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ARTICLEINFOARTICLEHISTORYRECEIVED25OCTOBER2010RECEIVEDINREVISEDFORM12JANUARY2011ACCEPTED14JANUARY2011AVAILABLEONLINE21JANUARY2011KEYWORDSMICROCELLULARINJECTIONMOLDINGPLASTICFOAMINGSWIRLFREESURFACEABSTRACTMICROCELLULARINJECTIONMOLDINGISTHEMANUFACTURINGMETHODUSEDFORPRODUCINGFOAMEDPLASTICPARTSMICROCELLULARINJECTIONMOLDINGHASMANYADVANTAGESINCLUDINGMATERIAL,ENERGY,ANDCOSTSAVINGSASWELLASENHANCEDDIMENSIONALSTABILITYINSPITEOFTHESEADVANTAGES,THISTECHNIQUEHASBEENLIMITEDBYITSPROPENSITYTOCREATEPARTSWITHSURFACEDEFECTSSUCHASAROUGHSURFACEORGASFLOWMARKSMETHODSFORIMPROVINGTHESURFACEQUALITYOFMICROCELLULARPLASTICPARTSHAVEBEENINVESTIGATEDBYSEVERALRESEARCHERSTHISPAPERDESCRIBESANOVELMETHODFORACHIEVINGSWIRLFREEFOAMEDPLASTICPARTSUSINGTHEMICROCELLULARINJECTIONMOLDINGPROCESSBYCONTROLLINGTHECELLNUCLEATIONRATEOFTHEPOLYMER/GASSOLUTIONTHROUGHMATERIALFORMULATIONANDGASCONCENTRATION,MICROCELLULARINJECTIONMOLDEDPARTSFREEOFSURFACEDEFECTSWEREACHIEVEDTHISPAPERPRESENTSTHETHEORETICALBACKGROUNDOFTHISAPPROACHASWELLASTHEEXPERIMENTALRESULTSINTERMSOFSURFACEROUGHNESSANDPROFILE,MICROSTRUCTURES,MECHANICALPROPERTIES,ANDDIMENSIONALSTABILITYINTRODUCTIONTHECOMMERCIALLYAVAILABLEMICROCELLULARINJECTIONMOLDINGPROCESSAKATHEMUCELLPROCESSCONSISTSOFFOURDISTINCTIVESTEPS,NAMELY,GASDISSOLUTION,NUCLEATION,CELLGROWTH,ANDSHAPING1INTHEGASDISSOLUTIONSTAGE,POLYMERINTHEINJECTIONBARRELISMIXEDWITHSUPERCRITICALFLUIDSCFNITROGEN,CARBONDIOXIDE,ORANOTHERTYPEOFGASUSINGASPECIALSCREWWHICHISDESIGNEDTOMAXIMIZETHEMIXINGANDDISSOLVINGOFTHEGASINTHEPOLYMERMELTDURINGINJECTION,ALARGENUMBEROFNUCLEATIONSITESORDERSOFMAGNITUDEHIGHERTHANCONVENTIONALFOAMINGPROCESSESAREFORMEDBYARAPIDANDSUBSTANTIALPRESSUREDROPASTHEPOLYMER/GASSOLUTIONISINJECTEDINTOTHEMOLDCAVITY,THUSCAUSINGTHEFORMATIONOFCELLSBUBBLESDURINGTHERESTOFTHEINJECTIONMOLDINGCYCLE,CELLSCONTINUETOGROWTOFILLANDPACKOUTTHEMOLDANDSUBSEQUENTLYCOMPENSATEFORTHEPOLYMERSHRINKAGEASTHEMATERIALCOOLSINSIDETHEMOLDTHECELLGROWTHISDRIVENBYTHEAMOUNTANDSPATIALDISTRIBUTIONOFTHEDISSOLVEDGASTHECELLGROWTHISALSOCONTROLLEDBYPROCESSINGCONDITIONSSUCHASMELTPRESSUREANDTEMPERATUREASWELLASMATERIALPROPERTIESSUCHASMELTSTRENGTHANDGASSOLUBILITYFINALLY,THESHAPINGOFTHEPARTTAKESPLACEINSIDETHEMOLDUNTILTHEMOLDOPENSALLOWINGTHEPARTTOBEEJECTEDSINCETHEMICROCELLULARINJECTIONMOLDINGPROCESSWASINVENTED,THEREHAVEBEENNUMEROUSSTUDIESONPROCESS,MATERIAL,ANDTECHNICALDEVELOPMENTSAIMEDATMATERIALIZINGTHEFULLPROCESSPOTENTIALACCORDINGTOPREVIOUSSTUDIES15,MICROCELLULARINJECTIONMOLDINGOFFERSANUMBEROFADVANTAGESSUCHASCOSTSAVINGS,WEIGHTREDUCTION,EASEINPROCESSINGDUETOLOWVISCOSITY,ANDOUTSTANDINGDIMENSIONALACCURACYDUETOTHESEADVANTAGES,THEMICROCELLULARINJECTIONMOLDINGPROCESSHASBEENUSEDINMANYINDUSTRIESSUCHASAUTOMOTIVE,ELECTRICALGOODS,ANDHOMEAPPLIANCESUSINGABROADRANGEOFTHERMOPLASTICSDESPITETHESEADVANTAGES,HOWEVER,THESURFACEIMPERFECTIONSASSOCIATEDWITHMICROCELLULARINJECTIONMOLDEDPARTSDSUCHASUNIQUEGASFLOWMARKS,REFERREDTOASSWIRLMARKSTHROUGHOUTTHISPAPER,ANDALACKOFSMOOTHNESSDSTILLREMAINONEOFTHEMAINDRAWBACKSSURROUNDINGMICROCELLULARINJECTIONMOLDINGINORDERTOELIMINATEORREDUCETHESESURFACEIMPERFECTIONSTHEREHAVEBEENSEVERALSTUDIESATTEMPTED,ASREPORTEDINREFS614SOMERESEARCHERSHAVEFOCUSEDONTEMPERATUREMODIFICATIONOFTHEMOLDSURFACETOIMPROVETHESURFACEQUALITYOFMICROCELLULARINJECTIONMOLDEDPARTS68WITHPOLYMERICFOAM,ITWASFOUNDTHATBUBBLESFORMINGATTHEADVANCINGMELTFRONTAREFIRSTSTRETCHEDBYTHEFOUNTAINFLOWBEHAVIORTOWARDTHEMOLDSURFACEANDSUBSEQUENTLYDRAGGEDAGAINSTTHEMOLDWALLCAUSINGSWIRLMARKS9DURINGTHEFILLINGSTAGEOFPOLYMERMELTS,KEEPINGTHEMOLDWALLTEMPERATUREHIGHENOUGHFORBUBBLESATTHEMOLDSURFACETOBEELIMINATEDIMPROVESTHESURFACEQUALITYOFMICROCELLULARINJECTIONMOLDEDPARTSBYCONTROLLINGTHEMOLDTEMPERATURERAPIDLYANDPRECISELYUSINGMOLDTEMPERATURECONTROLUNITSOROTHERKINDSOFTHERMALORSURFACEHEATINGDEVICES,MICROCELLULARFOAMEDPLASTICSWITHGLOSSYANDSWIRLFREESURFACESCANBEPRODUCEDTHEREHAVEALSOBEENEFFORTSTOELIMINATETHESWIRLMARKSONMICROCELLULARINJECTIONMOLDEDPARTSWITHOUTANYMOLDTEMPERATURECONTROLLERINPARTICULAR,ITWASPROPOSEDTHATINSERTINGANINSULATORONTOTHEMOLDWALLMIGHTHELPKEEPINGTHEINTERFACETEMPERATUREBETWEENTHEMOLDANDTHEPOLYMERMELTHIGHTHISTECHNIQUEBASICALLYYIELDSTHESAMERESULTASTEMPERATUREMODIFICATIONOFTHEMOLD10THERMALANALYSISANDEXPERIMENTALRESULTSPROVETHATTHEADDITIONOFANINSULATORLAYERONTHEMOLDCANIMPROVETHESURFACEQUALITYOFMICROCELLULARINJECTIONPARTS11ANOTHERMETHODOFPRODUCINGPARTSWITHANIMPROVEDSURFACEQUALITYLEADSTOAMICROCELLULARCOINJECTIONMOLDINGPROCESS12INTHISTECHNIQUE,APROPERAMOUNTOFSOLIDSKINMATERIALISINJECTEDPRIORTOTHEINJECTIONOFAFOAMINGCOREMATERIALTHISCANYIELDASANDWICHEDSOLIDSKINEFOAMEDCOREESOLIDSKINSTRUCTUREWITHASURFACEFINISHSIMILARTOACONVENTIONALLYMOLDEDCOMPONENTWHILEPARTIALLYMAINTAININGTHEADVANTAGESOFMICROCELLULARINJECTIONMOLDINGANOTHERAPPROACHFORIMPROVINGTHESURFACEQUALITYOFMICROCELLULARINJECTIONMOLDEDPARTSISTHEGASCOUNTERPRESSUREPROCESS13,14INTHISPROCESS,AHIGHPRESSUREGASISINJECTEDINTOTHEMOLDPRIORTOTHEPOLYMER/GASSOLUTIONTOSUPPRESSCELLNUCLEATIONANDBUBBLEGROWTHWHILETHEPOLYMER/GASSOLUTIONISBEINGINJECTEDINTOTHEMOLDCAVITYTOWARDTHEENDOFINJECTION,COUNTERGASPRESSUREISRELEASEDANDBUB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