form7NovemberFig.1.Water-assistedinjectionmoldingcanproducepartsincorporatingboththickandthinsectionswithlessshrink-involved.Watermayalsocorrodethesteelmold,andsomematerialsincludingthermoplasticcompositesarediculttomoldsuccessfully.Theremovalofwateraftermoldingisalsoachallengeforthisnoveltechnology.Table1liststheadvantagesandlimitationsofwater-assistedinjectionmoldingtechnology.*Correspondingauthor.Address:259,Wen-Hwa1stRoad,Kwei-San,Tao-Yuan333,Taiwan.E-mailaddress:.tw(S.-J.Liu).CompositesScienceandTechnologyCOMPOSITES1.IntroductionWater-assistedinjectionmoldingtechnology1hasproveditselfabreakthroughinthemanufactureofplasticpartsduetoitslightweight,fastercycletime,andrelativelylowerresincostperpart.Inthewater-assistedinjectionmoldingprocess,themoldcavityispartiallyfilledwiththepolymermeltfollowedbytheinjectionofwaterintothecoreofthepolymermelt.Aschematicdiagramofthewater-assistedinjectionmoldingprocessisillustratedinageandwarpageandwithabettersurfacefinish,butwithashortercycletime.Thewater-assistedinjectionmoldingprocesscanalsoenablegreaterfreedomofdesign,materialsavings,weightreduction,andcostsavingsintermsoftool-ingandpresscapacityrequirements24.Typicalapplica-tionsincluderodsandtubes,andlargesheet-likestructuralpartswithabuilt-inwaterchannelnetwork.Ontheotherhand,despitetheadvantagesassociatedwiththeprocess,themoldingwindowandprocesscontrolaremorecriticalanddicultsinceadditionalprocessingparametersareAbstractThepurposeofthisreportwastoexperimentallystudythewater-assistedinjectionmoldingprocessofpoly-butylene-terephthalate(PBT)composites.Experimentswerecarriedoutonan80-toninjection-moldingmachineequippedwithalabscalewaterinjectionsys-tem,whichincludedawaterpump,apressureaccumulator,awaterinjectionpin,awatertankequippedwithatemperatureregulator,andacontrolcircuit.ThematerialsincludedvirginPBTanda15%glassfiberfilledPBTcomposite,andaplatecavitywitharibacrosscenterwasused.Variousprocessingvariableswereexaminedintermsoftheirinfluenceonthelengthofwaterpenetrationinmoldedparts,andmechanicalpropertytestswereperformedontheseparts.X-raydiraction(XRD)wasalsousedtoidentifythematerialandstructuralparameters.Finally,acomparisonwasmadebetweenwater-assistedandgas-assistedinjectionmoldedparts.Itwasfoundthatthemeltfillpressure,melttemperature,andshortshotsizewerethedominantparametersaectingwaterpenetrationbehavior.Materialatthemold-sideexhibitedahigherdegreeofcrystallinitythanthatatthewater-side.Partsmoldedbygasalsoshowedahigherdegreeofcrystallinitythanthosemoldedbywater.Furthermore,theglassfibersnearthesurfaceofmoldedpartswerefoundtobeori-entedmostlyintheflowdirection,butorientedsubstantiallymoreperpendiculartotheflowdirectionwithincreasingdistancefromtheskinsurface.C2112006ElsevierLtd.Allrightsreserved.Keywords:Waterassistedinjectionmolding；Glassfiberreinforcedpoly-butylene-terephthalate(PBT)composites；Processingparameters；B.Mechanicalproperties；Crystallinity；A.Polymermatrixcomposites；ProcessingAnexperimentalstudyofthewater-assistedglassfiberfilledpoly-butylene-terephthalateShih-JungLiu*,Ming-JenPolymerRheologyandProcessingLab,DepartmentofMechanicalReceived12September2005；receivedinrevisedAvailableonline0266-3538/$-seefrontmatterC2112006ElsevierLtd.Allrightsreserved.doi:10.1016/pscitech.2006.09.016injectionmoldingof(PBT)compositesLin,Yi-ChuanWuEngineering,ChangGungUniversity,Tao-Yuan333,Taiwan29June2006；accepted11S/locate/compscitech67(2007)14151424SCIENCEANDTECHNOLOGYTable2Acomparisonofwaterandgas-assistedinjectionmoldingWaterGas1.CycletimeShortLong2.MediumcostLowHigh3.InternalfoamingNoYes4.ResidualwallthicknessSmallLarge5.OutsidesurfaceroughnessLowHigh6.OutsidesurfaceglossHighLow1416S.