先进制造技术双语2课件

AUTOMATEDMANUFACTURING

CHAPTER2AUTOMATEDMANUFACTURING

CHAPTE2.1CAD/CAM2.1.1CAD/CAMDefined

CAD:Theuseofcomputersystemstoassistinthecreation,modification,analysis,oroptimizationofadesign.

ACADmodelofamouse.2.1CAD/CAM2.1.1CAD/CAMDefin

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

ProcessDataControl

ControlSignalsProcessCAM:TheuseofcomputersyFormabilityAnalysisExampleFormabilityAnalysisExampleMoldandToolingExample.MoldandToolingExample.CAD/CAMmeansusingcomputersinthedesignandmanufacturingprocesses.SincetheadventofCAD/CAM,othertermshavedeveloped.Computergraphics(CG)Computer-aidedengineering(CAE)Computer-aideddesignanddrafting(CADD)Computer-aidedprocessplanning(CAPP)CAD/CAMmeansusingcompute先进制造技术双语2课件

AkeygoalofCAD/CAMistoproducedatathatcanbeusedinmanufacturingaproductwhiledevelopingthedatabaseforthedesignofthatproduct.Whensuccessfullyimplemented,CAD/CAMinvolvesthesharingofacommondatabasebetweenthedesignandmanufacturingcomponentsofacompany.

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

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

Aprototypeisanoriginaltype,form,orinstanceofsomethingservingasatypicalexample,basis,orstandardforotherthingsofthesamecategory.(4)commondatabasewithmanuf

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

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

(4)CommonDatabaseWithCAD/CAM,thedatageneratedduringthedesignofaproductcanbeusedinproducingtheproduct.Thissharingofacommondatabasehelpstoeliminatetheage-old"wall"separatingthedesignandmanufacturingfunctions(4)CommonDatabase先进制造技术双语2课件(5)ReducedPrototypeCostsWithCAD/CAM,3-Dcomputermodelscanreduceand,insomecases,eliminatetheneedforbuildingexpensiveprototypes.SuchCAD/CAMcapabilitiesassolidsmodelingallowdesignerstosubstitutecomputermodelsforprototypesinmanycases.(5)ReducedPrototypeCosts(6)FasterResponsetoCustomersResponsetimeiscriticalinmanufacturing.Byshorteningtheoveralldesigncycleandimprovingcommunicationbetweenthedesignandmanufacturingcomponents,CAD/CAMcanimproveacompany'sresponsetime.(6)FasterResponsetoCusto

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

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

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

WithCAD/CAM,thedrawingsneededtodocumentthedesigncanbeproducedusingthedatabasecreatedduringthedesignprocess.BecausethecomputercanstorethemathematicalmodelsofalldrawingsdoneonaCAD/CAMsystem,onceadrawinghasbeenproduced,itneverhastoberedrawn.Itcansimplybecalledupfromstorage,enteredintotheappropriatelocationinthedrawingpackage,andusedagainandagain.(4)DesignDocumentationTherealinterfaceisthecommondatabasetheyshare.TherealinterfaceisthecommWhatisDFA?

DFAmethodologiesweredevelopedtosupportthedesignerbygeneratingfeedbackontheconsequencesofdesigndecisionsonproductassembly.Theaimistohelpthedesignertoproduceanefficientandeconomicdesign.2.1.4DesignforAssembly,Manufacturing,andtheEnvironment(DFA/M/E)WhatisDFA?

