Investigation of Revolute Joint Clearances Created by an In-Mold Assembly Process.pdf

1、Proceedingsofthe2007IEEE MoC1.3 InternationalSymposiumonAssemblyandManufacturing AnnArbor,Michigan,USA,July22-25,2007 InvestigationofRevoluteJointClearancesCreatedbyanIn-Mold AssemblyProcess ArvindAnanthanarayanan,ChandrasekharThamire,andSatyandraK.Gupta Abstract-Revolutejointsarefrequentlyusedinart

2、iculatedthisjointarethefollowing: structures.Traditionally,suchajointisformedbyassembling 1)Theframeisfirstmoldedinthefirststagemoldusinga twocomponents.Asanalternative,revolutejointscanbecreated highmelting-pointpolymer. insidethemoldusinganin-moldassemblyprocess.Thisprocess 2)Theframeisinsertedint

3、othesecondstagemoldnext. eliminatestheneedforpost-moldingassembly,thussignificantly 3)Thesecondstagepartisthenmoldedinthecavity reducingthecycletimeandpartcount.The functionalfomdrmthfissagprtndheecdsae performanceofarevolutejointdependsontheclearanceinthefomdrmthfissagprtndhe ecdsae joint.Thecleara

4、nceinturndependsonthepartshrinkageandmold,usingalowermelting-pointpolymer. themolddeformationduringthemoldingprocess.Thepresence 4)Uponcooling,thein-moldassembledpartwitha ofapolymerpartduringthesecondmoldingstagemakesanin- revolutejointisejectedfromthemold. moldassemblyprocesssignificantlydifferent

5、fromthetraditional moldingprocessduetothedifferenceinheattransferandFisstg deformationcharacteristics.ThispaperpresentsexperimentalFisstg dataandapreliminarymodeltoexplainthedifferencesin clearanceproducedbyanAluminummoldandanAluminum moldwithanAcrylonitrilebutadienestyrene(ABS)insert.Our 0tg datain

6、dicatesthatthereisasignificantdifferencebetweentheScntg clearancesobservedfromthesetwodifferenttypesofmolds.We believethatclearancesproduceddependstronglyonthethermal historyoftheparts.Fig.1.Arevolutejointproducedusinganin-moldassemblyprocess 1.INTRODUCTIONPolymers usedinthesecondstagearetypicallyof

7、alower I.INTRODUCTION meltingpointcompared tothoseusedinthefirststage.Thisis INJECTIONmoldingisapopularmanufacturingprocessfor toensurethatthefirststagepolymerdoesnotmeltduringthe massproducingplasticparts.Usingthismethod,partsof injectionofthesecondstagepart,whichwillpromotean reasonablemechanicals

8、trength,surfacefinish,andcomplex adhesion-freerevolutejoint.Sincetheperformanceofthejoint geometrycanbeeasilyproduced.Moreover,partsproducedreliesheavilyontheclearancebetweentheconstituentparts,it donotnormallyrequiresecondaryprocessing.Whenrelative isimportanttoachievethedesignclearances. motionbet

9、weensuchpartswarrantsassembly,theyare Figure 2 presents asimplifiedillustrationofjoint manuallyassembledtocreatearticulatedjoints.TheassemblyclearancesformedinIn-MoldAssemblyprocesses.Thefirst process,however,canbetimeconsumingandlaborintensive, stagepartactsasamoldinsertduringthemoldingofthe In-mol

10、dassemblyprocesspresentsanalternativewayof secondstagepartandundergoesdeformationduetothe creatingarticulatedjoints.Inthisprocess,moldingoperationsprocesspressureandtemperatureinthesecondstage.This areperformedinmultiplemoldingstagesandassembledparts changesthe effectivesizeofthecavityfromdtodin.Dur

11、ing aredirectlyproducedinsidethemold,eliminatingtheneedfor solidification,shrinkageoccursinthesecondstagepart post-moldingassemblyoperations.Theexpected benefits causingitsfinaldimensiondptobedifferentfromdord,. includereducedcycletimeandpartcount,thelatterdueto Further,astheinjectionpressureisremov

12、edandcooling eliminationoffasteners. occurs,thefirststagepartmayrecoversomeofthe Figure 1showsarevolutejointthatcanbeproduced usingdmdp anin-moldassemblyprocess.Thestepsinvolvedinmolding anuscriptreceivedDecember16,2006. . rvindnanthanarayananisiththeechanical Engineering. ail:. ). aut