-J.Liuetal./CompositesScienceandTechnology67(2007)14151424Waterassistedinjectionmoldinghasadvantagesoveritsbetterknowncompetitorprocess,gasassistedinjectionmolding5,becauseitincorporatesashortercycletimetosuccessfullymoldapartduetothehighercoolingcapac-Fig.1.Schematicdiagramofwater-assistedinjectionmoldingprocess.ityofwaterduringthemoldingprocess.Theincompress-ibility,lowcost,andeaseofrecyclingthewatermakesitanidealmediumfortheprocess.Sincewaterdoesnotdis-solveanddiuseintothepolymermeltsduringthemoldingprocess,theinternalfoamingphenomenon6thatusuallyoccursingas-assistedinjectionmoldedpartscanbeelimi-nated.Inaddition,waterassistedinjectionmoldingpro-videsabettercapabilityofmoldinglargerpartswithasmallresidualwallthickness.Table2listsacomparisonofwaterandgasassistedinjectionmolding.Withincreasingdemandsformaterialswithimprovedperformance,whichmaybecharacterizedbythecriteriaoflowerweight,higherstrength,andafasterandcheaperproductioncycletime,theengineeringofplasticsisapro-cessthatcannotbeignored.Theseplasticsincludethermo-plasticandthermosetpolymers.Ingeneral,thermoplasticpolymershaveanadvantageoverthermosetpolymersinTable1Advantagesanddisadvantagesofwater-assistedinjectionmoldingAdvantagesDisadvanta1.Shortcycletime2.Lowassistingmediumcost(waterismuchcheaperandcanbeeasilyrecycled)3.Nointernalfoamingphenomenoninmoldedparts.termsofhigherimpactstrength,fractureresistanceandstrains-to-failure.Thismakesthermoplasticpolymersverypopularmaterialsinstructuralapplications.Poly-butylene-terephthalate(PBT)isoneofthemostfrequentlyusedengineeringthermoplasticmaterials,whichisformedbypolymerizing1.4butyleneglycolandDMTtogether.Fiber-reinforcedcompositematerialshavebeenadaptedtoimprovethemechanicalpropertiesofneatplas-ticmaterials.Today,shortglassfiberreinforcedPBTiswidelyusedinelectronic,communicationandautomobileapplications.Therefore,theinvestigationoftheprocessingoffiber-reinforcedPBTisbecomingincreasinglyimportant710.Thisreportwasmadetoexperimentallystudythewater-assistedinjectionmoldingprocessofpoly-butylene-tere-phthalate(PBT)materials.Experimentswerecarriedoutonan80-toninjection-moldingmachineequippedwithalabscalewaterinjectionsystem,whichincludedawaterpump,apressureaccumulator,awaterinjectionpin,awatertankequippedwithatemperatureregulator,andacontrolcircuit.ThematerialsincludedavirginPBTanda15%glassfiberfilledPBTcomposite,andaplatecavity7.FingeringGreaterLess8.AsymmetricalpenetrationMorestableUnstable9.MaterialcrystallinityLowHigh10.ParttransparencyHighLow11.Internalsurface(semi-crystallinematerials)SmoothLesssmooth12.Internalsurface(amorphousmaterials)RoughSmoothwitharibacrosscenterwasused.Variousprocessingvari-ableswereexaminedintermsoftheirinfluenceonthelengthofwaterpenetrationinmoldedparts,whichincludedmelttemperature,moldtemperature,meltfillingspeed,short-shotsize,waterpressure,watertemperature,waterholdandwaterinjectiondelaytime.Mechanicalpropertytestswerealsoperformedonthesemoldedparts,andXRDwasusedtoidentifythematerialandstructuralgesCorrosionofthesteelmoldduetowaterLargerorificesfortheinjectionpinrequired(easiertogetstuckbythepolymermelt)Somematerialsaremorediculttomold(especiallyamorphousthermoplastics)Removalofwateraftermoldingisrequiredparameters.Finally,acomparisonwasmadebetweenwater-assistedandgas-assistedinjectionmoldedparts.2.Experimentalprocedure2.1.MaterialsThematerialsusedincludedavirginPBT(Grade1111FB,Nan-YaPlastic,Taiwan)anda15%glassfiberfilledPBTcomposite(Grade1210G3,Nan-YaPlastic,Tai-wan).Table