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英文原文原文节选自JournalofMaterialsProcessingTechnology1032000318323Optimalselectionofparametersinmultitooldrilling原文Optimalselectionofparametersinmultitooldrillinga.DepartmentofMechanicalEngineering,IndianInstituteofTechnology,Chennai600036,Indiab.DepartmentofHumanitiesandSocialSciences,IndianInstituteofTechnology,Chennai600036,IndiaAccepted4January2000AbstractInholemakingoperation,thefinalsizemaybeobtainedbydrillingwithasingledrillorpilotdrillingofoneormoreholesfollowedbyenlargementtothefinalsize.Inthispaper,amodelbasedonproductioncostispresentedandtheoptimalconditionsareobtainedconsideringtechnologicalandmachinetoolconstraints.Thisapproachisquiteusefulinarrivingatthecuttingparametersautomaticallyinacomputerassistedprocessplanningsystem.KeywordsOptimalselectionMultitooldrillingComputerassistedprocessplanningsystemNomenclatureDdrilldiameter,mmdpilotdrilldiameter,mmFthrustforceindrilling,Nh1toolreturnrate,min/mmh2timefortoolretractadvance,mink1operatingcostofdrillingmachine,/minktdrillcost,ldepthofdrilling,mmMtorqueindrilling,Nmsfeed,mm/revTdrilllife,minTRpreventivetoollifetdepthofcut,错误未找到引用源。(Dd),mmtetimefortoolexchange,mintmdrillingtime,mintptoolpreparationtime,minUcostofdrilling,Vcuttingspeed,m/min1.IntroductionOneoftheimportantstepsinanycomputerassistedprocessplanningCAPPistodeterminethecuttingparametersautomatically.Oncetheoperationsequencesandtheappropriatetoolshavebeendetermined,successofthemachiningprocessdependsontheselectionofcuttingparameters.Forexample,inthecaseofturning,cuttingparametersincludedepthsofcut,feedsandcuttingspeeds.Thecuttingparametersareselectedtoachievethedesirableperformancesuchasgoodsurfacefinish,dimensionalaccuracyofthecomponent,easychipremovalandsoon.Inaddition,theymustalsosatisfyaneconomiccriterionlikeminimumproductioncostormaximumproductionrate.Thusmachiningeconomicsinvolvestheoptimalselectionofmachiningparameterssuchascuttingspeed,feedanddepthofcutsubjecttocertaintechnologicalconstraintssuchastoolwear,dimensionalaccuracy,surfacefinishandmachinetoolcapabilities.Ahumanprocessplannerselectsthepropermachiningparametersusinghis/herexperienceorfromhandbooksbasedonthepartgeometry,technologicalrequirements,themachinetool,cuttingtoolselectedandthepartmaterial.Analogously,inaCAPPsystem,toselectpropercuttingparameters,alltheinformationregardingthepartandthemachiningresourcesshouldbeavailabletothesystemincomputerinterpretableformat.Thereareseveralwaysthiscouldbeachieved.ExistingcomputerizedmachiningparameterselectionsystemscanbeclassifiedintofourmajorcategoriesDatastorageandretrievalsystems,empiricalequations,expertsystemsandmathematicalmodels.Ofthesefour,themathematicalapproachhasreceivedmuchattention,asiteliminatestheneedforalargeamountofdatastoragerequiredbytheretrievalprocedureandcanbeusedtoarriveatoptimalmachiningparameters.Optimizationofsingleandmultiplepassmachiningprocess,especiallyturninghasbeeninvestigatedextensively1,2.However,thedrillingprocesshasnotreceivedthesameattentionthoughasmuchas40ofthemachiningtimeisdevotedtoholemakingasrevealedbyasurveyofthemediumsizedindustry3.Whenthetotalstocktoberemovedtoachievethefinalholesizeexceedsthemaximumallowabledepthofcutduetovariousconstraintsonavailablemachinepower,toolforce,etc.itisimperativethatmultitoolmachiningisemployed.Forexample,ifaholeofbigsizeistobedrilled,thismaybeprecededbydrillingofoneortwopilotholes.Thus,thesubdivisionofdepthsofcutisanimportantconsiderationinmultitooldrillingalso.Inthispaper,multitooldrillingprocessisconsideredandtheminimumproductioncostistakenastheobjectivewiththeconstraintsofthespeedandfeedranges,strengthofthedrill,maximumaxialthrustallowedbythefeedmechanismandpowerofthemachinetool.Thismodelalsoincludesthepreventivetoolreplacementstrategypractisedinmanyindustries.Foratypicalcase,theresultsarepresentedinthispaper.2.MultitooldrillingmodelInmanufacturedcomponents,moreholesareproducedthananyothershapeandalargeproportionofthosearemadebydrilling.Thebasicmotionsrequiredfordrillingarerelativerotationbetweentheworkpieceandthetoolwithrelativelongitudinalfeeding.Beinganimportantproductionprocess,thegeometryofthedrill,thecuttingmechanicsandthelifeaspectshavebeenextensivelystudied48.However,theoptimalconditionsindrilling,particularlyinmultitoolmachining,havenotbeenstudied.Indrilling,multitoolmachiningisused,whenthetotalstocktoachievethefinalsizeexceedsthemaximumallowabledepthofcuti.e.thedrillsizeduetovarioustechnologicalconstraintsandthemachinecapabilities.Inmultitoolmachining,drillsofdifferentsizesareusedtoarriveatthefinaldimension.Whentherequiredsizecanbemachinedwithonedrillitselfi.e.withoutapilotholedrilling,itisreferredtoassinglestagedrilling.Iftheholesizetobedrilledislarge,oneormorepilotholeshavetobedrilledbeforeenlargingtheholewithafinalsizedrillFig.1.Thefirstholeisdrilledinsolidworkmaterialandhenceitisreferredtoasdirectdrilling.Theselectionofpilotdrills,whichdecidesthesubdivisionofdepthsofcut,canbedoneonthebasisoftotalproductioncostmodel.Totalproductioncostmodelforthemultitooldrillingwiththeconstraintsofthespeedandfeedranges,strengthofthedrill,maximumaxialthrustallowedbythefeedmechanismandpowerofthemachinetoolisgivenbelow.Themodelmakesuseoftoollifeequationandpreventivetoolreplacementstrategypractisedindustrially.ToollifeequationindrillingisexpressedintermsofcuttingspeedV,feedsanddrillsizeDaswhereCv,xv,yv,zvandmaretoollifeconstantandexponents,whosevaluesdependonthetoolandworkmaterialcombination.Kvisageneralcorrectionfactorforothermachiningconditions9.tintheaboveexpressionreferstodepthofcutinenlargingaholeanditsvalueisgivenbywheredisthepilotholesize.TotalcostUtThetotalcostofdrillingaholeisgivenbywhereUdisthecostofdirectdrilling,Ueithecostofenlargingtheithholeandnreferstothenumberofenlargingoperations.Inasinglestagedrilling,thesecondtermisabsent.A4representsthecostoftoolpreparationgivenbywheretpisthetoolpreparationtimeandk1theoverheadcost.Costofdirectdrilling/enlargingisgivenbyThefirsttermrepresentsthemachiningcostwherethetimerequiredfordrillingisgivenbywherelisthelengthofdrilling,sthedrillfeedandNtherpmofthedrill.Thesecondtermdenotesthetoolcostandthethirdtermrepresentsthetoolexchangecost.Thefourthtermgivesthecostcorrespondingtoidletoolmotions,whereh1referstotherateatwhichthetoolreturnisdoneafterthecompletionofdrillingandh2denotesthetimetakenforretractingandadvancingthedrilltostartthedrillingcycle.TheminimizationofcostfunctionEq.5isdoneforeachstageconsideringthefollowingaspects.ToollifeTThetoollifeindrillingisgivenbyEq.1.Forthepreventivetoolreplacementstrategy,thetoollifeisspecifiedonthebasisofshopfloorpractice.Thechosenparametershavetosatisfythisrequirement.UsingtheminimumandmaximumspeedlimitsthefollowingconstraintisobtainedThrustforceFThedrillcanwithstandonlyalimitedaxialforce.TheallowableaxialloadonthedrilltoavoidbucklingisgivenbywhereListhedrilllengthexcludingtheshankofthedrill,DavtheaveragediameterDav.0.7Dandthefactorofsafety,fs1.2.01.Also,thefeedmechanismofthedrillingmachineisdesignedtowithstandaspecifiedforce.Themaximumallowableforce,Fspisthereforespecifiedbythemachinetoolmanufacturers.Consideringtheaboveforces,themaximumallowablethrustforceistakenasThethrustforceindrillingisgivenbywhereCf,zf,yfandxfarethecoefficientandexponentsofforceequationandKfathrustcorrectionfactor9.ThedrillingparametersarechosensuchthattheFmaxgivenbyEq.9isnotreached.TorqueMThetorqueMthatthedrillcanwithstandisgivenby1
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