JournaloftheChineseInstituteofIndustrialEngineersVol.29,No.7,October2012,454465AninnovativemanufacturingprocessforbambooinjectionmoldingbyusingTRIZandTaguchimethodMu-TsaiChang*andChi-HaoYehDepartmentofIndustrialEngineeringandManagement,NationalTaipeiUniversityofTechnology,No.1,Sec.3,Chung-HsiaoEastRoad,Taipei,Taiwan,ROC(ReceivedFebruary2012;revisedJuly2012;acceptedAugust2012)Theappearanceof3C(computer,communication,consumerelectronic)electronicproductshasbeenconsideredas acritical attributetoattract consumers inthepast decade. Moreover, 3Celectronicenterpriseswithownbrandsaretryinghardtomeettherequirementssuchasuser-friendlyinterfaceandeco-environmental materials for increasingthe revenue andmarket share. Bamboohadbeenknown as a flexible and green raw-material worldwide for many years. However, there are no bamboo-made applications in any 3Celectronic products due to its manufacturing process to achievesatisfactory specifications. The innovative manufacturing process of bamboo injection molding on theappearanceof a 3C product suffered from a crucial quality issue,that is, bamboo deformation due tothedifferencebetweenshrinkageof plasticanditsinherent material characteristics. Theconcept issimilartoIMR(in-molddecorationbyroller)process. Theobjectiveofthisarticleistoproposeaninnovativeandrobustbambooinjectionmoldingprocessbyusingskillssuchasmeasurementsystemanalysis, the Taguchi method, process capability index, and TRIZ. In this study, the detailedexperimental process andsatisfactoryresult are demonstratedandgiven. The exploitedapproachconcerningbamboois avaluableoutcomeandreference for further advancedimplementations inelectricalindustryandothers.Keywords: bamboo injectionmolding;measurementsystemanalysis;Taguchi method;TRIZ;processcapabilityindex1. IntroductionConsumers are attracted by the functionalities,appearance,andpriceofa3C(computer,commu-nication, consumer electronic) electronic product.However, existingmanufacturingtechniques suchas electroplating andspray painting for anelec-tronic products appearance produce significantandnegativeimpactstoenvironment. 3Ccompa-nies with own brand need to provide moreeco-environment protection while using newfinish-machiningmethods [7]. Bamboohas manyadvantagessuchaseasytorecycle,easytodecom-pose,andgoodperformanceinphysicalattributes.It is a suitable material to produce home-livingproducts. AsusTek, oneof brandcompanies, hasbeen dedicated in developing innovativemanufacturing process and designed laptopsappearance by using bamboo as main material.Thisistheveryfirstbambooskinontolaptopandisfamousworldwide(Figure1).Inrecent years, in-moldinjectionhas beenapopular manufacturingprocess inlaptopappear-ance. AsusTekbegantoexplorein-moldinjectionmolding by using bamboo and give curved anddouble-sided arcs appearance. However, qualityissuessufferfrombreaking, blisters, wrinkles, anddeformationonbambooskin(Figure2).Themostcritical issue is the deformationdue todifferentshrinkageratiosforplasticandbamboo. Sincein-mold injection molding by using bamboo is the firstattempt all over the world, there is no existingempirical rule or data to solve the difficult problem.In this study, an innovative and robust manufactur-ing approach is exploited to solve the bamboodeformation occurring in in-mold injectionmolding.The approach is executed by traditional quality-relatedskills suchas Taguchis method, MSAbygauge repeatability and reproducibility (GRR),process capability index (PCI) by Cpk, t-test byone-samplet-test, andindependent samplest-test.In addition, TRIZ known as an innovative thinkingmethodology is utilized to solve problems neverbeenmet. Althoughthe traditional quality-assur-ancetechniques utilizedarenot newlydeveloped,however, the synergy of traditional skills and TRIZprovides a profitable quality level in such a difficultmanufacturingprocess.