先進(jìn)制造技術(shù)雙語(yǔ)2課件

AUTOMATEDMANUFACTURING

CHAPTER22.1CAD/CAM2.1.1CAD/CAMDefined

CAD:Theuseofcomputersystemstoassistinthecreation,modification,analysis,oroptimizationofadesign.

ACADmodelofamouse.

CAM:Theuseofcomputersystemstoplan,manage,andcontroltheoperationsofamanufacturingplant.TwokindsofCAM:(1)Computermonitoringandcontrol—directapplicationofcomputerintheprocess.(2)Computermanufacturingsupportapplications—indirectapplication.ComputerProcessProcessDataMonitoringComputer

ProcessDataControl

ControlSignalsProcessFormabilityAnalysisExampleMoldandToolingExample.CAD/CAMmeansusingcomputersinthedesignandmanufacturingprocesses.SincetheadventofCAD/CAM,othertermshavedeveloped.Computergraphics(CG)Computer-aidedengineering(CAE)Computer-aideddesignanddrafting(CADD)Computer-aidedprocessplanning(CAPP)

AkeygoalofCAD/CAMistoproducedatathatcanbeusedinmanufacturingaproductwhiledevelopingthedatabaseforthedesignofthatproduct.Whensuccessfullyimplemented,CAD/CAMinvolvesthesharingofacommondatabasebetweenthedesignandmanufacturingcomponentsofacompany.

CAD/CAMgrowsoutofaneedtocontinuallyimproveproductivity,quality,and,inturn,competitiveness.TherearealsootherreasonswhyacompanymightmakeaconversionfrommanualprocessestoCAD/CAM:(1)IncreasedProductivity

(2)betterquality(3)bettercommunication2.1.1RationaleforCAD/CAM(4)commondatabasewithmanufacturing(5)reducedprototypeconstructioncosts(6)fasterresponsetocustomers

Aprototypeisanoriginaltype,form,orinstanceofsomethingservingasatypicalexample,basis,orstandardforotherthingsofthesamecategory.

(1)IncreasedProductivityProductivityinthedesignprocessisincreasedbyCAD/CAM.TheamountoftimerequiredtodocumentadesigncanbereducedsignificantlywithCAD/CAM.Thesemeansashorterdesigncycle,shorteroverallprojectcompletiontime,andahigherlevelofproductivity.(2)BetterQualityBecauseCAD/CAMallowsdesignerstofocusmoreonactualdesignproblemsandlessontime-consuming,nonproductivetasks,productqualityimproveswithCAD/CAM.labor-intensivetasksareperformedbythecomputer,fewerdesignerrorsoccur.Theseallleadtobetterproductquality.

(3)BetterCommunicationDesigndocumentssuchasdrawings,partslists,billsofmaterial,andspecificationsaretoolsusedtocommunicatethedesigntothosewhowillmanufactureit.BecauseCAD/CAMleadstomoreuniform,standardized,andaccuratedocumentation,itimprovescommunication.

(4)CommonDatabaseWithCAD/CAM,thedatageneratedduringthedesignofaproductcanbeusedinproducingtheproduct.Thissharingofacommondatabasehelpstoeliminatetheage-old"wall"separatingthedesignandmanufacturingfunctions(5)ReducedPrototypeCostsWithCAD/CAM,3-Dcomputermodelscanreduceand,insomecases,eliminatetheneedforbuildingexpensiveprototypes.SuchCAD/CAMcapabilitiesassolidsmodelingallowdesignerstosubstitutecomputermodelsforprototypesinmanycases.(6)FasterResponsetoCustomersResponsetimeiscriticalinmanufacturing.Byshorteningtheoveralldesigncycleandimprovingcommunicationbetweenthedesignandmanufacturingcomponents,CAD/CAMcanimproveacompany'sresponsetime.