13、horphone:301-405-5306;e-mail:kunta.ded.).mechanical.deformation.and.expansion.it.has.undergone. Authorized licensed use limited to: GUILIN UNIVERSITY OF ELECTRONIC TECHNOLOGY. Downloaded on May 06,2010 at 04:22:46 UTC from IEEE Xplore. Restrictions apply. MoC1.3 earlier.Thefinalclearancebetweenthetw

14、opartsisthenprocessingconditionsonshrinkageoffouramorphousresins determinedbythedeformationretainedbythefirst-stagepartandtwosemicrystallinematerialswasinvestigatedinastudy andtheshrinkageproducedinthesecond-stagepart.byJansenetal.1.Athermoelasticmodelwaspresentedthat Thepresenceofapolymerduringthes

15、econdmoldingstagedescribedtheshrinkageofamorphousmaterialswell,but makesanin-moldassemblyprocesssignificantlydifferentoverpredictedthatofcrystallinematerials.Amodeldescribing fromasingle-stagemoldingprocess.Fortoolsteelortheanisotropicshrinkageofamorphous7andsemicrystalline aluminummolds,molddeforma

16、tioncanbeconsideredtobe8polymerswasproposedbyKwonetal.7,8,basedonthe negligible,comparedtotheshrinkagevalues.Ontheotherfrozen-inorientationfunctionandelasticrecoverydetermined hand,inIn-MoldAssemblies,thefirststageparthasastiffnessfromanon-linearviscoelasticconstitutiveequation.Their lowerthantoolst

17、eelandaluminumandhencemayundergopredictedresultswereinfairagreementwiththeexperimental considerabledeformation,whichshouldbeconsideredinresults.Delaunayetal9examinedthepossibilityofmold assessingclearances.Further,thermalbehaviorofpolymersisdeflectionduetoinjectionandpackingpressurechangingthe diffe

18、rentfromthoseofmetalsandalloys,whichcanaffectbasicshapeofthecavityandhenceaffectingtheoverall coolingofthesecond-stagepartssignificantly.Thisinturnshrinkage.BushkoandStokes10,11modeledthemechanics mayaffecttheshrinkageandhenceneedstobeconsideredforofpartshrinkageandwarpageandresidualstressesandstrai

19、ns estimatingtheclearances.forthesolidificationofamoltenlayerofamorphous Inthisstudy,clearancesformedduringthein-moldthermoplasticmaterialbetweencooledplates,assuming assemblyofaninjection-moldedrevolutejointcomprisingathermo-viscoelasticbehaviorforthematerial.Similarly,a cylindricalsleeveandpinaree

20、xamined,withthesleevenumberofotherstudiesinvolvingshrinkage-predictionmodels moldedinthefirststageandthepininthesecond.Tobetterbasedonprocessparametersandmaterialvariableshavebeen understandtheprocess,pinsofsimilarsizewerealsomoldedreported.Thereaderisreferredto3-11foranelaborate inAluminummoldsdire

21、ctly,withoutthepolymersleeves.reviewofsuchstudies.Whileseveralimportantresultswere Experimentaldataispresentedforthreejointsizes.Aproducedfromtheseinvestigations,mostofthepublished preliminarytheoreticalmodelisproposedtounderstandthestudieswerefocusedonshrinkageofpolymersintoolsteel differencesobser

22、vedinclearanceswithanAluminummoldandAluminumorotherhardmetallicmolds.Noworkappears andAluminummoldwiththepolymersleeve.tohavebeenreportedaddressingtheshrinkageofpolymersin softmolds.Thecurrentstudyattemptstoinitiatesuchastudy, II.RELATEDWORKinthecontextofin-moldassemblyprocessesfor Usingin-moldassem

23、blyforarticulateddevicesisamanufacturingrigid-bodyjoints. relativelynewtechnologyandtherearefewstudiesthat outlineasystematicmethodologyfordesigningpartsandIII.EXPERIMENTALSETUP molds.Priyadarshietal.1havepresentedamodelforAsdescribedearlier,anin-moldassemblytypicallyinvolves designingIn-MoldAssembl

24、iesandmoldingprocessthatthepartmoldedinthefirststageasamoldinsertforthe enablesonetodesignthejointclearanceandvariationinthesecondstage(Fig.1).Toexamineclearancesobtainedinan jointclearancetomeetthefunctionalgoals.TheyoutlinedaIn-MoldAssembledjoint,wehaveutilizedcomponents systematicapproachtoaidpro

