《机械工程专业英语》课件-机械工程专业英语课件-PART6

PART6PART6ElectricKnowledgeandAutomobileUNIT26:NumericalControlofProductionEquipments(I)UNIT27BasicElectricityandMagnetismUNIT28ElectricPowersUnit29NumericalControlSoftwareUnit30AutomaticControlSystemUNIT26:NumericalControlofProductionEquipments(I)NewwordsandexpressionsUNIT26:NumericalControlofProductionEquipments(I)Numericalcontrol(NC)isaformofprogrammableautomationinwhichtheprocessingequipmentiscontrolledbymeansofnumbers,letters,andothersymbols.Thenumbers,letters,andsymbolsarecodedinanappropriateformattodefineaprogramofinstructionsforaparticularworkpartorjob.Whenthejobchanges,theprogramofinstructionsischanged.ThecapabilitytochangetheprogramiswhatmakesNCsuitableforlow-andmedium-volumeproduction.Itismucheasiertowritenewprogramsthantomakemajoralterationsoftheprocessingequipment.BasicComponetsofNCAnumericalcontrolsystemconsistsofthefollowingthreebasiccomponents:.Programofinstructions.Machinecontrolunit.ProcessingequipmentThegeneralrelationshipamongthethreecomponentsisillustratedinFigure26-1.Theprogramisfedintothecontrolunit,whichdirectstheprocessingequipmentaccordingly.Theprogramofinstructionsisthedetailedstep-by-stepcommandsthatdirecttheprocessingequipment.Initsmostcommonform,thecommandsrefertopositionsofamachinetoolspindlewithrespecttotheworktableonwhichthepartisfixtured.Moreadvancedinstructionsincludeselectionofspindlespeeds,cuttingtools,andotherfunctions.Theprogramiscodedonasuitablemediumforsubmissiontotheworktableonwhichthepartisfixture.Moreadvancedinstructionsincludemediumforsubmissiontothemachinecontrolunit.Theprogramiscodedonasuitablemediumforsubmissiontothemachinecontrolunit.Themostcommonmediuminuseoverthelastseveraldecadeshasbeen1-in,-widepunchedtape.Comingintousemorerecentlyhavebeenmagnetictapecassettesandfloppydiskettes.Themachinecontrolunit(MCU)consistsoftheelectronicsandcontrolhardwarethatreadandinterprettheprogramofinstructionandconvertitintomechanicalactionsofthemachinetoolorotherprocessingequipment.TheprocessingequipmentisthethirdbasiccomponentofanNCsystem.Itisthecomponentthatperformsusefulwork.Inthemostcommonexampleofnumericalcontrol,onethatperformsmachiningoperations,theprocessingequipmentconsistsoftheworktableandspindleaswellasthemotorsandcontrolsneededtodrivethem.TypesofControlSystemTherearetwobasictypesofcontrolsystemsinnumericalcontrol:point-to-pointandcontouring.Inthepoint-to-pointsystem,alsocalledpositioning,eachaxisofthemachineisdrivenseparatelybyleadscrewsand,dependingonthetypeofoperation,atdifferentvelocities.Themachinemovesinitiallyatmaximumvelocityinordertoreducenonproductivetimebutdeceleratesasthetoolreachesitsnumericallydefinedposition.Thusisanoperationsuchasdrillingorpunching,thepositioningandcuttingtakeplacesequentially.Aftertheholeisdrilledorpunched,thetoolretracts,movesrapidlytoanotherposition,andrepeatstheoperation.Thepathfollowedfromonepositiontoanotherisimportantinonlyonerespect:thetimerequiredshouldbeminimizedforefficiency.Point-to-pointsystemsareusedmainlyindrilling,punching,andstraightmillingoperations.Inthecontouringsystem,alsoknownasthecontinuouspathsystem,positioningandcuttingoperationsarebothalongcontrolledpathsbutatdifferentvelocities.Becausethetoolcutsasittravelsalongaprescribedpath,accuratecontrolandsynchronizationofvelocitiesandmovementsareimportant.Thecontouringsystemisusedonlathes,millingmachines,grinders,weldingmachinery,andmachiningcenters.Movementalongthepath,orinterpolation,occursincrementally,byoneofseveralbasicmethods.Inallinterpolations,thepathcontrolledisthatofthecenterofrotationofthetool.Compensationfordifferenttools,differentdiametertools,ortoolwearduringmachiningcanbemadeintheNCprogram.Thereareanumberofinterpolationschemesthathavebeendevelopedtodealwiththevariousproblemsthatareencounteredingeneratingasmoothcontinuouspathwithacontouring–typeNCsystem,theyinclude:.Linearinterpolation.Circularinterpolation.Helicalinterpolation.Parabolicinterpolation.CubicinterpolationEachoftheseinterpolationprocedurespermitstheprogrammer(oroperator)togeneratemachineinstructionsforlinearorcurvilinearpaths,usingarelativelyfewinputparameters.TheinterpolationmoduleintheMCUperformsthecalculationsanddirectsthetoolalongthepath.Linearinterpolationisthemostbasicandisusedwhenastraight-linepathistobegeneratedincontinuous-pathNC.Two-axisandthree-axislinearinterpolationroutinesaresometimesdistinguishedinpractice,butconceptuallytheyarethesame.Theprogrammerisrequiredtospecifythebeginningpointandendpointofthestraightline,andtheratethatistobefollowedalongthestraightline.Theinterpolatorcomputesthefeedratesforeachofthetwo(orthree)axesinordertoachievethespecifiedfeedrate.Linearinterpolationforcreatingacircularpathwouldbequiteinappropriatebecausetheprogrammerwouldberequiredtospecifythelinesegmentsandtheirrespectiveandpointsthataretobeusedtoapproximatethecircle.Circularinterpolationschemeshavebeendevelopedthatpermittheprogrammingofapathconsistingofacircularbyspecifyingthefollowingparametersofthearc:thecoordinatesofitsendpoints,thecoordinatesofitscenter,itsradius,andthedirectionofthecutteralongthearc.Thetoolpaththatiscreatedconsistsofaseriesofstraight-linesegments,butthesegmentsarecalculatedbytheinterpolationmoduleratherthantheprogrammer.Thecutterisdirectedtomovealongeachlinesegmentonebyoneinordertogeneratethesmoothcircularpath.AlimitationofcircularinterpolationisthattheplaneinwhichthecirculararcexistsmustbeaplanedefinedbytwoaxesoftheNCsystem.Helicalinterpolationcombinesthecircularinterpolationschemefortwoaxesdescribedabovewithlinearmovementofathirdaxis.Thispermitsthedefinitionofahelicalpathinthree-dimensionalspace.Parabolicandcubicinterpolationroutinesareusedtoprovideapproximationsoffree-fromcurvesusinghigher-orderequations.Theygenerallyrequireconsiderablecomputationalpowerandarenotascommonaslinearandcircularinterpolation.Theirapplicationsareconcentratedintheautomobileindustryforfabricatingdiesforcarbodypanelsstyledwithfree-formdesignsthatcannotaccuratelyandconvenientlybeapproximatedbycombininglinearandcircularinterpolations.ProgrammingforNCAprogramfornumericalcontrolconsistsofasequenceofdirectionsthatcausesanNCmachinetocarryoutacertainoperation,machiningbeingthemostcommonlyusedprocess.ProgrammingforNCmaybedonebyaninternalprogrammingdepartment,ontheshopfloor,orpurchasedfromanoutsidesource.Also,programmingmaybedonemanuallyorwithcomputerassistance.Theprogramcontainsinstructionsandcommands.Geometricinstructionspertaintorelativemovementsbetweenthetoolandtheworkplace.Geometricinstructionspertaintorelativespeeds,feeds,tools,andsoon.Travelinstructionspertaintothetypeofinterpolationandsloworrapidmovementsofthetoolorworktable.Switchingcommandspertaintoon/offpositionforcoolantsupplies,spindlerotation,directionofspindlerotation,toolchanges,workplacefeeding,clamping,andsoon.