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JournalofUniversityofScienceandTechnologyBeijingVolume13,Number3,June2006,Page240Correspondingauthor:YingTang,E-mail:tangydlMaterialsOptimizationstrategyinendmillingprocessforhighspeedmachiningofhardeneddie/moldsteelYingTangMechanicalEngineeringSchool,UniversityofScienceandTechnologyBeijing,Beijing100083,China(Received2005-02-21)Abstract:Anoptimizationstrategyforhighspeedmachiningofhardeneddie/moldsteelbasedonmachiningfeatureanalysiswasstudied.Itisafurtherextensionofthepreviouslypresentedstudyonthethermalmechanismofendmillingandconstantcuttingforcecontrol.Anobjectivefunctionconcerningmachiningcostandassociatedoptimizationalgorithmbasedonmachiningtimeandcuttinglengthcalculationwasproposed.Constraintstosatisfyspecificmachiningstrategieswhenhighspeedmachiningthehardeneddie/moldsteel,trochoidtoolpathpatterninslotendmillingtoavoidover-heatandfeedrateadaptationtoavoidover-load,werealsodiscussed.Asacasestudy,thetoolselectionproblemwhenmachiningadiepartwithmultiplemachiningfeatureswasinvestigated.Keywords:optimizationalgorithm;hardeneddie/moldsteel;machiningcost;machiningfeature1.IntroductionTheintroductionofadvancedcuttingtoolslikeAlTiN-coatedmicro-graincarbideendmillsincethe1990shaschangedthetrendindie/moldmanufacturingtowardshardmachiningbothinroughingandfinishing1.Nowadays,highspeedmachiningofhardeneddieandmoldsteelsisaproventechnologyalready,wheremanyspecificmachiningconceptsandstrategiesaredevelopedtofacilitateit2.Representatively,ma-chiningfeaturesthataredefinedasdistinctivevolumetricshapetoberemovedbydistinctivema-chiningoperations(i.e.cuttingtoolandtoolpathpat-tern),isputforwardtoeaseNC(numericalcontrol)programming3.Usuallytoolpathpatternforeachfeaturetypecanbestandardizedandfixed.Oncemachiningfeaturesandrelevanttoolpathpat-ternarefixed,itbecomesabsolutelynecessarytoopti-mizeotheroperationparametersbecausewhenweconsiderbothproductivityandtoolcost,thelattercontributestoasmuchas20%ofthetotalcostofdieandmoldmanufacturing.Suchoptimizationismadepossiblewithmachiningfeatureandfixedtoolpathpatternanalysis,whichreducesthenumberofvariablesthathavetobeconsideredatthesametime.Productiv-ityandtoolcostcanbetreatedasfunctionsoftheseindependentcuttingconditionvariablessothattheimpactofthesevariablesontheproductivityandtoolcostorthecombinedobjectivefunctionofthesetwocanbecalculatedandoptimized.Thispaperisorganizedasfollows:anobjectivefunctionconcerningmachiningcostanditsassociatedoptimizationalgorithmisproposedinSection2,fol-lowedbyacasestudytousetheproposedalgorithmfortoolselectioninendmillingdiepartwithmultiplemachiningfeaturesinSection3.Constraintsfacedinattemptingtosatisfyspecificmachiningstrategieswhenhighspeedmachiningthehardeneddie/moldsteelarediscussedinthesamesection.ConclusionsarepresentedinSection4basedontheresultsofthecasestudy.2.OptimizationstrategyAsconcerningproductivity,thetimeinvolvedinmachiningprocessneedstobecalculated.Thema-chiningtimemTconsideredincludesthecuttingtimecTandtheaircuttingtimencT.Basically,theexactcuttingtimecTiscalculatedbyaddingthetimesspentoneverychipandtheaircuttingtimencTisthetotaltimeofaircuttinginthetoolpath,whichcannormallybecalculatedwitheasebasedonfixedtoolpathpattern,mcncnczeiiiLTTTTf=+=+(1)wherethecuttinglengthiLofthei-thchipiscalculat-edbasedontheengagementgeometrybetweentheworkpieceandthecuttingtool,andzeifistheinstantfeedoftoolwhencuttingthechip.Inthecaseofendmillingconcavecontour,iL,zeifandotherparametersY.Tang,Optimizationstrategyinendmillingprocessforhighspeedmachining241associatedwithitareshowninFig.1.Fig.1.Tool-workengagementinconcavecontourend-millingprocess.tmimaximumuncutthicknessofthei-thchip;Licuttinglengthofthei-thchip;fziinstantfeedpertoothatthetoolcenter;fzeiinstantfeedpertoothatthetooltip;iangleformedbyfziandfzei;enicutting-relatedangle;Rdiradialdepthofcut;rendmillradius;Rconcavecontourradius.Indieandmoldindustry,thetoollifefLisoftenmeasuredbythetotallengththatatoolisengagedincuttingtillitfails.ThevalueoffLcanbeobtainedfromthetoolmanufacturerdirectlyorthroughtoollifeexperiments.Ifthetotalcuttinglengthatanygiventimeduringthetoollife,tL,canbeintegratedbyad-dingallthechiplengthsundercuttilltheconsideredtimepoint,tiiLL=(2)thentheratiooftLtofLindicatesthetoollifethathasbeenconsumed.Theoptimizationstrategycouldbetominimizethemachiningtimeormaximizethetoollifeforacertainwork.Amoregeneralobjectivefunctionisthema-chiningcost,whichisacombinationofboth.Machin-ingprocessinvolvesvariousmiscellaneouscosts;butinthisstudywetakeintoconsiderationonlythema-chiningtimecostandthetoolcost,whichareidentifiedasthemajorcostsfordieandmoldmachiningproc-esses.Thetotalcost(C)formachiningoneworkpieceistmmtfLCcTcL=+(3)wheremcisthecostperunitmachinetimeandtcisthepricepertool.TheoptimizationwithminimumCsuggestsadesiredbalancebetweensavedmachiningtimeandreducedtoolcost.3.Casestudyfortoolselectioninhighspeedmachiningofhardeneddie/moldsteelAsacasestudy,thetoolselectionproblemfacedwhenmachiningadiepartwithmultiplemachiningfeatureswasinvestigated.Supposethattwoslotsof100mminlength,10mmindepthand50mmand15mminwidth,respectively,needtobemachinedonadiework(Fig.2).TheworkpiecematerialisJISSKC61diesteelofHRC53inhardness.AlTiN-coatedmicro-graincarbideendmillcutterswithsixbladeswereusedtoimplementtheslotendmilling.Endmillcuttersunderconsiderationareof6,8,10,12,14and18mmindiameter.Theaimistoseekanoptimaltoolselectiontoachievetheminimummachiningcosttoremovethetwoslots.Fig.2.Diepartwithtwoslotstobemachined.Themodelandcalculationpresentedinthispaperaresubjecttocertainconstraintsdiscussedasfollows:theneedtosatisfyspecificmachiningstrategiesindieandmoldindustryandalsomethodsthatareinaccor-dancewithstate-of-the-artunderstandingofhighspeedmachininghardeneddie/moldsteel.