25、ductdesignersdeterminepartfeaturingcylindricalgeometrybecauseofaxisymmetry dimensionsandmaterialproperties,providingprovenmoldconsiderations.ThustomanufactureanIn-MoldAssembled designtemplatesforrealizingrevolute,prismatic,andrevolutejoint,acylindricalsleevewasfirstmoldedinthefirst sphericaljoints.B

26、anerjeeetal.2haverecentlypresentedastage.Thispartwassubsequentlyusedasamoldinsertforthe comprehensivereviewofmulti-materialinjectionmoldingpininthesecondstage.Uponcooling,anIn-MoldAssembled (MMM)processes.Theypresentedanapproachforrevolutejointwasproduced.Themethodologyofmoldingthe systematicallyide

27、ntifyingpotentialmanufacturabilityissuespinintotheholeemployedinthestudyenabledustoexamine thatareuniquetosuchprocessesandproposeddesignrulestosituationswhererunningclearancesweredesired. avoidsuchproblems.TheiranalysisshowsthattherulesThepartstestedweremadefromlow-densityPolyethylene applicablefort

28、raditionalsinglematerialmoldingneedtobe(LDPE).Inordertocomparetheshrinkagebetweenhardand suppressedormodifiedsometimesfortheMMMprocesses.softmolds,partsofdifferentsizesweremoldedinaluminum Severalstudieshaveexaminedmodelingofin-moldaswellassleevesmadefromAcrylonitrilebutadienestyrene shrinkageofther

29、moplasticsinmetallicmolds.Asimplemodel(ABS).ThepartswereinjectionmoldedinMilacrons describingtheshrinkagebyfollowingthePressure-Volume-BabyplastInjectionmoldingmachine.Themoldassembly Temperature(PVT)diagramfromglasstransitiontoambientconsistedofanABSsleeveandanLDPEpinwithinan conditionsandobtaining

30、thefinalproductvolumewasAluminumhousingforthein-moldassembliesandanLDPE consideredinearlystudies3.JansenandTitomanlio4,5pininanAluminummoldforthesingle-stagemolding.For examinedtheeffectsofpressureandPoissonexpansiononthelattercase,AluminummoldsweremachinedandtheLDPE thicknessshrinkagethroughathermo

31、elasticmodel.Effectofpartsweremoldedusingmoldsthuscreated. 113 Authorized licensed use limited to: GUILIN UNIVERSITY OF ELECTRONIC TECHNOLOGY. Downloaded on May 06,2010 at 04:22:46 UTC from IEEE Xplore. Restrictions apply. MoC1.3 DimensionsofABSinsertsandAluminummoldswere measuredbeforeandaftermoldi

32、ng.TheLDPEpartswere measuredaftermoldingandsubsequentcoolingtoconstant scaledcoolingtimes.Temperaturesatlocationsindicatedin Fig.4andFig.5weremeasuredforthreesetsof3/8and parts,usingaNationalInstrumentsdataacquisitionsystemthat includedaPCI-4221dataacquisitioncard,SCXI1000and 1102modules,andaTC-2095

33、thermocouplepanel.FourK- typethermocoupleswereusedtomeasuretemperaturesfor configurationsinvolvingABS,whilethreewereusedforthose Fig.3.MoldassemblyshownwiththeABSsleevenotinvolvingABS.Twowereattachedtothemoldsurfaces, TheprocessforobtainingtheABSsleevesinvolvedtheoneatapointcentrallylocatedwithinthe

34、moldformeasuring followingsteps:MoldsformakingtheABSmoldinsertswerethetemperaturehistoryoftheparts,andafourthone,if firstmachined.ABSsleeveswerethenmadeusingtheseapplicable,atthebaseoftheABSinsertforevaluationofheat molds.Aluminummoldhousingsweremachinednext.Finallytransferthroughtheinsert.Thethermo

35、coupleatthecentral moldassembliesconsistingofABSmoldsandtheAluminumpointinthemoldwasheldinpositionusingarigidcopper housingswereassembled(Fig.3).LDPEpartswerenexttubethroughwhichthethermocouplewaspassed. moldedusingthesemoldassemblies. Threesizesofpinswereusedintheexperiments,withIV.THEORY nominaldi

