大学本科毕业设计

LibraryofCtheCNCindustrialdevelopedtensofthousandsandeducationalfield,hehasNUMERICALCONTROLNumericalControltechnologyasitisknowntoday,emergedinthemid20thcentury.Itcanbetracedtotheyearof1952,theU.S.AirForce,andthenamesofJohnParsonsandtheMassachusettsInstituteofTechnologyinCam-bridge,MA,USA.Itwasnotappliedinproductionmanu-facturinguntiltheearly1960's.TherealboomcameintheformofCNC,aroundtheyearof1972,andadecadelaterwiththeintroductionofaffordablemicrocomputers.Thehistoryanddevelopmentofthisfascinatingtechnologyhasbeenwelldocumentedinmanypublications.Inthemanufacturingfield,andparticularlyintheareaofmetalworking,NumericalControltechnologyhascausedsomethingofarevolution.Eveninthedaysbeforecomput-ersbecamestandardfixturesineverycompanyandinmanyhomes,themachinetoolsequippedwithNumericalControlsystemfoundtheirspecialplaceinthemachineshops.Therecentevolutionofmicroelectronicsandtheneverceasingcomputerdevelopment,includingitsimpactonNumericalControl,hasbroughtsignificantchangestothemanufacturingsectoringeneralandmetalworkingin-dustryinparticular.DEFINITIONOFNUMERICALCONTROLInvariouspublicationsandarticles,manydescriptionshavebeenusedduringtheyears,todefinewhatNumericalControlis.Itwouldbepointlesstotrytofindyetanotherdefinition,justforthepurposeofthishandbook.Manyofthesedefinitionssharethesameidea,samebasicconcept,justusedifferentwording.Themajorityofalltheknowndefinitionscanbesummedupintoarelativelysimplestatement:NumericalControlcanbedefinedasanoperationofmachinetoolsbythemeansofspecificallycodedinstructionstothemachinecontrolsystemTheinstructionsarecombinationsofthelettersofalpha-bet,digitsandselectedsymbols,forexample,adecimalpoint,thepercentsignortheparenthesissymbols.Allin-structionsarewritteninalogicalorderandapredeterminedform.Thecollectionofallinstructionsnecessarytoma-chineapartiscalledanNCProgram,CNCProgram,oraPartProgram.Suchaprogramcanbestoredforafutureuseandusedrepeatedlytoachieveidenticalmachiningre-sultsatanytime.NCandCNCTechnologyInstrictadherencetotheterminology,thereisadiffer-enceinthemeaningoftheabbreviationsNCandCNC.TheNCstandsfortheolderandoriginalNumericalControltechnology,wherebytheabbreviationCNCstandsforthenewerComputerizedNumericalControltechnology,amodemspin-offofitsolderrelative.However,inpractice,CNCisthepreferredabbreviation.Toclarifytheproperus-ageofeachterm,lookatthemajordifferencesbetweentheNCandtheCNCsystems.Bothsystemsperformthesametasks,namelymanipula-tionofdataforthepurposeofmachiningapart.Inbothcases,theinternaldesignofthecontrolsystemcontainsthelogicalinstructionsthatprocessthedata.Atthispointthesimilarityends.TheNCsystem(asopposedtotheCNCsystem)usesafixedlogicalfunctions,thosethatarebuilt-inandperma-nentlywiredwithinthecontrolunit.Thesefunctionscan-notbechangedbytheprogrammerorthemachineopera-tor.Becauseofthefixedwiringofthecontrollogic,theNCcontrolsystemissynonymouswiththeterm'hardwired'.Thesystemcaninterpretapartprogram,butitdoesnotal-lowanychangestotheprogram,usingthecontrolfeatures.Allrequiredchangesmustbemadeawayfromthecontrol,typicallyinanofficeenvironment.Also,theNCsystemre-quiresthecompulsoryuseofpunchedtapesforinputoftheprograminformation.ThemodemCNCsystem,butnottheoldNCsystem,usesaninternalmicroprocessor(i.e.,acomputer).Thiscomputercontainsmemoryregistersstoringavarietyofroutinesthatarecapableofmanipulatinglogicalfunctions.Thatmeansthepartprogrammerorthemachineoperatorcanchangetheprogramonthecontrolitself(atthema-chine),withinstantaneousresults.ThisflexibilityisthegreatestadvantageoftheCNCsystemsandprobablythekeyelementthatcontributedtosuchawideuseofthetech-nologyinmodernmanufacturing.TheCNCprogramsandthelogicalfunctionsarestoredonspecialcomputerchips,assoftwareinstructions,ratherthanusedbythehardwareconnections,suchaswires,thatcontrolthelogicalfunc-tions.IncontrasttotheNCsystem,theCNCsystemissyn-onymouswiththeterm'softwired'.Whendescribingaparticularsubjectthatrelatestothenumericalcontroltechnology,itiscustomarytouseeitherthetermNCorCNC.KeepinmindthatNCcanalsomeanCNCineverydaytalk,butCNCcanneverrefertotheoldertechnology,describedinthishandbookundertheabbrevia-tionofNC.Theletter'C'standsforComputerized,anditisnotapplicabletothehardwiredsystem.AllcontrolsystemsmanufacturedtodayareoftheCNCdesign.AbbreviationssuchasC&CorC'n'Carenotcorrectandreflectpoorlyonanybodythatusesthem.CONVENTIONALAMDCNCMACHININGWhatmakestheCNCmachiningsuperiortotheconven-tionalmethods?Isitsuperioratall?Wherearethemainbenefits?IftheCNCandtheconventionalmachiningpro-cessesarecompared,acommongeneralapproachtoma-chiningapartwillemerge:ObtainandstudythedrawingSelectthemostsuitablemachiningmethodDecideonthesetupmethod(workholding)SelectthecuttingtoolsEstablishspeedsandfeedsMachinethepartThisbasicapproachisthesameforbothtypesofmachin-ing.Themajordifferenceisinthewayhowvariousdataareinput.Afeedrateof10inchesperminute(10in/min)isthesameinmanualorCNCapplications,butthemethodofapplyingitisnot.Thesamecanbesaidaboutacoolant-itcanbeactivatedbyturningaknob,pushingaswitchorprogrammingaspecialcode.Alltheseactionswillresultinacoolantrushingoutofanozzle.Inbothkindsofmachin-ing,acertainamountofknowledgeonthepartoftheuserisrequired.Afterall,metalworking,particularlymetalcut-ting,ismainlyaskill,butitisalso,toagreatdegree,anartandaprofessionoflargenumberofpeople.Soistheappli-cationofComputerizedNumericalControl.Likeanyskillorartorprofession,masteringittothelastdetailisneces-sarytobesuccessful.Ittakesmorethantechnicalknowl-edgetobeaCNCmachinistoraCNCprogrammer.Workexperienceandintuition,andwhatissometimescalleda'gut-feel',isamuchneededsupplementtoanyskill.Inaconventionalmachining,themachineoperatorsetsupthemachineandmoveseachcuttingtool,usingoneorbothhands,toproducetherequiredpart.Thedesignofamanualmachinetooloffersmanyfeaturesthathelptheprocessofmachiningapart-levers,handles,gearsanddi-als,tonamejustafew.Thesamebodymotionsarere-peatedbytheoperatorforeverypartinthebatch.However,theword'same'inthiscontextreallymeans'similar'ratherthan'identical'.Humansarenotcapabletorepeateveryprocessexactlythesameatalltimes-thatisthejobofma-chines.Peoplecannotworkatthesameperformancelevelallthetime,withoutarest.Allofushavesomegoodandsomebadmoments.Theresultsofthesemoments,when*appliedtomachiningapart,aredifficulttopredict.Therewillbesomedifferencesandinconsistencieswithineachbatchofparts.Thepartswillnotalwaysbeexactlythesame.Maintainingdimensionaltolerancesandsurfacefin-ishqualityarethemosttypicalproblemsinconventionalmachining.Individualmachinistsmayhavetheirowntime'proven'methods,differentfromthoseoftheirfellowcol-leagues.Combinationoftheseandotherfactorscreateagreatamountofmconsistency.Themachiningundernumericalcontroldoesawaywiththemajorityofinconsistencies.Itdoesnotrequirethesamephysicalinvolvementasmanualmachining.Numericallycontrolledmachiningdoesnotneedanyleversordialsorhandles,atleastnotinthesamesenseasconventionalma-chiningdoes.Oncethepartprogramhasbeenproven,itcanbeusedanynumberoftimesover,alwaysreturningconsistentresults.Thatdoesnotmeantherearenolimitingfactors.Thecuttingtoolsdowearout,thematerialblankinonebatchisnotidenticaltothematerialblankinanotherbatch,thesetupsmayvary,etc.Thesefactorsshouldbeconsideredandcompensatedfor,whenevernecessary.Theemergenceofthenumericalcontroltechnologydoesnotmeananinstant,orevenalongterm,demiseofallman-ualmachines.Therearetimeswhenatraditionalmachin-ingmethodispreferabletoacomputerizedmethod.Forex-ample,asimpleonetimejobmaybedonemoreefficientlyonamanualmachinethanaCNCmachine.Certaintypesofmachiningjobswillbenefitfrommanualorsemiauto-maticmachining,ratherthannumericallycontrolledma-chining.TheCNCmachinetoolsarenotmeanttoreplaceeverymanualmachine,onlytosupplementthem.Inmanyinstances,thedecisionwhethercertainmachin-ingwillbedoneonaCNCmachineornotisbasedonthenumberofrequiredpartsandnothingelse.Althoughthevolumeofpartsmachinedasabatchisalwaysanimportantcriteria,itshouldneverbetheonlyfactor.Considerationshouldalsobegiventothepartcomplexity,itstolerances,therequiredqualityofsurfacefinish,etc.Often,asinglecomplexpartwillbenefitfromCNCmachining,whilefiftyrelativelysimplepartswillnot.Keepinmindthatnumericalcontrolhasnevermachinedasinglepartbyitself.Numericalcontrolisonlyaprocessoramethodthatenablesamachinetooltobeusedinapro-ductive,accurateandconsistentway.NUMERICALCONTROLADVANTAGESWhatarethemainadvantagesofnumericalcontrol?Itisimportanttoknowwhichareasofmachiningwillbenefitfromitandwhicharebetterdonetheconventionalway.ItisabsurdtothinkthatatwohorsepowerCNCmillwillwinoverjobsthatarecurrentlydoneonatwentytimesmorepowerfulmanualmill.Equallyunreasonableareex-pectationsofgreatimprovementsincuttingspeedsandfeedratesoveraconventionalmachine.Ifthemachiningandtoolingconditionsarethesame,thecuttingtimewillbeverycloseinbothcases.SomeofthemajorareaswheretheCNCusercanandshouldexpectimprovement:SetuptimereductionLeadtimereductionAccuracyandrepeatabilityContouringofcomplexshapesSimplifiedtoolingandworkholdingConsistentcuttingtimeGeneralproductivityincreaseEachareaoffersonlyapotentialimprovement.Individ-ualuserswillexperiencedifferentlevelsofactualimprove-ment,dependingontheproductmanufacturedon-site,theCNCmachineused,thesetupmethods,complexityoffixturing,qualityofcuttingtools,managementphilosophyandengineeringdesign,experienceleveloftheworkforce,individualattitudes,etc.SetupTimeReductionInmanycases,thesetuptimeforaCNCmachinecanbereduced,sometimesquitedramatically.Itisimportanttorealizethatsetupisamanualoperation,greatlydependentontheperformanceofCNCoperator,thetypeoffixturingandgeneralpracticesofthemachineshop.Setuptimeisunproductive,butnecessary-itisapartoftheoverheadcostsofdoingbusiness.Tokeepthesetuptimetoamini-mumshouldbeoneoftheprimaryconsiderationsofanymachineshopsupervisor,programmerandoperator.BecauseofthedesignofCNCmachines,thesetuptimeshouldnotbeamajorproblem.Modularfixturing,standardtooling,fixedlocators,automatictoolchanging,palletsandotheradvancedfeatures,makethesetuptimemoreefficientthanacomparablesetupofaconventionalmachine.Withagoodknowledgeofmodernmanufacturing,productivitycanbeincreasedsignificantly.Thenumberofpartsmachinedunderonesetupisalsoimportant,inordertoassessthecostofasetuptime.Ifagreatnumberofpartsismachinedinonesetup,thesetupcostperpartcanbeveryinsignificant.Averysimilarre-ductioncanbeachievedbygroupingseveraldifferentoper-ationsintoasinglesetup.Evenifthesetuptimeislonger,itmaybejustifiedwhencomparedtothetimerequiredtosetupseveralconventionalmachines.LeadTimeReductionOnceapartprogramiswrittenandproven,itisreadytobeBsedagaininthefuture,evenatashortnotice.Althoughtheleadtimeforthefirstrunisusuallylonger,itisvirtuallynilforanysubsequentrun.Evenifanengineeringchangeofthepartdesignrequirestheprogramtobemoditied,itcanbedoneusuallyquickly,reducingtheleadtime.Longleadtime,requiredtodesignandmanufacturesev-eralspecialfixturesforconventionalmachines,canoftenbereducedbypreparingapartprogramandtheuseofsim-plifiedfixturing.AccuracyandRepeatabilityThehighdegreeofaccuracyandrepeatabilityofmodernCNCmachineshasbeenthesinglemajorbenefittomanyusers.Whetherthepartprogramisstoredonadiskorinthecomputermemory,orevenonatape(theoriginalmethod),italwaysremainsthesame.Anyprogramcanbechangedatwill,butonceproven,nochangesareusuallyrequiredanymore.Agivenprogramcanbereusedasmanytimesasneeded,withoutlosingasinglebitofdataitcontains.True,programhastoallowforsuchchangeablefactorsastoolwearandoperatingtemperatures,ithastobestoredsafely,butgenerallyverylittleinterferencefromtheCNCpro-grammeroroperatorwillberequired.ThehighaccuracyofCNCmachinesandtheirrepeatabilityallowshighqualitypartstobeproducedconsistentlytimeaftertime.ContouringofComplexShapesCNClathesandmachiningcentersarecapableofcon-touringavarietyofshapes.ManyCNCusersacquiredtheirmachinesonlytobeabletohandlecomplexparts.AgoodexamplesareCNCapplicationsintheaircraftandautomo-tiveindustries.Theuseofsomeformofcomputerizedpro-grammingisvirtuallymandatoryforanythreedimensionaltoolpathgeneration.Complexshapes,suchasmolds,canbemanufacturedwithouttheadditionalexpenseofmakingamodelfortrac-ing.Mirroredpartscanbeachievedliterallyattheswitchofabutton.Storageofprogramsisalotsimplerthanstorageofpatterns,templates,woodenmodels,andotherpatternmakingtools.SimplifiedToolingandWorkHoldingNonstandardand'homemade'toolingthatcluttersthebenchesanddrawersaroundaconventionalmachinecanbeeliminatedbyusingstandardtooling,speciallydesignedfornumericalcontrolapplications.Multi-steptoolssuchaspilotdrills,stepdrills,combinationtools,counterborersandothersarereplacedwithseveralindividualstandardtools.Thesetoolsareoftencheaperandeasiertoreplacethanspecialandnonstandardtools.Cost-cuttingmeasureshaveforcedmanytoolsupplierstokeepaloworevenanonexistentinventory,increasingthedeliverylimetothecustomer.Standard,off-the-shelftoolingcanusuallybeob-tainedfasterthennonstandardtooling.FixturingandworkholdingforCNCmachineshaveonlyonemajorpurpose-toholdthepartrigidlyandinthesamepositionforallpartswithinabatch.FixturesdesignedforCNCworkdonotnormallyrequirejigs,pilotholesandotherholelocatingaids.CuttingTimeandProductivityIncreaseThecuttingtimeontheCNCmachineiscommonlyknownasthecycletime-andisalwaysconsistent.Unlikeaconventionalmachining,wheretheoperator'sskill,experi-enceandpersonalfatiguearesubjecttochanges,theCNCmachiningisunderthecontrolofacomputer.Thesmallamountofmanualworkisrestrictedtothesetupandload-ingandunloadingthepart.Forlargebatchruns,thehighcostoftheunproductivetimeisspreadamongmanyparts,makingitlesssignificant.Themainbenefitofaconsistentcuttingtimeisforrepetitivejobs,wheretheproductionschedulingandworkallocationtoindividualmachinetoolscanbedoneveryaccurately.ThemainreasoncompaniesoftenpurchaseCNCma-chinesisstrictlyeconomic-itisaseriousinvestment.Also,havingacompetitiveedgeisalwaysonthemindofeveryplantmanager.Thenumericalcontrolteclmologyoffersexcellentmeanstoachieveasignificantimprovementinthemanufacturingproductivityandincreasingtheoverallqualityofthemanufacturedparts.Likeanymeans,ithastobeusedwiselyandknowledgeably.WhenmoreandmorecompaniesusetheCNCtechnology,justhavingaCNCmachinedoesnotoffertheextraedgeanymore.Thecom-paniesthatgetforwardarethosewhoknowhowtousethetechnologyefficientlyandpracticeittobecompetitiveintheglobaleconomy.Toreachthegoalofamajorincreaseinproductivity,itisessentialthatusersunderstandthefundamentalprinciplesonwhichCNCtechnologyisbased.Theseprinciplestakemanyforms,forexample,understandingtheelectroniccir-cuitry,complexladderdiagrams,computerlogic,metrol-ogy,machinedesign,machiningprinciplesandpracticesandmanyothers.Eachonehastobestudiedandmasteredbythepersonincharge.Inthishandbook,theemphasisisonthetopicsthatrelatedirectlytotheCNCprogrammingandunderstandingthemostcommonCNCmachinetools,theMachiningCentersandthelathes(sometimesalsocalledtheTurningCenters).Thepartqualityconsiderationshouldbeveryimportanttoeveryprogrammerandma-chinetooloperatorandthisgoalisalsoreflectedinthehandbookapproachaswellasinthenumerousexamples.TYPESOFCNCMACHINETOOLSDifferentkindsofCNCmachinescoveranextremelylargevariety.Theirnumbersarerapidlyincreasing,asthetechnologydevelopmentadvances.Itisimpossibletoiden-tifyalltheapplications,theywouldmakealonglist.HereisabrieflistofsomeofthegroupsCNCmachinescanbepartof:*MillsandMachiningcentersLathesandTurningCentersDrillingmachinesBoringmillsandProfilersEDMmachinesPunchpressesandShearsFlamecuttingmachinesRoutersWaterjetandLaserprofilersCylindricalgrindersWeldingmachinesBenders,WindingandSpinningmachines,etc.CNCmachiningcentersandlathesdominatethenumberofinstallationsinindustry.Thesetwogroupssharethemarketjustaboutequally.Someindustriesmayhaveahigherneedforonegroupofmachines,dependingontheirneeds.Onemustrememberthattherearemanydifferentkindsofladiesandequallymanydifferentkindsofma-chiningcenters.However,theprogrammingprocessforaverticalmachineissimilartotheoneforahorizontalma-chineorasimpleCNCmill.Evenbetweendifferentma-chinegroups,thereisagreatamountofgeneralapplica-tionsandtheprogrammingprocessisgenerallythesame.Forexample,acontourmilledwithanendmillhasalotincommonwithacontourcutwithawire.MillsandMachiningCentersStandardnumberofaxesonamillingmachineisthree-theX,YandZaxes.Thepartsetonamillingsystemisal-waysstationary,mountedonamovingmachinetable.Thecuttingtoolrotates,itcanmoveupanddown(orinandout),butitdoesnotphysicallyfollowthetoolpath.CNCmills-sometimescalledCNCmillingmachines-areusuallysmall,simplemachines,withoutatoolchangerorotherautomaticfeatures.Theirpowerratingisoftenquitelow.Inindustry,theyareusedfortoolroomwork,maintenancepurposes,orsmallpartproduction.Theyareusuallydesignedforcontouring,unlikeCNCdrills.CNCmachiningcentersarefarmorepopularandeffi-cientthandrillsandmills,mainlyfortheirflexibility.ThemainbenefittheusergetsoutofaCNCmachiningcenteristheabilitytogroupseveraldiverseoperationsintoasinglesetup.Forexample,drilling,boring,counterboring,tap-ping,spotfacingandcontourmillingcanbeincorporatedintoasingleCNCprogram.Inaddition,theflexibilityisenhancedbyautomatictoolchanging,usingpalletstominimizeidletime,indexingtoadifferentsideofthepart,usingarotarymovementofadditionalaxes,andanumberofotherfeatures