(1)ManualProgramming. Manualpartprogrammingconsistsoffirstcalculatingdimensionalrelationshipsofthetool,workplace,andworktable,basedontheengineeringdrawingsofthepart,andmanufacturingoperationstobeperformedandtheirsequence.Aprogramsheetiscuttingtools,spindlespeeds,feeds,depthofcut,cuttingfluids,power,andtoolorworkplacerelativepositionsandmovements.Basedonthisinformation,thepartprogramisprepared.Usuallyapapertapeisfirstpreparedfortryingoutanddebuggingtheprogram.Dependingonhowoftenitistobeused,thetapemaybemadeofmoredurableMylar.Manualprogrammingcanbedonebysomeoneknowledgeableabouttheparticularprocessandabletounderstand,read,andchangepartprograms.Becausetheyarefamiliarwithmachinetoolsandprocesscapabilities,skilledmachinistscandomanualprogrammingwithsometraininginprogramming.However,theworkistedious,timeconsuming,anduneconomical—andisusedmostlyinsimplepoint-to-pointapplications.(2)Computer-AidedProgramming.Computer-aidedpartprogramminginvolvesspecialsymbolicprogramminglanguagesthatdeterminethecoordinatepointsofcorners,edges,andsurfacesofthepart.Programminglanguageisthemeansofcommunicatingwiththecomputerandinvolvestheuseofsymboliccharacters.Theprogrammerdescribesthecomponenttobeprocessedinthislanguage,andthecomputerconvertsittocommandsfortheNCmachine[1].Severallanguageshavevariousfeaturesandapplicationsarecommerciallyavailable.ThefirstlanguagethatusedEnglish-likestatementswasdevelopedinthelate1950sandiscalledAPT(forAutomaticallyProgrammedTools).Thislanguage,initsvariousexpandedforms,isstillthemostwidelyusedforbothpoint-to-pointandcontinuous-pathprogramming.Computer-aidedpartprogramminghasthefollowingsignificantadvantagesovermanualmethod:.Useofrelativelyeasytousesymboliclanguage.Reducedprogrammingtime.Programmingiscapableofaccommodatingalargeamountofdataconcerningmachinecharacteristicsandprocessvariables,suchaspower,speeds,feed,toolshape,compensationfortoolshapechanges,toolwear,deflections,andcoolantuse..Reducedpossibilityofhumanerror,whichcanoccurinmanualprogramming.Capabilityofsimplechangeoverofmachiningsequenceorfrommachinetomachine.LowercostbecauselesstimeisrequiredforprogrammingSelectionofaparticularNCprogramminglanguagedependsonthefollowingfactors:(a)Levelofexpertiseofthepersonnelinthemanufacturingfacility(b)Complexityofthepart.