*Correspondingauthor.Email:Arthur_chang@asus.comISSN10170669print/ISSN21517606online2012ChineseInstituteofIndustrialEngineershttp://dx.doi.org/10.1080/10170669.2012.727477http://www.tandfonline.com2. An innovative and robust manufacturingapproachThemost critical issueis thedeformationduetodifferent shrinkage ratios between plastic andbamboo(thedesiredspecificationfordeformationis 03 mm, mean14.3 mm, standarddeviation1.04). This article proposes an innovative androbust manufacturing approach to solve thisunwanteddeformation. Theproblem-solvingpro-cess is suggested in four steps and is shown inFigure3. Thedetailedexperiment arrangement isexplainedinthefollowingsections.2.1 MSAexperimentTheMSAis processedat stageA inFigure3.The measure systemis composed by measuringinstrument, operator, and operational environ-ment. If the measurement variationis toolarge,themeasurementdatamaynotbeappropriateforfurther analysis [1]. MSAmethodology includesevaluation bias, evaluation stability, evaluationdiscrimination, GRR analysis, Kappa analysis,etc. The GRRanalysis using continuous data isexecutedtomeasure repeatability (the variabilitybetweentheoperatorsandequipment) andrepro-ducibility(thevariabilityamongtheoperators)[6].Four basic GRR are defined in terms of %contribution,%studyvariation,%tolerance,andthe number of distinct category. The field isemphaticallyinprecisionofmeasuringinstrument,which holds tolerance ratio [1]. Therefore, %tolerance is chosen to carry on MSA in thisstudy, that is, the formulae are as shown inEquation(1).%Tol PT 6x

2Measurement SystemqUSL LSL, 1where%Tol isthepercentageoftolerance, Ptheprecision, T the tolerance, USL the upper specifica-tionlimit, andLSLthelower specificationlimit.The operational requirements are at least twooperatorsandsixanalysestocarryout twotimesmeasurement [1]. The criteria for determining if theprocessiscapableare: GRR510%isacceptable(PASS), 10% GRR530%is a conditionalacceptance, and GRR30%is not acceptable(NG) based on practical experience for 3Celectronicproducts.As mentionedearlier, thedeformationis veri-fiedbyGRRprocess.TheMSAexperimentneedstwolaboratoryoperatorsand10injectedbambooproducts. Each operator measures his (her) injectedbamboo products for three cycle times. If the GRRresult is NG, the quality assurance department willask component suppliers to provide correctiveactionreport(CAR)forfacilitatingthemeasuringimprovement. The measurement systemis evalu-atedagainandrepeatedlycarriedout until GRRresult is acceptable (PASS) or a conditionalacceptance.2.2 TRIZexperimentThe TRIZ method is applied at stage B shown inFigure 3. TRIZwas inventedanddeveloped byRussian Genrich Altshuller. Genrich Altshuller hadfound a variety of different engineering systems andtechnologies sharing common evolution, whichhaveguidedpeopletoavoidmanyfruitless trailsanderrorsin1950s.TRIZhadbeenprovedtobeawell-structuredand innovative way of problem solving in technicaland non-technical areas [9]. Many well-knownimprovement methods like the Six Sigma, QFD,the Taguchi method, and DFM/Ahave recom-mended TRIZ as a valuable complement forinnovation,nomatterintechnology,management,business strategy, and creativity [8]. Therefore,TRIZis a feasible innovative theory in solvingmany contradictions in engineering and technol-ogy. Manypractical TRIZ-basedusages inengi-neeringareacanbereviewed[11]. TRIZincludesFigure 2. Abnormalities at bamboos appearance byusing in-mold injection molding process: (a) breaking, (b)blisters,(c)wrinkles,and(d)deformation.Figure1. AsusU6VBamboonotebook.JournaloftheChineseInstituteofIndustrialEngineers 455contradiction analysis, idle resources utilization,increasing the ideality of final result, prediction fortheevolutionof bothproblems andsolutions, 39engineeringparameters, 40TRIZinnovativeprin-ciples, and contradiction matrix [8]. In addition, 40TRIZ innovative principles have been confirmed tobeshortcutstoideal final result evenwithout theanalysisof contradictionsandresource. Theycanbeusedasindependenttoolstoobtaininnovativeorcreativeideasforresolvingconflicts.FortyTRIZinnovative principles were devel-oped by Altshuller in the early 1970s. In mostsituations, one principle will give a concept forinitial solution, but several iterations may beneeded to achieve a feasible solution. The 40TRIZinnovative principles are listedinTable 1.One can find the detailed description of eachinnovative principle easily on website or in aTRIZ-relatedbook.A technical contradiction (trade-off) means thatwhenonefeaturegetsbetter, anotherfeaturewillgetworsesimultaneously.Altshullerhadproposed39engineeringparameterstoincludeall engineer-ing features (Table 2). He also developed andproposedthecorresponding39 39contradictionmatrixtabletoindicatethesuggestedmoreeffec-tive TRIZinnovative principles for solving eachpairofconflictingengineeringparameters.Thatis,cuesforfindinginnovativeprinciplesforeachpairof trade-offs are summarizedinthe 39 39con-tradictionmatrixtable.Mannet al. [5] have adjusted39 engineeringparametersto48onestomeettherequirementofrecent and advanced technology. They created48 48 contradiction matrix referred by theirexperienceandAltshullersmatrix. However, Yeh[12] hadintegratedtheoriginal 39 39contradic-tion matrix by Altshuller and 48 48 contradictionmatrix by Mann et al. into a new 39 39contradictionmatrix. The new39 39contra-diction matrix contains more suggested innovativeprinciples, but still 39parameters remain. Inthisstudy, new 39 39 contradiction matrix isimplementedtofindmorecuesforsolving difficultproblems.For instance, breaking-resistance of a smartphone is a critical specification in dropping test formanufacturers. To strengthen a mobile phone fromFigure3. Theflowchartofexperimentalprocedure.Table 1. 