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JournalofUniversityofScienceandTechnologyBeijiregVolume13,Number1,February2006,Page60MaterialsEvaluationofthemoldfillingabilityofalloymeltinsqueezecastingHaiyingZhang,ShumingXing,QinghuaZhang,JianboandWenLid1SemisolidFormingResearchCenter,BeijingJiaotongUniversity,Beijing100044,China2ShijiazhuangLocomotiveDepot,Shijiazhuang050000,China3DepartmentofMaterialandEngineering,HebeiUniversityofScienceandTechnology,Shijiazhuang050018,ChinaReceived20041213AbstractThemoldfillingabilityofalloymeltinsqueezecastingprocesswasevaluatedbymeansofthemaximumlengthofArchimedesspiralline.Atheoreticalevaluatingmodeltopredictthemaximumfillinglengthwasbuiltbasedontheflowingtheoryoftheincompressibleviscousfluid.Itwasprovedbyexperimentsandcalculationsthatthemoldfillingpressureandvelocityareprominentinfluencingfactorsonthemoldfillingabilityofalloymelt.Themoldfillingabilityincreaseswiththeincreaseofthemoldfillingpressureandthedecreaseofthepropermoldfillingvelocity.Moreover,thepouringtemperaturerelativelyhaslesseffectonthemoldfillingabilityundertheexperimentalconditions.Themaximumdeviationoftheoreticalcalculatingvalueswithexperimentalresultsislessthan15.Themodelcanquantitativelyestimatetheeffectofeveryfactoronthemoldfillingability.Keywordssqueezecastingprocessparametersmoldfillingabilitytheoreticalcalculationexperimentalevaluation1.IntroductionThemoldfillingabilityofalloymeltcandirectlyaffecttheinnerqualityandsurfaceroughnessoftheproducts,andisregardedasabasicprobleminthefieldofmaterialformingprocess,especiallyintheresearchesofnewmaterialsandprocesses.Inthetraditionalcastingtechnology,theevaluationofthemoldfillingabilityiscarriedonbymeasuringthemaximumfillinglengthofaspirallinespecimenhowever,thisevaluationislimitedforcastingmaterials,mouldmaterials,pouringtechnologiesandformingmethods.Henceinspecialcastingprocesssuchassqueezecasting,semisolidmetalcasting,lostfoamcastingandsoon,itisanewproblemtoevaluatethemoldfillingabilityofalloymelt.S.M.Xinginvestigatedthemoldfillingabilityofsemisolidalloyinthemoldwithmanyholesofdifferentdiametersunderapressure,andproposedatheoreticalformulaofthefillinglength11.Recently,JulioAguilar2designedameandersampleofAZ91alloywithalengthof2420mmtoevaluatethefillingabilityofalloysinthediecastingprocess.Becausethereisnotanavailableformulatopredictfillinglength,thisevaluationmethodisnotconvenientinengineering.T.J.Zhang3investigatedtherelationshipbetweenmagneticfluxdensityandinputvoltageaswellasdistance,andfoundthatthemoldfillinglengthofthemeltincreasesrapidlywiththeincreaseoftheaveragemagneticfluxdensity,andCorrespondingauthorHaiyingZhang,Emailyingyingzh126.comthattheuppersteelmoldissuperiortotheuppergypsummold.Moreover,inresearchingonhighpressurediecasting,S.Kulasegaram4,Z.Liu5,andClearyPaul6studiedthemoldfillingabilityofalloysbysimulations.E.N.Pan7studiedtheeffectsofpouringtemperature,coatingthicknessetc.onthemoldfilingabilityoflostfoamA356alloy,thecalculatedflowlengthbasedonamodifiedEPCFlowSolidificationequationshowedagoodagreementwiththeexperimentalresults.Theevaluationmethodofmoldfillingabilitymainlyincludesthreetypes,experimentalevaluation,theoreticalcalculation,andsimulation.Theexperimentalevaluationmethodisabasiconebecauseofitsintuitionaleffects,butitislimitedfortheexperimentalconditionsandisdifficultforpopularuse.Thesimulationmethodisnotconvenientinengineeringthoughitismoreexactthantheexperimentalmethodingivenconditions.However,thetheoreticalcalculationmethodcanbeusedconvenientlytopredictthefillingabilityofvariousalloysinvariousprocesseswithoutanyspecialequipment.Squeezecastingisanewformingtechnologythatisexpectedtobewidelyusedinthefuture.However,thefillingabilityofalloymeltintheprocessisnotclear.Studiesevaluatingthemoldfillingabilityofalloymeltinsqueezecastingarefew.Inthisarticle,experimentalevaluationandtheoreticalcalculationarecombined,andamathematicalmodelforcalculatingmoldfillingabilityisobtained.H.Y.Zhngetal.,Evaluationofthemoldfillingabilityofalloymeltinsqueezecasting612.ExperimentalevaluationofthemoldfillingabilityinsqueezecastingBasedonspirallinespecimeningravitycasting,aspecialspirallinespecimenmoldisdesignedshowninFig.l,whichisusedforexperimentalevaluationofthemoldfillingabilityofalloymeltinsqueezecasting.ThemoldismadeofH13steel.Itsconstructionmainlyincludesthreeparts,theuppermold,thelowermold,andthepunch.Fittedontheglidepieceoftheformingdevice,theuppermoldhasanArchimedesspirallinecavitywithatotallengthof1350mm.Thelowermoldisfittedontheworktableoftheformingdeviceitsmoldcavityisthecylindricalpressingchamber.Inthesidewallofthepressingchamber,thereisarunnerthatconnectswiththeArchimedesspirallinecavity.Thepunchconnectswithmoldfillingpistonoftheformingdevice.Theformingdeviceisthedoubleactionhydraulicpresseswhichhasthefunctionssuchasmoldlocking,moldfilling,ejecting,andmoldfillingvelocitytransiting.Theprocessparameterssuchasmoldfillingpressure,pressingvelocitymoldfillingvelocityetc.canbesetandtheexperimentaldatacanbesavedautomaticallybyacomputercontrollingsystem.TheformingtypeisinvertedextrusioninwhichthealloymeltinthecylindricalchamberispressedintotheArchimedesspirallinecavitythroughtherunnerinvertedtothepunchmovingdirection.3Fig.2.Archimedesspirallinespecimen.Aftermelting,alloymeltispouredintothecylindricalchamberofthelowermold,theuppermoldmovesdowntooclosetothelowermoldunderahydraulicpress.Then,thepunchdropsnearthealloysurfacewithafastvelocityandthenpressesthealloymeltwithaslowvelocityintotheArchimedesspirallinecavity.Keepingasettime,theuppermolddetacheswiththelowermold,andtheArchimedesspirallinespecimenisobtainedshowninFig.2.Finally,thelengthsoftheArchimedesspirallinesaremeasured.3.Mathematicalevaluationofthemoldfillingability3.1.DatapreparationThegeometricaldimensionsofthepressingchamber,therunnerandthespirallinecavityareshowninFig.3.Fig.1.Spirallinespecimenmold1thepunch2theuppermold3thelowermold4thepressingchamber.diFig.3.Schematicdiagramofthemold.1thepunch2thepressingchamber3therunner4thespirallineDuringthemoldfillingprocessinsqueezecasting,thereexiststwotypesofforcesoneisthedrivingpowersthatforcealloymelttoflowtotheArchimedes62J.Univ.Sci.Technol.Beijing,Voh13,No.1,Feb2006spirallinecavitytheotheristheresistantpowerswhichblockoffflowingandcausethepressurelosing.Whenthedrivingpowersarelessthantheresistantpowers,alloymeltwillstopfilling,andthefillinglengthreachesthemaximumlengthL,,simultaneously.Thedrivingpowersmainlyincludethemoldfillingpressureprovidedbythepunchandthegravityofalloymelt.Itisconsideredthatthegravityisfarlessthanmoldfillingpressurethatcanbeignored.Theresistantpowersmainlyincludethefrictionresistanceandthepartialresistance.HencetheconditionsforkeepingalloymeltfillingcanbedescribedbythefollowingequationP2F1wherePisthemoldfillingpressureandFisthetotalresistanceofthefrictionresistanceandthepartialresistance.Insqueezecasting,alloymeltcanberegardedasastable,incompressibleviscousfluid.Thatistosay,thealloydensitypisaconstantinthefillingprocess.Supposetheviscositycoefficientofalloymeltvkeepsaconstantinthewholemoldfillingprocess.ThepressureprovidedbythepunchinthepressingchamberisnamedasmoldfillingpressureP.ThemovingvelocityofthepunchisregardedastheaverageflowiligvelocityVofalloymeltinthepressingchambernamedasmoldfillingvelocity.Basedonthecontinuousequationoffluid,theaveragevelocityofalloymeltintherunnerisVoAV/AoandtheaveragevelocityofalloymeltinthespirallinecavityisVlAV/Al,whereA,Ao,Alarethecrosssectionareaofthepressingchamber,therunner,andthespirallinecavity,respectively.Supposethewholepressingchamberispouredwithalloymeltatthebeginning,themovingheightofthepunchthedescendheightofalloymeltinthepressingchamberisHandconsequentlythelengthfilledspirallineisL.Basedonthemassconservationlaw,therelationshipofHandLisHZA1LA3.2