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JournalofZhejiangUniversitySCIENCEAISSN1673-565X(Print);ISSN1862-1775(Online)wwwzjueducnjzus;wwwspringerlinkcomE-mail:jzuszjueducaLfefalJZhejiangUnivSciA20078(7):10771083SinglegateoptimizationforplasticinjectionmoldLIJi-quan十,LIDequn,GUOZhiying,LVHaiyuan(DepartmentofPlasticityTechnology,ShanghaiJiaoTongUniversity,Shanghai200030,China)Email:hutli163cornReceivedNov22,2006;revisionacceptedMar19,20071077Abstract:ThispaperdealswithamethodologyforsinglegatelocationoptimizationforplasticinjectionmoldTheobjectiveofthegateoptimizationistominimizethewarpageofinjectionmoldedparts,becausewarpageisacrucialqualityissueformostinjectionmoldedpartswhileitisinfluencedgreatlybythegatelocationFeaturewarpageisdefinedastheratioofmaximumdisplacementonthefeaturesurfacetotheprojectedlengthofthefeaturesurfacetodescribepartwarpageTheoptimizationiscombinedwiththenumericalsimulationtechnologytofindtheoptimalgatelocation,inwhichthesimulatedannealingalgorithmisusedtosearchfortheoptimumFinally,anexampleisdiscussedinthepaperanditcanbeconcludedthattheproposedmethodiseffectiveKeywords:Injectionmold,Gatelocation,Optimization,Featurewarpagedoi:101631jzus2007A1077Documentcode:ACLCnumber:TQ32066INTRODUCTIONPlasticinjectionmoldingisawidelyusedcomplexbuthighlyefficienttechniqueforproducingalargevarietyofplasticproducts,particularlythosewithhighproductionrequirement,tighttolerance,andcomplexshapesThequalityofinjectionmoldedpartsisafunctionofplasticmaterial,partgeometry,moldstructureandprocessconditionsThemostimportantpartofaninjectionmoldbasicallyisthefollowingthreesetsofcomponents:cavities,gatesandrunners,andcoolingsystemLamandSeow(2000)andJinandLain(2002)achievedcavitybalancingbyvaryingthewallthicknessofthepartAbalancefillingprocesswithinthecavitygivesanevenlydistributedpressureandtemperaturewhichcandrasticallyreducethewarpageofthepartButthecavitybalancingisonlyoneoftheimportantinfluencingfactorsofpartqualitiesEspecially。theparthasitsfunctionalrequirementsanditsthicknessesshouldnotbevariedusuallyProject(No50675080)supportedbytheNationalNaturalScienceFoundationofChinaFromthepointviewoftheinjectionmolddesign,agateischaracterizedbyitssizeandlocationandtherunnersystembythesizeandlayoutThegatesizeandruIlllerlayoutareusuallydeterminedasconstantsRelatively,gatelocationsandrunnersizesaremoreflexiblewhichcanbevariedtoinfluencethequalityofthepartAsaresult,theyareoftenthedesignparametersforoptimizationLeeandKimrl996a)optimizedthesizesofrunnersandgatestobalancerunnersystemformultipleinjectioncavitiesTherunnerbalancingwasdescribedasthedifferencesofentrancepressuresforamulticavitymoldwithidenticalcavitiesandasdifferencesofpressuresattheendofthemeltflowpathineachcavityforafamilymoldwimdifferentcavityvolumesandgeometriesThemethodologyhasshownuniformpressuredistributionsamongthecavitiesduringtheentiremoldingcycleofmultiplecavitiesmoldZhaieta1(2005a1presentedthetwogatelocationoptimizationofonemoldingcavitybyanef前一cientsearchmethodbasedonpressuregradient(PGSS),andsubsequentlypositionedweldlinestothedesiredlocationsbyvaryingrunnersizesfor维普资讯1078L,ea1dZhejiangUnivSciA20078(7):1077-1083multigateparts(Zhaieta1,2006)Aslargevolumepart,multiplegatesareneededtoshortenthemaximumflowpath,withacorrespondingdecreaseininjectionpressureThemethodispromisingfordesignofgatesandrunnersforasinglecavitywichmultiplegatesManyofinjectionmoldedpartsareproducedwithonegatewhetherinsinglecavitymoldorinmultiplecavitiesmoldThereforethegatelocationofasinglegateisthemostcommondesignparameterforoptimizationAshapeanalysisapproachwaspresentedbyCOHrbebaisseandGarcia(2002),bywhichthebestgatelocationofiniectionmoldingwasestimatedSubsequently,theydevelopedthismethodo1ogyfurtherandappliedittosinglegatelocationoptimizationofanLshapeexample(Courbebaisse,2005)Itiseasytouseandnottimeconsumingwhileitonlyservestheturningofsimpleflatpartswichuniforii1thicknessPandelidisandZour1990)presentedtheoptimizationofgatelocationbyindirectqualitymeasuresrelevanttowarpageandmaterialdegradationwhichisrepresentedasweightedsumofatemperaturedif-ferentialtermanoverpacktermandafrictionaloverheatingtermWarpageisinfluencedbytheabovefactorsbuttherelationshipbetweenthemisnotclearTherefore,theoptimizationeffectisrestrictedbythedeterminationoftheweightingfactorsLeeandKimrl996b)developedanautomatedselectionmethodofgatelocation,inwhichasetofinitialgatelocationswereproposedbyadesignerandthentheoptimalgatewaslocatedbytheaacentnodeevaluationmethodTheconclusiontoagreatextentdependsmuchonthehumandesignersintuitionbecausethefirststepofthemethodisbasedonthedesignerspropositionSotheresultistoalargeextentlimitedtothedesignersexperienceLamandJin(200l、developedagatelocationoptimizationmethodbasedontheminimizationoftheStandardDeviationofFlowPathLength(SDL)andStandardDeviationofFillingTime(SDT)duringthemoldingfillingprocessSubsequently,Shenet口,004a;2004b)optimizedthegatelocationdesignbyminimizingtheweightedsumoffillingpressure,fillingtimedifferencebetweendifferentflowpaths,temperaturedifference,andoverpackpercentageZhaieta1(2005b)investigatedoptimalgatelocationwithevaluationcriteriaofiniectionpressureattheendoffillingTheseresearcherspresentedtheobiectivefunctionsasperformancesofiniectionmoldingfillingoperation,whicharecorrelatedwithproductqualitiesButthecorrelationbetweentheperforii1ancesandqualitiesisverycomplicatedandnoclearrelationshiphasbeenobservedbetweenthemyetItisalsodifficulttoselectappropriateweightingfactorsforeachtermAnewobjectivefunctionispresentedheretoevaluatethewarpageofinjectionmoldedpartstooptimizegatelocationTomeasurepartqualitydirectly,thisinvestigationdefinesfeaturewarpagetoevaluatepartwarpage,whichisevaluatedfromthe“flowpluswarpagesimulationoutputsofMoldflowPlasticsInsight(MPI)softwareTheobjectivefunctionisminimizedtoachieveminimumdeformationingatelocationoptimizationSimulatedannealingalgorithmisemployedtosearchfortheoptimalgatelocationAnexampleisgiventoillustratetheeffectivityoftheproposedoptimizationprocedureQUALITYMEASURES:FEATUREWARPGEDefinitionoffeaturewarpageToapplyoptimizationtheorytothegatedesign,qualitymeasuresofthepartmustbespecifiedinthefirstinstanceTheterm“quality”maybereferredtomanyproductproperties,suchasmechanical,thermal,electrical,optical,ergonomicalorgeometricalpropertiesTherearetwotypesofpartqualitymeasures:directandindirectAmodelthatpredictsthepropertiesfromnumericalsimulationresultswouldbecharacterizedasadirectqualitymeasureIncontrastanindirectmeasureofpartqualityiscorrelatedwithtargetquality,butitcannotprovideadirectestimateOfchatqualityForwarpage,theindirectqualitymeasuresinrelatedworksareoneofperformancesofiniectionmoldingflowingbehaviororweightedsumofthoseTheperformancesarepresentedasfillingtimedif-ferentialalongdifferentflowpathstemperaturedif-ferential,overpackpercentage,andsoonItisobviousthatwarpageisinfluencedbytheseperforii1ances,buttherelationshipbetweenwarpageandtheseperformancesisnotclearandthedeterminationoftheseweightingfactorsisratherdifficultThereforetheoptimizationwiththeaboveObiectivefunction维普资讯LfefalJZhejiangUnivSciA20078(:1077-1083probablywillnotminimizepartwarpageevenwithperfectoptimizationtechniqueSometimes,improperweightingfactorswillresultinabsolutelywrongresultsSomestatisticalquantitiescalculatedfromthenodaldisplacementswerecharacterizedasdirectqualitymeasurestoachieveminimumdeformationinrelatedoptimizationstudiesThestatisticalquantitiesareusuallyamaximumnodaldisplacement,anaverageoftop10percentilenodaldisplacements,andanoverallaveragenodaldisplacement(LeeandKim,l995;I996b)ThesenodaIdisplacementsareeasytoobtainfromthesimulationresults,thestatisticalvalues,tosomeextents,representingthedeformationButthestatisticaldisplacementcannoteffectivelydescribethedeformationofthein_iectionmoldedpartsInindustrydesignersandmanufacturersusuallypaymoreattentiontothedegreeofpartwarpageonsomespecificfeaturesthanthewholedeformationofthein,_iectionmoldedpartsInthisstudyfeaturewarpageisdefinedtodescribethedeformationoftheinjectionpartsThefeaturewarpageistheratioofthemaximumdisplacementofthefeaturesurfacetotheprojectedlengthofthefeaturesurface(Fig1):_h100,Lwhereyisthefeaturewarpage,histhemaximumdisplacementonthefeaturesurfacedeviatingfromthereferenceplatform,andListheprojectedlengthofthefeaturesurfaceonareferencedirectionparallelingthereferenceplatformSurfaceceplaneFig1ThedefinitionoffeaturewarpageForcomplicatedfeatures(onlyplanefeaturediscussedhere),thefeaturewarpageisusuallyseparatedintotwoconstituentsonthereferenceplane,whicharerepresentedona2Dcoordinatesystem:=hl0=l00oo,1079where,yyaretheconstituentfeaturewarpagesintheXYdirectionandLx,LaretheprojectedlengthsofthefeaturesurfaceonYcomponentEvaluationoffeaturewarpageAtierthedeterminationoftargetfeaturecombinedwithcorrespondingreferenceplaneandproiectiondirection,thevalueofLcanbecalculatedimmediatelyfromthepartwiththecalculatingmethodofanalyticgeometry(Fig2)LisaconstantforanypartonthespecifiedfeaturesurfaceandproiecteddirectionButtheevaluationofhismorecomplicatedthanthatofLyFeatureFig2TheprojectedlengthevaluationSimulationofiniectionmoldingprocessisacommontechniquetoforecastthequalityofpartdesign,molddesignandprocesssettingsTheresultsofwarpagesimulationareexpressedasthenodaldeflectionsonZcomponent(,),andthenodaldisplacementWisthevectorlengthofvectorsumof,andWzk,where,karetheunitvectorsonZcomponentThehisthemaximumdisplacementofthenodesonthefeaturesurface,whichiscorrelatedwiththenormalorientationofthereferenceplane,andcanbederivedfromtheresultsofwarpagesimulationTocalculatehthedeflectionoffthnodeisevaluatedfirstlyasfollows:=COSO+cosfl+W,zcosy一(+),(3)whereisthedeflectioninthenormaldirectionofthereferenceplaneofithnode;W,WI1、,WizarethedeflectionsonX,Y,Zcomponentofithnode;伐,B,aretheanglesofnormalvectorofthereference;AandBaretheterminalnodesofthefeaturetoproiectingdirection(Fig2);andarethedeflectionsofnodesAand:维普资讯1080LfefaldZhefiangUnivSciA20078(1077-1083f=COSa+cosfl+:cosy,lCOSa+cosfl+Gzcosy,whereWA,WAy,:arethedeflectionsonZcomponentofnode;Wsx,andWezarethedeflectionsonX,Y,ZcomponentofnodeCOiAandlBaretheweightingfactorsoftheterminalnodedeflectionscalculatedasfollows:(2)iA=1一LiAL,co=1一(J)iA,whereLiAistheprojectordistancebetweenfthnodeandnodeAUltimately,histhemaximumoftheabsolutevalueof:h=maxlI,I,1Inindustry,theinspectionofthewarpageiscarriedoutwiththehelpofafeelergauge,whilethemeasuredpartshouldbeplacedonareferenceplat-formThevalueofhisthemaximumnumericalreadingofthespacebetweenthemeasuredpartsurfaceandthereferenceplatformGATEL0CAT10N0PTIMIZAT10NPR0BLEMFORMATIONThequalityterm“warpage”meansthepermanentdeformationofthepart,whichisnotcausedbyanappliedloadItiscausedbydifferentialshrinkagethroughoutthepart,duetotheimbalanceofpolymerflow,packing,cooling,andcrystallizationTheplacementofagateinaniniectionmoldisoneofthemostimportantvariablesofthetotalmolddesignThequalityofthemoldedpartisgreatlyaf-fectedbythegatelocationbecauseitinfluencesthemannerthattheplasticf1owsintothemoldcavityTherefore,differentgatelocationsintroduceinhomogeneityinorientation,density,pressure,andtemperaturedistribution,accordinglyintroducingdifferentvalueanddistributionofwarpageThereforegatelocationisavaluabledesignvariabletominimizetheinjectionmoldedpartwarpageBecausethecorrelationbetweengatelocationandwarpagedistributionistoalargeextentindependentofthemeltandmoldtemperatureitisassumedthatthemoldingconditionsarekeptconstantinthisinvestigationTheinjectionmoldedpartwarpageisquantifiedbythefeaturewarpagewhichwasdiscussedintheprevioussectionThesinglegatelocationoptimizationcanthusbeformulatedasfo11ows:Minimize:mini(X
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