(c)Typeofequipmentandcomputersavailable(d)Timeandcostsinvolvedinprogramming.Becausenumericalcontrolinvolvestheinsertionofdataconcerningworkplacematerialsandprocessingparameters,programmingmustbedonebyoperatorsorprogrammerswhoareknowledgeableabouttherelevantaspectsofthemanufacturingprocessesbeingused.Beforeproductionbegins,programsshouldbeverified,eitherbyviewingasimulationoftheprocessonaCRTscreenorbymakingthepartfromaninexpensivematerial,suchasaluminum,wood,orplastic,ratherthanthe,materialspecifiedforthefinishedpart.NCPartProgrammingLanguagesProbablyover100NCpartprogramminglanguageshavebeendevelopedsincetheinitialMITresearch[2]onNCprogrammingsystemsin1956.Mostofthelanguagesweredevelopedtoserveparticularneedsandmachinesandhavenotsurvivedthetestoftime.However,agoodnumberoflanguagesarestillinusetoday.Inthissubsectionwereviewsomeofthosewhicharegenerallyconsideredimportant.APT(AutomaticallyProgrammedTools).TheAPTlanguagewastheproductoftheMITdevelopmentworkonNCprogrammingsystems.ItsdevelopmentbeganinJune1956,anditwasfirstusedinproductionaround1959.TodayitisthemostwidelyusedlanguageintheUnitedStates.Althoughfirstintendedasacontouringlanguage,modernversionsofAPTcanbeusedforbothpositioningandcontinuous-pathprogrammingandcontinuous-pathprogramminginuptofiveaxes.AUTOSPOT(AutomaticSystemforPositioningTools).ThiswasdevelopedbyIBMandfirstintroducedin1962forPTPprogramming.Today’sversionofAUTOSPOTcanbeusedforcontouringaswell.COMPACT11.ThisisapackageavailablefromManufacturingDataSystems,Inc.(MDSI),afirmbasedinAnnArbor,Michigan.TheNClanguageissimilartoSPLITinmanyofitsfeatures.MDSIleasestheCOMPACT11systemtoitsusersonatime-sharingbasis.ThepartprogrammerusesaremoteterminaltofeedtheprogramintotheMDSIcomputers,whichinturnproducestheNCtape.ADAPT(AdaptationofAPT).SeveralpartprogramminglanguagesarebaseddirectlyontheAPTprogram.OneoftheseisADAPT,whichwasdevelopedbyIBMunderAirForcecontract.ItwasintendedtoprovidemanyofthefeaturesofAPTbuttoutilizeasignificantlysmallercomputer.ADAPTisnotaspowerfulasAPT,butcanbeusedtoprogramforbothpositioningandcontouringjobs.EXAPT(ExtendedSubsetofAPT)thiswasdevelopedinGermanystaringaround1964andisbasedontheAPTlanguage.Therearethreeversions:EXAPTⅠ—designedforpositioning(drillingandalsostraight-cutmilling),EXAPTⅡ—designedforturning,andEXAPTⅡ—designedforlimitedcontouringoperations.OneoftheimportantfeaturesofEXAPTisthatitattemptstocomputeoptimumfeedsandspeedsautomatically.APTisnotonlyanNClanguage;itisalsothecomputerprogramthatperformsthecalculationstogeneratecutterpositionsbasedonAPTstatements.Therearefourtypesofstatementsintheaptlanguages:·Geometrystatements.Thesedefinethegeometricelementsthatcomprisetheworkpart.Theyarealsosometimescalleddefinitionstatements.·Motionstatements.Theseareusedtodescribethepathtakenbythecuttingtool.·Postprocessorstatements.Theseapplytothespecificmachinetoolandcontrolsystem.Theyareusedtospecifyfeedsandspeedsandtoactuateotherfeaturesofthemachine.·Auxiliarystatements.Thesearemiscellaneousstatementsusedtoidentifythepart,tool,tolerances,andsoon.UNIT27BasicElectricityandMagnetismNewwordsandexpressionsUNIT27BasicElectricityandMagnetismNewwordsandexpressionsUNIT27BasicElectricityandMagnetismTounderstandthetheoryofhowanelectriccurrentflow,youmustunderstandsomethingaboutthestructureofmatter.Matterismadeupofatoms.Atomsaremadeupofprotons,neutrons,andelectrons.Protonsandneutronsarelocatedatthecenter(ornucleus)oftheatom.Protonshaveapositivecharge.Neutronshavenochargeandhavelitterornoeffectasfaraselectricalcharacteristicsareconcerned.Electronshaveanegativechargeandtravelaroundthenucleusinorbits.Thenumberofelectronsinanatomisthesameasthenumberofprotons.Electronsinthesameorbitisthesamedistancefromthenucleusbutdonotfollowthesameorbitalpaths(Figure27-1).Thehydrogenatomisasimpleatomtoillustratebecauseithasonlyoneprotonandoneelectron(Figure27-2).Notallatomsareassimpleasthehydrogenatom.Mostwiringsusedtoconductanelectricalcurrentsmadeofcopper.Figure27-3illustratesacopperatom,whichhas29protonsand29electrons.Someelectronorbitsarefartherawayfromthenucleusthanothers.Ascanbeseen,2travelinaninnerorbit,8inthenext,18inthenext,and1intheouterorbit.Itisthissingleelectronintheouterorbitthatmakescopperagoodconductor[1].Whensufficientenergyorforceisappliedtoanatom,theouterelectron(orelectrons)becomesfreeandmoves.Ifitleavestheatom,theatomwillcontainmoreprotonsthanelectrons.Protonshaveapositivecharge.Thismeansthatthisatomwillhaveapositivecharge[2],Fig.27-4(a).Theatomtheelectronjoinswillcontainmoreelectronsthanprotons,soitwillhaveanegativecharge,Fig.27-4(b).Likechargesrepeleachother,andunlikechargeattracteachother.Anelectroninanatomwithasurplusofelectrons(negativecharges)willbeattractedtoanatomwithashortageofelectrons(positivecharge).Anelectronenteringanorbitwithasurplusofelectronswilltendtorepelanelectronalreadythereandcauseittobecomeafreeelectron.Goodconductorsarethosewithfewelectronsintheouterorbit.Threecommonmetals—copper,silver,andgold—aregoodconductors,andeachhasoneelectronintheouterorbit.Theseareconsideredtobefreeelectronsbecausetheymoveeasilyfromoneatomtoanother.Atomswithseveralelectronsintheouterorbitarepoorconductors.Theseelectronsaredifficulttofree,andmaterialsmadewiththeseatomsareconsideredtobeinsulators.Glass,rubber,andplasticareexamplesofgoodinsulators.UNIT28ElectricPowersNewwordsandexpressionsUNIT28ElectricPowersNewwordsandexpressionsUNIT28ElectricPowersTheunitofelectricpowerinboththeU.S.Customaryandthemetricsystemsisthewatt.InSIunits,onewattisdefinedasbeingequaltoworkbeingdoneattherateofonejoulepersecond.Thewattisalsodefinedastheenergyexpendedortheworkdonepersecondbyanunvaryingcurrentofoneampereflowingunderapressureofonevolt,orP=IE(28-1)whereP=power,W;I=current,A;E=voltage,V.Example28-1Whatisthepowerusedbyanelectriclampthatdraws2.5Afroma120Vline?P=IEP=2.5*120=300WThefactthatthewattisaunitofpoweroraunitofarateofdoingworkcannotbeemphasizedtoostrongly[1]..Itwillberememberedthatcurrentinamperesisarateofflowofelectricityorisequaltothenumberofcoulombspersecond.ThepowerformulamaythenbewrittenPowerinwatts=coulombs/second*voltsInotherwords,thewattisameasureofhowfastaquantityofelectricityisbeingmovedthroughadifferenceinpotential.SincebyOhm’slawE=IR,thisvalueofEmaybesubstitutedinEq.(9-1)toobtainanotherusefulpowerformulaP=IE=I*IR,orP=I²R(28-2).Example28-2Whatisthepowerusedina60-ohmgeneratorfieldrheostatwhenthefieldcurrentis2A?P=I²RP=2²*60=4*60=240WAthirdpowerformulamaybederivedfromthefactthatI=E/RbyOhm’slaw.SubstitutinginEq.(28-1)P=IE=E*E/R(28-3)orP=E²/RExample28-3Whatisthepowerusedbya15-ohmelectricheaterwhenavoltageof120Visapplied?P=E²/RP=120²/15=14400/15=960WAsillustratedintheaboveexamples,Eq.(28-1)isusedtofindthepowerinacircuitwhenthecurrentandvoltageareknown,Eq.(28-2)whenthecurrentandresistanceareknown,andEq.