.CNCmachiningcenterscanbeequippedwithspecialsoftwarethatcontrolsthespeedsandfeeds,thelifeofthecuttingtool,automaticin-processgaugingandoffsetadjustmentandotherproductionenhancingandtimesavingdevices.TherearetwobasicdesignsofatypicalCNCmachiningcenter.Theyaretheverticalandthehorizontalmachiningcenters.Themajordifferencebetweenthetwotypesisthenatureofworkthatcanbedoneonthemefficiently.ForaverticalCNCmachiningcenter,themostsuitabletypeofworkareflatparts,eithermountedtothefixtureontheta-ble,orheldinaviseorachuck.Theworkthatrequiresma-chiningontwoormorefacesmasinglesetupismorede-sirabletobedoneonaCNChorizontalmachiningcenter.Angoodexampleisapumphousingandothercubic-likeshapes.Somemulti-facemachiningofsmallpartscanalsobedoneonaCNCverticalmachiningcenterequippedwitharotarytable.Theprogrammingprocessisthesameforbothdesigns,butanadditionalaxis(usuallyaBaxis)isaddedtothehori-zontaldesign.Thisaxisiseitherasimplepositioningaxis(indexingaxis)forthetable,orafullyrotaryaxisforsimul-taneouscontouring.ThishandbookconcentratesontheCNCverticalma-chiningcentersapplications,withaspecialsectiondealingwiththehorizontalsetupandmachining.Theprogram-mingmethodsarealsoapplicabletothesmallCNCmillsordrillingand/ortappingmachines,buttheprogrammerhastoconsidertheirrestrictions.LathesandTurningCentersACNClatheisusuallyamachinetoolwithtwoaxes,theverticalXaxisandthehorizontalZaxis.Themainfeatureofalathethatdistinguishesitfromamillisthatthepartisrotatingaboutthemachinecenterline.Inaddition,thecut-tingtoolisnormallystationary,mountedinaslidingturret.Thecuttingtoolfollowsthecontouroftheprogrammedtoolpath.FortheCNClatheswithamillingattachment,socalledlivetooling,themillingtoolhasitsownmotorandrotateswhilethespindleisstationary.Themodemlathedesigncanbehorizontalorvertical.Horizontaltypeisfarmorecommonthantheverticaltype,butbothdesignshavetheirpurposeinmanufacturing.Sev-eraldifferentdesignsexistforeithergroup.Forexample,atypicalCNClatheofthehorizontalgroupcanbedesignedwithaflatbedoraslantbed,asabartype,chuckertypeorauniversaltype.Addedtothesecombinationsaremanyac-cessoriesthatmakeaCNClatheanextremelyflexiblema-chinetool.Typically,accessoriessuchasatailstock,steadyrestsorfollow-uprests,partcatchers,pullout-fingersandevenathirdaxismillingattachmentarepopularcompo-nentsoftheCNClathe.?CNClathecanbeveiyversatile-soversatileinfact,thatitisoftencalledaCNCTurningCenter.AlltextandprogramexamplesinthishandbookusethemoretraditionaltermCNClathe,yetstillrecogniz-ingallitsmodernfunctions.中文翻译：数控正如我们现在所知，数控技术出现于20世纪中叶。它能被追溯到1952年，美国空军、JohnParsons公司、美国马萨诸塞州坎布里奇的麻省理工学院（MIT）。直到20世纪六十年代初期，数控技术才被应用于产品制造，而数控技术真正的繁荣出现在1972年左右CNC形成以及十年后微机的普及。这项热门技术的历史和发展在很多出版物中都有很好地记录。在制造领域，尤其在金属加工领域，数控技术已经引起了一场变革。甚至在计算机变成公司和家庭的标配之前，装备有数控系统的机床已经在市场上占有一席之地了。近来微电子的革命和从不停息的计算机技术的发展及其对数控的影响引起了制造部门，尤其金属加工工业的重大变革。数控的定义这些年来，种类繁多的出版物和文章对数控有很多的描述，为了这本手册再寻找另外一种定义毫无意义。