Alldesigntasksaccomplishedusingacomputerfallintooneoffourbroadcategories:(1)DesignModelingInCAD/CAMdesignmodeling,ageometricmodelofaproductisdevelopedthatdescribesthepartmathematically.Thegeometricmodelalsoallowsthegraphicimagetobeeasilyeditedandmanipulatedoncedisplayed.2.1.2ComputersandDesign

(2)DesignAnalysisOnceaproposeddesignhasbeendeveloped,itisnecessarytoanalyzehowitwillstanduptotheconditionstowhichitwillbesubjected.Suchanalysismethodsasheattransferandstress-straincalculationsaretime-consumingandcomplex.WithCAD/CAM,specialcomputerprogramswrittenspecificallyforanalysispurposesareavailable.Onesuchprogramisfinite-elementanalysis.FEAinvolvesbreakinganobjectupintomanysmallrectangularortriangularelements,thenanalyzingeachindividualelementbycomputer.Byanalyzingtheresponseofeachfiniteelementoftheobjecttothestress,strain,heat,orotherforceactingonit,thecomputercanpredictthereactionofthewholeobject.ModernCAD/CAMsystemswithFEAcapabilitymaketheprocesssimpletoachieve.FEARepresentationMisesstressTemperaturefieldTemperaturestress

(3)DesignReviewThefirstisthesemiautomaticdimensioningcapabilityofmanyCAD/CAMsoftwarepackages.ThelayeringcapabilityofCAD/CAMsoftwarealsosimplifiesdesignreview.AnotherCAD/CAMsoftwarecapabilitythathassimplifieddesignreviewiscalledinterferencechecking.WithKinematiccapability,CAD/CAMsoftwarecansimulatemotiononCRT/LEDdisplay.(4)DesignDocumentation

WithCAD/CAM,thedrawingsneededtodocumentthedesigncanbeproducedusingthedatabasecreatedduringthedesignprocess.BecausethecomputercanstorethemathematicalmodelsofalldrawingsdoneonaCAD/CAMsystem,onceadrawinghasbeenproduced,itneverhastoberedrawn.Itcansimplybecalledupfromstorage,enteredintotheappropriatelocationinthedrawingpackage,andusedagainandagain.Therealinterfaceisthecommondatabasetheyshare.WhatisDFA?

DFAmethodologiesweredevelopedtosupportthedesignerbygeneratingfeedbackontheconsequencesofdesigndecisionsonproductassembly.Theaimistohelpthedesignertoproduceanefficientandeconomicdesign.2.1.4DesignforAssembly,Manufacturing,andtheEnvironment(DFA/M/E)TheapplicationofDFAguidesthedesignertowardsaproductwithanoptimumnumberofparts,thatrequiressimple,cost-effectiveassemblyoperationsandthemostappropriatemanufacturingprocessesandmaterialsforitscomponents.Ingeneral,thedesignerisguidedthroughtheanalyses,whicharepresentedinaseriesofassessmentcharts.Thechartsarebasedonempiricaldatagatheredbyknowledgeengineeringexerciseswithindustrialexpertsandorganisedinaneasy-to-useworksheetformat.Duringtheevaluation,thedesignerisrequiredtoassesscomponentfunctionality,formmanufacturingprocessesandassemblycharacteristicsusingvaluesextractedfromthechartsaccordingtocomponentproperties.Thesenumbersarethencompiledintabularformat,andcalculationsperformed.Inthisway,thedesignerisabletoquantifythesuitabilityofthedesign.TheLucasDFAMethodologyhasbeenchosenforusewithintheDesigners'Sandpitprojectbecauseofexistingexpertisewithinthegroup.TheDesignersSandpitisanassembly-orienteddesignenvironmentcontainingtoolsandtechniquestogenerateeconomicdesigns.Aspartofthisenvironment,designersneedmethodsforassessingtheassembliabilityoftheirdesigns.TheLucasDFAmethodwasdevelopedintheearly1980'sbytheLucasCorp.intheU.K.Themethodisbasedonthreeseparateandsequentialanalyses:Specification,Design,Functionalanalysis.WhatisDFM?Followedduringthedesignprocess,DFMisanapproachwhichhastheaimofimprovingmanufacturingproductivity.Itbringsmajorbenefitswhenusedduringthedesignofnewgenerationsofproducts.Itisamethodofworkingwhich:Helpstheteamfocusonclearandcommonobjectives