40 TRIZinnovativeprinciples.1 Segmentation 15 Dynamicparts 28 Mechanicalinteractionsubstitution2 Separation 16 Partialorexcessiveactions 29 Pneumaticsandhydraulics3 Localquality 17 Dimensionalitychange 30 Flexibleshellsandthinfilms4 Symmetrychange 18 Mechanicalvibration 31 Porousmaterials5 Merge 19 Periodicaction 32 Opticalpropertychanges6 Multi-functionality 20 Continuityofusefulaction 33 Homogeneity7 Nesteddoll 21 Hurrying 34 Discardingandrecovering8 Weightcompensation 22 Blessingindisguise 35 Parameterchange9 Preliminarycounteraction 23 Feedback 36 Phasetransition10 Preliminaryaction 24 Intermediary 37 Thermalexpansion11 Beforehandcompensation 25 Self-service 38 Strongoxidants12 Equi-potentiality 26 Copying 39 Inertatmosphere13 Theotherwayaround 27 Cheapdisposables 40 Compositematerials14 Curvatureincrease456 M.-T.ChangandC.-H.Yehbreaking,designersoftenaddmorepartsordesigncomplicatedinnerstructure. However, morepartsand assembling cost are incurred. In this case,smart phone manufacturers want to enhancestrengthbutavoidthesystemgettingcomplicatedsimultaneously. Therefore, theimprovedengineer-ingparameterisselectedtobestrength(14)andworsen engineering parameter is decided to besystemcomplexity (36). The TRIZinnovativeprinciples2,5,15,13,18,17,25,and28basedonnew39 39contradictionmatrix havethelarg-est possibility to solve this conflict (Table 3), unlikethe original contradiction matrix developed byAltshuller. Theinnovativeprinciples 2, 5, 15, 13,18, 17, 25, and28haveequal probabilitytosolvecorresponding trade-off conflicts. Notice that other32innovative principles couldsuggest innovativesolutions as well, so it is not surprised if thesolutions come fromthe rest of 32 innovativeprinciples. Original TRIZ 39 39 contradictionmatrixcouldbeeasilyfoundinanyTRIZ-relatedbooksorwebsite.The execution of TRIZ methodology isarrangedintofivestepsasfollows:(1) Problem description: A problem descriptionidentifies problems, errors, or causes. Tocollect all dataanddocuments that mightbe helpful to define the problem moreprecisely. Generally, three levels method,5W1H(Who, What, Where, When, Why,and How), nine windows, diagram ofsource of error the problem thenegative effect, andsoonare suggestedtoexecutethistask.Table 2. 39 TRIZengineeringparameters.1 Weightofmovingobjects 14 Strength 27 Reliability2 Weightofstationaryobjects 15 Durationofactionbymovingobject28 Measurementaccuracy3 Lengthofmovingobjects 16 Durationofactionbystationaryobject29 Manufacturingprecision4 Lengthofstationaryobjects 17 Temperature 30 Externalharmaffectstheobject5 Areaofmovingobjects 18 Illuminationintensity 31 Object-generatedharmfulfactors6 Areaofstationaryobjects 19 Useofenergybymovingobject 32 Easeofmanufacture7 Volumeofmovingobjects 20 Useofenergybystationaryobject33 Easeofoperation8 Volumeofstationaryobjects 21 Power 34 Easeofrepair9 Speed 22 Lossofenergy 35 Adaptabilityorversatility10 Force 23 Lossofsubstance 36 Devicecomplexity11 Stressorpressure 24 Lossofinformation 37 Difficultyofdetectingandmeasuring12 Shape 25 Lossoftime 38 Extentofautomation13 Stabilityofobjectscomposition26 Quantityofsubstance/matter 39 ProductivityTable 3. Aportion of new 39 39 contradiction matrix for improved parameter (14) and worsen parameter (36).WorsenparametersImprovedparameters 34 35 36 37 3812 Shape 17,13,1,235,2235,1,28,2915,3,3129,2,5,2228,1,1628,37,13,3115,24,7,391,29,15,322,25,3513 Stabilityofobjectscomposition2,10,24,1635,15,17,1340,35,15,3031,29,2,10,3413,31,2,10,4035,26,17,227,24,17,35,937,32,28,23,3924,1,10,168,14,3514 Strength 1,2,3,5,1324,25,3,11,2740,35,1,4,1715,3,24,322,5,15,13,1817,25,282,40,32,2813,15,18,3,2715,2,3510,17,1315 Durationofactionbymovingobject3,10,17,19,734,13,27,297,13,30,351,17,4,405,15,10,4,228,29,2510,37,4,32,1935,39,28,2910,30,17,624,31,1,1316 Durationofactionbystationaryobject3,10,191,28,1313,5,4,172,35,405,10,2,25,417,1432,35,25,6,4,37,39,281,17,1324,6,31JournaloftheChineseInstituteofIndustrialEngineers 457(2) Contradiction analysis: Defining theimproved and worsen engineeringparameters in problem description step,respectively.