DFAmethodologiesTheapplicationofDFAguidesthedesignertowardsaproductwithanoptimumnumberofparts,thatrequiressimple,cost-effectiveassemblyoperationsandthemostappropriatemanufacturingprocessesandmaterialsforitscomponents.Ingeneral,thedesignerisguidedthroughtheanalyses,whicharepresentedinaseriesofassessmentcharts.Thechartsarebasedonempiricaldatagatheredbyknowledgeengineeringexerciseswithindustrialexpertsandorganisedinaneasy-to-useworksheetformat.TheapplicationofDFAguides先进制造技术双语2课件Duringtheevaluation,thedesignerisrequiredtoassesscomponentfunctionality,formmanufacturingprocessesandassemblycharacteristicsusingvaluesextractedfromthechartsaccordingtocomponentproperties.Thesenumbersarethencompiledintabularformat,andcalculationsperformed.Inthisway,thedesignerisabletoquantifythesuitabilityofthedesign.Duringtheevaluation,thedesTheLucasDFAMethodologyhasbeenchosenforusewithintheDesigners'Sandpitprojectbecauseofexistingexpertisewithinthegroup.TheDesignersSandpitisanassembly-orienteddesignenvironmentcontainingtoolsandtechniquestogenerateeconomicdesigns.Aspartofthisenvironment,designersneedmethodsforassessingtheassembliabilityoftheirdesigns.TheLucasDFAmethodwasdevelopedintheearly1980'sbytheLucasCorp.intheU.K.Themethodisbasedonthreeseparateandsequentialanalyses:Specification,Design,Functionalanalysis.TheLucasDFAMethodologyhasWhatisDFM?Followedduringthedesignprocess,DFMisanapproachwhichhastheaimofimprovingmanufacturingproductivity.Itbringsmajorbenefitswhenusedduringthedesignofnewgenerationsofproducts.Itisamethodofworkingwhich:Helpstheteamfocusonclearandcommonobjectives

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

RecyclablepackagingmaterialsBio-degradablepackagingmaterialsDesignforenvironmentalpackaDesignfordisposal&recycleabilityinvolvesthefollowingconsiderations:Materialselectiontoenablere-useandminimizetoxicityMinimumnumberofmaterials/colorstofacilitateseparatingmaterialsandre-useMaterialidentificationtofacilitatere-useDesigntoenablematerialstobeeasilyseparatedDesignfordisassemblyDesignfordisposal&recycleaNewtechniquestoanalyzeaparticulardesignforitsmanufacturabilityincludethedesignformanufacturingandassembly(DFMA)softwaretoolsbyBoothroydandDewhurst(1999).Asuiteoftoolsisavailablethatcontain,forexample,DFMsoftwareformachining,DFMsoftwareforsheetmetalworking,DFEsoftwaretoassessenvironmentalimpacts,andtheirbest-knownDFAmoduleforevaluatingassembly.NewtechniquestoanalyzeTheDFAforassemblymoduleinvolvestwokeyideas:Thequalityofindividualsubcomponentsmustbehigh.Also,theirnumbermustbereducedasmuchasfeasible.Assemblyoperationsmustbeassimpleaspossible.Forexample,factorylayoutsshouldbeorderly,theshapeofindividualcomponentsshouldbesimple,designfeaturesshouldsimplifytheassemblyofonecomponentwithanother,andassemblyoperationsshouldnotfightgravity.TheDFAforassemblymodule先进制造技术双语2课件DFMformachiningmodule"MachiningforWindows"assistsadesignerwiththefollowingissues:developingoperationandprocessplans,obtainingcostestimatesattheearlieststagesofconceptualdesign,developingquotations,andplanningforproduction.DFMformachiningmodule"M先进制造技术双语2课件Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).Thevarietydemandedinviewofthevaryingtastesoftheconsumercallsforverysmallbatchsizes.Smallbatchsizesarenotabletotakeadvantageofmassproductiontechniquessuchasspecialpurposemachinesortransferlines.2.2NumericalControlOneofthemostfundamentalThereisaneedforflexibleautomationwhereyoucangetthebenefitsofrigidautomationandalsobeabletomanufactureavarietyofproducts,thusbringinginflexibility.Themethodofnumericalcontrolisappropriateforthispurpose,andinfuturemanufacturingisexpectedtobeincreasinglydependentonnumericalcontrol.Thereisaneedforflexible

NChasbeendefinedbytheElectronicIndustriesAssociation(EIA)as“asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.