(1)Slotendmillingwithtrochoidtoolpathpattern.Fromthemachiningpointofview,machiningfea-turesinmillingcanusuallybeclassifiedintofivecate-gories:hole,pocket,openpocket,faceandboss3.SlotmachininginFig.2belongstothesortofopenpocket,whichischaracterizedbytwoopensidessothatcuttingtoolcanapproachpartfromoneofthetwosides.Aconventionalwayofslotendmillinginvolvesusingthefulldiameteroftheendmillinthematerial.Inthiscase,theteethwillcontactwiththepartresultinginbuild-upofheatduring50%oftherevolution,andthencooldownduringtheremaining50%oftherevo-lution.Thetoollifewillbedrasticallyreducedduetoexcessiveheatbuild-uponthecuttingteeth,ifthereisnoenoughtimeforthecuttingteethtocooldown,accordingtothethermalmechanisminendmilling242J.Univ.Sci.Technol.Beijing,Vol.13,No.3,Jun2006processpresentedinpreviousworks4-5.Itbecomesessentialtoseekaspecificmachiningstrategytore-ducecuttingheataccumulationforimprovingtoollife.Thekeyissueliesinthelimitationofcontactbetweenthetoolandthepartperrevolution.Trochoidtoolpathpatternwithsuccessivetrochoidcyclesofthesamepitch,showninFig.3,issuchasubstitutedesignedforendmillingaslotintothehardenedsteelathighspeed6.Bymaintainingalimitedpitch,thearcofcontactisminimized.Incon-junctionwithproperfeedsandspeeds,endmillinginthismannercanremovealargeamountofmaterialwithoutthegenerationofexcessiveheat.Fig.3.Slotendmillingwithtrochoidtoolpathpattern.Bisaslotofgivenwidth.(2)Feedrateadaptationtokeepconstantcuttingforce.Anotherconcepttakenasabasisforhardeneddiesteelendmillingistomaintainthecuttingforcecon-stantunderasafetylimitespeciallyinroughingorintermediateroughingoperation,becausechippingoccurssoonifexcessivecuttingforcesatthecuttingedgearepresent.Chippingononecuttingedgecancauseacascadeeffectofsuccessivechippingontheremainingintactcuttingedges.Thismakesthetoolunusableveryquickly.Astraightforwardapproachtokeepconstantcuttingforceistoadaptfeedratealongtoolpath.Thebasicprincipleofthestrategyistosolvetheinstantfeedrateaccordingtotool-workengagementgeometrywithasecondorderforcemodel,whichwaspresentedinpreviousworks7-8,220112211221212YXXXXX=+(4)whereYdenotestheaveragecuttingforcevalueinXY-planexyF.ThecontroltargetforceYisdeter-minedfromexperiences.1Xand2Xarethenormal-izedmaximumuncutchipthicknessmitandchipcut-tinglengthiLrespectively.Thesixcoefficients(012,)areidentifiedbyconductingasetofpre-processexperimentsofstraightcutbyusingleastsquaresmethod.Undertheseconstraints,thesimulationwascon-ductedfirstlytoseektheoptimalcutterdiameterDwhenamachiningfeature,aslotofgivenwidthB,neededtobemachined.Fig.4istheB-Dplaneofthecontourplotofmachiningcostwhenmachinedwithapitchof0.5mmandaspindlespeedof9600r/min.Thetargetcuttingforcesareequaltothevaluesmeasuredincuttingexperimentswithdifferentdiametercutterstocutalongstraightcontoursatthesamepitchandspin-dlespeed.ThetoollifefL=112mm/bladeandcostpermachiningtimemc=750yuanRMB/hweredeter-minedaccordingtoourindustrialpartnersexperience.Cuttercostswerenamedaccordingtotheirmarketprices.Fig.4.MachiningcostConB-Dplaneinthecaseofone-slotendmillingwithtrochoidtoolpath.Theblackdottedlineacrossmachiningcostcon-toursontheB-DplaneinFig.4indicatestheoptimaltooldiameterDtotheminimumcostachievementforthegivenslotwidthB.Forexample,a10mmcuttershouldbeusedtocutthe50mm-widthslot,whilea6mmcuttertocutthe15mm-widthslot.Inotherwords,twocuttersareneededifcutterdiameterselectionisconsideredseparatelyforeachmachiningfeature.Asalsoseeninthefigure,theblackdottedlinelocatedintheleftendoftheB-Dplaneimpliesthatsmallendmillcuttersof6,8and10mmindiameterarepreferredinslotend-millingmachining.Ithastobepointedoutthatthesimulationisconductedundertheassumptionthattheslotcanberemovedinonelayerwithallendmillcutters.Inthecaseofdeepslot,morelayerswillbeneededifasmallerdiametercutterisused.Theresult-ingmachiningcostincreasewillpushoptimalcutterdiameterpositionstotherightendinFig.4.Further-more,thesimulationisconductedundertheassump-tionthattheslotisnarrow,sothetrochoidtoolpathpatternneedstobeused.Forawideslothowever,acombinationoftrochoidtoolpathpatterntomachineY.Tang,Optimizationstrategyinendmillingprocessforhighspeedmachining243intothepartfirstandthenasidetoolpathpatterntoremoveleftstockwillsavetimeandthusismoreprac-ticable.Inthepracticeofdie/moldmanufacturingindustryhowever,asingleendmillcutterisgenerallyexpectedtofinishallmachiningfeaturesonapart,onaccountofthetimetakentoexchangethecutterandalltheassoci-atedcutterandholderpreparations.Thatmeanstoolselectionshouldnotbeundertakenforeachmachiningfeatureseparatelybutforallfeaturesasawhole.Fig.5illustratesthemachiningcostinvolvedinthetwo-slotmachiningprocessbyusingonecutterof6,8and10mmrespectively.Themachiningcostwhenusingthe6mmendmilltoremovea15mm-widthslotandthe10mmendmilltoremovea50mm-widthslotisshowninthesamefigureforcomparison.Datainthebottomcolumnsdenotethemachiningcoststoremovethe50mm-widthslot,whiledatainthetopcolumnsdenotethemachiningcoststoremovethe15mm-widthslot.Anddataabovecolumns,thesumofthemrespec-tivelyarethetotalmachiningcosts.Fig.5.Machiningcostwhenendmillingtwoslotsatdiffer-enttoolselections.SeenintheFig.5,themachiningcostwithtwocut-tersissmallerthanthatwithonecutter.ItsaresultthatcoincideswiththesimulationanddiscussionofFig.4.Fig.5alsoshowsifonlyonecutterisneeded,the8mmcuttercanprovidelessmachiningcostthanthe10mmor6mmcutter.Machiningcostdifferencebe-tweenthetwo-cutterselectionandtheoptimalone-cutterselectionis4.2yuanRMB.However,thema-chiningcosthereincludesonlythemachiningtimecostandthecutterswearcost.Ifthetimecostofcuttertransportandexchangeandtheassociatedcostoncut-terandholderpreparationetc.areincluded,thenitisexpectedthatthecostdifferencecanbecompensated.4.ConclusionsAnoptimizationstrategyforhighspeedmachiningofhardenedDie/Moldsteelisstudied.Anobjectivefunctionconcerningmachiningcostandassociatedoptimizationalgorithmbasedonmachiningtimeandcuttinglengthcalculation,areproposed.Constraintstosatisfyspecificmachiningstrategieswhenhighspeedmachiningthehardeneddie/moldsteel,trochoidtoolpathpatterninslotendmillingtoavoidover-heatandfeedrateadaptationtoavoidover-load,arealsodis-cussed.Asacasestudy,thetoolselectionproblemwhenamachiningdiepartwithmultiplemachiningfeaturesisinvestigated.Simulationsshow:(1)Theoptimizationwithminimummachiningcostsuggestsadesiredbalancebetweensavedmachiningtimeandreducedtoolcost.