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JOURNALOFMATERIALSPROCESSINGTECHNOLOGY1392003422427NEWPROCESSESTOPREVENTAFLOWDEFECTINTHECOMBINEDFORWARDBACKWARDCOLDEXTRUSIONOFAPISTONPINDJLEEA,DJKIMB,BMKIMC,ADEPARTMENTOFPRECISIONMECHANICALENGINEERING,GRADUATESCHOOL,PUSANNATIONALUNIVERSITY,PUSAN,SOUTHKOREABDEPARTMENTOFMECHANICALDESIGNENGINEERING,GRADUATESCHOOL,PUSANNATIONALUNIVERSITY,PUSAN,SOUTHKOREACDEPARTMENTOFMECHANICALENGINEERING,ENGINEERINGRESEARCHCENTERFORNETSHAPEANDDIEMANUFACTURING,PUSANNATIONALUNIVERSITY,NO3,JANJEONDONG,KUMJEONGKU,PUSAN609735,SOUTHKOREAABSTRACTAFLOWDEFECTOFAPISTONPINFORAUTOMOBILEPARTSAREINVESTIGATEDINTHISSTUDYINTHECOMBINEDCOLDEXTRUSIONOFAPISTONPIN,ALAPPINGDEFECT,WHICHISAKINDOFFLOWDEFECT,APPEARSBYTHEDEADMETALZONETHISDEFECTISEVIDENTINPRODUCTSWITHASMALLTHICKNESSTOBEPIERCEDANDISDETRIMENTALTODIMENSIONALACCURACYANDDECREASEOFMATERIALLOSSTHEFLOWDEFECTTHATOCCURSINTHEPISTONPINHASBADEFFECTSONTHESTRENGTHANDTHEFATIGUELIFEOFTHEPISTONPINTHEREFORE,ITISIMPORTANTTOPREDICTANDPREVENTTHEDEFECTINTHEEARLYSTAGEOFPROCESSDESIGNTHEBESTMETHODTHATCANPREVENTTHEFLOWDEFECTISREMOVINGORREDUCINGDEADMETALZONETHROUGHTHECONTROLOFMATERIALFLOWFINITEELEMENTSIMULATIONSAREAPPLIEDTOANALYZETHEFLOWDEFECTTHISSTUDYPROPOSESNEWPROCESSESWHICHCANPREVENTTHEFLOWDEFECTBYREMOVINGTHEDEADMETALZONETHENTHERESULTSARECOMPAREDWITHTHERESULTSOFEXPERIMENTSFORVERIFICATIONTHESEFESIMULATIONRESULTSAREINGOODAGREEMENTWITHTHEEXPERIMENTALRESULTS2003ELSEVIERSCIENCEBVALLRIGHTSRESERVEDKEYWORDSFLOWDEFECTPISTONPINMATERIALFLOWCONTROLFORWARDBACKWARDEXTRUSIONDEADMETALZONEFESIMULATION1INTRODUCTIONCOLDFORMINGISEXTREMELYIMPORTANTANDECONOMICALPROCESSES,ESPECIALLYFORPRODUCINGPARTSINLARGEQUANTITIESBECAUSEOFADVANTAGESOFCOLDFORMINGSUCHASHIGHPRODUCTIONRATES,EXCELLENTDIMENSIONALTOLERANCESANDSURFACEFINISH,MECHANICALANDMETALLURGICALPROPERTIES,COLDFORMINGISBYFARTHELARGESTAPPLICATIONOFINDUSTRYFORPRODUCINGPARTSHOWEVER,COLDFORGEDPARTSAREALSOUSEDINMANUFACTURINGAIRCRAFT,MOTORCYCLES,NUTSANDBOLTS1,BUTITISPOSSIBLEFORDEFECTSTOOCCURINFORGEDPARTS,DEPENDINGONTHEDEFORMATIONHISTORY,FORMINGCONDITIONSANDMATERIALFLOWPATTERN,ETCTHEKINDOFDEFECTSAREDUCTILEFRACTURECAUSEDBYTHESTATEOFSTRESSANDTHEDEFORMATIONHISTORY,FLOWDEFECTSCAUSEDBYUNSTABLEMATERIALFLOW,ANDPOORDIMENSIONALTOLERANCESCAUSEDBYINFERIORITYOFTHEDIEANDFRICTIONCONDITIONFURTHER,DEFECTSINFORGEDPARTSARECLASSIFIEDASINTERNALDEFECTSANDEXTERNALDEFECTS24THESEDEFECTSHAVEHARMFULEFFECTSONTHEQUALITYOFTHEPRODUCTANDANINCREASEINTHECOSTOFPRODUCTIONTHEREFORE,CORRESPONDINGAUTHORTEL82515103074FAX82515147640EMAILADDRESSBMKIMPUSANACKRBMKIMITISIMPORTANTTOPREDICTANDPREVENTDEFECTSINTHEEARLYSTAGEOFPROCESSDESIGNWIFIETAL5STUDIEDDUCTILEFRACTUREINBULKFORMEDPARTS,USINGDIFFERENTWORKABILITYCRITERIABYTHEFINITEELEMENTMETHODKIMANDKIM6STUDIEDINTERNALANDEXTERNALDEFECTSOFCOLDEXTRUDEDPRODUCTSWITHDOUBLERIBSANDPERFORMEDPROCESSDESIGNTOPREVENTTHESEDEFECTSINTHISSTUDYISEXAMINEDADEFECTWHICHOCCURSINPRODUCINGAFORWARDBACKWARDEXTRUSIONPRODUCT,APISTONPINFORANAUTOMOBILEPART,ANDNEWPROCESSESAREDESIGNEDTOPREVENTTHEDEFECTBYFINITEELEMENTMETHODINTHEEARLYSTAGEOFPROCESSDESIGNTHENTHERESULTSARECOMPAREDWITHTHERESULTSOFEXPERIMENTSFORVERIFICATION2FORMINGANDDEFECTOCCURRENCEANALYSIS21FORMINGPROCESSTHEPISTONPINISANAUTOMOBILECOMPONENTSUSEDINTHETRANSMISSIONOFPOWERBETWEENTHECONNECTINGRODANDTHECRANKSHAFTINTHECOLDEXTRUSIONOFAPISTONPIN,THEDESIGNREQUIREMENTSARETOKEEPTHESAMEHEIGHTOFTHEFORWARDEXTRUDEDPARTANDTHEBACKWARDPARTFIG1WITHOUTANYDEFECTINTHEFORGEDPRODUCT,FORUSEUNDERHIGHANDREPEATED09240136/03/SEEFRONTMATTER2003ELSEVIERSCIENCEBVALLRIGHTSRESERVEDDOI101016/S0924013603005156DJLEEETAL/JOURNALOFMATERIALSPROCESSINGTECHNOLOGY1392003422427423FIG1SHAPEANDDIMENSIONOFTHEPISTONPINFIG2PHOTOGRAPHOFAFLOWDEFECTOFAPISTONPINLOADTHEMATERIALUSEDFORTHEPISTONPINISAISI4135HFIG2ALLOYSTEEL,WITHTHEFOLLOWINGFLOWSTRESSBEHAVIOR768060139MPAFIG4DISTRIBUTIONOFEFFECTIVESTRAINANDFRACTUREVALUEFIG3CONVENTIONALFORMINGPROCESSFORAPISTONPINTHELUBRICANTUSEDISPHOSPHATECOATINGANDBONDLUBETHEFRICTIONFACTOR,M,ISASSUMEDTOBE01,WHICHISCONFIRMEDBYTHERINGCOMPRESSIONTESTTHESEQUENCEOFTHECONVENTIONALPROCESSFORTHEPISTONPINISPERFORMEDUSINGAMULTISTAGEFORMERFIG3THEFIRSTANDSECONDSTAGESAREPREUPSETTINGTOELIMINATEDEFECTSBYTHECROPPINGPROCESSSUCHASOVALITYANDECCENTRICITYOFTHEBILLETFORIMPROVEMENTOFDIMENSIONALTOLERANCESANDDIELIFEWHILSTTHETHIRDANDFORTHSTAGESAREFORWARDORBACKWARDEXTRUSIONFORTHEFORMINGOFONEDIRECTIONFROMTHEWEB,ANDFINALSTAGEISTHEPIERCINGPROCESSFORTHEPINSHAPEHOWEVER,THERESULTSOFEXPERIMENTFORTHECONVENTIONALPROCESSDISPLAYEDADEFECTINTHEWEBPARTFORMEDEARLYINTHETHIRDPROCESSFIG3ESPECIALLY,ANONUNIFORMFLOWPATTERNISOBSERVEDINPARTOFTHEDEFECTOCCURRENCE,WHICHLOOKSLIKEAFLOWDEFECTSIMILARTOLAPPINGWITHANUNDESIRABLEFLOWPATTERN22PREDICTIONOFDEFECTSBYFEANALYSISDEFORMISUSED,WHICHISCOMMERCIALCODEOFARIGIDPLASTICFEPROGRAMFORFORMINGANDDEFECTANALYSISTHEDIAMETEROFTHEINITIALBILLETIS30MMANDTHEHEIGHTIS61MM,THEWHOLEVOLUMEOFFINALPRODUCTBEING424DJLEEETAL/JOURNALOFMATERIALSPROCESSINGTECHNOLOGY1392003422427FIG5METALFLOWANDVELOCITYDISTRIBUTION,WHEREADEFECTOCCURSACCORDINGTOSTROKE43,118MM3THEFORMINGISSIMULATEDWITHACONVENTIONALPROCESSSEQUENCETHEMAXIMUMFRACTUREVALUETHATCANESTIMATETHEOCCURRENCEOFACRACK7ISSMALLAT008ANDISDISTRIBUTEDINAPOSITIONWITHINTHEHEADPARTOFTHEPUNCH,SOTHATADEFECTDOESNOTOCCURTHUSTHISDEFECTISNOTONEDUETODUCTILEFRACTUREFIG4THENFLOWLINETRACKINGSCHEMETHATWASPROPOSEDBYALTANANDKNOERR8ISPERFORMEDFORDEFECTANALYSISACCORDINGTOTHEPROGRESSOFTHEPUNCHSTROKE,SEVEREVARIATIONOFFLOWLINESAPPEARSANDDISCONTINUITYOFVELOCITYOCCURSINTHEPARTTHATADEFECTOCCURREDINTHEEXPERIMENTFIG5CONSEQUENTLY,THEMETALFLOWSONLYINTHEBACKWARDDIRECTIONWITHOUTFLOWTOTHEFORWARDDIRECTIONINTHEFOURTHPROCESSANDMETALNEARTHEWEBPARTISPULLEDUPINTHERIBPARTLIKEALAPPINGDEFECTTHEREFORE,THECAUSEOFTHEINITIATIONANDDEVELOPMENTOFTHEFLOWDEFECTTHATOCCURREDINPISTONPINISTHEVELOCITYDISCONTINUITYBETWEENBACKWARDANDFORWARDDIRECTIONBYTHEFORMATIONOFADEADMETALZONETHISAPPEARANCEEVIDENTLYOCCURSINPRODUCTSLIKEAPISTONPINWITHALOWTHICKNESSTOBEPIERCEDFORTHEDIMENSIONALACCURACYANDTHEDECREASEOFMATERIALLOSSAFLOWDEFECTOCCURRINGINAPISTONPINHASHARMFULEFFECTSONTHESTRENGTHANDTHEFATIGUELIFEOFAPISTONPINTHATHASHIGHANDREPEATEDLOADATHIGHTEMPERATURETHEREFORE,ITISNECESSARYFORANEWPROCESSTOPREVENTTHEFLOWDEFECT3PROCESSREDESIGNANDANALYSISFORTHEPREVENTIONOFDEFECTTHECAUSEOFTHEINITIATIONANDDEVELOPMENTOFTHEFLOWDEFECTISTHERESTRICTIONOFMETALFLOWBYTHEDEADMETALZONEFORTHEELIMINATIONOFTHEDEADMETALZONEINTHEEARLYEXTRUDEDPART3RDPROCESSINTHECONVENTIONALPROCESS,THEFORWARDORBACKWARDEXTRUSIONPROCESSISMODIFIEDTOCOMBINEDFORWARDBACKWARDEXTRUSION,WHICHISPERFORMEDSIMULTANEOUSLYINTHETWODIRECTIONSBECAUSEOFTHEVARIETYOFEXTRUSIONRATIOSANDLENGTHSINTHEFORWARDANDBACKWARDDIRECTIONS,THESIMULTANEOUSCOMPLETIONOFTHEMATERIALFLOWINTHEBOTHDIRECTIONSISVERYDIFFICULTCONSEQUENTLY,ONEOFTHEDIRECTIONSISCOMPLETEDEARLY,THENMATERIALFLOWSTOPPEDANDDEADMETALZONEAPPEARSINTHISPARTJUSTLIKETHATINTHECONVENTIONALPROCESSTHEREFORE,INTHECASEOFPISTONPINFORMING,THEEXTRUSIONRATIOANDTHELENGTHOFBOTHDIRECTIONSARETHESAMEAT189AND51MMFIRST,ANALYSISOFOPENDIEFORWARDBACKWARDEXTRUSIONISPERFORMEDFORANINVESTIGATIONOFEXTRUSIONLENGTHSOFTHEPISTONPINTHEDIFFERENCEOFTWOEXTRUDEDRIBSIS249MMANDTHEBACKWARDEXTRUDEDRIBISSHORTERTHANTHEFORWARDEXTRUDEDRIBASSHOWNINFIG6THEMETALFLOWOFBACKWARDDIRECTIONMUSTBERESTRICTEDCOMPULSORILYFORTHESATISFACTIONOFTHEDESIGNCONDITIONSANDTHISMEANSTHEOCCURRENCEOFADEADMETALZONETHEREFORE,FORTHESAMEEXTRUSIONLENGTHINBOTHDIRECTIONS,THREEFIG6EXTRUSIONLENGTHINFORWARDBACKWARDEXTRUSIONDJLEEETAL/JOURNALOFMATERIALSPROCESSINGTECHNOLOGY1392003422427425FIG7MODIFIEDPROCESSSEQUENCEFORAMULTISTAGEFORMERMETHODSAREPROPOSEDTOCONTROLTHEMETALFLOWWITHOUTTHECOMPULSORYRESTRICTIONOFMETALFLOW31CHANGEOFPREFORMSHAPETOSECURETHESAMELENGTHOFBOTHDIRECTIONSFROMTHECENTEROFWEB,ITISREQUIREDTHATTHEBACKWARDEXTRUDEDRIBISPERFORMEDBYPREFORMDESIGNASTHEDIFFERENCEOFBOTHDIRECTIONLENGTHSAT249MMFROMTHEABOVERESULTS,BEFOREFORWARDBACKWARDEXTRUSIONFIG7SHOWSTHEMODIFIEDPROCESSSEQUENCE,ANDFIG8SHOWSTHEMETALFLOWOFTHEFINALSTAGEOFFORWARDBACKWARDEXTRUSIONINTHISCASEFROMTHERESULTSOFSIMULATION,THELENGTHSOFTWOEXTRUDEDRIBSARE51MM,WHICHISTHEDIMENSIONOFTHEPISTONPINANDSATISFIEDTHEDESIGNCONDITIONINADDITION,THEMETALFLOWISUNIFORMINTHEDEFECTZONEWHERETHEFLOWDEFECTOCCURREDINTHECONVENTIONALPROCESS,ANDTHEREISNOTADISCONTINUITYOFVELOCITYINBOTHEXTRUSIONDIRECTIONSTHISMEANSTHATMETALFLOWSUNIFORMLYINTHEWHOLEPROCESSWITHOUTADEADMETALZONEBYRESTRICTIONOFMETALFLOWFIG8METALFLOWOFWEBINCASEOFUSINGPREFORMFIG9SCHEMATICDIAGRAMOFTHEAXIALLYMOVINGCONTAINERDIESTRUCTURE32DRIVINGOFEXTRUSIONCONTAINERTHEDRIVINGEXTRUSIONCONTAINERMETHOD9ISUSEDFORMETALFLOWCONTROLFORTHESATISFYINGOFTHEDESIGNCONDITIONTHISSTRUCTUREISTHATTHEEXTRUSIONCONTAINERISMOVEDINTHECOUNTERDIRECTIONTOTHEEARLYEXTRUDEDONEFIG9THISHASTHEEFFECTOFINCREASINGTHEMETALFLOWINTHELATEEXTRUDEDDIRECTIONANDRESTRICTINGMETALFLOWINTHEEARLYEXTRUDEDDIRECTIONINTHECASEOFTHEPISTONPIN,BECAUSEOFTHEEARLYCOMPLETIONOFBACKWARDEXTRUSION,THEEXTRUSIONCONTAINERISMOVEDINTHEFORWARDDIRECTIONFORTHEINCREASEOFMETALFLOWTOTHISDIRECTIONINTHISPROCESS,THEPRINCIPALPROCESSVARIABLESARETHERELATIVEVELOCITYRATIOOFTHEPUNCHANDTHEMOVINGEXTRUSIONCONTAINER,ANDTHEFRICTIONCONDITIONBETWEENTHEMATERIALANDTHEMOVINGEXTRUSIONCONTAINERINTHISSTUDY,BECAUSETHEFRICTIONFACTOR,M,IS01BETWEENTHEMATERIALANDCONTAINER,SIMULATIONISPERFORMEDONLYACCORDINGTOTHEVARIATIONOFTHERELATIVEVELOCITYRATIOVC/VP01,025,05,075,10IFTHERELATIVEVELOCITYRATIOISSMALLERTHANTHEOPTIMUMWHICHCANCOMPLETEFORMINGSIMULTANEOUSLY,EXTRUSIONINTHEBACKWARDDIRECTIONISCOMPLETEDEARLIERTHANINTHEFORWARDDIRECTIONANDAFLOWDEFECTOCCURINTHESAMEPARTASINTHECONVENTIONALPROCESSOTHERWISE,IFTHERELATIVEVELOCITYRATIOISLARGERTHANTHEOPTIMUMONE,EXTRUSIONINTHEFORWARDDIRECTIONISCOMPLETEEARLIERTHANBACKWARDDIRECTIONANDAFLOWDEFECTOCCURSINTHEOPPOSITEPARTTOWHEREADEFECTOCCURSINTHECONVENTIONALPROCESSTHEREFORE,FORSATISFACTIONOFTHEDESIGNCONDITIONS,THEOPTIMUMRELATIVEVELOCITYRATIOISSEARCHEDFORBYANOPTIMIZATIONTECHNIQUE,THEBISECTIONMETHODFROMTHERESULT,THEOPTIMUMRELATIVEVELOCITYRATIOIS048FIGS10AND11SHOWTHEDEFORMATIONMODALITYANDMETALFLOWACCORDINGTOTHERELATIVEVELOCITYRATIO01,048,10FORAPUNCHSTROKEOF427MM,RESPECTIVELYFIG11CSHOWSTHEMETALFLOW426DJLEEETAL/JOURNALOFMATERIALSPROCESSINGTECHNOLOGY1392003422427FIG10DEFORMATIONMODALITYOFTHEPISTONPINACCORDINGTOTHERELATIVEVELOCITYRATIOFIG11COMPARISONSOFMETALFLOWACCORDINGTOTHERELATIVEVELOCITYRATIOATTHEOPTIMUMRELATIVEVELOCITY048WHEREANIMPROVEDFLOWPATTERNWITHOUTAFLOWDEFECTCANBENOTED33MODIFICATIONOFDIESTRUCTUREAMODIFICATIONOFTHEDIESTRUCTUREISPROPOSEDWHICHCANRESTRICTTHEMETALFLOWOFBACKWARDDIRECTION,WHICHISDEFORMEDEARLY,FORSIMULTANEOUSCOMPLETIONOFEXTRUSIONINBOTHDIRECTIONSINTHISCASE,FORSIMULTANEOUSCOMPLETIONANDTHESAMELENGTHINBOTHDIRECTIONS,THESTRIPPER,WHICHISFIG12SCHEMATICDIAGRAMOFDIESTRUCTUREUSINGSTRIPPEREQUIPMENTFORPUNCHEXTRACTIONFROMPRODUCTS,ISREDESIGNEDIFAFIXEDSTRIPPEROFCONVENTIONALTYPEISUSED,ADEADMETALZONEAPPEARSFROMTHEMIDDLESTAGEOFBACKWARDFORWARDEXTRUSIONBYTHERESTRICTIONOFMATERIALFLOWTHEREFORE,ASTRUCTUREISUSEDTHATCANDELAYTHEMETALFLOWINTHEBACKWARDDIRECTIONBYSPRINGFORCEFIG12SHOWSTHEDIESTRUCTUREFORTHISMETHOD,ITISVERYIMPORTANTTODECIDETHEPROPERSPRINGFORCEFORSIMULTANEOUSCOMPLETIONOFFORMINGTHEREFORE,THENECESSARYSPRINGFORCEFORTHISISCALCULATEDBYFESIMULATIONFROMTHESIMULATIONRESULT,ITWAS5TTOBEAPPLIEDLOADTOSTRIPPERFIG13SHOWSMETALFLOWINTHISCASETHEMETALFLOWISSIMILARLYUNIFORMATTHEDEFECTZONEWITHOUTDISCONTINUITYOFVELOCITYINCOMPARISONWITHOTHERMODIFICATIONMETHODSFIG13METALFLOWOFWEBINCASEOFUSINGSTRIPPERDJLEEETAL/JOURNALOFMATERIALSPROCESSINGTECHNOLOGY1392003422427427TABLE1COMPARISONPROCESSFOREACHOFTHEPROPOSEDMETHODCONVENTIONALMETHODUSEOFPREFORMUSEOFSTRIPPERUSEOFMOVINGCONTAINERMAXIMUMLOADT972963961840PROCESSOFEXTRUSION2STAGE2STAGE1STAGE1STAGEDEFECTEXISTNONENONENONE4RESULTSANDEXPERIMENTFROMTHEFESIMULATION,THETHREEPROPOSEDMETHODSAREPROPERTOPREVENTAFLOWDEFECTBYMETALFLOWCONTROLTHECHARACTERISTICSOFEACHPROCESSAREASFOLLOWSTHEFIRSTMETHODTHATUSESAPREFORMNEEDSTHREESTAGEPROCESSESPREFORMING,FORWARDBACKWARDEXTRUSION,PIERCINGANDHASASIMPLEDIESTRUCTUREHOWEVER,THESECONDMETHODTHATUSESASTRIPPERANDTHETHIRDMETHODTHATUSESANAXIALLYMOVINGCONTAINERNEEDTWOSTAGEPROCESSESFORWARDBACKWARDEXTRUSION,PIERCINGANDHAVEACOMPLEXDIESTRUCTUREINRESPECTOFTHEFORMINGLOAD,THEPROCESSESARESIMILARTOEACHOTHERESPECIALLY,THEMAXIMUMFORMINGLOADISSMALLERTHANTHATOFOTHERPROCESSESBYABOUT10TINTHECASEOFTHEAXIALLYMOVINGCONTAINER,BECAUSETHEAXIALLYMOVINGCONTAINERINCREASESMATERIALFLOWINTHEDIRECTIONPUNCHMOVEMENTITISCOMPAREDWITHTHEPROPOSEDMETHODFORFORMINGBYAPRESSINTABLE1INTHISSTUDY,ANEXPERIMENTUSINGAPREFORMISPERFORMEDANDUSESAMULTISTAGEFORMERHAVING250TCAPACITYFORTHEVERIFICATIONOFSIMULATIONETCHINGFOROBSERVATIONOFMETALFLOWISPERFORMEDTOEXAMINEFORAFLOWDEFECTFORTHEPISTONPINBEFOREPIERCINGFIG14SHOWSTHEEXPERIMENTRESULT,BASEDONTHEFIRSTPROPOSEDMETHOD,CHANGINGTHEPREFORMTHEEXPERIMENTRESULTSHOWSTHATMETALFLOWISUNIFORMINTHEDEFECTZONEWHERETHEFLOWDEFECTHADOCCURRED,ANDSATISFIEDTHESIMULTANEOUSCOMPLETIONOFFORMINGANDTHESAMELENGTHINBOTHEXTRUSIONDIRECTIONSTHISTENDENCYISINGOODAGREEMENTWITHTHESIMULATIONRESULTFIG14THEELIMINATIONOFTHEFLOWDEFECTBYTHEFIRSTPROPOSEDMETHOD5CONCLUSIONSINTHISSTUDY,THEFLOWDEFECTTHATOCCURSINTHEMANUFACTURINGPROCESSOFTHEPISTONPINISEXAMINEDANDANEWPROCESSTOPREVENTTHEDEFECTISREDESIGNEDBYFEANALYSISFIRST,THECAUSEOFTHEDEF