3liststhecharacteristicsofthecompositematerials.polymermelt.Table4liststheseprocessingvariablesaswellasthevaluesusedintheexperiments.2.4.GasinjectionunitInordertomakeacomparisonofwaterandgas-assistedinjectionmoldedparts,acommerciallyavailablegasinjec-tionunit(GasInjectionPPC-1000)wasusedforthegas-assistedinjectionmoldingexperiments.DetailsofthegasinjectionunitsetupcanbefoundintheRefs.1115.Theprocessingconditionsusedforgas-assistedinjectionmoldingwerethesameasthatofwater-assistedinjectionmolding(termsinboldinTable4),withtheexceptionofgastemperaturewhichwassetat25C176C.2.5.XRDInordertoanalyzethecrystalstructurewithinthewater-assistedinjection-moldedparts,wide-angleX-raydiraction(XRD)with2Ddetectoranalysesintransmis-sionmodewereperformedwithCuKaradiationat40kVand40mA.Morespecifically,themeasurementswereperformedonthemold-sideandwater-sidelayersofthewater-assistedinjection-moldedparts,withthe2hanglerangingfrom7C176to40C176.ThesamplesrequiredfortheseanalysesweretakenfromthecenterportionoftheseFig.2.Layoutanddimensionsofmoldcavity(unit:mm).S.-J.Liuetal./CompositesScienceand2.2.WaterinjectionunitAlabscalewaterinjectionunit,whichincludedawaterpump,apressureaccumulator,awaterinjectionpin,awatertankequippedwithatemperatureregulator,andacontrolcircuit,wasusedforallexperiments3.Anori-fice-typewaterinjectionpinwithtwoorifices(0.3mmindiameter)onthesideswasusedtomoldtheparts.Duringtheexperiments,thecontrolcircuitofthewaterinjectionunitreceivedasignalfromthemoldingmachineandcon-trolledthetimeandpressureoftheinjectedwater.Beforeinjectionintothemoldcavity,thewaterwasstoredinatankwithatemperatureregulatorfor30mintosustainanisothermalwatertemperature.2.3.MoldingmachineandmoldsWater-assistedinjectionmoldingexperimentswerecon-ductedonan80-tonconventionalinjection-moldingmachinewithahighestinjectionrateof109cm3/s.Aplatecavitywithatrapezoidalwaterchannelacrossthecenterwasusedinthisstudy.Fig.2showsthedimensionsofthecavity.Thetemperatureofthemoldwasregulatedbyawater-circulatingmoldtemperaturecontrolunit.Variousprocessingvariableswereexaminedintermsoftheirinflu-enceonthelengthofwaterpenetrationinwaterchannelsofmoldedparts:melttemperature,moldtemperature,meltfillpressure,watertemperatureandpressure,waterinjec-tiondelaytimeandholdtime,andshortshotsizeoftheTable3CharacteristicsoftheglassfiberreinforcedPBTcompositePropertyASTMPBT15%G.F.PBTYieldstrength(kg/cm2)D-6386001000Bendingstress(kg/cm2)D-5709001500Hardness(R-scale)D-785119120Heatdistortiontemperature(C176C)(18.6kg/cm2)D-64860200Meltflowindex(MFI)D-12384025Impactstrength(Kg-cm/cm)D-25655Meltingtemperature(C176C)DSC224224Technology67(2007)141514241417moldedparts.ToobtainthedesiredthicknessfortheXRDsamples,theexcesswasremovedbypolishingthesamplesonarotatingwheelonarotatingwheel,firstwithwetsiliconcarbidepapers,thenwith300-gradesiliconcar-bidepaper,followedby600-and1200-gradepaperforabettersurfacesmoothness.2.6.MechanicalpropertiesTensilestrengthandbendingstrengthweremeasuredonatensiletester.Tensiletestswereperformedonspecimensobtainedfromthewater-assistedinjectionmoldedparts(seeFig.3)toevaluatetheeectofwatertemperatureon20mm10mm1mm.BendingtestswereperformedinamicrotensiletesteraccordingtotheASTMD256test.A200Nloadcellwasusedandthecrossheadspeedwas50mm/min.2.7.MicroscopicobservationThefiberorientationinmoldedspecimenswasobservedunderascanningelectronmicroscope(JeolModel5410).Specimensforobservationwerecutfrompartsmoldedbywater-assistedinjectionmoldingacrossthethicknessTable4TheprocessingvariablesaswellasthevaluesusedintheexperimentsABCDEFMeltpressure(Mpa)Melttemperature