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AUTOMATED AUTOMATED MANUFACTURINGMANUFACTURINGCHAPTER 2AUTOMATEDMANUFACTURINGCHAPTE2.1 CAD/CAM2.1 CAD/CAM2.1.1 CAD/CAM DefinedCAD:Theuseofcomputersystemstoassistinthecreation,modification,analysis,oroptimizationofadesign.ACADmodelofamouse.2.1CAD/CAM2.1.1CAD/CAMDefinCAM:Theuseofcomputersystemstoplan,manage,andcontroltheoperationsofamanufacturingplant.TwokindsofCAM:(1)Computermonitoringandcontroldirectapplicationofcomputerintheprocess.(2)Computermanufacturingsupportapplicationsindirectapplication.Computer ProcessProcessDataMonitoringComputer ProcessDataControl Control SignalsProcessCAM:TheuseofcomputersyFormabilityAnalysisExampleFormabilityAnalysisExampleMoldandToolingExample.MoldandToolingExample.CAD/CAMmeansusingcomputersinthedesignandmanufacturingprocesses.SincetheadventofCAD/CAM,othertermshavedeveloped.Computergraphics(CG)Computer-aidedengineering(CAE)Computer-aideddesignanddrafting(CADD)Computer-aidedprocessplanning(CAPP)CAD/CAMmeansusingcompute先进制造技术双语课件AkeygoalofCAD/CAMistoproducedatathatcanbeusedinmanufacturingaproductwhiledevelopingthedatabaseforthedesignofthatproduct.Whensuccessfullyimplemented,CAD/CAMinvolvesthesharingofacommondatabasebetweenthedesignandmanufacturingcomponentsofacompany.CAD/CAMgrowsoutofaneedtocontinuallyimproveproductivity,quality,and,inturn,competitiveness.TherearealsootherreasonswhyacompanymightmakeaconversionfrommanualprocessestoCAD/CAM:(1)IncreasedProductivity(2)betterquality(3)bettercommunication2.1.1 Rationale for CAD/CAM2.1.1 Rationale for CAD/CAMCAD/CAMgrowsoutofaneed(4)commondatabasewithmanufacturing(5)reducedprototypeconstructioncosts(6)fasterresponsetocustomersA prototype is an original type,form,or instance of something serving as a typical example,basis,or standard for other things of the same category.(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-oldwallseparatingthedesignandmanufacturingfunctions(4)CommonDatabase先进制造技术双语课件(5)ReducedPrototypeCostsWithCAD/CAM,3-Dcomputermodelscanreduceand,insomecases,eliminatetheneedforbuildingexpensiveprototypes.SuchCAD/CAMcapabilitiesassolidsmodelingallowdesignerstosubstitutecomputermodelsforprototypesinmanycases.(5)ReducedPrototypeCosts(6)FasterResponsetoCustomersResponsetimeiscriticalinmanufacturing.Byshorteningtheoveralldesigncycleandimprovingcommunicationbetweenthedesignandmanufacturingcomponents,CAD/CAMcanimproveacompanysresponsetime.(6)FasterResponsetoCustoAlldesigntasksaccomplishedusingacomputerfallintooneoffourbroadcategories:(1)DesignModelingInCAD/CAMdesignmodeling,ageometricmodelofaproductisdevelopedthatdescribesthepartmathematically.Thegeometricmodelalsoallowsthegraphicimagetobeeasilyeditedandmanipulatedoncedisplayed.2.1.2 Computers and Design2.1.2 Computers and DesignAlldesigntasksaccomplish(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)DesignDocumentationWithCAD/CAM,thedrawingsneededtodocumentthedesigncanbeproducedusingthedatabasecreatedduringthedesignprocess.BecausethecomputercanstorethemathematicalmodelsofalldrawingsdoneonaCAD/CAMsystem,onceadrawinghasbeenproduced,itneverhastoberedrawn.Itcansimplybecalledupfromstorage,enteredintotheappropriatelocationinthedrawingpackage,andusedagainandagain.(4)DesignDocumentationThe real interface is the common database they share.TherealinterfaceisthecommWhatisDFA?DFAmethodologiesweredevelopedtosupportthedesignerbygeneratingfeedbackontheconsequencesofdesigndecisionsonproductassembly.Theaimistohelpthedesignertoproduceanefficientandeconomicdesign.2.1.4 Design for Assembly,2.1.4 Design for Assembly,Manufacturing,and the Manufacturing,and the