.Frictionresistance1Frictionresistancegeneratedfromthealloymeltflowinthepressingchamber.WhentheReynoldsnumberislessthan2300,theflowingstateofalloymeltisregardedasalaminarflow,andwhentheReynoldsnumberismorethan4000,theflowingstateisregardedasaturbulentflow.Otherwise,theflowingstateisatransitionalflowstateinterveninglaminarflowwithturbulentflow.TheReynoldsnumberofthealloymeltflowinthepressingchamberisReVDlv,whereDisthediameterofthepressingchamber.Ifitisalaminarflow,thefrictionresistancecoefficientist1641Re8.Basedonthemomentumtransmitequationoftheincompressibleviscousfluid,thefrictionresistanceinthepressingchamberisHpV202ReD02313.6HpV2313.6HpvVFl9.8t134Ifitisaturbulentflow,thecoefficientoffrictionS,sothefric0.1290.129resistanceisclRe0.2fVDOUJtionresistanceisIHpV20.632HpV20.632HpV2F19.8D2D.,,.123b2Frictionresistancegeneratedfromtheflowofalloymeltintherunner.Similarly,theReynoldsnumberofthealloymeltflowintherunnerisRe0VoDo/vAVDo/Aov,whileDoisshownintheFig.3.TheReynoldsnumbervarieswiththedifferenceoftheflowvelocityandtherunnerdimension.Sotheflowingstateisalaminarfloworaturbulentflowunderdifferentconditions.Ifitisalaminarflow,thecoefficientoffrictionresistanceist2641Re064Aov/AVDo,andhencethefrictionresistanceisHpVo2313.6HpAV2313.6HApvVF29.852Do2ReoDoAo2AoDo244Ifitisaturbulentflow,thecoefficientoffriction,thereforeI0.129resistanceisl2Reoo.12AVD\.thefrictionresistanceisF29.852,HpVo2___0.632HpAVDO2Reo0.12DoAo20.6328pA2V0.12AVDo3FrictionresistancegeneratedfromthealloymeltflowintheArchimedesspirallinecavity.H.Y.ZhangetaL,Evaluationofthemoldfillingabilityofalloymeltinsqueezecasting63AccordingtothedimensionoftheArchimedesspirallinecavity,themaximumofd/D1isonly0.1,dandD,areshowninFig.3,sothecoefficientofpartialresistanceisverylittle,thealloymeltflowintheArchimedesspirallinecavityisregardedastheflowinthedirectpipeandthepartialresistanceisignored.TheReynoldsnumberisdenotedasRelVldlvAVd/Alv.Thecoefficientoffrictionresistanceforalaminarflowist3/Rel64A1v/AVd,thereforethefrictionresistanceisLpV12d2Re,dA12Ald313.6LPAV313.6LApvVF39.85354Ifitisaturbulentflow,thecoefficientoffrictionresistanceist30129,andhencetheRelo.fAVd12frictionresistanceisF39.853ILpV120.632LpAV2d2Re10.2dl0.632LApV3.3.PartialresistanceWhenalloymeltflowsfromthepressingchambertotherunnerandthentothespirallinecavity,thepartialresistanceisgeneratedfromthemomentumlosingcausedbychangesinflowvelocitydirectionandinflowspace.Whentheflowingstateisaturbulentflow,theresistancelosingincreasesproportionallywiththesquareofaveragevelocityandisshowninthefollowingequation8whereKPartisthecoefficientofpartialresistance.Whenthemeltflowfromthepressingchambertotherunner,thecoefficientofpartialresistanceisasshowninthefollowingequationKk1A2A71wherekistheamendingcoefficientintherangeof0.51.758.HencethepartialresistanceisSimilarly,whenthemeltflowfromtherunnertothespirallinecavity,thepartialresistanceis93.4.TotalresistanceIftheflowingstatesofalloymeltareallthelaminarflowinthepressingchamber,therunner,andthespirallinecavity,thetotalresistanceis313.6HpvV313.6HApvV313.6LApvV4.9kFF.il02AoDoAidBringtheEq.2into10andsimplifyF313.6C1pvVL4.9kC2pA2V211whereC1,C2aretheconstantsrelatedwiththemolddimensionswhicharedeterminedasinthefollowingA1A1AADAoDo2Ald2C1Iftheflowingstatesofalloymeltaretheturbulentflowinthepressingchamber,therunnerandthespirallinecavity,thetotalresistanceisFF3,F2F3F4F50.632pV2LA1A1AA2IADRe.Ao2DoReo0.12A12dRe10.124.9kC2pA2V143.5.CriticalconditionsoffillingmoldandthefillinglengthofalloymeltBasedonEq.l,iftheflowingstatesofalloymeltarethelaminarflowinthepressingchamber,therunnerandthespirallinecavity,thenthecriticalfillingconditionsofalloymeltisasshowninthefollowingequationP2313.6ClpvVL4.9kC2pA2V215SothefillinglengthofalloymeltislimitedbyP4.9kC2pA2VLI3I3.6ClpvVThemaximumfillinglengthisdeterminedbyP4.9kC2pA2VLmax313.6ClpV
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