(3) Contradictionmatrixandinnovativeprin-ciples: Usingcontradictionmatrixtoselectsuggestedinnovativeprinciplesforguidingsolutions.(4) Exploring alternative solutions based onsuggested innovative principles: Using brainstorming, mind mapping, or six thinkinghats tofindalternative andfeasible solu-tionstoeaseorsolveproblems.(5) Evaluation for ideality of proposed solu-tions: Judgingthe most ideal andfeasiblesolutionamongalternativeswithrespecttolimitedresource. Theselectedsolutionwillbe further processed by the Taguchi methodforoptimalmanufacturingparameters.2.3 TaguchiexperimentThe Taguchi experimental design is applied at stageC shown in Figure 3. Finding key factors such asfemale molding temperature, male molding tem-perature, holdingpressure, holdingpressuretime,andcoolingtimeinbambooinjectionmoldingaredecidedbydesigners experiences, trial errors, andfeedback fromfurther manual visual inspection.That will be time-consuming to conduct a full-factorial analysis. In addition, the Taguchiexperimental design provides a simple, efficient,andsystematic approachtooptimize designs forperformance, quality, and cost with a minimumamount of testing [10]. Therefore, the static orthog-onal array configuration of the Taguchi experi-mental design is used to measure bamboodeformation and find out the most appropriatefactors. The analysis of main effects plot for meansandSNratiosisabletofindoutmostappropriatefactors.This stage is divided into three steps as follows:(1) identifyingthekeyfactors causingqualityinstabilityinbambooinjectionmolding,(2) based on the setting values of existingbamboo injection molding factors, selectingappropriateTaguchiorthogonalarraycon-figurationand(3) findingout thebambooinjectionmoldingfactorsviaanalysisofthemaineffectsplotformeansandSNratios. Inaddition, anyadjustable factor(s) for movingtowardtonominalvalueshouldbeidentified.Once the optimal parameters are found, PCImass production evaluationis executed.Ifthey arenot found, Taguchi experimental design willcontinueuntil theoptimal manufacturingparame-tersfactorisfound.2.4 PCIexperimentPCIsarewidelyusedtomeasurethemanufactur-ability of process and judge whether meetingestablishedspecificationlimits [4]. TherearefourbasicPCIs:Cp, Cpk, Cpm,and Cpmk.TheCpkisused to carry on the PCI analysis in this study [2,3].TheformulaisasshowninEquation(2).Cpk MINXLSL, USL X3 , 2where Xis the mean,the standarddeviation,USLthe upper specificationlimit, andLSLthelower specificationlimit. Touse Cpk, it requirespre-defined specific quality management plan(QMP).Thecriteriafordeterminingthecapabilityof process are: CpkActualCpkNominal is consideredas acceptable (PASS), CpkNominal4CpkActual

CpkNominal0.9is aconditional acceptance, andCpkNominal0.9 4CpkActual is considered as unac-ceptable(NG).The factors of bambooinjectionmoldingareverified by Cpk to determine whether they meet theacceptable productionyieldfor current demands.The acceptance of CpkActualis pre-defined byspecificQMP. WhentheCpkActualisNG, compo-nents suppliers need to provide the CAR foreffective improvement action. Then, the Taguchiexperimental design implementation will be exe-cutedoncemore. Theprocess will becarriedoutrepeatedlyuntiltheCpkActualisnotNG.3. ExperimentalresultsThefrontcoverof ASUSNB U43isselectedto betesting sample in this study. The front cover ismade by TN3715B plastics and restricted to 28 mmthickness.SimilartoIMRprocess,bambooskinisdecoratedontothe plastic front cover. Alot ofdeformedoccurrences onfront covers are foundafter injection. Toverifythemagnitudeof defor-mation,ajigwithfeelergaugeonthemid-pointoftestingsampleswasused.Thedesireddeformationis less than 3 mm, however, the resultingdeformation is close to 14.3 mm (Figure 4).Figure4. Thedeformationdescriptionoffrontcoverofbambooinjectionmolding.458 M.-T.ChangandC.