Environment(DFA/M/E)Environment(DFA/M/E)WhatisDFA?DFAmethodologiesTheapplicationofDFAguidesthedesignertowardsaproductwithanoptimumnumberofparts,thatrequiressimple,cost-effectiveassemblyoperationsandthemostappropriatemanufacturingprocessesandmaterialsforitscomponents.Ingeneral,thedesignerisguidedthroughtheanalyses,whicharepresentedinaseriesofassessmentcharts.Thechartsarebasedonempiricaldatagatheredbyknowledgeengineeringexerciseswithindustrialexpertsandorganisedinaneasy-to-useworksheetformat.TheapplicationofDFAguides先进制造技术双语课件Duringtheevaluation,thedesignerisrequiredtoassesscomponentfunctionality,formmanufacturingprocessesandassemblycharacteristicsusingvaluesextractedfromthechartsaccordingtocomponentproperties.Thesenumbersarethencompiledintabularformat,andcalculationsperformed.Inthisway,thedesignerisabletoquantifythesuitabilityofthedesign.Duringtheevaluation,thedesTheLucasDFAMethodologyhasbeenchosenforusewithintheDesignersSandpitprojectbecauseofexistingexpertisewithinthegroup.The Designers Sandpit is an assembly-oriented design environment containing tools and techniques to generate economic designs.As part of this environment,designers need methods for assessing the assembliability of their designs.The Lucas DFA method was developed in the early 1980s by the Lucas Corp.in the U.K.The method is based on three separate and sequential analyses:Specification,Design,Functional analysis.TheLucasDFAMethodologyhasWhat is DFM?Followedduringthedesignprocess,DFMisanapproachwhichhastheaimofimprovingmanufacturingproductivity.Itbringsmajorbenefitswhenusedduringthedesignofnewgenerationsofproducts.Itisamethodofworkingwhich:HelpstheteamfocusonclearandcommonobjectivesWhatisDFM?Encouragesproblem-ownershipandpreventsmanufacturingproblemsbeingshiftedfromareatoarea(e.g.fromdirecttooverheadcosts)Usesatop-downapproach(preventingearlyandwastefulfocusondetail)toproductdesignDuringDFM,theconsiderablebackgroundworkrequiredfortheconceptualphasesiscompensatedforbyashorteningoflaterdevelopmentphases.Problem ownership:Willingness to accept ownership and responsibility Encouragesproblem-ownershipaWhat is Design for the Environment?DesignfortheEnvironment(DFE)istheconsiderationofpollutionpreventionandresourceconservationwithinthedesignprocess.DFEstartswiththedevelopmentofenvironmentalgoalswithinanexamplesetofenvironmentalpolicy,needs,andconcerncategories.Goalsshouldbelargeinscope:consideringthefulllifecycleofperformance,cost,andenvironmentalimplications.WhatisDesignfortheEnvironTherearethreemajorelementsofdesignfortheenvironment:designforenvironmentalmanufacturing,designforenvironmentalpackaging,anddesignfordisposalandrecycleability.Designforenvironmentalmanufacturinginvolvesthefollowingconsiderations:Non-toxicprocesses&productionmaterialsMinimumenergyutilizationMinimizeemissionsMinimizewaste,scrap&by-productsTherearethreemajorelementsDesignforenvironmentalpackaginginvolvesthefollowingconsiderations:MinimumofpackagingmaterialsReusablepallets,totesandpackagingRecyclablepackagingmaterialsBio-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先进制造技术双语课件DFMformachiningmoduleMachiningforWindowsassistsadesignerwiththefollowingissues:developingoperationandprocessplans,obtainingcostestimatesattheearlieststagesofconceptualdesign,developingquotations,andplanningforproduction.DFMformachiningmoduleM先进制造技术双语课件Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).Thevarietydemandedinviewofthevaryingtastesoftheconsumercallsforverysmallbatchsizes.Smallbatchsizesarenotabletotakeadvantageofmassproductiontechniquessuchasspecialpurposemachinesortransferlines.2.2 Numerical Control2.2 Numerical ControlOneofthemostfundamentalThereisaneedforflexibleautomationwhereyoucangetthebenefitsofrigidautomationandalsobeabletomanufactureavarietyofproducts,thusbringinginflexibility.Themethodofnumericalcontrolisappropriateforthispurpose,andinfuturemanufacturingisexpectedtobeincreasinglydependentonnumericalcontrol.ThereisaneedforflexibleNChasbeendefinedbytheElectronicIndustriesAssociation(EIA)as“asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.Thesystemmustautomaticallyinterpretatleastsomeportionofthisdata.”Thenumericaldatarequiredtoproduceapartisknownasapartprogram.