(2)Withtheproposedoptimizationalgorithm,theplotofmachiningcostcontoursontheB-Dplaneisobtained,whichcanbeusedtoseektheoptimalcutterdiameterDforagivenslotwidthBwhenslotendmillingisrequired.(3)Theoptimizationwhenallmachiningfeaturesaretakenintoconsiderationasawholecanachieveacompromiseontoolselectioncomparingwiththatwheneachmachiningfeatureisconsideredseparately.References1TaylanAtlan,BlainLilly,andY.C.Yen,Manufacturingofdiesandmolds,Ann.CIRP,50(2001),No.2,p.405.2EdKwasnickandRobKeenan,High-speedmachiningofhardeneddieandmoldsteels:atotalconcept,MoldmakingTechnol.Mag.,2002,No.11,p.1.3X.R.Yan,KazuoYamazaki,J.C.Liu,etal.,Autonomousmillingprocessanalysisandmachiningknow-howda-tabasegenerationforoperationplanning,inProceedingsofthe2000Japan-USASymposiumonFlexibleAutomationConference,Michigan,2000,p.7.4Y.Tang,Theoreticalmodelingofcuttingtemperatureinhigh-speedendmillingprocessfordie/moldmachining,J.Univ.Sci.Technol.Beijing,12(2005),No.1,p.90.5Y.TangandYoshiakiKakino,StudyonheatregulatingstrategyinNCendmillingforhardmetalmachining,J.Univ.Sci.Technol.Beijing,12(2005),No.2,p.187.6W.L.Wang,Y.Tang,YoshiakiKakino,etal.,Optimiza-tionofslotendmillingprocessbyfixedcycleanalysisforDie/Moldmachining,inProceedingsofthe6thInterna-tionalConferenceonMechatronicsTechnology(ICMT2002),Kitakyushu,2002,p.213.7Y.Kakino,H.Ohtsuka,H.Nakagawa,etal.,NCProgram-mingforconstantcuttingforceindiemachining,inPro-ceedingof2000InternationalConferenceonAdvancedManufacturingSystemsandManufacturingAutomation,Guangzhou,2000,p.471.8Y.Kakino,H.Otsuka,H.Nakagawa,etal.,Studyonendmillingofhardenedsteel,J.JSPE,66(2000),No.5,p.730.现代制造工程2005(2)Pro/E在注塑模具设计中的应用陈光忠文求实摘要探讨Pro/E在注塑模具设计中的应用,分析其CAD/CAE针对不同零件时出现的问题及解决办法。关键词:Pro/E软件模具设计CAD/CAE中图分类号:TP399文献标识码:B文章编号:16713133(2005)02009502TheapplicationofPro/EforinjectionmoulddesignChenGuangzhong,WenQiushiAbstractApplicationprobingintoPro/Einmouldingplasticsthewholedesignofthemould,ProblemandsolutionappearingwhileanalysingitsCAD/CAEtodifferentparts.Keywords:Pro/EsoftwareMoulddesignCAD/CAEPro/E提供了模具CAD/CAE/CAM系统集成,建立了单一的图形数据库,在CAD、CAE、CAM各单元之间实现数据的自动传递与转换,使CAM、CAE阶段完全吸收CAD阶段的三维图形,减少中间建模的时间和误差,借助计算机对模具结构、加工精度、浇注件在模具中的流动情况等进行反复修改和优化,及时发现问题,大大缩短制模具时间,提高模具加工精度。在模具设计过程中应引入并行工程技术,这样就可在产品三维零件设计时考虑模具的成型工艺、影响模具寿命的因素等,并进行校对、检查,应用到模具制造时不但提高了模具的制造精度,而且能缩短设计、数控编程及加工时间。具体在模具设计中注意以下几方面。图1拔模斜度与倒角1注意精度的设置对于两个要兼容的Pro/E建模的模型,它们必须具有相同的绝对精度(即Pro/E内设置的精度)。Pro/E使用绝对精度和相对精度,在型芯操作过程中,为制造和铸型设计而设计模型,将输入的几何精度匹配到其目标模型等几种情况都使用绝对精度,一般通过提高精度(给一个较小的Accuracy数值)来解决。2倒角的处理倒角应在拔模斜度设计完成后才进行,若先完成倒角,与倒角关联的曲面可能无法完成拔模斜度的设计。如图1所示,如果要完成内、外壁的拔模斜度构建,则不能先倒角。倒角面可在屏幕显示,但无法完成倒角,这时将AttachmentType的选项中选择MakeSurface可产生倒角曲面,再将产生的倒角曲面相合并,用合并后产生的曲面切实体就可获得所需的倒角结构。3创建分模面Pro/E在模具设计中最复杂,也是最重要的莫过于创建分模面。创建分模面的方法是多种多样的,不同零
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