockcontainsthenumericaldatarequiredtoproduceonesegmentoftheworkpiece.Thepunchedtapeismovedforwardbyoneblockeachtimethecuttingofasegmentiscompleted.Thepunchedcontains,incodedform,alltheinformationneededforprocessingasegmentoftheworkpiece:
thesegmentlength,itscuttingspeed,feed,etc..Dimensionalinformation(lenth,width,andradiiofcircles)andthecontourform(linear,circular,orother)aretakenformanengineeringdrawing.Dimensionsaregivenseparatelyforeachaxisofmotion(x,y,etc.).Cuttingspeed,feedrate,andauxiliaryfunction(coolantonandoff,spindledirection,clamp,gearchange,etc.)areprogrammedaccordingtosurfacefinishandtoleracerequirements.
PreparingthepartprogramforaNCmachinetoolrequiresapartprogrammer.Thepartprogrammermustpossessknowledgeandexperiencesinmechanicalengineering.PartProgrammersmustbefamiliarwiththefunctionofNCmachinetoolsandmachiningprocessandhavetodecideontheoptimalsequenceofoperations.
InNCmachinetoolseachaxisofmotionisequippedwithaseparatedrivingdevicewhichreplacesthehandwheeloftheconventionalmachine.Thedrivingdevicemaybeadirectcurrent(DC)motor,ahydraulicactuator,orasteppingmotor.Thetypeselectedisdeterminedmainlybythepowerrequirementofthemachine.
TheNCmachinetoolsystemcontainsthemachinecontrolunit(MCU)andthemachinetoolitself.TheMCUhastoreadanddecodethepartprogram,toprovidethedecodedinstructionstothecontrolloopsofthemachineaxesofmotion,andtocontrolthemachinetooloperation.
TheMCUconsistsoftwomainunits:
thedataprocessingunit(DPU)andthecontrolloopsunti(CLU).ThefunctionoftheDPUistodecodetheinformationreceivedformthetape,processitandprovidedatatotheDLU.Suchdatacontainsthenewrequiredpositionofeachaxis,itsdirectionofmotionandvelocity,andauxiliarycontrolsignalstorelays.Ontheotherhand,theCLUprovidesasignalannouncingthatthepreviousiscompletedandthattheDPUcanreadanewblockofthepartprogram.TheCLUoperatesthedrivesattachedofthemachinelead-screwsandreceivesfeedbacksignalsontheactualpositionandvelocityofeachoneoftheaxes.Eachlead-screwisequippedwithaseparatedrivingdeviceanfaseparatefeedbackdevice,butthelatterexistsonlyinaclosed-loopsystem.
InCNCsystem,theDPUfunctionsareperformedbythecontrolprogramcontainedintheCNCcomputer.ThemajorpartoftheCLU,however,isalwaysimplementedinthemostsophisticatedCNCsystem.
NumbericalControlofMachiningProcess
Numbericalcontrolofmachinetoolsbycomputershasgreatadvanceinrecentyears.Generally,automaticmachinetoolsareefficientandaccuratewhenlargequantitiesofpartsofthesameshapearerequired,butchangingfromoneautomaticcycletoanotherisalongandexpensiveprocessandwouldonlybecarriedoutforalongrun.Buttherearemanyexampleswhenonlyafewpartsarerequiredanditisinsuchworkthatthecomputer-controlledmachineisvaluable.
Therearetwotypesofcomputers-digitalandanalogue.Adigitalcomputerworkswithnumbersgivenindigitalform,adigitbeingoneofacertainsetofsymbolsusedtoshownumbers.Itisthedigitalcomputerwhichisusedinelectronicdataprocessing.Theanaloguecomputerisbasedonananalogyofquantity.Itdealswithphysicalquantitiesandnotnumbers.
Inadigitalcontrolsysteminformationformadrawingisputonadiscwhichisputintoacomputerwhichcomputersfromtheinformationtothecontinuousmotionofthecuttingtool.Theoutputisputonadiscwhichisputintothemachinetoolcontroluntilwhenrequired.Onecomputerservicesanumberofmachines.Disccanbestoredandusedanynumberoftimesinfuturecases,simplybyreplayingthemifthesamepartsarewantedagain.Forbestresult,theelectronicequipmentandthemachinetoolmustbedesignedtogether.
Thismethodhasalsobeenappliedtothecontrolofoxygencuttingofsteelplates.Whenirregularshapesarerequired,asinshipbuilding,ithasbeenthepracticetomakeamodelandtofollowitsoutlinebyhandcontrol,amethodwhichdoesnotalwaysgiveaccuateresults.Again,informationisprocessedbyaspecialcomputerwhichthenpreparesadiscforuseinthecontrolconsoleofthecuttingmachine.Withthisdiscthemachinecanautomaticallycutplatesofcomplicatedshapesveryaccurately.Thisdevelopmenthasparticularimportanceformakingsteelplatesandisagoodexampleofautomationappliedtobatchproduction.
ProgrammingforNC
AprogramfornumericalconsistsofasequenceofdirectionsthatcausedaNCmachinetocarryoutacertainoperation,machiningbeingthemostcommonlyusedprocess.ProgrammingforNCmaybedonebyaninternalprogrammingdepartment,ontheshopfloor,orpurchasedfromanoutsidesource.Also,programmingmaybedonemanuallyorwithcomputerassistance.
Theprogramcontainsinstructionsandcommands.Geometicinstructionspertaintorelativemovementbetweenthetoolandtheworkpiece.Processinginstructionspertaintospindlespeeds,feed,tools,andsoon.Travelinstructionspertaintothetypeofinterpolationandsloworrapidmovementsofthetoolorworktable.Switchingcommandspertaintoon/offpositionforcoolantsupplies,spindlerotation,directionofspindlerotation,toolchange,workpiecefeeding,clamping,andsoon.
(1)Manualprogramming.Manualpartprogrammingconsistsoffirstcalculatingdimensionalrelationshipsofthetool,workpiece,andworktable,basedontheengineeringdrawingsofthepart,andmanufacturingoperationstobeperformedandtheirsequence.Aprogramsheetisthenprepared,whichconsistsofthenecessaryinformationtocarryouttheoperation,suchascuttingtools,spindlespeeds,feeds,depthofcut,cuttingfluids,power,andtoolorworkpiecerelativepositionsandmovements.Basedonthisinformation,thepartprogramisprepared.Usuallyapapertapeisfirstpreparedfortryingoutanddebuggingtheprogram.Dependingonhowoftenitistobeused,thetapemaybemadeofmoredurablemylar.
Someonekonledgeableabouttheparticarprocessandabletounderstand,read,andchangepartprogramscandomanualprogramming.Becausetheyarefamiliarwithmachinetoolandprocesscapabilities,skilledmachinistscandomanualprogrammingwithsometraininginprogramming,however,theworkistedious,andtimeconsuming,anduneconomicalandisusedmostlyinsimplepointto-pointapplications.
(2)Computer-AidedProgramming.Computer-aidedpartprogramminginvolvesspecialsymbolicprogramminglanguagesthatdeterminethecoordinatepointsofcorners,edges,andsurfacesofthepart.Becausenumericalcontrolinvolvestheinsertionofdataconcerningworkpiecematerialsandprocessingparameters,programmingmustbedonebyoperatorsorprogrammerswhoareknowledgeableaboutther
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