Encouragesproblem-ownershipandpreventsmanufacturingproblemsbeingshiftedfromareatoarea(e.g.fromdirecttooverheadcosts)Usesatop-downapproach(preventingearlyandwastefulfocusondetail)toproductdesignDuringDFM,theconsiderablebackgroundworkrequiredfortheconceptualphasesiscompensatedforbyashorteningoflaterdevelopmentphases.Problemownership:WillingnesstoacceptownershipandresponsibilityWhatisDesignfortheEnvironment?DesignfortheEnvironment(DFE)istheconsiderationofpollutionpreventionandresourceconservationwithinthedesignprocess.DFEstartswiththedevelopmentofenvironmentalgoalswithinanexamplesetofenvironmentalpolicy,needs,andconcerncategories.Goalsshouldbelargeinscope:consideringthefulllifecycleofperformance,cost,andenvironmentalimplications.Therearethreemajorelementsofdesignfortheenvironment:designforenvironmentalmanufacturing,designforenvironmentalpackaging,anddesignfordisposalandrecycleability.Designforenvironmentalmanufacturinginvolvesthefollowingconsiderations:Non-toxicprocesses&productionmaterialsMinimumenergyutilizationMinimizeemissionsMinimizewaste,scrap&by-productsDesignforenvironmentalpackaginginvolvesthefollowingconsiderations:MinimumofpackagingmaterialsReusablepallets,totesandpackaging

RecyclablepackagingmaterialsBio-degradablepackagingmaterialsDesignfordisposal&recycleabilityinvolvesthefollowingconsiderations:Materialselectiontoenablere-useandminimizetoxicityMinimumnumberofmaterials/colorstofacilitateseparatingmaterialsandre-useMaterialidentificationtofacilitatere-useDesigntoenablematerialstobeeasilyseparatedDesignfordisassemblyNewtechniquestoanalyzeaparticulardesignforitsmanufacturabilityincludethedesignformanufacturingandassembly(DFMA)softwaretoolsbyBoothroydandDewhurst(1999).Asuiteoftoolsisavailablethatcontain,forexample,DFMsoftwareformachining,DFMsoftwareforsheetmetalworking,DFEsoftwaretoassessenvironmentalimpacts,andtheirbest-knownDFAmoduleforevaluatingassembly.TheDFAforassemblymoduleinvolvestwokeyideas:Thequalityofindividualsubcomponentsmustbehigh.Also,theirnumbermustbereducedasmuchasfeasible.Assemblyoperationsmustbeassimpleaspossible.Forexample,factorylayoutsshouldbeorderly,theshapeofindividualcomponentsshouldbesimple,designfeaturesshouldsimplifytheassemblyofonecomponentwithanother,andassemblyoperationsshouldnotfightgravity.DFMformachiningmodule"MachiningforWindows"assistsadesignerwiththefollowingissues:developingoperationandprocessplans,obtainingcostestimatesattheearlieststagesofconceptualdesign,developingquotations,andplanningforproduction.Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).Thevarietydemandedinviewofthevaryingtastesoftheconsumercallsforverysmallbatchsizes.Smallbatchsizesarenotabletotakeadvantageofmassproductiontechniquessuchasspecialpurposemachinesortransferlines.2.2NumericalControlThereisaneedforflexibleautomationwhereyoucangetthebenefitsofrigidautomationandalsobeabletomanufactureavarietyofproducts,thusbringinginflexibility.Themethodofnumericalcontrolisappropriateforthispurpose,andinfuturemanufacturingisexpectedtobeincreasinglydependentonnumericalcontrol.

NChasbeendefinedbytheElectronicIndustriesAssociation(EIA)as“asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.

Thesystemmustautomaticallyinterpretat

leastsomeportionofthisdata.”Thenumericaldatarequiredtoproduceapartis

knownasapartprogram.Anumericalcontrolmachinetoolsystemcontainsamachinecontrolunit(MCU)andthemachinetoolitself.TheMCUisfurtherdividedintotwoelements:thedataprocessingunit(DPU)andthecontrolloopsunit(CLU).TheDPUprocessesthecodeddatafromthetapeorothermediaandpassesinformationonthepositionofeachaxis,requireddirectionofmotion,feedrate,andauxiliaryfunctioncontrolsignalstotheCLU.TheCLUoperatesthedrivemechanismsofthemachine,receivesfeedbacksignalsconcerningtheactualpositionandvelocityofeachoftheaxes,andsignalsthecompletionofoperation.TheDPUsequentiallyreadsthedata.WheneachlinehascompletedexecutionasnotedbytheCLU,anotherlineofdataisread.Adataprocessingunitconsistsofsomeorallofthefollowingparts:

