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JournalofMaterialsProcessingTechnology182(2007)418–426TheuseofTaguchimethodinthedesignofplasticinjectionmouldforreducingwarpageS.H.Tang∗,Y.J.Tan,S.M.Sapuan,S.Sulaiman,N.Ismail,R.SaminDepartmentofMechanicalandManufacturingEngineering,UniversitiPutraMalaysia,43400Serdang,Selangor,MalaysiaReceived3September2004;receivedinrevisedform27July2006;accepted10August2006AbstractPlasticinjectionmouldingisoneofthemostimportantpolymerprocessingoperationsintheplasticindustrytoday.However,lackofskillinmouldmakingandinjectionmouldingmachinecontrolwillleadtodefectiveplasticproduct.Warpageisonetypeofdefectthatusuallyappearsinproductswiththicknesslessthan1mm.Thisprojectisgoingtofabricateamouldthatproducedathinplatewithdimension120mm×50mm×1mm.Thethinplatewillbeusedforwarpagetesting.Inmouldfabrication,themouldbasethatpurchasewillbemachinedandassembled.Afterthat,themouldisfixedontheinjectionmouldingmachine.Themachinesettingshouldbemadetoproducetheproduct.Then,theproductwillbeusedfortestingontheeffectivefactorsinwarpageproblembyapplyingtheexperimentaldesignofTaguchimethod.Fromtheresults,itshowsthatthemosteffectivefactoronthewarpageismelttemperature.Thefillingtimeonlyslightlyinfluencedonthewarpage.Theoptimumparametersthatcanminimizethewarpagedefectaremelttemperature(240◦C),fillingtime(0.5s),packingpressure(90%)andpackingtime(0.6s).©2006ElsevierB.V.Allrightsreserved.Keywords:Plasticinjectionmould;Taguchimethods;Experimentaldesign;Warpage1.IntroductionMouldmakingisanimportantsupportingindustrybecausetheirrelatedproductsrepresentmorethan70%amongthecom-ponentsinconsumerproducts.Thehighdemandforshorterdesignandmanufacturingleadtimes,gooddimensionalityandoverallquality,andrapiddesignchangeshasbecomethebottle-necksinmouldindustries[1].Itisacomplicatedprocess,andrequiredskilledandexperiencedmouldmaker.Generally,injectionmouldingisoneofthemostimportantpolymerprocessingoperationsintheplasticindustrytoday.Approximatelyone-thirdofallplasticsareconvertedintopartsusinginjectionmoulding[2].Thisisoneoftheprocessesthataregreatlypreferredinmanufacturingindustrybecauseitcanproducecomplex-shapeplasticpartswithgooddimensionalaccuracyandveryshortcycletimes[3].Typicalexamplesarecasingsandhousingsoftheproductssuchascomputermonitorandmobiletelephone,whichhaveathinshellfeature.These∗Correspondingauthor.E-mailaddress:[e-mail](S.H.Tang).productstendtobecomelighter,thinnerandsmaller.Hence,theinternalcomponentsofproductshavetobepackedintohous-ing,whichhassmallervolume.Onewaytoincreasethespaceofhousingpartsistoreducethewallthickness.However,theinjectionmouldingoperationbecomesmoredifficultasthewallthicknessofplasticpartsbecomesthinner[4].Thisisbecausethesignificantwarpagedefectwillbeappeared.Toreducethissignificantdefect,testingprocedureregardingtotheeffectivefactorsisrequired.Athinplatewithdimension120mm×50mmand1mmthicknesswillbeproduced.Itisusefortestingontheeffec-tivefactorstominimizethewarpagedefect.Firstly,fabricatingtheplasticinjectionmouldisneeded.Afterthat,themouldisgoingtobeassembledontheinjectionmouldingmachine.Whenthethinplateshavebeenproduced,theywillbeusedfortest-ingontheeffectivefactorsinwarpageproblembyapplyingtheexperimentaldesignofTaguchimethod.2.PreparationInfabricatingthemould,somepreparationsareneeded.Thecapabilityofthemachinethatareavailableinfacultyare0924-0136/$–seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.jmatprotec.2006.08.025S.H.Tangetal./JournalofMaterialsProcessingTechnology182(2007)418–426419investigated.Themachinesthatrequiredinfabricatingthemouldaredrillingmachine,millingmachineandgrindingmachine.Theplasticinjectionmouldingmachineisalsoneededforproducingtheproduct.ThemachinethathasbeenusedisBOY22D.Besidesthat,itisalsorequiredtosearchandpurchasethemouldbase,whichcanfittheinjectionmouldingmachine.CarbonsteelAISI1050hadbeenselectedasmaterialforthemouldbase.Sincesomecomponentssuchasejectorpin,locatingring,spruebush,waterjunctionsandspringsarenotincludedinthemouldbase,thesecomponentsarepurchasedindependently.TheplasticmaterialthathasbeenusedisABS.3.MoulddesignTherearefourdesignconceptsthatcanbeusedinthisproject.Thedescriptionofthesedesignconceptsisasfollows:(a)Three-platemould—Havingtwopartinglineswithsinglecavity.(b)Two-platemould—Havingonepartinglinewithsinglecav-itywithoutgatingsystem.(c)Two-platemould—Havingonepartinglinewithdoublecav-itieswithgatingsystemandwithejectorpinatthecavities.(d)Two-platemould—Havingonepartinglinewithdoublecavitieswithgatingsystemandwithoutejectorpinatthecavities.Sincethisprojectislimitedinbudget,thetypeofmouldbasethathasbeenchosenistwoplatemouldinsteadofthreeplatemould.Amongthedesignconceptsfortwoplatemould,theconcept‘d’hasbeenchosen.Thisisbecauseconcept‘b’isnon-productivewhileconcept‘c’maydamagetheproductduringejection.Generally,twoplatemouldconsistofeightplatesandtherearetheirstandarddimensions,respectively.Themouldbasethathasbeenchosenmustbaseonthespecificationoftheinjectionmouldingmachinethatwillbeused.Inthisproject,thestandardmouldbasewith250mm×250mmhasbeenusedanditsplatesdimen