-H.YehFurthermore, the desired thickness of bamboo skinonfrontcoverofASUSNBU43is3.5 mm.A450ton stand-up forming machine is used in thisexperiment.3.1 MSAGRRresultThedeformationof testingsamplesaremeasuredandcollected. ThedatacollectionplanislistedinTable 4. The GRR measurement for deformation is12.3% (repeatability 11.9% and reproducibil-ity 3.4%), which gives a PASS result.In addition, the testing rawdata are shown inTable 5. Therefore, the process can move tostageB,3.2 TRIZimplementation3.2.1 ProblemdescriptionThe plastic front cover and bamboo skin areprocessedbyinjectionmolding, theresultingsyn-ergywillbereleasedafteraperiodofpressureandstress. Because of different shrinkage ratios ofplasticfront coverandbambooskin, it generatesserious deformation (specification: 3 mm,average 14.31 mm; standard deviation 1.04;p 0.753 0.05, it is normally distributed;Cpk 3.31 51.33).3.2.2 ContradictionanalysisIf weneedtoimprovestress andpressure, at thesametime, thelinersizeforthesynergyofplasticfront cover and bamboo skin should remainstationaryas possible. This is atypical trade-offcontradiction. TRIZ are used to find cues and solvethis contradiction. The improved engineeringparameter is stress or pressure (11) and theworsenparameter islengthof stationaryobjects(4), Thesuggestedinnovativeprinciples tosolvethiscontradictionarelistedinnew39 39contra-dictionmatrix(Table6).3.2.3 Contradictionmatrixandsuggestedinno-vativeprinciplesThe suggested innovative principles can be found inTable 6: Principle 3 (local Quality), Principle14(curvature increase), Principle 17 (dimensionalitychange), Principle 35 (parameter change), Principle40 (composite materials), Principle 4 (symmetrychange), Principle 9 (preliminary counteraction),andPrinciple1(segmentation).3.2.4 ExploringalternativesolutionsbasedonsuggestedinnovativeprinciplesAccording to suggested innovative principles in theprevious section, the project teamleader invitedTable 5. The deformationofrawdatafortheMSAexperiment.Table 4. MSAdatacollectiontable.Data OperationaldefinitionandprocedureMeasuredata Datatype Measuretools Datatype Measuredata DatatypeDeformation ContinuetypeMeasureFixtureRecordsamplenoDatetimeOperationalpersonnelMeasurer:twopersonsSample:10piecesRepeatability:threetimesGRRformJournaloftheChineseInstituteofIndustrialEngineers 459experts good at injection, physical characteristics ofbambooskin, molding, andmechanical designtoworktogetherforpotential andfeasiblesolutions.Eachsuggestedinnovativeprinciplecouldnotleadtoaconceptual orfeasiblesolutionormore. Theresultingsolutionsguidedbysuggestedinnovativeprinciplesandconceptualizedbytheproject teamaredemonstratedinTable7.3.2.5 EvaluationforidealityforproposedsolutionsTheconceptual solutions inspiredbyTRIZinno-vative principles such as 17, 35, 40, and 9 areproposed and verified in this step. They aredescribedasfollows:(1) Principle17(dimensionalitychange)A rib-shape design is applied to plasticstructure toincrease supportingforce andreduce bending deformation. Hence, thegate of injectionmoldingis changedfromtwo gates to length-extending one(Figure 5). Thirty-five pieces of bambooskin by injection molding were verified usingthisproposedsolution.The result shows that the specificationofdeformationis 03 mm, theaverageof thedeformation is 10.14 mm, the standard devi-ationis0.83 mm, andp 0.056 0.05. Itisnormally distributed and the resultingCpk2.82 51.33. However, it does notmeet thepre-definedspecification. But theindependent samples t-test result shows thatthe improvement of deviation is obvious(p 0.000 50.05).(2) Principle35(parameterchange)After plastic injection molding, gapsbetween plastic molecules are produced.By switching holding pressure andholding time, plastic molecules can betighter, thereby reducing shrinkageand deformation. The original holdingTable 7. Conceptualizedsolutionsinspiredbysuggestedinnovativeprinciples.Innovativeprinciple Inspiredsolution(s) Conceptualizeddescription3 Localquality Nonesofar 14 Curvatureincrease Nonesofar 17 Dimensionalitychange Yes Changing the direction of gel-gate in mold and making it a rib-shapetoreducethemagnitudeofdeformation35 Parameterchange Yes Byincreasingholdingtimeandholdingpressure,theproductdensitydoesnotshrinkeasily40 Compositematerials Yes Addinganotherbambooskinatthebacksideofplasticforsupportingpurposewhileprocessinginjection-molding.Inthismanner,theformingforceisevenlydistributedsotheshrinkagecouldbeminimized4 Symmetrychange Nonesofar 9 PreliminarycounteractionYes Changingtheformingparameterstoachievedeformationintheoppositedirectioninadvance,theresultingsynergyofbamboo skin and plastic will achieve normal flatness due tothisprioraction1 Segmentation Nonesofar Table 6. Aportionofnew39 39contradictionmatrixforimprovedparameter(11)andworsenparameter(4).WorsenparametersImprovedparameters 2 3 4 5 609 Speed 1,13,210,35,313,17,28,229,14,1,817,15,302,14,117,14,4,1,2930,3,5,3414,5,3,171,4,1310 Force 9,13,28,135,40,1817,35,9,3,1419,28,36,2935,28,17,940,10,3715,17,10,1419,3,29,39,401,3,17,40,3718,36,9,3511 Stressorpressure 35,10,13,3129,40,2,17,1835,9,40,17,314,4,13,10,363,14,17,3540,4,9,110,35,40,1417,28,15,3,1640,14,35,1037,17,3,15,3612 Shape 15,3,10,3126,35,404,14,29,515,13,2,7,3417,14,4,135,7,31,104,17,5,2,1432,10,3417,14,5,282,32,413 Stabilityofobjectscomposition40,35,31,1739,1,24,4,2617,1,35,1315,13,2,7,3417,4,35,3713,1,4031,13,11,3517,4,3,2,1235,31,4,339,13,17460 M.