(28-3)whenthevoltageandresistanceareknown.Sincethewattissmallunit,alargerunit,thekilowatt(kW)isoftenusedinstead.Onekilowattisequalto1000watts.Calculationsconcerningelectricmachineryofteninvolveboththeelectricunitorpower(watt)andthemechanicalunit(horsepower).Onehorsepowerisequalto746watts.therefore,tochangepowerinwattstopowerinhorsepower,itisnecessarytodividethenumberofwattsby746.Theinputtomotoris20kW.Whatisthehorsepowerinput?20kW=20*1000=20000WHorsepower=watts/746=20000/746=26.8hpFormostpurposes,therelationbetweenthehorsepowerandthekilowattmaybetakenas1hp=3/4kW(approximately)Powerisameasureofhowfastworkisbeingdoneorofhowfastenergyisbeingexpended,thatis,Power=workorenergy/timeThus,theenergyusedbyanelectricdeviceistherateatwhichtheenergyisbeingused(thepower)multipliedbythetimeduringwhichthedeviceisinuse.Whenpowerismeasuredinwattsandtimehours,thenPower*time=energyorWatts*hours=watthoursthewatt-hours(Wh)beingtheenergyexpendedwhen1wattisusedfor1hour.Thewatthoursisarelativelysmallunit;thekilowatthourbeingusedmuchmoreextensivelyincom.Onekilowatthourisequalto1000watthours.Example28-5Howmuchenergyusedbya1500Wheaterin8h?Energy=Power*time=1500*8=12000W•h=12000/1000=12kW•hIfpowerismeasuredinwattsandtimeinseconds,thenPower*time=energyandWatts*seconds=watt-seconfsThewatt-secondiscalledajoule,whichistheSIunitforelectricaswellasmechanicalenergy.Sincethereare3600secondsinanhourand1000wattsinakilowatt,onekilowatthourisequalto3600000joulesor3.6megajoules(3.6MJ).Example28-6Howmuchenergyinjoules,megajoules,andkilowatthoursisusedbya100-wattlampin12hour?Energyinjoules=watts*seconds=100*12*3600=4320000J=4.32MJEnergyinkW•h=watts*hours/1000=100*12/1000=1.2kW•h1.2kW•h*3.6=4.32MJ(chech).Poweristherateofexpendingenergyjustasspeedisarateofmotion.Iftheaveragespeedofanautomobileisknownforagiventime.Thedistancetraveledistheaveragespeedmultipliedbythetimetraveled.Likewise,iftheaveragepowerrequiredbyanelectricmotorforagiventimeisknown,theenergyusedbythemotoristheaveragepowermultipliedbythetimethemotorisused[2].Thereadershouldmakesurethatheunderstandsthedifferencebetweenpowerandenergy.Poweristherateofexpendingenergyorofdoingwork,justasspeedisarateofmotion.Thecommonlyusedelectricalunitsofenergy,work,andpoweraresummarizedinthefollowing:TheUSCSunitofworkorenergy=watthour(W•h).TheSIunitofworkorenergy=joule(J).Onewatthour=3600joulesOnekilowatthour=3.6megajoules(MJ)TheUSCSunitofpower=watt(W).TheSIunitofpower=watt(W).Unit29NumericalControlSoftwareNewwordsandexpressionsUnit29NumericalControlSoftwareOverviewofNumericalControlToday,theproductdesignprocessbeginswithcomputer-generatedproductconceptsanddesigns,whicharesubjectedtodetailedanalysisoffeasibility,manufacturability,andevendisposability.Traditionally,beforeprocessplanningcangenerateadetailedplanformanufacturingapartorassembly,designtradeoffsaremade.Assembliesarebrokenintoparts.Producedspecificationsareproduced.Qualitycriteriaaredeterminedtomeetsafety,environmental,andconformancewithcompanyandindustrystandards.Engineeringdrawingsareproducedaswellasthebillofmaterial.Finaldesigndecisionsaremaderelatingtostyling,function,performance,materials,tolerances,make-versus-buy,purchasedparts,supplierselection,manufacturability,quality,andreliability.Intheprocessofplanningstage,toolingdecisionsaremade.Thesequenceofproductionstepsisplannedwithactionstakenateachstepcontrolspecified,i.e.theactionstakenateachstep,controlstobefollowed,andthestateoftheworkpieceateachworkstation.Incomputer-aidedprocessplanning(CAPP),anapplicationprogramstorespriorplansandstandardsequencesofmanufacturingoperationsforfamiliesofpartscodedusingthegrouptechnologyconcept,whichclassifiespartsbasedonsimilarityofgeometricshape,manufacturingprocess,orsomeotherpartcharacteristics.Alltoolsrequiredproducingthefinalpartorassemblyarespecifiedordesigned.Thisincludesmolds,stampingandformingdies,jigsandfixtures,cuttools,andothertooling.Thetooldesigngrouptypicallyworkscloselywiththetoolroomandwithsupplierstoproducethenecessarytoolsintimetomeetproductionschedules.Numericalcontrolprovidestheoperationalcontrolofamachineormachinesbyaseriesofcomputer-codedinstructionscomprisingnumbers,letters,andothersymbols,whicharetranslatedintopulsesofelectricalcurrentorotheroutputsignalsthatactivatemotorsorotherdevicestorunthemachine.WithNC,machinesrunconsistently,accurately,predictably,andessentiallyautomatically.Qualityandproductivityareincreased,andreworkandlead-timesarereducedcomparedwithmanualoperationAPT(AutomaticallyProgrammedTools)wasthefirstNClanguage.ATPwasdesignedtofunctionasanoff-line,batchprogramusingamainframecomputersystem.Becauseofthecomputerresourcesneededandtheexpense,time-sharingwasemployed,anewsimplerlanguagetousedeveloped.Eventually,interactivegraphics-basedNCprogramsusingterminalsandworkstationswereintroducedtoimprovevisualizationandprovidetheopportunityforimmediatefeedbacktotheuser.ThesedevelopmentsremainthestandardforNCprogrammingtodayandareavailableonallcomputingplatformsfromPCstomainframes.RequirementsofNCSoftwareNCsoftware,accordingly,maybeobtainedasindependentsoftwarepackages,asdedicatedNCturnkeysystemsthatincludeaprinter,plotterandtapepunch,orascomponentsofCAD/CAMsoftwarepackagesthatalsoprovidedesignanddrafting.Interactivegraphics-basedNCpart-programmingtechnologyincreasesproductqualityandsimplifiestheprocessbyreducingsetuptimeforlathes,mills,EDMs,andothermachinetools.Craphicssoftwareletsuserseasilydefinepartgeometry,obtainimmediatefeedback,andvisualizetheresultswhilechangesaremadequickyandefficiently.NCPackagesaccomplishfourmajorfunctions:partdescription,machiningstrategy,post-processing,andfactorycommunications.Todescribeapart,mostNCProgrammingsystemsprovidetheirowngeometricmodelingcapabilityasanintegralcomponentofthesyetem.TheseCAD-likefrontendpermitsuserstocreatepartsbydrawinglines,circle,arcs,andsplines.AllNCpackagessupport2Dgeomertrycreationandmanyhaveoptional3DModules.The3DmodulepermitsthecreationofcomplexsurfacesordirectmachiningfromthesolidmodelwillbecomeacceptedinNC.Acloserelationshipbetweenthemodelcreationandmachiningofthatmodelisimportant.MajorCAD/CAMvendorsprovideNCSoftwarethatisintegratedwiththedesignanddraftingfunctionforjustthisreason.Operatingfromthesameoraco-existentdatabase,theNCSoftwarecandirectlyaccessamodelthathasbeencreatedwithinthedesignmoduleoftheCAD/CAMsystem.Thiseliminatesthere