數(shù)控機床與原理外文翻譯文獻

數(shù)控機床與原理外文翻譯文獻數(shù)控機床與原理外文翻譯文獻(文檔含中英文對照即英文原文和中文翻譯)FundamentalsNumbercalControlofmachinetoolsMachineToolsMachinetoolsaremachinesforcuttingmetals.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.FundamentalsNumberControlControllingamachinetoolbymeansofapreparedprogramisknownasnumericalcontrol,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.NumbericalControlofMachiningProcessNumbericalcontrolofmachinetoolsbycomputershasgreatadvanceinrecentyears.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.ProgrammingforNCAprogramfornumericalconsistsofasequenceofdirectionsthatcausedaNCmachinetocarryoutacertainoperation,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,programmingmustbedonebyoperatorsorprogrammerswhoareknowledgeableabouttherelevantaspectsofthemanufacturingprocessesbeingused.Beforeproductionbegins,programsshouldbeverified,eitherbyviewingasimulationoftheprocessiononaCRTscreenorbymakingthepartfromaninexpensivematerial,suchasaluminum,wood,orplastic,ratherthanthematerialspecifiedforthefinishedpart.MachiningCenterTheflexibilityandversatilityofnumberialcontrolhaveledtothedevelopmentofanewtypeofmachinetoolcalledthemachiningcenter.Usingsimplerworkholdingfixturesandfewercuttingtools,thismachinedosetheworkformerlydoneonseveralmachines.Themachiningcenterisprovidedwithanautomatictoolchanger.OnacommandfromtheNCsystem,thetoolchangearmlocatedabovethespindlerotatesclockwise,simultane-ouslygrippingthetoolinthespindleandanothertoolinaninterchangestationlocatedonthefaceofthemachinewhichisusedtostorethetooltemporarily.Thearmthemmovesforward,removingthetoolsfromthespindleandfromtheinterchangestation.Afterrotatingclockwise180degrees,thearmretracts,insertthenewtoolinthespindle,andplacestheusedtoolintheinterchangesystem,thearmthenreturnstotheoriginalposition.Amechanicalhandinsidethedrumremovesthetoolfromtheinterchangestationandstoresitinthetooldrum.Themachanicalhandremovedthenexttooltobeusedfromthedrumandplacesitintheinterchangestationinpreparationforthenextoperation.Thetoolchangeoperationmaybecompletedin5seconds.Thetooldrumcanholdalargenumberofdifferenttools.Eachtoolholderbeingcoded,thetoolscanbeselectedinarandomorderandinanysequence.MachiningcenterscanalsobeavailablewithoutNC,however,providedwithnumericalcontrol,thepotentialofthesemachinescanbefullyrealized.Soanewgenerationof?exibleintelligentNCmachinesisacurrentmachinemanufacturingindustrytodevelopnumbercontrolprocessoftoolmachineprinciple.Newchallengesforintelligentrecon?gurablemanufacturingsystemsareontheagendaforthenextgenerationofmachinetoolcentres.Zerodefectworkpiecesandjust-in-timeproductionaresomeoftheobjectivestobereachedforbetterqualityandhighperformanceproduction.Sustainabilityrequiresaholisticapproachtocovernotonly?exibleintelligentmanufacturebutalsoproductandservicesactivities.Newroutesphilosophyofpossiblemachinearchitecturewithcharacteristicssuchashybridprocesseswithin-processinspectionandself-healingwillbepresentedwithgreatfeaturesaswellaschallengesrelatedtovariousaspectsofthenextgenerationofintelligentmachinetoolcentres.數(shù)控機床及其基本原理機床機床是用于切削金屬的機器。工業(yè)上使用的機床要屬數(shù)控車、鉆床和銑床最為重要。其它類型的金屬切削機床在金屬切削加工方面應用不及這三種機床廣泛。鉆削是由旋轉的鉆頭完成的。大多數(shù)金屬的鉆削有麻花鉆來完成。用來進行鉆削加工的機床成為鉆床，擴孔和攻螺紋也歸為鉆削，擴孔是從已經鉆好的孔上在切除少量的金屬。攻螺紋實在內孔上加工出螺紋以使螺桿和螺栓擰進孔內。車床通常被稱為所有類型車床的始祖。為了進行車削，當工件旋轉時，車床用一把單刃刀具切除金屬。用車削可以加工各種圓柱體形狀的工件，如軸、齒輪坯、帶輪和四桿軸。鏜削可以將孔擴大，提高孔的表面質量和加工定位精度高的孔。銑削由旋轉的，多切削刃的銑刀來完成，銑刀有多種類型和尺寸。有些銑刀只有兩個切削刃，而有些則多達三十或者更多的切削刃。銑刀根據使用的刀具不同能形成平面、斜面、溝槽、狹槽、齒輪和其它外形輪廓。牛頭刨床和龍門刨床用單刃刀具來加工平面。用牛頭刨床進行加工時，工件朝向刀具自動進給，刀具往復運動；而在用龍門刨床進行加工時，工件安裝在工作臺上，工作臺往復經過刀具切除金屬。刀具每完成一個行程則自動向工件進給一個小的進給量。磨削利用磨粒來完成切削工作。根據加工要求，磨削可分為精密磨削和非精密磨削。精密磨削用于公差小河非常光潔的表面，非精密磨削用于在精度要求不高的地方切除多余的金屬。數(shù)字控制基本原理用準備好的程序控制機床，這種工作方式被稱為數(shù)字控制或NC。美國電子工業(yè)協(xié)會把數(shù)控設備定義為：“采用在某些點直接插入數(shù)字數(shù)據來控制操作的系統(tǒng)，此系統(tǒng)必須能夠自動解釋翻譯這些信息中的一部分?！痹诘湫偷臄?shù)控系統(tǒng)中，加工零件所需的數(shù)控數(shù)據是保存在穿孔帶上的，被稱為零件程序。零件程序是以信息模塊的方式排布的，每一模塊中包含了對工件局部進行加工所需的數(shù)字信息。當一部分切削完之后，穿孔帶移動一個程序塊。代碼形式的程序塊包含了零件分段加工所需的所有信息如分段加工部分長度、切削速度、進給量等。尺寸信息（長、寬及圓半徑）和輪廓形狀（直線、圓弧或者其它）可以工程圖上得到。分別給出每個軸（X、Y等）的運動尺寸，根據表面粗糙度及所需公差對切削速度、進給率及輔助功能（切削液的開、關，主軸的轉向、夾緊、換齒輪等）進行編程。要有一個零件編程人員為數(shù)控機床準備程序。零件編程人員必須具有機械工程的知識和經驗。零件編程人員要熟悉數(shù)控機床的功能及加工工藝，并決定最佳加工工序。在數(shù)控機床中，，每個軸的運動都要有單獨的驅動設備代替普通機床中的手輪來驅動。驅動設備可以是直流電動機、液壓發(fā)動機或步進電動機，所選的設備的類型主要取決于機床所需的動力。數(shù)控機床系統(tǒng)包括有機床控制單元和加工主機本身。機床控制單元（MCU）必須對零件程序讀和譯碼，提供譯碼指令以控制機床軸的運動并控制機床操作。MCU有兩個主要單元：數(shù)據處理單元（DPU）和控制回路單元（CLU）。DPU的主要功能是對從穿孔帶得到的信息進行譯碼、處理并給CLU提供數(shù)據。這些數(shù)據包括每個軸所需要的新位置，運動方向和速度，傳遞的輔助控制信號。另一方面，CLU提供說明前一部分已經加工完的信號，DPU可以讀入新的一段零件程序。CLU操縱連在絲杠上的驅動設備，并接收每個軸的實際位置及速度的反饋信號。每個絲杠都有一個單獨的驅動設備和反饋設備，不過后者只出現(xiàn)在閉環(huán)系統(tǒng)中。在計算機數(shù)控系統(tǒng)中，DPU的功能總是由CNC計算機的控制程序來執(zhí)行。而CLU的主要部分是在最復雜的CNC系統(tǒng)中實現(xiàn)的。加工過程的數(shù)控今年來，基礎的計算機數(shù)控已經取得了重大的進展。通常形狀相同的零件大批量生產時，自動檢查顯得有效率，加工的精度也高，但由一個自動循環(huán)變?yōu)榱硪粋€自動是一個時間長而又花費高的過程，只能長期運行。但是，又是同一個零件只需要價格幾個，這種工作用計算機數(shù)控機床進行加工時非常值得的。有計算機數(shù)字控制和模擬控制兩種類型。數(shù)字計算機已數(shù)字形式顯示數(shù)碼來工作，一個數(shù)字就是一套用以表示數(shù)碼的符號中的一個符號，它是用在電子數(shù)據處理中的數(shù)字計算機。模擬計算機是以模擬兩位基礎的，它處理物理量和非數(shù)字量。在數(shù)字控制系統(tǒng)中，來自于圖樣的信息放在磁盤上，計