Thesystemmustautomaticallyinterpretat

leastsomeportionofthisdata.”Thenumericaldatarequiredtoproduceapartis

knownasapartprogram.NChasbeendefinedbytheAnumericalcontrolmachinetoolsystemcontainsamachinecontrolunit(MCU)andthemachinetoolitself.AnumericalcontrolmachinetoTheMCUisfurtherdividedintotwoelements:thedataprocessingunit(DPU)andthecontrolloopsunit(CLU).TheDPUprocessesthecodeddatafromthetapeorothermediaandpassesinformationonthepositionofeachaxis,requireddirectionofmotion,feedrate,andauxiliaryfunctioncontrolsignalstotheCLU.TheMCUisfurtherdividedintTheCLUoperatesthedrivemechanismsofthemachine,receivesfeedbacksignalsconcerningtheactualpositionandvelocityofeachoftheaxes,andsignalsthecompletionofoperation.TheDPUsequentiallyreadsthedata.WheneachlinehascompletedexecutionasnotedbytheCLU,anotherlineofdataisread.TheCLUoperatesthedriveAdataprocessingunitconsistsofsomeorallofthefollowingparts:

(1)Datainputdevicesuchasapapertapereader,magnetictapereader,RS232-Cport,etc(2)Data-readingcircuitsandparity-checkinglogic(3)Decodingcircuitsfordistributingdataamongthecontrolledaxes(4)Aninterpolator,whichsuppliesmachine-motioncommandsbetweendatapointsfortoolmotionAdataprocessingunitconsAcontrolloopsunit,ontheotherhandconsistsofthefollowing:(1)Positioncontrolloopsforalltheaxesofmotion,whereeachaxishasaseparatecontrolloop(2)Velocitycontrolloops,wherefeedcontrolisrequired(3)Decelerationandbacklashtakeupcircuits(4)Auxiliaryfunctionscontrol,suchascoolanton/off,gearchanges,spindleon/offcontrolAcontrolloopsunit,ontheNumericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveralotherinnovationsinmanufacturingtechnology:ElectricdischargemachiningLaser-cuttingElectronbeamweldingNumericalcontrolmachinesNumericalcontrolhasallowedmanufacturerstoundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetoolsandprocesses.Afactoryworkerin1940sFortWorth,Texas.NumericalcontrolhasallowNumericalcontrolorcontrolbynumbers,isaconceptwhichhasrevolutionizedthemanufacturingscene.Thisispartiallyduetotherapidadvancementinmicroelectronicsthathastakenplacesincelate1960s.ThekeyfactorresponsibleforthepopularityofNumericalControlistheflexibilityitoffersinmanufacturing.2.2.1HistoricalDevelopmentofNCNumericalcontrolorcontrolbLikesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirForce.Initsearlieststages,NCmachineswereabletomakestraightcutsefficientlyandeffectively.LikesomanyadvancedtechnoloTowardsendofthesecondworldwar,therewasincreasedactivityinaerospacemanufacturinginUSA.JohnParsonsofParsonsCorporationwhichwasoneofthesubcontractorstoUSAF(UnitedStatesAirForce),wastoyingwiththeideaofutilizingdigitalcomputerswhichwerethenbecomingpopular.TowardsendofthesecondworlMachining(milling)ofcomplexcurvaturewasahighlyskilledjob.Parsonsproposedthattheco-ordinatepointsofacomplexthreedimensionalprofilemaybeutilizedforcontrollingthemillingmachinetablesothataccuratejobscouldbeproduced.TheUSAFacceptedhisproposalandacontractwasawardedtohimtodevelopsuchamachine.Machining(milling)ofcomplexTheprojectwasthenawardedtotheServomechanismLaboratoryofMassachusettsInstituteofTechnologyin1951,whofinallydemonstratedaworkingmillingmachinein1952,ThiswasaCincinnatiHydrotelVerticalSpindlemillingmachinewithacontrollerbuiltusingvalves(transistorswerenotavailablethen).Theprojectwasthenawardedt先进制造技术双语2课件NCPunchedTapeNCPunchedTapeHowever,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorterthestraightlinesmakingupthesteps,thesmootheristhecurve(Fig.2.17).EachlinesegmentinthestepsshowninthecloseupinFig.2.17hadtobecalculated.ThiswasacumbersomeapproachthathadtobeovercomeifNCwastodevelopfurther.However,curvedpathswereap先进制造技术双语2课件Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)language.ThisisaspecialprogramminglanguageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.ThisproblemledtothedeveloTheoriginalNCsystemswerevastlydifferentfromthoseusedtoday.Themachineshadhardwiredlogiccircuits.Theinstructionalprogramswerewrittenonpunchedpaper,whichwaslatertobereplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.TheoriginalNCsystemswerev

Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapertapecontainingtheprogrammedinstructionstobreakortearduringamachiningprocess.Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtobererunthroughthereader.AmajorproblemwasthefragiThisledtothedevelopmentofaspecialmagneticplastictape.Whereasthepapertapecarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theplastictapecarriedtheinstructionsasaseriesofmagneticdots.Theplastictapewasmuchstrongerthanthepapertape,whichsolvedtheproblemoffrequenttearingandbreakage.However,itstilllefttwootherproblems.ThisledtothedevelopmentofThemostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Itwasalsostillnecessarytorunthetapethroughthereaderasmanytimesastherewerepartstobeproduced.Themostimportantofthesewa(1)AdventofDirectNumericalControlThedevelopmentofaconceptknownasdirectnumericalcontrol(DNC)solvedthepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.(1)AdventofDirectNumeriIndirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputer(Fig2.18).Programsforoperatingthemachinetoolsarestoredinthehostcomputerandfedtothemachinetoolasneededviathedatatransmissionlinkage.Indirectnumericalcontrol,m先进制造技术双语2课件DNCissubjecttothesamelimitationsasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,ashappenswithallhostcomputers,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.DNCissubjecttothesamelim

(2)AdventofComputerNumericalControl

Thedevelopmentofthemicroprocessorallowedforthedevelopmentofprogrammablelogiccontrollers(PLCs)andmicrocomputers.Thesetwotechnologiesallowedforthedevelopmentofcomputernumericalcontrol(CNC).WithCNC,eachmachinetoolhasaPLCoramicrocomputerthatservesthesamepurpose.Thisallowsprogramstobeinputandstoredateachindividualmachinetool.(2)AdventofComputerNumeriItalsoallowsprogramstobedevelopedoff-lineanddownloadedattheindividualmachinetool.CNCsolvedtheproblemsassociatedwithdowntimeofthehostcomputer,butitintroducedanotherproblemknownasdatamanagement.ItalsoallowsprogramstobeThisisaproblemallworksettingsdependentonmicrocomputershave.Thesameprogrammightbeloadedonthedifferentmicrocomputerswithnocommunicationamongthem.Thisproblemisintheprocessofbeingsolvedbylocalareanetworksthatconnectmicrocomputersforbetterdatamanagement.Theproblemofdatamanagementledtothedevelopmentofdistributednumericalcontrol.Thisisaproblemallworkset

(3)AdventofDistributedNumericalControlDistributednumericalcontrol(alsocalledDNC)takesadvantageofthebestaspectsofdirectnumericalcontrolandcomputernumericalcontrol.Withdistributednumericalcontroltherearebothhostcomputersandlocalcomputersattheindividualmachinetools(Fig2.19).(3)AdventofDistributed先进制造技术双语2课件Thisallowstheprogramstobestoredinthehostcomputerand,thereby,bettermanaged.However,italsoallowsthemtobedownloadedtolocalmicrocomputersorPLCs.ItalsoallowsforlocalinputandinteractionthroughmicrocomputersorPLCsatthemachinelevel.ThisallowstheprogramstobeBasicallyaNCmachinerunsonaprogramfedtoit.Theprogramconsistsofpreciseinstructionsaboutthemanufacturingmethodologyaswellasthemovements.Sincetheprogramisthecontrollingpointforproductmanufacture,themachinebecomesversatileandcanbeusedforanypart.AllthefunctionsofanNCmachinetoolarethereforecontrolledelectronically,hydraulicallyorpneumatically.2.2.2NCMachineandComponentsBasicallyaNCmachinerunson