这些定义中有很多相同之处，基本概念相同，只是说法不同而已。大多数定义可以概括成一个相对简单的描述：数控指给机床控制系统专门的编码指令来实现机床的工作。这些指令由字母，数字，特定的符号如一个小数点、百分比符号、括号符号等组成。所有的指令程序。这样的程序可以存储下来以备将来使用，也可以重复使用以便不同的时间获得相同的加工结果。数控和计算机数控技术严格的按术语说，NC和CNC的缩写意义是有差别的。NC代表原先的旧的数字控制技术，而CNC代表新的计算机数字控制技术，是原来老技术在现代的衍生物。然而，在实践中，CNC是较常用的缩写。为了恰当的应用这两个缩写，让我们来看看这二者的主要不同点。二者执行的任务相同，即通过对数据的操作来加工零件。控制系统内部的设计都包含处理数据的逻辑指令。这就是主要的相同之处。NC系统（相对于CNC系统）使用预定的逻辑功能，这些功能被永久的写入控制单元中，不能被程序员或者机床操作人员改变。因为这种固定的控制逻辑，NC系统相当于“硬接线”。NC系统应用了这些细则，能读零件程序，但不能对它做任何改变。所有必要的改变都必须在像办公室这样远离控制系统的环境中做出。而且NC系统的程序输入只能用穿孔纸带。与旧的NC系统不同，现代化的CNC系统用一个内置的微处理器（即计算机）。这个计算机有寄存器来存储各种各样的程序，能够完成逻辑处理功能。这意味着零件编程人员或者机床操作员能在控制系统（机床）上改变程序，同时获得结果。这种灵活性是CNC系统最大的优点，可能也是这项技术在现代加工中广泛应用的主要因素。CNC系统中，程序和逻辑功能存储在特殊的电脑芯片上，比如软件存储区，而不是用电线那样的硬接线的方式来控制逻辑功能。相比NC系统，CNC系统相当于是“软接线”。当描述与数控技术相关的特殊题目时，我们通常用NC或者CNC表达。记住，通常NC也带表“computerized”（计算机控制的），这不适用于硬接线系统。现在制造的所有的控制系统均是CNC。像“C&C”或者“CnC”这样的缩写是不正确的，反映出使用它们的任何人的知识缺乏。传统加工与数控加工什么使CNC加工优于传统加工模式呢？各方面均有优势吗？主要的优点何在？如果把CNC加工与传统加工过程进行对比，在加工零件上概括地讲有如下过程：得到并研究零件图选择最合适的加工方法确定装夹方法（工件夹持）选择切削刀具确定切削速度和进给量加工零件两种加工类型加工工件的基本过程是相同的，主要的不同之处在于各种信息的输入方式不同。每分钟10英寸（254mm/min）的进给速率在手工机床和数控机床上是相同的，但是应用的方法不同。相同之处比如启用冷却液都可以通过旋转按钮、按下开关或者编一个特殊的指令来实现，这些动作均可以使切削液从喷嘴喷出。两种加工方式均需要工人对零件有一定的知识，毕竟金属加工，尤其是金属切削，主要是一项技术，相当程度上，也是一门手艺，很多人的一种职业。计算机数控的应用也是如此，像其他的技术、艺术或者职业一样，它的成功需要精通每个细节。要成为一个CNC机械员或者CNC程序员，这些细节比学习技术操作要花费更多的时间。工作经验和态度，还有我们有时候称之为“直觉”的东西，对任何一项技能的掌握都很有必要。在传统的加工方式中，机床操作工人手工调整机床和移动刀具，来生产所要求的零件。手工机床上有很多帮助加工工件的装置如控制杆、手柄、传动装置、转盘等，这里仅举数例。同一批工件，操作人员重复同样的动作。但是，此处“同样的”是指相似的而不是完全相同的，因为人是不可能精确地重复每一个过程的——这是机器的工作。不休息的话，人不可能一直保持同样的工作水平。我们每个人的状态都有好的时候和坏的时候。当加工零件时，很难预知状态什么时候好，什么时候坏，这将使同一批零件产生不一致的情况。这些零件将不会精确的相同。保持尺寸公差和表面粗造度是普通机床加工的最典型的问题。一个机床工人可能有与同事不同的能够保证一致性的方法。这些因素，加上其他的一些因素，共同导致了比较大的不一致性。数控机加工则不会出现大多数不一致情况。它不会像手工机床那样需要涉及相同的肢体介入。数控的机加工不需要任何控制杆或者转盘、手柄等，即便有也与传统机床上的意义不同。零件的加工程序一旦被证明可靠，就可以无限次重复使用，并且得到稳定的结果。但这也不意味着没有限制因素，刀具会磨损，不同批次的坯料有差异，工件的安装也多种多样，等等。有必要时，这些因素应该考虑和补偿。数控技术的出现并不意味着马上，甚至相当长一段时间内，取代所有的手工机床。有些时候，传统的机加工方式比数控方式优越。例如，单件一次性生产用手工机床可能比数控机床效率更高，有些特定种类的加工任务使用手工机床或者半自动化机床比数控机床经济性更好。数控机床是手工机床的补充，并不意味着要取代所有的手工机床。很多情况，加工任务要不要在数控机床上完成仅仅取决于所要求的零件生产量。一批零件的生产量虽然是一项重要的标准，但决不是唯一标准。零件的复杂程度、公差，表面粗糙度要求等也应该考虑进去。通常，单件复杂零件在数控机床上加工能获得好的效益，但五十件相对简单的零件就不行。记住，数控本身决不能加工任何一个零件，数控仅仅是一个能让机床变得高效、精确、稳定的过程或方法。数控的主要优点是什么呢？知道哪些加工用数控机床比较好哪些用普通机床比较好很重要。认为相当于两匹马的力量的数控磨削完全胜过现在所用的手工磨削，因为前者的力量是后者的二十倍，是荒诞的。同样，盲目追求在切削速度和进给量方面相对于普通机床的大的提升也是不合理的。如果机械加工和刀具的条件相同的话，两者的切削时间将非常接近。CNC使用人员应该期待如下方面的提升：安装时间的缩短生产周期的缩短精度和一致性复杂形状的轮廓刀具和夹具的简化稳定的切削时间总体生产率的提高每个方面只是有一个提高的潜在的可能性，使用者将感受到实际提高程度的不同，这些不同取决于产品的大小、使用的数控机床、装夹方法、装夹的复杂程度、刀具的性能、管理学和工程设计、劳动力的经验水平、个人态度等等。♦安装时间的缩短很多情况下，数控机床上工件的安装时间都能够缩短，有时还能缩短很多。意识到安装工件是项手工操作很重要，它很大程度上依靠数控机床操作工人的表现、夹具的类型、车间的实践经验。安装时间是非生产性的，但是必要的一一它是经营中重要花费的一部分。保持安装时间最短是每个车间由于数控机床的设计方面的原因，工件安装时间应该不是主要问题。模块化夹具、标准化工具、固定的定位元件、自动化换刀、随行夹具和其他先进的特点使数控机床上工件的安装相比普通机床更高效。对现代制造有了较好的认识后，生产率能大大提高。为便于对安装时间的评估，一次装夹中工件的数量也很重要。如果一次装夹中所加工的工件很多，那么每个工件的装夹时间就无关紧要了。类似地，将几个不同的操作步骤合并成一