Design-of-internal-pins-in-injection-mold-CAD-via-

Computer-AidedDesign42(2010)582597ContentslistsavailableatScienceDirectComputer-AidedDesignjournalhomepage:DepartmentofMechanicalEngineering,TheHongKongPolytechnicUniversity,HungHom,Kowloon,HongKongarticleinfoArticlehistory:Received19May2009Accepted11March2010Keywords:UndercutfeaturePartingdirectionPartinglineInternalpindesignInjectionmoldCADabstractAmethodologytodealwiththeautomaticdesignofinternalpinsininjectionmoldCADviatheautomaticrecognitionofundercutfeaturesisdeveloped.Theapproachtoautomaticallyidentifyingtheundercutfeaturesisfirstproposed.Forthegivenpartingdirections,alltheinnerandouterundercutfeaturesareidentifiedbasedonthetopologicalrelationshipofgeometricalentities.Theouteredgeloop,whichrepresentsthelargestcross-sectionboundaryalongthegivenpartingdirections,isextractedandpatchedup.Thesurfacesofmoldingarethenidentifiedbasedontheclassificationsoftheirgeometricalentities.Toidentifythedeepinnerundercutsinthemolding,theprojectionofthemaincore,internalpinsandtheirboundingboxesalongthepartingdirectionandthepinwithdrawaldirectionaregenerated.Upondeterminationofwhethertheboundingboxesofanytwointernalpinsandthemaincoreprojectionhaveintersectionarea,thedeepinnerundercutsarelocated.Thecompletemethodologyisfinallyimplementedandverifiedthroughcasestudiesandtheefficiencyofthemethodologyinhandlingcomplexmoldedpartsisthusillustrated.'2010ElsevierLtd.Allrightsreserved.1.IntroductionInjectionmoldingisanimportantmanufacturingprocess.Theplasticmoldedcomponentsmanufacturedbythisprocess,theso-calledmoldingsinthispaper,aresuffusedinourdailylifeandwidelyusedinindustries.Toshortendesignanddevelopmentlead-times,automaticandrapiddesigniscritical.NewCAD-enabledandtailor-madetechnologyisthusneededtorealizetheautomaticandrapiddesignininjectionmoldCAD.InmoldCAD,undercutfeaturerecognitionisanimportantstep,asitisrelatedtothedeterminationofpartingdirectionsandpartinglines,generationofcoreandcavity,andthecreationofsecondarymoldingtoolswhichincludeside-coresandinternalpins.Torecognizeundercutfeatures,thetopologicalrelationshipsofgeometricalentitiesinamoldingneedtobeextracted.Intandemwiththis,manyresearchersconductedresearchonundercutfeaturerecognition.Fuetal.developedamethodologytocategorizeandrecognizeundercutfeatures[1,2].Theundercutfeaturesareclassifiedintodifferentcategoriesbasedontheedgenumberandedgecharacteristicsofthetargetsurface.Theundercutdirectionisthendefinedasthedirectionwherebythelocaltoolcanbewithdrawneasilyandmosteffectivelytoavoidthewarpageofthemolding.Itisthusalsothewithdrawaldirectionofthelocaltoolbywhichtheundercutismolded.ToidentifyCorrespondingauthor.Tel.:[phone].E-mailaddress:[e-mail](M.W.Fu).undercutfeatures,Yeetal.proposedamethodforidentificationofundercutfeaturesbasedontheextendedattributedface-edgegraph(EAFEG)[3].Thedepressionsandprotrusionsinamoldingareextractedanddefinedasthepotentialundercuts.Ismailetal.presentedamethodologyforrecognitionofcylindrical-basedfeatures[4].Basedontheedgeboundaryclassification,thetypesofallthecylindrical-basedfeaturesaredeterminedaccordingtothethreetestpoints.Thepotentialundercutexistinginthesecylindrical-basedfeaturesaremarkedforfurtherrecognition.Khardekaretal.providedanalgorithmtoefficientlyidentifyanddisplayundercuts[5].WiththeimplementationofGaussMap,thecandidatedirectionsfortestingatwo-piecemoldarechosen.Todeterminethepartingdirection,muchresearchhasbeenconducted.ThedefinitionsofsurfacevisibilityinbothglobalandlocalinterferencesareproposedbyChenandWoo[68].Thevisibilitymap(V-map),whichisasphericallyconvexregionconsistingofthevisibledirectionsoftheentirelocallyvisiblesurfaces,isimplementedtodeterminetheoptimalpartingdirection.The3Dmodelofthemoldingismappedontoaunitsphereandthedeterminationofitsvisibilityismade.Guetal.[9]presentedanapproachtorecognizingthefeaturesautomatically.Theoptimalpartingdirectionisdeterminedaccordingtothecandidatepartingdirectionsandfeaturetype.Yinetal.conductedanapproachtorecognizingundercutfeaturesfornearnet-shapemanufactureparts[10].Byusingthelocalfreedomofsub-assembliesinthedirectedblockinggraphs,theinteractingundercutfeaturesandtheirconvexhullareisolatedandidentified.Dhaliwaletal.alsodescribedalgorithmsforcomputingtheglobal0010-4485/$seefrontmatter'2010ElsevierLtd.Allrightsreserved.doi:10.1016/j.cad.2010.03.001J.Q.Ran,M.W.Fu/Computer-AidedDesign42(2010)582597583accessibilityconesforeachfaceonapolyhedralobjectandthesetofdirectionsfromwhichtheyareaccessed[11].Thepartinglinecanbegenerateduponthedeterminationofthepartingdirection.Wongetal.proposedanalgorithmwhichadoptsanunevenslicingonthemoldingtolocatethepartinglineandpartingsurface[12].Weinsteinetal.presentedamethodologyusingthemulti-objectivefunctioncriteria[13].Severalmolddesignfactors,includingdrawdepthandthenumberofundercuts,areconsidered.Thedrawdirectionrangeandthepartinglinelocationarethenidentified.Furthermore,Fuetal.proposedanapproachtogeneratingt