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COMPUTERAIDEDCNCPROGRAMMINGFORTHEMACHININGOFNONTYPICALPARTSGrzegorzNikielGrzegorzNIKIEL,Ph.D.,Eng.,UniversityofBielskoBiała,DepartmentofManufacturingTechnologyandAutomation,43309BielskoBiała,ul.Willowa2,gnikielath.bielsko.pl1.IntroductionManymanufacturingfirms,especiallymediumandsmall,hastosolveproblemofproductiondevelopmentandsearchofnewcustomers.Inmanycasesthisleadstotheassortmentenlargingofalreadymanufacturedproducts.Oftenthisisjoinedwithimplementationofthenewmanufacturingprocesses.InconditionsofmarketcompetitionitdemandshighflexibilitywhichisoftengotinwayreplacingofconventionalmanufacturingresourcesbythemodernCNCtoolmachines1.Thisisessentialsconditionformoreefficientdevelopment,higherqualityandfasteradoptiontonewrequirements2.FormaintenanceofthelowcostsofmanufacturingforproductionofsmallandmediumbatchesveryoftentheGroupTechnologyisapplied3.Withhelpofgroupingofthemanufacturedcomponentsintofamiliesmoreefficientthemachines,devices,workersareused.IntheprocessesplanningonefrommostimportanttasksistheCNCmachinetoolprogramming4,5.VeryoftentheCAD/CAMsystemsareusedfromreasontheirpossibilityofflexibleprogramming.Inthecaseoftypicalcomponentssuchapproachthepositiveresultsgives,thoughitdemandsanefficientcooperationsbetweenconstructorsandtechnologist.Sometimesfromdifferentreasonsitisimpossible,especiallywhentheGroupTechnologyisapplied.Usuallythepartprogramsformachiningofsinglecomponentsarecreated,butthemodernCNCcontrollersoffersomemethodsofprogramming,whichtomachiningofsomesimilarcomponentscanbeused.Suchmethodsare1.Cycles6.Thecyclesaredesignformachiningoftypicalsurfacestheholes,threads,slotsetc..Usuallyaparametricdescriptionofmachinedsurfacesisappliedwhichenabletheeasyandfastchangesoftheirgeometry.Unfortunatelytheybecharacterizedbysmallflexibilityandsmallinfluenceontostrategyofmachining,dependentonlyfromtheparametersofcycle.InthemoderncontrollersitpermitontoaWorkshopOrientedProgrammingWOP,i.e.programmingdirectlybytheoperators,oftenaidedbyadialogprogrammingsometimesaconversationalprogrammingcalled.Thereforethisisrelativesimpleprogrammingmethod,veryoftenusedinindustrialpractice.2.Parametricprogramming5,6.Atypicalpartprogramisexecutedfrombeginningtoendinonerun.Inparametricprogrammingtheexecutionofpartprogramcanrunintodifferentwaye.g.byconditionalinstructionIF..THEN..use.Inaddition,amultiplerepetitionofthepartprogramfragmentisaccessibleREPEATloop,WHILEloopetc..Furthermore,thearithmeticalfunctionsandotheradvancedfunctionsarepossible.Theaxispositions,feedandspeedfunctions,etc.canbespecifiedbyaparametricexpressionsbyRparametersuse.Intothiswayitwasbeenpossibletocreateownmachiningcyclesalso.Thisapproachdemandshighskillsofprogrammingandisverylabourconsumingalso.Exactverificationoftheprogramisnecessary,inthisitsimmunityinthedangeroussituationse.g.joinedwithapplicationofincorrectvalueoftheinputparameters.Thereforeinviewofabovementioneddefectsitisinfrequentlyusedinindustrialpractice.3.Programmingbasedonthefreelydefinedcontours.ThetaskdependsondefiningofmachinedcontouranditsautomaticconversiontotheCNCcodes.IftheautomaticcutterradiuscompensationtheG41andG42functionsisnotusedthenadditionallyaequidistanthastobegenerated.ThissubtaskiseasytorealizationifmentionedcontourisrepresentedinaCADsystem–withhelpoftheOffsetfunction.SecondsubtaskoftenisrealizedinwayofexportofgraphicformofthetoolpathtothetypicalformatsofdataexchangeDXF,HPGLetc..Innextstepbythesuitablepostprocessorsuseforexamplethesolutiongivenin7conversionoftoolpathontotheCNCcodesisperformed.Frompracticalregardsthisapproachingeneralityforthesimpleoperationsisapplied,e.g.alasercutting,awaterjetcuttingetc.Asolutionintegratingbothsubtasksinoneapplicationprogramareappliedalso–theAutoCUTisthebestexample8.Inpracticethissolutionisnotappliedtoooftenalthoughitpossessesmanyadvantages.IntheconditionsofsmallbatchproductionaprocessplanningtotheCNCprogrammingisoftenrestricted9.InthissituationlargemeaninghasintegrationoftheCAD/CAMsystemswithomissionofCAPPstage.TheFeaturesideaisthenaeffectivemethodofdataexchange10,11,12.WhentheGroupTechnologyisused,aftersupplementbyappropriatedatabasesandknowledgebases,itcanbebestsolutionforproductionoftypicalelements13,14.Incaseofnontypicalpartssuchapproachgenerallyisineffective.MainlyinviewofthewidelyappliedmethodsofFeaturesrecognizingwhichlimitnumberoftheFeaturetypes10,12.MaybeinfutureasolutionwillbringintegrationofCAD/CAM/CNCsystemsbasedontheSTEPNCstandardsISO14649,ISO1030323815,16whichwillreplacetraditionallyappliedCNCprogrammingwithGcodesontothingoftheneutralformatofdataexchange.2.AnalysisoftheexamplesPresentedbelowexamplesofthegroupCNCmachiningareafragmentofproductionprogramfromthesmallfirm.Generallythiscomponentshavenontypicalshapes,theyaremanufacturedfromhardmaterialse.g.austeniticstainlesssteel,usuallyneededthespecialjigsandfixtures,intheconditionsofsmallbatchproduction.Theplanningprocessesinthiscasedemandaparticipationoftechnologistswithlargeexperience.AspecificcharacterofaccessibletoolmachinesfordefiningofthemethodofCNCprogrammingshouldtoconsideralso.AfterexecutionofdetailedanalysisontosubjectofthediscussedmethodsthefollowingconclusionswereformulatedThemachinedshapesexcludeapplyingofthestandardcycles.Mostoftheprogramsisdesignforthecomplicatedprofilesmachining.Fromheredescriptionoftheseprofilesislargestproblem.Moreover,machiningofthecomponentsisperformedonthedifferenttoolmachines,equippedindifferentcontroller.Formostofmachinedcomponentstheexactdrawingdocumentationisnotmade.Inaproductionorderthegeneraldrawingsareincluded,oftendescribedbyparametricdimensions.Thencurrentvaluesofthisparametersaregivenalso.Shortseriesandlargevarietyofthecomponentsdemandsfastmodifyingofcurrentproductionprogram.FastCNCprogrammingandtheprogramsimplementationisnecessary,bestdirectlyattoolmachineWOP.Oftentheoperatorsoftoolmachinespossesslargeknowledgeandexperienceintheareaofmanufacturingtechnology,sufficientforpreparationofsimpleprograminrangeofthetechnology.Fastpreparationofthetoolpathislimitationonly.Generalconclusionissuch,thatinpresentedcaseuseoftheuniversalCAD/CAMsystemsforCNCprogrammingisverydifficult.Moreover,itjoinswithhighcostsofshoppingandtrainingsfortheworkers.Lowflexibilityofthismethodisexpectedalso,especiallytimeofprogrammingcanbeagreatproblem.Inthissituationaparametricprogrammingasthebestsolutionwasconsidered.But,asitwasshewontheexamples,theparametricprogrammingcanberealizedindifferentway.2.1.ExampleI–thegroovedrollersfinishmachiningFinishmachiningofthegroovedrollersfamilywassubjectofresearchFig.1.Basicchangingdimensionsforrollerswereexternaldiameterd,workingprofilelengthLandprofileangleα.Theprofileofcooperaterollerismovedbyhalfpitch.FinishmachiningisperformedbyturningwithuseoftoolwiththeVtyperhombicinsertnoseangleequal35°,wherethenoseradiusrεisequal0,4mmFig.1.Thetoolreferencepointislocatedintheinsertnosecenter.ForeachpairofrollerstheirprofileisdesignedinaCADenvironmentaccordingtothedimensionsofrollingelements.Afastmethodoftoolpathgenerationwasthemainsubjectofperformedresearch.Firstofallgeneratingofthetoolpathonlyfinishing,withoutroughmachiningwhichisprogrammedinamanualmodeandformingitinaccordancewithrequirementsofappropriatelanguage.Ashasbeenmentionedabovetheuseofparametricprogramwasconsidered.Withhelpoftheadvancedprogramming
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