-T.ChangandC.-H.Yehpressureissetto20andholdingtimeissetto 8 s. They are switched to 40 and 12 s,respectively. Thirty-five pieces of bambooskinbyinjectionmoldingareverifiedusingthisproposedsolution.The result shows that the specificationofdeformationis 03 mm, theaverageof thedeformationis5.15 mm, thestandarddevi-ationis0.96 mm, andp 0.156 0.05. Itisnormally distributed and the resultingCpk 0.74 51.33. However, it does notmeet thepre-definedspecification. But theindependent samples t-test result shows thatthe improvement of deviation is obvious(p 0.000 50.05). Unfortunately, largerholding pressure and longer holding timetendtoreducetheproductioncapacityforinjectionmolding.Therefore,furtherexper-iments bytheTaguchi methodfor investi-gating the most appropriate formingparametersarenecessary.(3) Principle40(compositematerials)The surface of bamboo skin and plastic maynotshrinkconcurrentlyinprocessinginjec-tionmolding.Therefore,thedeformationiscausedbydistortion. Inthisstudy, anotherbambooskinis addedat the backside ofplastic. Inthismanner, thetensionformedon both sides is evenly distributed. Theshrinkage anddeformationcouldbemini-mized as much as possible. Thirty-five piecesof bamboo skin by injection molding areverifiedusingthisproposedsolution.The result shows that the specificationofdeformationis 03 mm, theaverageof thedeformation is 1.14 mm (maxi-mum1.6 mm; minimum0.6 mm), thestandard deviation is 0.265 mm, andp 0.336 0.05. It is normally distributedand the resulting Cpk 1.42 41.33. Itmeetsthepre-definedspecification. Buttheindependent samples t-test result shows thatthe improvement of deviation is obvious(p 0.000 50.05). Oneof thespecimensisshowninFigure6.(4) Principle9(priorcounteraction)Bypre-heating, themaleandfemalemoldsare set to appropriate temperature differ-ence,the plasticwillbein arch-shapebut inopposite direction. And more blendingstress is produced and released by increasingcooling time. The temperature differencebetween male and female molds is originallyaround 20

C, switching to around 40

C.The original cooling time is around 10 s,switching to 20 s. Thirty-five pieces ofbambooskinbyinjectionmoldingarever-ifiedusingthisproposedsolution.The result shows that the specificationofdeformationis 03 mm, theaverageof thedeformationis8.02 mm, thestandarddevi-ationis 0.64 mm, andp 0.28 0.05. It isnormally distributed and the resultingCpk2.6 51.33. It does not meet thepre-defined specification. However, theindependent samples t-test result showsthat theimprovement of deviationisobvi-ous (p 0.000 50.05). Unfortunately,morecoolingtimetendstoreducetheproductioncapacity for injection molding. Therefore,furtherexperimentsbytheTaguchimethodfor investigating the most appropriate form-ingparametersarenecessary.Inpractice,usingonlyoneinspiredsolutionbyTRIZmaynot fullyachievehigheridealityif theproblemisverydifficult.Therefore, foursolutionsaforementionedareusedtoreachhighidealityorspecification.Thesolutioninspiredbyprinciple40(composite materials) is able to meet thespecification. Implementing this solution aidedby changing two plastic mold gates to length-extending one (principle 17: dimensionalitychange). Furthermore, furtherexperimentsbytheTaguchi methodforinvestigatingthemostappro-priate forming parameters are necessary as well(Principle 35: parameter change andPrinciple 9:priorcounteraction).3.3 Taguchiexperimentaldesignresult3.3.1 IdentifyingthekeyfactorofthebambooinjectionmoldingSincefurtherexperimentsbytheTaguchi methodfor investigating the most appropriate formingFigure 5. Rib-shape design is applied to plastic structure:(a)twogatesand(b)thelength-extendinggate.Figure 6. The improved testing sample using TRIZinnovative principle 40(right) andthe original testingsample(left).JournaloftheChineseInstituteofIndustrialEngineers 461parameters are necessary, key and controllablefactors for bamboo injection molding are listedandabbreviatedbyAEasfollows:. A: femalemoldtemperature(40

C, 65

C,90

C,threelevels);. B: male mold temperature (40

C, 65

C,90