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.2.2.1 Historical Development of NC2.2.1 Historical Development of NCNumericalcontrolorcontrolbLikesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirForce.Initsearlieststages,NCmachineswereabletomakestraightcutsefficientlyandeffectively.LikesomanyadvancedtechnoloTowardsendofthesecondworldwar,therewasincreasedactivityinaerospacemanufacturinginUSA.JohnParsonsofParsonsCorporationwhichwasoneofthesubcontractorstoUSAF(UnitedStatesAirForce),wastoyingwiththeideaofutilizingdigitalcomputerswhichwerethenbecomingpopular.TowardsendofthesecondworlMachining(milling)ofcomplexcurvaturewasahighlyskilledjob.Parsonsproposedthattheco-ordinatepointsofacomplexthreedimensionalprofilemaybeutilizedforcontrollingthemillingmachinetablesothataccuratejobscouldbeproduced.TheUSAFacceptedhisproposalandacontractwasawardedtohimtodevelopsuchamachine.Machining(milling)ofcomplexTheprojectwasthenawardedtotheServomechanismLaboratoryofMassachusettsInstituteofTechnologyin1951,whofinallydemonstratedaworkingmillingmachinein1952,ThiswasaCincinnatiHydrotelVerticalSpindlemillingmachinewithacontrollerbuiltusingvalves(transistorswerenotavailablethen).Theprojectwasthenawardedt先进制造技术双语课件NC Punched TapeNCPunchedTapeHowever,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorterthestraightlinesmakingupthesteps,thesmootheristhecurve(Fig.2.17).EachlinesegmentinthestepsshowninthecloseupinFig.2.17hadtobecalculated.ThiswasacumbersomeapproachthathadtobeovercomeifNCwastodevelopfurther.However,curvedpathswereap先进制造技术双语课件Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)language.ThisisaspecialprogramminglanguageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.ThisproblemledtothedeveloTheoriginalNCsystemswerevastlydifferentfromthoseusedtoday.Themachineshadhardwiredlogiccircuits.Theinstructionalprogramswerewrittenonpunchedpaper,whichwaslatertobereplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.TheoriginalNCsystemswerevAmajorproblemwasthefragilityofthepunchedpapertapemedium.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先进制造技术双语课件DNCissubjecttothesamelimitationsasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,ashappenswithallhostcomputers,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.DNCissubjecttothesamelim(2)AdventofComputerNumericalControlThedevelopmentofthemicroprocessorallowedforthedevelopmentofprogrammablelogiccontrollers(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先进制造技术双语课件Thisallowstheprogramstobestoredinthehostcomputerand,thereby,bettermanaged.However,italsoallowsthemtobedownloadedtolocalmicrocomputersorPLCs.ItalsoallowsforlocalinputandinteractionthroughmicrocomputersorPLCsatthemachinelevel.ThisallowstheprogramstobeBasicallyaNCmachinerunsonaprogramfedtoit.Theprogramconsistsofpreciseinstructionsaboutthemanufacturingmethodologyaswellasthemovements.Sincetheprogramisthecontrollingpointforproductmanufacture,themachinebecomesversatileandcanbeusedforanypart.AllthefunctionsofanNCmachinetoolarethereforecontrolledelectronically,hydraulicallyorpneumatically.2.2.2 NC Machine and Components2.2.2 NC Machine and ComponentsBasicallyaNCmachinerunsonInNCmachinetoolsoneormoreofthefollowingfunctionsmaybeautomatic:(i)Startingandstoppingofthemachinetoolspindle.(ii)Controllingthespindlespeed.(iii)Positioningthetooltipatdesiredlocationsandguidingitalongdesiredpathsbyautomaticcontrolofthemotionofslides.InNCmachinetoolsoneor(iv)Controllingtherateofmovementofthetooltip(i.e.feedrate).(v)Changingoftoolsinthespindle.(iv)ControllingtherateofmNCmachineshavebeenfoundsuitableforthefollowing:(i)Partshavingcomplexcontours,thatcannotbemanufacturedbyconventionalmachinetools.(ii)Smalllotproduction,oftenforevensingle(oneoff)jobproduction,suchasforprototyping,toolmanufacturing,etc.(iii)Jobsrequiringveryhighaccuracyandrepeatability.NCmachineshavebeenfound(iv)Jobsrequiringmanyset-upsand/orwhentheset-upsareexpensive.(v)Partsthataresubjectedtofrequentchangesandconsequentlyrequiremoreexpensivemanufacturingmethods.(vi)Theinspectioncost,whichisasignificantportionofthetotalmanufacturin
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