一种使用设计特征和工艺参数来估计模具成本的集成框架毕业课程设计外文文献翻译.docx
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一种使用设计特征和工艺参数来估计模具成本的集成框架毕业课程设计外文文献翻译
Anintegratedframeworkfordieandmoldcostestimationusingdesignfeaturesandtoolingparameters
Received:
5August2003/Accepted:
6January2004/Publishedonline:
2February2005
Springer-VelaLondonLimited2005
Abstract
Toolingisanessentialelementofnearnetshapemanufacturingprocessessuchasinjectionmoldinganddiecasting,whereitmayaccountforover25%ofthetotalproductcostanddevelopmenttime,especiallywhenorderquantityissmall.Developmentofrapidandlowcosttooling,combinedwithascientistapproachtomoldcostestimationandcontrol,hasthereforebecomeessential.Thispaperpresentsanintegratedmethodologyfordieandmoldcostestimation,basedontheconceptofcostdriversandcostmoodier.Costdriversincludethegeometricfeaturesofcavityandcore,handledbyanalyticalcostestimationapproachtoestimatethebasicmoldcost.Costmoodierincludetoolingparameterssuchaspartingline,presenceofsidecore(s),surfacetexture,ejectormechanismanddiematerial,contributingtothetotalmoldcost.Themethodologyhasbeenimplementedandtestedusing13industrialexamples.Theaveragedeviationwas0.40%.Themodelisedibleandcanbeeasilyimplementedforestimatingthecostofavarietyofmoldsanddiesbycustomizingthecostmoodierusingqualityfunctiondeploymentapproach,whichisalsodescribedinthispaper.
Keywords:
Costestimation;Diecasting;Injectionmolding;Qualityfunctiondeployment。
1Introduction
Productlifecyclestodayaretypicallylessthanhalfofthoseinthe1980s,owingtothefrequententryofnewproductswithmorefeaturesintothemarket.Manufacturingcompetitivenessismeasuredintermsofshorterlead-timetomarket,withoutscribingqualityandcost.Onewaytoreducethelead-timeisbyemployingnearnetshape(NNS)manufacturingprocesses,suchasinjectionmoldinganddiecasting,whichinvolvefewerstepstoobtainthedesiredshape.However,thetooling(dieormold),whichisanessentialelementofNNSmanufacturing,consumesconsiderableresourcesintermsofcost,timeandexpertise.
Atypicaldiecastingdieorplasticinjectionmoldismadeintwohalves:
movingandaxedwhichbutttogetherduringmoldlingandmoveapartduringpartejection.TheconstructionofatypicalcoldchamberpressurediecastingdieisshowninFig.1.
Themainfunctionalelementsofthedieandmoldincludethecoreandcavity,whichimpartthedesiredgeometrytotheincomingmelt.Thesemaybemanufacturedassingleblocksorbuilt-upwithanumberofinserts.Thesecondaryelementsincludethefeedingsystem,ejectionsystem,sidecoreactuatorsandfasteners.Thefeedingsystemcomprisingofspreebush,runner,gateandoveraweenablesthetownofmeltfrommachinenozzletomoldcavity.Theejectormechanismisusedforejectingthemoldedpartfromthecoreorcavity.Alltheaboveelementsarehousedinamoldbaseset,comprisingofsupportblocks,guidesandotherelements.Part-specieelements,includingcoreandcavityandfeedingsystemaremanufacturedinatoolroom.Otherelementsareavailableasstandardaccessoriesfromvendors.Moldassemblyandfunctionaltrialsareconductedbyexperiencedtoolmakersinconsultationwithtooldesigners.
Fig.1.Constructionofatypicalpressurediecastingdie
ThetoolingindustryispresentlydominatedbyJapan,Germany,USA,Canada,Korea,Taiwan,China,Malaysia,SingaporeandIndia.Themajorusersoftoolingincludeautomobiles,electronics,consumergoodsandelectricalequipmentsectors.Plasticmoldsaccountforthemajorshareoftoolingindustry.About60%oftoolroomsbelongtosmallandmediumscaleindustriesworldwide[1].ThetoolingrequirementisoverUS$600millionperyearinIndiaalone,withanannualgrowthrateofover10%duringthelastdecade.InIndia,theshareofdifferenttypesofmoldsanddiesis:
plasticmolds33%,sheetmetalpunchesanddies31%,diecastingdies13%,jigs&stores13%,andgauges10%[2].
Thetoolingindustryisincreasinglyfacingthepressuretoreducethetimeandcostofdieandmolddevelopment,offerbetteraccuracyandsurfaceknish,provideedibilitytoaccommodatefuturedesignchangesandmeettherequirementsofshorterproductionruns.Tomeettheserequirements,newtechnologieslikehighspeedmachining,hardenedsteelmachining,processmodeling,toolingdesignautomation,concurrentengineering,rapidprototypingandrapidtoolinghavebeenapplied.Forsuccessfuloperationsandtomaintainthecompetitiveedge,itisnecessarytoestablishquantitativemethodsforcostestimation.
