Injection moulding process optimisation and contro

PlasticsBusinessGroupPracticalInformationInjectionmoulding:processoptimisationandcontrolPI061eGeneralAfterfollowingtheguidancegiveninthePracticalInformationbrochureProcess-ingDataandAdvicefortheselectionofproductionfacilitiesandbasicmachinesettings,itwillgenerallystillbenecessaryfortheprocessparametersettingstobeoptimised.Thesesettingsrequireoptimisationinrespectof•quality•qualityconsistencyandproductionreliability•costeffectiveness.Theoptimisationisgenerallyconductedaspartoftherunning-inprocedureforanewmould.Thetargetisthus:toproducethemouldedpartqualityrequiredineachindividualcase,with-inthespecifiedoragreedtolerances,inthemostcost-effectivemannerpossible.Theoutlayonoptimisationandverifica-tionought,ofcourse,tobecommensuratewiththestringencyofthequalityrequire-mentsand,whereappropriate,withthesizeoftheoveralljobandthebatchsizeoftheindividualseriestobesupplied.AdditionalincentivesOntheotherhand,theharshercompetitionthatisnowprevailingandtheproofofqualitycapabilitythatcustomersaremorefrequentlydemandingconstituteafurtherincentiveforprocessoptimisation.Theharsherthecompetition,themorecaretheprocessormusttakeina)producingasinexpensivelyaspossibleand,b)despitethis,gainingthereputationofbeingareliablesupplierinrespectofqualityanddeliverydeadlines.ProofofqualitycapabilitytoDINISO9000ffissuppliedthrough•auditingbythecustomerand/or•certificationbyanauthorisedInstituteIneachcase,theprocesscontrolandqual-itysurveillancedocumentationisrequired.FurtherPossibilitiesApartfromtheadditionalincentives(ifnottosayconstraints),itisimportantnottoforgetthepossibilitiesthathavebeenopenedupbytechnicalprogress,whichcanfurtherfacilitateprocessoptimisationandcontrol.Theseinclude:•bettermachines(especiallywithregardtosettingaccu-racy,closedandopen-loopcontrolsys-temsandprocessdataacquisition),•improvedmeasuringtechnologyanddataacquisitionunits(forretrofittingoldermachinestoo),•tolerancemonitoringfacilities,•simulationcalculationsforoptimisingmouldedpartandmoulddesign,•facilities,experimentalproceduresandcomputationalmethodsforsup-portingprocessoptimisation(statisticalexperimentdesignandregressioncalculations,calculationofprocessmodels;processparameterandqualitysurveillance),•computerunitandprogramforauto-maticparameteroptimisation(withtheaidoftheevolutionstrategy,fromtheIboscompany)QualityThechiefqualitycriteriaare:•appearance(colour,surface,absenceofdefects),•mechanical(andphysical)properties,•dimensionalandshapeaccuracy.Duringproduction,theonlyparameterswhichhaveadirecteffectonthequalityofthemouldedpartsarethelevelsandpro-filesofthepressures,temperaturesandflowfrontvelocitiesinsidethemould.Theremainingparametershaveonlyanindi-rectinfluenceonmouldedpartquality.AsComputer-aidedsystemsareavailablefortheoptimisationofoperatingpoints(fromtheIboscompany,Fig.2)andforthecom-pilationofprocessmodels(Fig.1).Iftheprocessparametersarecontinuous-lymonitored,thenthesesystemscanbeused:•todetectdefectivepartsimmediatelytheyareproduced•andtoeliminatethemviaarejectsegre-gationunit.Unitswhichautomaticallycorrectprocessparametersthatstrayoutsidethetolerancerangearecurrentlyundergoingtrials.2hasalreadybeenshowninPI62ePro-cessingDataandAdvice,itispossibletoallocatebasicqualitycharacteristicstotheindividualprocessphases(seeFig.3).Itisthusimportanttoensurethecorrectmachinesetting,andasettingwhichcanbereproduced.1Onceprocessmodelshavebeencompiledasdescribedabove,qualitycontrolcanbeperformedautomaticallyonthemachine.Source:KUNSTSTOFFESynthetics,7/95.2Theevolutionstrategy(withtheappropri-atehardwareandsoftware)canbeusedtoestablishtheoptimumpointofoperationdur-ingstart-uporrunningproduction.Thecom-putermodifiestheprocessparameterswith-inmeaningfullimitstothisend.Thequalityresultsobtainedinthiswayareratedauto-maticallyormanuallyandnotifiedtothecom-puter.Drawingacomparisonwiththepre-cedingsettingsandresults,thecomputerrepeatedlyselectsnewsettingsandthusapproachesthepointofoperationthatoffersthemostfavourablecompromisebetweentheindividualqualitycharacteristics.Thecom-puterthenmaintainstheoptimumpointofoperationfoundinthiswaywithinpre-settol-erancelimits.Thecycletimecansimilarlybeoptimisedwhilemaintainingaconstantqual-ity.Fig.1:Qualityassuranceininjectionmoulding1Fig.2:Establishingtheoptimumpointofoperationbytheevolutionstrategy(Iboscompany)2Today:•injectionmouldingprocess•manualqualityinspection•controlanddocumen-tationbasedonsam-pling•manualsortingofrejectpartsgoodbadgoodbadTomorrow:•injectionmouldingprocess•automaticqualitycalculation•100%inspection•gap-freedocumentation•automaticsegregationofrejectpartsSource:KUNSTSTOFFESynthetics,7/95QualityParameter2Parameter1ParentProgenyAppearanceAppearanceisakeysellingaidinalargenumberofapplicationsandisthussubjecttocriticalexamination.Sensitivecolours,forinstance,shouldnotbediscolouredthroughthematerialbeingoverheated.Thiscanplacealimitonthemaximumpermittedmelttemperature.Itisalsoimportanttoavoidexcessivelyhighshearheatingthroughaninadmissiblyhighscrewcircumferentialvelocity3orinjectionvelocity(inconjunctionwithtightcros