C,threelevels);. C: hold pressure (20, 30, 40 pressure, threelevels);. D:holdtime(8,10,12 s,threelevels);. E:coldtime(10,15,20 s,threelevels).3.3.2 TaguchiorthogonalarrayconfigurationInthissection, anoptimal combinationoffactorsforbambooinjectionmoldingprocessisidentifiedby constrained developingtime and manufacturingunit cost for mass production. Based on the settingvalue of existing bamboo injection molding param-eters by L27(35) orthogonal configuration (Table 8),there are six testing samples for each run.Therefore, there are 162 pieces testing samples,that is, 6 (injected testing samples) 27 (runs). Theexperimental datafortheaveragesofdeformationarelistedinTable8.3.3.3 ConfirmationformostappropriatefactorsofbambooinjectionmoldingThe main effects for SNratios and means canbe easily calculated by using the data listed inTable 8. The results are shown in Figure 7(a)and (b), respectively. In order to adjust the mean ofdeformation to the minimal value (0 mm), anyexisting adjustable factor(s) should be identified forachievingthisgoal.Accordingtothesuggestedsequenceandpro-cedure of the Taguchi experimental design, improv-ing SN ratio, adjusting the average value, and thenreducing cost are arranged in this study.Controllable factors are categorizedandlistedinTable9,theycanbeeasilyidentifiedbasedontheresults indicated by Figure 7(a) and (b). Thefollowing steps are executed to find the mostappropriate factors of bambooinjectionmoldingprocess:(1) IncreasingtheSNratios(reducethevaria-tion): According to the main effects plot forSNratios, the bambooinjectionmoldingprocessfactorsaredesignedas:A(3)B(?)C(3)D(?)E(?).(2) Adjusting average value to target value:According to the main effects plot forTable 8. Experimental dataofbambooinjectionmolding.RunFactors Sampledata BasicstatisticsA B C D E 1 2 3 4 5 6 X S1 40 40 20 8 10 2.2 2 1.9 2.1 2 1.8 2.00 0.142 40 40 20 8 15 1.7 1.6 1.7 1.6 1.7 1.8 1.68 0.083 40 40 20 8 20 1.7 1.7 1.6 1.8 1.6 1.8 1.70 0.094 40 65 30 10 10 1.5 1.6 1.5 1.6 1.6 1.7 1.58 0.085 40 65 30 10 15 1.7 1.7 1.6 1.7 1.8 1.7 1.70 0.066 40 65 30 10 20 1.9 2 2.1 1.9 1.8 1.8 1.92 0.127 40 90 40 12 10 1.9 2.1 1.8 1.7 1.8 1.9 1.87 0.148 40 90 40 12 15 1.9 1.8 1.7 1.8 1.7 1.8 1.78 0.089 40 90 40 12 20 1.8 1.7 1.8 1.6 1.9 1.5 1.72 0.1510 65 40 30 12 10 1.2 1.1 1.1 1.1 1.1 1 1.10 0.0611 65 40 30 12 15 0.9 0.8 0.9 0.9 0.9 0.9 0.88 0.0412 65 40 30 12 20 1 1.2 1.1 1.1 1.1 1.1 1.10 0.0613 65 65 40 8 10 1.2 1.2 1 1.2 1.1 1.2 1.15 0.0814 65 65 40 8 15 1.1 1.1 1.2 1.2 1.2 1.2 1.17 0.0515 65 65 40 8 20 1.2 1.2 1.2 1.2 1.1 1.2 1.18 0.0416 65 90 20 10 10 1.6 1.6 1.4 1.7 1.6 1.5 1.55 0.1017 65 90 20 10 15 1.4 1.3 1.2 1.4 1.4 1.5 1.37 0.1018 65 90 20 10 20 1.2 1.3 1.4 1.3 1.3 1.3 1.30 0.0619 90 40 40 10 10 0.6 0.5 0.5 0.5 0.5 0.5 0.52 0.0420 90 40 40 10 15 0.5 0.5 0.5 0.5 0.4 0.4 0.47 0.0521 90 40 40 10 20 0.4 0.4 0.5 0.5 0.5 0.6 0.48 0.0822 90 65 20 12 10 0.9 0.8 1.1 1.1 1 1 0.98 0.1223 90 65 20 12 15 0.8 0.7 0.7 0.7 0.8 0.8 0.75 0.0524 90 65 20 12 20 0.6 0.7 0.8 0.7 0.7 0.7 0.70 0.0625 90 90 30 8 10 0.8 0.7 0.9 0.9 0.9 0.9 0.85 0.0826 90 90 30 8 15 0.9 0.9 0.8 0.9 1 0.8 0.88 0.0827 90 90 30 8 20 0.7 0.7 0.9 0.8 0.8 0.8 0.78 0.08462 M.-T.ChangandC.-H.Yehmeans, the bamboo injection moldingprocessfactorsaredesignedas:A(3)B(1)C(3)D(2)E(2).For instance, the predicted results forcombination A(3) B(1) C(3) D(2) E(2) is0.446 mmfor deformation and the resulting SNratiois6.47.3.4 VerificationformostappropriatefactorsinbambooinjectionmoldingprocessTo verify the correctness of most appropriatefactors inbambooinjectionmolding process for3Celectronic products, 35 testing samples pro-cessed by bamboo injection molding to measure theaveragesof deformation.Theresultsshowthatthespecification of deformation is 03 mm, the averageof the deformation is 0.525 mm, the standarddeviation is 0.15 mm; p 0.093 0.05, it is nor-mally distributed, Cpk 5.25 41.33. The experi-mental results are satisfactory and meet pre-definedspecifications. Theproposedapproachfor identi-fying the most appropriate combined factors inbambooinjectionmoldingprocessisabletoreachhigher profit and lower cost concerning a 3Celectronic product. In addition, the proposedapproachcanbeimplementedforon-lineproduc-tionimmediately.4. ConclusionsIn recent years, the appearance, user-friendlyinterface, and eco-environmental material of 3Celectronicproduct havebeencritical attributes toattract customers. Electroniccompanieswithownbrandscontinuetosearchforgreenmaterialsandeco-qualifiedmanufacturingprocesses toenhancethe appearance of their products. This studyproposed a straightforward and easy-to-useapproach to solve the difficulties in bambooinjectionmoldingprocess, whichis the veryfirstprocessworldwide.The proposedapproachutilizes skills suchasMSA, the Taguchi method, TRIZ, and Cpk toprovideinnovativeandrobustthinkingforsolvingtrade-off contradictions in bamboo injection mold-ing. The proposed approach decides the mostappropriate factors toincrease significant manu-facturabilityandreducethe R&Dtime-durationinbamboo injection molding. In the study, TRIZ-basedsolutions (composite materials anddimen-sionalitychange) reduce the magnitude of defor-mationsignificantly.Finally,themostappropriateof bambooskinprocessparameters areidentifiedbyusingtheTaguchimethod.Themostappropri-ate factors are female temperature (90