(1)Datainputdevicesuchasapapertapereader,magnetictapereader,RS232-Cport,etc(2)Data-readingcircuitsandparity-checkinglogic(3)Decodingcircuitsfordistributingdataamongthecontrolledaxes(4)Aninterpolator,whichsuppliesmachine-motioncommandsbetweendatapointsfortoolmotionAcontrolloopsunit,ontheotherhandconsistsofthefollowing:(1)Positioncontrolloopsforalltheaxesofmotion,whereeachaxishasaseparatecontrolloop(2)Velocitycontrolloops,wherefeedcontrolisrequired(3)Decelerationandbacklashtakeupcircuits(4)Auxiliaryfunctionscontrol,suchascoolanton/off,gearchanges,spindleon/offcontrolNumericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveralotherinnovationsinmanufacturingtechnology:ElectricdischargemachiningLaser-cuttingElectronbeamweldingNumericalcontrolhasallowedmanufacturerstoundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetoolsandprocesses.Afactoryworkerin1940sFortWorth,Texas.Numericalcontrolorcontrolbynumbers,isaconceptwhichhasrevolutionizedthemanufacturingscene.Thisispartiallyduetotherapidadvancementinmicroelectronicsthathastakenplacesincelate1960s.ThekeyfactorresponsibleforthepopularityofNumericalControlistheflexibilityitoffersinmanufacturing.2.2.1HistoricalDevelopmentofNCLikesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirForce.Initsearlieststages,NCmachineswereabletomakestraightcutsefficientlyandeffectively.Towardsendofthesecondworldwar,therewasincreasedactivityinaerospacemanufacturinginUSA.JohnParsonsofParsonsCorporationwhichwasoneofthesubcontractorstoUSAF(UnitedStatesAirForce),wastoyingwiththeideaofutilizingdigitalcomputerswhichwerethenbecomingpopular.Machining(milling)ofcomplexcurvaturewasahighlyskilledjob.Parsonsproposedthattheco-ordinatepointsofacomplexthreedimensionalprofilemaybeutilizedforcontrollingthemillingmachinetablesothataccuratejobscouldbeproduced.TheUSAFacceptedhisproposalandacontractwasawardedtohimtodevelopsuchamachine.TheprojectwasthenawardedtotheServomechanismLaboratoryofMassachusettsInstituteofTechnologyin1951,whofinallydemonstratedaworkingmillingmachinein1952,ThiswasaCincinnatiHydrotelVerticalSpindlemillingmachinewithacontrollerbuiltusingvalves(transistorswerenotavailablethen).NCPunchedTapeHowever,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorterthestraightlinesmakingupthesteps,thesmootheristhecurve(Fig.2.17).EachlinesegmentinthestepsshowninthecloseupinFig.2.17hadtobecalculated.ThiswasacumbersomeapproachthathadtobeovercomeifNCwastodevelopfurther.Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)language.ThisisaspecialprogramminglanguageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.TheoriginalNCsystemswerevastlydifferentfromthoseusedtoday.Themachineshadhardwiredlogiccircuits.Theinstructionalprogramswerewrittenonpunchedpaper,whichwaslatertobereplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.

Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapertapecontainingtheprogrammedinstructionstobreakortearduringamachiningprocess.Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtobererunthroughthereader.Thisledtothedevelopmentofaspecialmagneticplastictape.Whereasthepapertapecarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theplastictapecarriedtheinstructionsasaseriesofmagneticdots.Theplastictapewasmuchstrongerthanthepapertape,whichsolvedtheproblemoffrequenttearingandbreakage.However,itstilllefttwootherproblems.Themostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Itwasalsostillnecessarytorunthetapethroughthereaderasmanytimesastherewerepartstobeproduced.(1)AdventofDirectNumericalControlThedevelopmentofaconceptknownasdirectnumericalcontrol(DNC)solvedthepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputer(Fig2.18).Programsforoperatingthemachinetoolsarestoredinthehostcomputerandfedtothemachinetoolasneededviathedatatransmissionlinkage.DNCissubjecttothesamelimitationsasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,ashappenswithallhostcomputers,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.