36、ametersof1/4,3/8,and/2.SinceclearancesAssemblyclearanceinin-moldassembliesisaffectedbya obtainedusingdifferentmoldmaterialswereofprimaryvarietyofparameters,includingtheclearancebetweenthe interest,mostoftheothervariableswereheldconstantthroughmoldandtheinsert,physicalpropertiesofthematerials, scalin

37、g.Lengthswerekeptthesameasdiameterstoretainantemperatureandpressurehistories,geometry,andprocess aspectratioofunityfortheparts.Injectionpressureandparameters.Inthemodelproposedhere,weassumethatsuch temperaturewerekeptconstantat700barsand1300C.Partanassemblyclearanceoccursduetothedeformationofthe dia

38、meterwasusedasthescalinglengthandthediametertopolymerinsertattheelevatedpressureandtemperatureitis injection-timeratioasthescalingvelocity.Coolingtimesweresubjectedto,thermalexpansionofthepolymerinsert, scaledbytheratioofthesquareofthediametertothethermalvolumetricshrinkageduetoenhancedcrystallizati

39、onfrom diffusivityofthepartmaterial.Thisresultedinconstantscaledreducedheattransfer,andvolumetricexpansiondueto pressuresandcoolingtimesforallsizesused.Scaledthicknesssolidificationunderpressure.Forsimplicity,creepand forABSinserts,however,couldnotbemaintainedconstantrelaxationeffectsarenotincluded.

40、Incylindricalgeometry,the duetomachiningconstraints.diametricalclearanceatanytimetafterthesolidificationhas endedmaythenbeexpressedas R C(0,Z,t)=,5(0,z,t)+fca(T,-T(O,z,t)+ ,r,-A,BP -PWA)ir.(1) _R Intheaboveexpression,Cisthediametricalclearance,Tis theinstantaneoustemperatureatthelocationofinterest,P

41、,is thepressureduringsolidification,Pistheinstantaneous Fig.4PositionsofthermocouplesforAlmold pressureinthepolymerpart,and5I is thepermanent deformationretainedbytheABSinsert.Theremaining parameterspertaintoLDPE:aisthelinearthermalexpansion coefficient, T, isthesolidificationtemperature, 5, isthe c

42、rystallinityfactor,and/8isthecompressibility.Ristheradius ofthepinand8 andzaretheangularandaxialcoordinates, respectively.Theexpressionprovidedaboveissimilartothat developedbyJansenandTitomanlio4,andTitomanlioand Jansen5,andJansenetal.1,butdiffersfromtheirsdueto thetermsrepresentingthedeformationoft

43、heinsertand Fig.5PositionsofthermocouplesforABSmoldtemperature-dependentcrystallinityduringcuring. FiveLDPEpartsweremoldedforeachsizewithandToevaluatedzandP,oneneedstoexaminetheflow withouttheABSinserts.DOWPolyethylene722wasusedascharacteristicsofthemelt,whileheattransfershouldbe thepartmaterial,Hiv

44、alABSHG6NaturalXwasusedforABSexmndfrcluaigndTInteurntsdythe inserts,andanAluminum-basedalloywasusedforAluminum .wereperformedinthefollowingmanner.Firstthenon- moldpieces. isothermal flowproblemwassolvedtoevaluatethepressures 114 Authorized licensed use limited to: GUILIN UNIVERSITY OF ELECTRONIC TEC

45、HNOLOGY. Downloaded on May 06,2010 at 04:22:46 UTC from IEEE Xplore. Restrictions apply. MoC1.3 occurringduringsolidificationandattheinsert.Heattransfernext.Thecoolingpolymer,surroundingABSsleeve,when wasthenevaluatedtodeterminethethermalexpansionapplicable,andtheAlmoldwereconsidered.Incylindrical c

46、omponentandshrinkageduetocrystallization.Fortheflowcoordinates,thegoverningequationforthisstepmaybe problem,thegoverningequationsaregivenbywrittenas: (2a(pOcPT) = IadT 1a3kaT a kTd3 at+V.(pV)= o at=rarKdrr2 K)+ aoa azKZXdt +(pv) ( =V.-PI+/J(VV+VVT)+pb (3)(6) At +V.V(PV) = VJ_ PI+,U(V )1+pb Intheabov

47、eequation,;Iisthemaximumpossible paT+V.VT=kV2T+k2+ (4) crystallinity forthematerial,AHcistheexothermicheatof atcrystallizationperunitmass,and 4 istherelativecrystallinity. Whereyistherateofshearingstrain,4istherateofThegoverningequationsfortheABSsleeveandAluminum solidification,cpisthespecificheatca

