ABSTRACT A METRIC-BASED APPROACH TO 2D TOOL-PATH O

1ABSTRACTConventionaltool-pathgenerationstrategiesarereadilyavailabletogenerategeometricallyfeasibletrajectories.Suchapproachesseldomtakeintoconsiderationphysicalprocessconcernsordynamicsystemlimitations.Inthepresentwork,anapproachforimprovingageometricallyfeasibletool-pathtrajectorybasedonquantifiableprocessmetricsisdeveloped.Twospecificmeasuresoftoolpathqualityareincorporatedintotheiterativeimprovementalgorithm:instantaneouspathcurvatureandinstantaneouscutterengagement.Thesemetricsaremotivatedbyadesiretominimizeaccelerationrequirementsandmaintainastablesteady-statecuttingprocessduringhigh-speedmachining.Thealgorithmhasbeenimplementedfortwo-dimensionalcontiguousend-millingoperationswithflatend-mills,andcasestudiesarepresentedtoillustratetheapproach.Keywords:high-speedmachining,tool-path,engagement,curvatureINTRODUCTIONHighspeedmachining(HSM)isakeyenablingtechnologyinanincreasingnumberofindustries.Intheaerospaceindustry,structuralcomponentsareincreasinglybeingmachinedasmonolithicstructuresfromasinglebillet.Theresultisdrasticallyreducedpartcounts,assemblycosts,andevenmaintenancecosts.TheBoeingF/A18E/Ftacticalaircraftrealizeda42%reductioninpartsanda25%weightsavingsoverpreviousmodels,attributednotinsmallparttothedesignchangesmadepracticalbytheapplicationofhighspeedmachiningtechnology[1].Inthetoolingindustry,highspeedmachiningtechnologycontinuestogrowincreasinglyimportantformaintainingeconomiccompetitiveness.SuccessfulapplicationsofHSMtotheproductionoftoolingforforging,extrusion,sheetforming,diecasting,andinjectionmoldinghavebeenreported[2-4].High-velocity(HV)machinetoolswith1,000+ipmtraverserates,and50,000+RPMhigh-powerspindles,arereadilyavailable.However,thevelocitycapabilitiesofsuchmachinesareseldomreachedinindustrialpractice.Often,conservativefeedratesareemployedincontouringduetoconcernsarisingfromprocessstabilityandaccelerationlimitations.Toaddresstheseissues,significantattentionhasbeenfocusedontheimportantproblemsofAMETRIC-BASEDAPPROACHTO2DTOOL-PATHOPTIMIZATIONFORHIGH-SPEEDMACHININGHongchengWang,PeterJang,andJamesA.StoriDepartmentofMechanicalandIndustrialEngineeringUniversityofIllinoisatUrbana-ChampaignUrbana,IL61801tel:[phone],fax:[phone],e-mail:[e-mail]2dynamicmodelling,parameteroptimization,andfeedratescheduling.Oftenoverlooked,however,isthepotentialforimprovementinprocessefficiencythroughchangestothetool-pathitself.Tool-pathplanninghasbeentraditionallyapproachedfromapurelygeometricperspective.Thevastmajorityofbulkmaterialremovaloccursin2.5Droughingoperations.Forsuchoperations,tool-pathtrajectoriesaregeneratedthroughconventionalstrategiessuchascontour-parallelordirection-paralleloffsetting.Whenthedynamicsandmechanicsoftheprocessandmachinetoolsystemareconsidered,conventionaltool-pathgenerationtechniquesareobservedtobefarfromideal.Inthepresentwork,anapproachisdevelopedtooptimizeageometricallyfeasibletoolpathbasedonquantifiablemetricsdrivenbyimportanttechnologicalconcerns.TechnicalChallengesinHSMNumeroustechnologicalissuesinhighspeedmachining(HSM)poseparticularchallengesfromtheperspectiveofprocessplanning,optimization,andcontrol.Conventionaltool-pathstrategiesfailtoadequatelyaddressconcernssuchasdynamicstability,accelerationdemands,andconstantlyvaryingtoolengagementthatlimitproductionrates,increasetoolwear,andreducepartquality.First,andpossiblyforemost,arelimitationsimposedbyconsiderationofdynamicstability.Dynamicstabilityissuesdrivethemajorityofeffortstoeffectivelyimplementhighspeedmachiningontheshopfloor.Tlustystates:“Ithaslongbeenrecognizedthattheoccurrenceofchatterisoneofthemostsignificantlimitationsinincreasingthemetalremovalrateinmilling”[6].Thedifferencebetweensuccessfulstablecuttingandcatastrophicunstablecuttingcanbetracedtosubtleinteractionsbetweenthedynamicsofthetool,spindle,andworkpiece,instantaneouschiploadsandcutterengagements.Numerousmodelshavebeendevelopedfordynamicsimulationofthemachiningprocess,andserveasincreasinglyaccuratetoolsforselectionofthespindlespeedandcuttingparametersforchatter-freemachining[6-9].Additionally,systemshavebeendevelopedforavoidanceordetectionandcontrolofchatterbyvaryingthe(constant)spindlespeedorcuttingwithavaryingspindlespeed[10-12].Asecondcrucialissueinhighspeedmachiningismakingeffectiveuseofthedynamiccapabilitiesofthemachinetool,actuators,andservodrives.RentonandElbestawi[13]demonstratethatbymakingcompleteuseoftheperformanceenvelopeofeachservocontrolledaxis,feedratescanbeincreasedwhilesimultaneouslydecreasingtrackingpatherror.RichardBertsche,ofBertscheEngineering,amanufacturerofhighvelocitymachinetools,emphasizesthecrucialrolethataccelerationcapabilitiesplayinthehighspeedmachiningprocess[14].Henotesthattwomachineswithsimilarvelocityyetdifferentaccelerationcapabilitiesmaydifferby50%intotalprocessingtimewhencuttingamoderatelysizedpocket.Formanypracticalmachiningtasks,ahigh-velocitymachinetoolmayspendthemajorityofitstimeacceleratinganddecelerating[15].Duringtheinevitableperiodsofdwelling,tooltemperaturesclimbsharply,drasticallyreducingtoollife.F