(2)AdventofComputerNumericalControl

Thedevelopmentofthemicroprocessorallowedforthedevelopmentofprogrammablelogiccontrollers(PLCs)andmicrocomputers.Thesetwotechnologiesallowedforthedevelopmentofcomputernumericalcontrol(CNC).WithCNC,eachmachinetoolhasaPLCoramicrocomputerthatservesthesamepurpose.Thisallowsprogramstobeinputandstoredateachindividualmachinetool.Italsoallowsprogramstobedevelopedoff-lineanddownloadedattheindividualmachinetool.CNCsolvedtheproblemsassociatedwithdowntimeofthehostcomputer,butitintroducedanotherproblemknownasdatamanagement.Thisisaproblemallworksettingsdependentonmicrocomputershave.Thesameprogrammightbeloadedonthedifferentmicrocomputerswithnocommunicationamongthem.Thisproblemisintheprocessofbeingsolvedbylocalareanetworksthatconnectmicrocomputersforbetterdatamanagement.Theproblemofdatamanagementledtothedevelopmentofdistributednumericalcontrol.

(3)AdventofDistributedNumericalControlDistributednumericalcontrol(alsocalledDNC)takesadvantageofthebestaspectsofdirectnumericalcontrolandcomputernumericalcontrol.Withdistributednumericalcontroltherearebothhostcomputersandlocalcomputersattheindividualmachinetools(Fig2.19).Thisallowstheprogramstobestoredinthehostcomputerand,thereby,bettermanaged.However,italsoallowsthemtobedownloadedtolocalmicrocomputersorPLCs.ItalsoallowsforlocalinputandinteractionthroughmicrocomputersorPLCsatthemachinelevel.BasicallyaNCmachinerunsonaprogramfedtoit.Theprogramconsistsofpreciseinstructionsaboutthemanufacturingmethodologyaswellasthemovements.Sincetheprogramisthecontrollingpointforproductmanufacture,themachinebecomesversatileandcanbeusedforanypart.AllthefunctionsofanNCmachinetoolarethereforecontrolledelectronically,hydraulicallyorpneumatically.2.2.2NCMachineandComponents

InNCmachinetoolsoneormoreofthefollowingfunctionsmaybeautomatic:(i)Startingandstoppingofthemachinetoolspindle.(ii)Controllingthespindlespeed.(iii)Positioningthetooltipatdesiredlocationsandguidingitalongdesiredpathsbyautomaticcontrolofthemotionofslides.(iv)Controllingtherateofmovementofthetooltip(i.e.feedrate).(v)Changingoftoolsinthespindle.

NCmachineshavebeenfoundsuitableforthefollowing:(i)Partshavingcomplexcontours,thatcannotbemanufacturedbyconventionalmachinetools.(ii)Smalllotproduction,oftenforevensingle(oneoff)jobproduction,suchasforprototyping,toolmanufacturing,etc.(iii)Jobsrequiringveryhighaccuracyandrepeatability.(iv)Jobsrequiringmanyset-upsand/orwhentheset-upsareexpensive.(v)Partsthataresubjectedtofrequentchangesandconsequentlyrequiremoreexpensivemanufacturingmethods.(vi)Theinspectioncost,whichisasignificantportionofthetotalmanufacturingcost.

TherearefourcomponentsinanyNCmachine:theactualNCtool

TheactualNCmachinemaybeamillingmachine,lathe,drill,oranyothertypeofmachinetool.themachinecontrolunit(MCU)

TheMCUisthecontrolunitthatholdstheprogramsthatinstructtheNCmachine.TheMCUalsohasvariousdevicesavailableforoperatorinput.EveryNCmachinetoolisfittedwithamachinecontrolunit(MCU)whichperformsthevariouscontrollingfunctionsundertheprogramcontrol.TheMCUmaybegenerallyhousedinaseparatecabinet-likebodyormaybemountedonthemachineitself.Whenseparatelymounted,itmaysometimesbependantwhichcouldswingaroundforconvenienthandlingbytheoperator.Appearancewiseitlookslikeacomputerwithadisplaypanelgenerallyofasmallsize(9inches)andanumberofbuttonstocontrolthemachinetoolalongwithakeyboard.Thiscontrolunitcontrolsthemotionofthecuttingtool,spindlespeeds,feedrate,toolchanges,cuttingfluidapplicationandseveralotherfunctionsofthemachinetool.thecommunicationinterfacebetweentheNCmachineandtheMCUInformationcontainedintheMCUiscarriedtotheactivatorsontheNCmachinethroughthecommunicationinterface.TheseactivatorsreceivetheelectronicsignalsfromtheMCUandcausethemechanicalapparatusoftheNCmachinetooperate.avarietyofaccessoriesforperformingspecificjobsontheNCmachineTheaccessoriesarespecialtoolsrequiredtocarryoutaspecificjob.TheprincipleofoperationofanNCmachinetoolisshowninFig.16.1.Thebasicinformationthat