48、pacity,kisthethermalmoldaresimilarto(6),withtheexceptionthattheheat conductivity,AHistheexothermicheatofpolymerization,uisgenerationtermduetochangeincrystallinityisassumedtobe thedynamicviscosity,pisthedensity,andVisthevelocityabsent.Boundaryconditionsappliedwerenatural-convection vector,bisthebody-

49、forcevector.wasevaluatedusingaboundaryconditionsonallsidesofthemoldexceptatthe modelproposedbyKamalandRyan12becauseofitsabilitynozzlelocation,aperfectthermalcontactattheinterfaces tomatchcloselywiththeexperimentaldata.Valuesforp,k, during the application ofthe holdingpressure, and axisylmmetryatthea

50、xis.Thermalcontactconductancewas andcpweretakenfromreferences13-15.,uwasassumedto axpsymetry athecais.Trcon.tactcnctnciwa beoftheollowingorm16:replaced bya convectionconditionwithconvectionbeofthe following form 16: coefficients applicable fornaturalconvectionin cylindrical A=ml8V,/i3r|)(5)annuli.Th

51、iswasincludedtoaccountforthegapconductance mintheaboveequationrepresentstheNewtonianthatarisesonceshrinkagebegins.Aftertheejectiontime, viscosity,whereasnrepresentsthedeviationfromthenatural-convectionboundaryconditionwasappliedoverthe Newtonianfluids,whichissmallerthanunityformostsurfaceofthepartan

52、dtheinnerdiameteroftheABSinsert. polymermelts14.0-dependencewaskeptintheequationtoexaminetheeffect Thegoverningequationsweresolvedundertheassumptionofnon-uniformthermalcontactatthecontactregionforusein ofaxisymmetry.Bodyforceswereneglectedandafully-laterstudies. developedflowwasassumedattheflowfront

53、.BoundaryThegoverningequationwasintegratednumericallyusing conditionsassumedwereno-slipconditionattheinterfacetheAlternatingDirectImplicit(ADI)method18subjectto betweentheinsertandthepart,axisymmetryalongtheaxis,theboundaryandinitialconditions. Initially,zero pressurebeingatmosphericattheflowfront15

54、,andacrystallizationwasassumedandthetemperatureswere constantflowrateconditionatz=0,determinedfromcalculatedbasedonaninitialestimateoftheproperties.After experimentalconditions.Convectionboundaryconditionseachtimestep,propertieswereadjustedtomatchthe wereassumedforthetemperaturefieldoutsideofthetemp

55、eraturedistributioncalculated.Thisprocesscontinued Aluminummoldandatthemoldfront,whiletheprocessinguntilsteadystatewasreached.Steadystatesolutionswere temperaturewasassumedtobehelduntilthegateshut-offconsideredconvergedwhenthemaximumchangeinthelocal occursatz=0.valuesofTandineachoftheglobalenergyrat

56、esatthe Becauseofthe energydissipation terminthe energyexteriorsurfacesbecamelessthan10-4percent.Gridsizewas equation,thevelocityprofileandpressureswereinitiallyrefinedwhenanyoftheaboverequirementswasnotsatisfied. guessedandthetemperaturefieldwascalculated.AnewGrid-independencewascheckedforallthrees

57、izesusedinthe viscosityprofilewasthencalculatedusingthenewexperiment.Spatialresolutionwasvariedfrom21to101in temperatureprofile.Thelinearmomentumequationwasthezdirection,from21to81intherdirection,andfrom17to solvednexttocalculatethenewvelocityprofiles.Newton-97inthe 0direction.Gridindependencewasnot

58、edforgrids Raphsonmethod17wasappliedforconvergenceoffinerthan51x41x41.Forthecalculationsconsideredhere,a pressuresandthevelocityprofilesforthecalculated gridsizeof61x61x49wasused. temperaturevalues.Withthenewvaluesforthevelocityfield,Temperaturehistoriescalculatedatthecenteroftheinjected thetemperat

59、urefieldwascalculatedagain,andtheprocedure partwerecomparedwiththosemeasured.Curingkineticswere wasrepeateduntilconvergencecriteriaweremetforboththe thenadjustedinanattempttomatchthetemperatureprofiles temperatureandvelocityfields.Thesolutionwasthenthroughaniterativeprocess.Oncetheprocesswasstabilized, marchedinthez