C), maletemperature(40

C), holdpressure(40), holdtime(10 s),andcoldtime(15 s).The experimental results showthat the pro-posed approach is able to solve the quality issues orproblemsinbambooinjectionmolding. Thispro-posedapproachnotonlyachievesattractivecolorappearance for a3Celectronic product, but alsoresultsinlowercostanddesiredyieldrate(100%)for further mass production as well. Same practicescould be implemented to the decorative appearanceonthesurfaceofother3Celectronicproducts.Figure7. Maineffectsplotfor:(a)SNratiosand(b)means.Table 9. The categoriesforcontrollablefactorsinbambooinjectionmolding.Type PurposeSignificanceforSNratioseffectSignificanceformeaneffectControllablefactor1 Variation/targetreduced Yes Yes A2 Targetvalueadjusted No Yes B3 Variationreduced Yes No C4 Costdown No No D,EJournaloftheChineseInstituteofIndustrialEngineers 463AcknowledgementsThe TRIZ-based solutions proposed by this researchwere applied to the patents at the United States, Taiwan,andMainlandChina: TaiwanPatent (no. 098135215),MainlandChinaPatent (no. 200910180849.0), andtheUnitedStatesPatent(no.12/906,749).NotesoncontributorsMu-Tsai Changis astudent of adoctors class intheDepartmentofIndustrialEngineeringandManagementat National Taipei University of Technology, Taipei,Taiwan, R.O.C. He works at AsusTek COMPUTERINC. and holds a chief position at the Corporate QualityAssuranceCenter(CQA).Hisresearchactivitiesincludeproduct life-circle management, product development,supplymanagement,problemsolving,andSixSigma.Chi-HaoYehachievedhis MSdegreefromIowaStateUniversity in 1993 and PhDdegree fromYuan-ZenUniversityin2001. He is currentlyaProfessor at theDepartment of Industrial Engineering and Management,NTUT, Taipei, Taiwan. His researchinterests includeinnovative Product R&Dprocess management, TRIZ-based innovative design in engineering and management,and E-Business in TRIZ-based evolutionary patentsearching.References[1] Chrysler, Ford and Motors General, Measure SystemAnalysis (MSA), 3rd Edn, Automotive IndustryActionGroup(AIAG),USA(2002).[2] Kane, V.E., Process capability indices, QualityTechnology,18(1),4152(1986).[3] Kotz, S. and N.L. Johnson, Process CapabilityIndices,Chapman&Hall,London(1993).[4] Lin, H.C., Using normal approximation on testingand determining sample size for Cpk, Journal of theChinese Institute of Industrial Engineers, 23, 111(2006).[5] Mann, D., S. Dewulf, B. ZlotinandA. Zusman,Matrix 2003: Updating the TRIZ ContradictionMatrix,CREAXPress,Belgium(2003).[6] Michael, L.G., R. David, M. John and P. Mark, TheLean Six Sigma Pocket Tool book, McGraw-HillEducation,Taiwan,R.O.C.(2005).[7] News Release Centre, Recycled computers andproject hope, Available online at: sinwen.com/?p1769(accessedMay7,2012).[8] Rantanen, K. and E. Domb, Simplified TRIZ, CRCPressLLC,BocaRaton,FL(2000).[9] Su, C.T. and C.S. Lin, An innovative way to createnew services: applying the TRIZ methodology,Journal of ChineseInstituteof Industrial Engineers,24,142152(2007).[10] Taguchi, G., Quality Design Experiment DesignMethod (Chinese edition), China ProductivityCentre,Taiwan,R.O.C(1991).[11] The TRIZ Journal, For people interested in the TRIZmethods of creativity and innovation, Availableonline at: www.triz-journal.com/ (accessedSeptember17,2012).[12] Yeh, C.H., Implementationof InnovativeR&DandInnovative thinking TRIZ-based Practices andApplicationsinEngineeringandManagementAreas,ChineseSocietyforQuality,Taipei,Taiwan,R.O.C(2009).464 M.-T.ChangandC.-H.Yeh*106083C 3C..: ; ; ; ;(* :Arthur_chang@asus.com)JournaloftheChineseInstituteofIndustrialEngineers 465Copyright of Journal of the Chinese Institute of Industrial Engineers is the property of Taylor & Francis Ltd andits content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder'sexpress written permission. However, users may print, download, or email articles for individual use.