hastobeinputintothesystemconsistsofthepartgeometryandcuttingprocessparametersfollowedbythecuttingtoolsused.Thispartprogramisthenenteredintothecontrollerofthemachine,whichinturnrunsthemachinetooltomakethepart.Thecommandreceivedfromtheoperatoriscommunicatedtothecorrespondingaxisdrivingsystem

forexecution.Theaxismotioncontrolsystemoperatesinafeedbackloopwithsuitabletransducerssuchaslinearscalesand/orrotaryencoderstogettheappropriatepositionorvelocityfeedbackasshowninFig.16.2.Mostofthesesystemshaveaveryhighresponsewithgoodresolutionoftheorderof1μm(micron)orless.Thecontrollershaveanumberofmodesinwhichtheyoperate.Therecanbefourpossiblemodes

inwhichthecontrollercanfunctionasshowninFig.16.3inrelationtoamachiningcentre.Thefirstshowsatypicaldrillingmachineoperation,termedaspoint-to-pointmode.Inthis,thecontrolhasthecapacitytooperateallthethreeaxes,butnotnecessarilysimultaneously.Asaresult,itwouldbepossiblemovethetooltoanypoint(inXandY-axes)inthefastestpossiblespeedandcarryoutthemachiningoperationinoneaxis(Z-axis)atthatpoint.Thiswouldbeusefulfordrillingandpunchingmachine.Thesecondtypeisanimprovementoverthisinwhichinadditiontothepointtopointmode,themachinetoolhasthecapabilitytocarryoutacontinuousmotionineachoftheaxisdirection.Thiswouldhelpinobtainingthemillinginastraightlinealonganyoftheaxes.Thethirdtypeshowsacontrolsystem,whichimprovestheprevioustypebyaddingthesimultaneous

motioncapabilityinanytwoaxes.Thisiswhatisrequiredinmostofthecases.Any3Dprofilesmachinedcanbecompletedusingtheconceptof2.5Dmode,inviewofthelimitationofthemachine.

Thelastoneisthehighestformofcontrolthatisgenerallyfoundinmostofthecurrentdaycontrol

systems,Thisgivesthecapabilityofsimultaneousthreeormoreaxesmotion.Thiswouldbeusefulformachiningmostofthecomplex3Dprofilesencounteredinindustrialpracticesuchasaerospacecomponents,mouldsanddies.Numericalcontrolmachinesrequireorneedaprogramtoperformwork.ThisprogramsarecalledpartprogramsandthepartprogrammingisconcernedwithplanninganddocumentationofthesequenceofprocessingstepstobeperformedontheNCmachine.However,planningoftheprogramrequiresknowledge

ofmachining,geometryandtrigonometry.Thesequenceofstepswhichconstitutesthepartprogramgovernthemovementsoftheprocessingheadwithrespecttothemachinetableandworkpart.

2.2.3NCProgrammingThepartprogramisaveryimportantsoftwareelementinanNCmanufacturingsystem.Itlookslikeacomputerprogramcontaininganumberoflines/statements/instructions(calledNCblocks).Itisthereforethedetailedplanofmanufacturinginstructionsproposedformachiningthepart.ItiswrittenkeepinginviewthevocabularyunderstoodbytheMCUintermsofvariousstandardwords,codesandsymbols.TheformatandthelanguagearedependentonthemachinetoolhardwareandtheMCU.SpecifyingCommands

Acommonformatisthe“Wordaddressformat”:

N_G_X_Y_Z_I_J_K_F_S_T_M_where:theletterdenotesatypeofinstructionorinstructionparameter,‘_’isanumberthatgivestheinstructionnumberorparametervalueletterandnumberpairs(words)canbeomittediftheyhavenotchangedfromthelastcommand.CodeMeaningN–sequencenumberG–preparatoryfunctionG00:Initialpositioning;G01:linearinterpolation;G02:circularF–feedfunctionS–spindlespeedfunctionT–toolfunctionM–miscellaneousfunctionEOB–endofblock

TherearefourwaystoprogramanNCmachine:

ⅰ)manualprogramming

manualprogramm