Ourcurrentresearchaimsatdevelopingasystematicandintegratedframeworkfordevelopmentofrapidhardtooling(diesandmolds)forinjectionmoldingandpressuredie-castingapplications.Thenecessityofasystematiccostestimationmodelforcomparativeevaluationofdifferentroutestotoolingdevelopmentmotivatedustoreviewtheexistingmodels,presentedinthenextsection,followedbyourproposedmethodology.
2Previousworks
Thereisconsiderablesimilarityincostestimationapproachesusedforproductandtoolingasreportedintechnicalliterature.Theseapproachescanbeclassedintovetgroups:
intuitive,analogical,analytical,geometricfeaturebasedandparametricbasedmethods,brieryreviewedhere.
Intheintuitivemethod,theaccuracyofcostestimationdependsonthecostappraiser’sexperienceandinterpretations.Theestimationisusuallyperformedinconsultationwiththetooldesigner.Theestimatoracquiresthewisdomandintuitionconcerningthecoststhroughlongassociationwithdiesandmolddevelopment.Thismethodisstillinpracticeinsmallworkshopsandtoolrooms.
Intheanalogicalmethod,thecostofdieandmoldisestimatedbasedonsimilaritycoefficientsofpreviousdiesandmoldsmanufacturedbytherm.Inthistechnique,diesarecodedconsideringfactorssuchasdiesize,diematerial,complexity,ejectorandgatingmechanism.Theappraiserstartsbycomparingthenewdiedesignwiththeclosestmatchamongallpreviousdesigns.Thebasichypothesesare:
similarproblemshavesimilarsolutions,andreuseismorepracticalthanproblemsolvingfromscratch[3].However,thisapproach,alsoreferredtoascasebasedreasoning,requiresacompletecasebaseandanappropriateretrievalsystem,whichhasnotbeenreportedfordieandmoldcostestimationsofar.
Intheanalyticalcostestimation,theentiremanufacturingactivityisdecomposedintoelementarytasks,andeachtaskisassociatedwithanempiricalequationtocalculatetheManufacturingcost.Forexample,acommonequationformachiningcostis:
Machiningcost=(cuttinglength/feedperminute)×Machineoperationcost.
Wilson(quotedin[4,Chap.6,p.121])suggestedamathematicalmodelforincorporatingageometriccomplexityfactorinturningandmillingoperations,givenby:
di=ithdimensionoffeature
ti=correspondingdimensionaltolerance
N=totalnumberofdimensions.
Thisisexplainedwiththehelpofanexamplelater.
Anothermethodcalledactivitybasedcosting(ABC)involvesapplyingtheanalyticalmethodtoallstepsinmanufacturingagivenproduct,toestimatetheresources(material,laborandenergy)involvedineachstep.Suchadetailedapproachforvariousprocesses,includingcastinghasbeendevelopedbyCrease[5].Intoolrooms,thisapproachisusedinthecaseofdieswithcomplexcavitygeometry.Thesourcesofmoldcostcanbedividedintothreecategories:
moldbasecost,functionalelements(core,cavityinserts)costandsecondaryelementscost.Ineachcategory,thetimeneededtoobtainthedesiredgeometrybymachiningisconsideredasareferenceforcosting[4].Ascanbeexpected,establishingandvalidatingthecostingequation,aswellasusingitinpractice,arecumbersometasks.
Inthefeaturebasedmethod,moldgeometricfeatures(cylinder,slot,hole,rib,etc.)areusedasthecostdrivers.Thediemanufacturingcostisthenestimatedusingeitherempiricalequationsortoolssuchasknowledge-basedsystemsandarterialneuralnetworks.ChenandLiu[6]usedthefeaturerecognitionmethodtoevaluateanewinjectionmoldedproductdesignforitscosteffectiveness.Theyassumedthataproductisanaggregationofasetoffeaturesandfeaturerelationships.Thesefeaturerelationshipsweremappedtoconvertapartfeatureintomoldrelatedcostevaluations.ChinandWong[7]useddecisiontableslinkedtoaknowledgebasetoestimateinjectionmoldcost.
Intheparametriccostestimation,technical,physicalorfunctionalparametersareusedasbasisforcostevaluation.Thismethodallowsonetoproceedfromtechnicalvaluescharacterizingtheproduct(availablewithdesignengineers)toeconomicdata.SandaracandMaslekar[8]usedregressionmodelapproachininjectionmoldcostestimation.LoweandWalshe[9]usedlaborinvolvementininjectionmoldmakingasareference;moldcostwasestimatedusinglinearregressionanalysis.
Tosummarize,costsimilarityandcostfunctions(costfactors)arethetwosetsofmethodsforestimatingthemoldcost.
Intherestset,similaritybetweenanewmoldandapreviousmolddevelopedinthetoolroomsisusedasareference.Intuitiveandanalogicalmethodsfallunderthiscategory.Inthewidelyusedintuitivemethod,thecostappraisermaynotbeinapositiontoidentifyalltheriskfactorsandtoquantifymanyofthem.Theanalogicalmethodcanbesuccessfullyusedforestimatingthecostofdiebasesandothersecondaryelementswheregroupingismucheasier.However,inthecaseoffunctionalelements(coreandcavity),groupingbecomesadifficulttaskastheirgeometry,machiningsequenceandtolerancegreatlyvarywithprod