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

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

TherearefourcomponentsinanyNCmachine:theactualNCtool

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

TheMCUisthecontrolunitthatholdstheprogramsthatinstructtheNCmachine.TheMCUalsohasvariousdevicesavailableforoperatorinput.themachinecontrolunit(MCU)EveryNCmachinetoolisfittedwithamachinecontrolunit(MCU)whichperformsthevariouscontrollingfunctionsundertheprogramcontrol.TheMCUmaybegenerallyhousedinaseparatecabinet-likebodyormaybemountedonthemachineitself.Whenseparatelymounted,itmaysometimesbependantwhichcouldswingaroundforconvenienthandlingbytheoperator.EveryNCmachinetoolisfitteAppearancewiseitlookslikeacomputerwithadisplaypanelgenerallyofasmallsize(9inches)andanumberofbuttonstocontrolthemachinetoolalongwithakeyboard.Thiscontrolunitcontrolsthemotionofthecuttingtool,spindlespeeds,feedrate,toolchanges,cuttingfluidapplicationandseveralotherfunctionsofthemachinetool.AppearancewiseitlookslikethecommunicationinterfacebetweentheNCmachineandtheMCUInformationcontainedintheMCUiscarriedtotheactivatorsontheNCmachinethroughthecommunicationinterface.TheseactivatorsreceivetheelectronicsignalsfromtheMCUandcausethemechanicalapparatusoftheNCmachinetooperate.thecommunicationinterfacebeavarietyofaccessoriesforperformingspecificjobsontheNCmachineTheaccessoriesarespecialtoolsrequiredtocarryoutaspecificjob.avarietyofaccessoriesforp先进制造技术双语2课件TheprincipleofoperationofanNCmachinetoolisshowninFig.16.1.Thebasicinformationthat

hastobeinputintothesystemconsistsofthepartgeometryandcuttingprocessparametersfollowedbythecuttingtoolsused.Thispartprogramisthenenteredintothecontrollerofthemachine,whichinturnrunsthemachinetooltomakethepart.TheprincipleofoperationofThecommandreceivedfromtheoperatoriscommunicatedtothecorrespondingaxisdrivingsystem

forexecution.Theaxismotioncontrolsystemoperatesinafeedbackloopwithsuitabletransducerssuchaslinearscalesand/orrotaryencoderstogettheappropriatepositionorvelocityfeedbackasshowninFig.16.2.Mostofthesesystemshaveaveryhighresponsewithgoodresolutionoftheorderof1μm(micron)orless.Thecommandreceivedfromthe先进制造技术双语2课件Thecontrollershaveanumberofmodesinwhichtheyoperate.Therecanbefourpossiblemodes

inwhichthecontrollercanfunctionasshowninFig.16.3inrelationtoamachiningcentre.Thefirstshowsatypicaldrillingmachineoperation,termedaspoint-to-pointmode.Inthis,thecontrolhasthecapacitytooperateallthethreeaxes,butnotnecessarilysimultaneously.Asaresult,itwouldbepossiblemovethetooltoanypoint(inXandY-axes)inthefastestpossiblespeedandcarryoutthemachiningoperationinoneaxis(Z-axis)atthatpoint.Thiswouldbeusefulfordrillingandpunchingmachine.Thecontrollershaveanumber先进制造技术双语2课件先进制造技术双语2课件Thesecondtypeisanimprovementoverthisinwhichinadditiontothepointtopointmode,themachineto