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1Minimizingmanufacturingcostsforthininjectionmoldedplasticcomponents1.IntroductionInmostindustrialapplications,themanufacturingcostofaplasticpartismainlygovernedbytheamountofmaterialusedinthemoldingprocess.Thus,currentapproachesforplasticpartdesignandmanufacturingfocusprimarilyonestablishingtheminimumpartthicknesstoreducematerialusage.Theassumptionisthatdesigningthemoldandmoldingprocessestotheminimumthicknessrequirementshouldleadtotheminimummanufacturingcost.Nowadays,electronicproductssuchasmobilephonesandmedicaldevicesarebecomingevermorecomplexandtheirsizesarecontinuallybeingreduced.Thedemandforsmallandthinplasticcomponentsforminiaturizationassemblyhasconsiderablyincreasedinrecentyears.Otherfactorsbesidesminimalmaterialusagemayalsobecomeimportantwhenmanufacturingthinplasticcomponents.Inparticular,forthinparts,theinjectionmoldingpressuremaybecomesignificantandhastobeconsideredinthefirstphaseofmanufacturing.Employingcurrentdesignapproachesforplasticpartswillfailtoproducethetrueminimummanufacturingcostinthesecases.Thus,tacklingthinplasticpartsrequiresanewapproach,alongsideexistingmolddesignprinciplesandmoldingtechniques.1.1CurrentresearchToday,computer-aidedsimulationsoftwareisessentialforthedesignofplasticpartsandmolds.Suchsoftwareincreasestheefficiencyofthedesignprocessbyreducingthedesigncostandleadtime[1].Majorsystems,suchasMoldFlowandC-Flow,usefiniteelementanalysistosimulatethefillingphenomena,includingflowpatternsandfillingsequences.Thus,themoldingconditionscanbepredictedandvalidated,sothatearlydesignmodificationscanbeachieved.Althoughavailablesoftwareiscapableofanalyzingtheflowconditions,andthestressandthetemperaturedistributionconditionsofthecomponentundervariousmoldingscenarios,theydonotyielddesignparameterswithminimummanufacturingcost[2,3].Theoutputdataofthesoftwareonlygiveparametervaluerangesforreferenceandleavesthedecisionmakingtothecomponentdesigner.Severalattemptshavealsobeenmadetooptimizetheparametersinfeeding[4–7],cooling[2,8,9],andejectionTheseattemptswerebasedonmaximizingtheflowabilityofmoltenmaterialduringthemoldingprocessbyusingempiricalrelationshipsbetweentheproductandmolddesignparameters.SomeresearchershavemadeeffortstoimproveplasticpartqualitybyReducingthe2sinkmark[11]andthepartdeformationaftermolding[12],analyzingtheeffectsofwallthicknessandtheflowlengthofthepart[13],andanalyzingtheinternalstructureoftheplasticpartdesignandfillingmaterialsflowsofthemolddesign[14].Reifschneider[15]hascomparedthreetypesofmoldfillingsimulationprograms,includingPartAdviser,Fusion,andInsight,withactualexperimentaltesting.Alltheseapproacheshaveestablishedmethodsthatcansavealotoftimeandcost.However,theyjusttackledthedesignparametersoftheplasticpartandmoldindividuallyduringthedesignstage.Inaddition,theydidnotprovidethedesignparameterswithminimummanufacturingcost.Studiesapplyingvariousartificialintelligencemethodsandtechniqueshavebeenfoundthatmainlyfocusonoptimizationanalysisofinjectionmoldingparameters[16,17].Forin-stanceHeetal.[3]introducedafuzzy-neuroapproachforautomaticresettingofmoldingprocessparameters.Bycontrast,Helpsetal.[18,19]adoptedartificialneuralnetworkstopredictthesettingofmoldingconditionsandplasticpartqualitycontrolinmolding.Clearly,thedevelopmentofcomprehensivemoldingprocessmodelsandcomputer-aidedmanufacturingprovidesabasisforrealizingmoldingparameteroptimization[3,16,17].Moketal.[20]proposeahybridneuralnetworkandgeneticalgorithmapproachincorporatingCase-BasedReasoning(CBR)toderiveinitialsettingsformoldingparametersforpartswithsimilardesignfeaturesquicklyandwithacceptableaccuracy.Mok’sapproachwasbasedonpastproductprocessingdata,andwaslimitedtodesignsthataresimilartopreviousproductdata.However,norealR&Defforthasbeenfoundthatconsidersminimizingmanufacturingcostsforthinplasticcomponents.Generally,thecurrentpracticalapproachforminimizingthemanufacturingcostofplasticcomponentsistominimizethethicknessandthedimensionsofthepartattheproductdesignstage,andthentocalculatethecostsofthemolddesignandmoldingprocessforthepartaccordingly,asshowninFig.1.Thecurrentapproachmaynotbeabletoobtaintherealminimummanufacturingcostwhenhandlingthinplasticcomponents.1.2ManufacturingrequirementsforatypicalthinplasticcomponentAsatestexample,thetypicalmanufacturingrequirementsforathinsquareplasticpartwithacenterhole,asshowninFig.2,aregiveninTable1.3Fig.1.ThecurrentpracticalapproachFig.2.TestexampleofasmallplasticcomponentTable1.Customerrequirementsfortheexamplecomponent2.ThecurrentpracticalapproachAsshowninFig.1,thecurrentapproachconsistsofthreephases:productdesign,molddesignandmoldingprocessparametersetting.Amainobjectiveintheproductdesignistoestablishthephysicaldimensionsofthepartsuchasitsthickness,width4andlength.Thephasesofmoldedsignandmoldingsubsequentlytreattheestablishedphysicaldimensionsasgiveninputstocalculatetherequireddetailsformoldmakingandmoldingoperations.Whenapplyingthecurrentpracticalapproachfortacklingthegivenexample,thekeyvariablesarehandledbythethreephasesasfollows:Productdesign*Establishtheminimumthickness(h