JournalofUniversityofScienceandTechnologyBeijiregVolume13,Number1,February2006,Page60MaterialsEvaluationofthemold-fillingabilityofalloymeltinsqueezecastingHaiyingZhang),ShumingXing),QinghuaZhang,JianboandWenLid)1)SemisolidFormingResearchCenter,BeijingJiaotongUniversity,Beijing100044,China2)ShijiazhuangLocomotiveDepot,Shijiazhuang050000,China3)DepartmentofMaterialandEngineering,HebeiUniversityofScienceandTechnology,Shijiazhuang050018,China(Received2004-12-13)Abstract:Themold-fillingabilityofalloymeltinsqueezecastingprocesswasevaluatedbymeansofthemaximumlengthofAr-chimedesspiralline.Atheoreticalevaluatingmodeltopredictthemaximumfillinglengthwasbuiltbasedontheflowingtheoryoftheincompressibleviscousfluid.Itwasprovedbyexperimentsandcalculationsthatthemold-fillingpressureandvelocityareprominentinfluencingfactorsonthemold-fillingabilityofalloymelt.Themold-fillingabilityincreaseswiththeincreaseofthemold-fillingpressureandthedecreaseofthepropermold-fillingvelocity.Moreover,thepouringtemperaturerelativelyhaslessef-fectonthemold-fillingabilityundertheexperimentalconditions.Themaximumdeviationoftheoreticalcalculatingvalueswithex-perimentalresultsislessthan15%.Themodelcanquantitativelyestimatetheeffectofeveryfactoronthemold-fillingability.Keywords:squeezecasting；processparameters；mold-fillingability；theoreticalcalculation；experimentalevaluation1.IntroductionThemold-fillingabilityofalloymeltcandirectlyaffecttheinnerqualityandsurfaceroughnessoftheproducts,andisregardedasabasicprobleminthefieldofmaterialformingprocess,especiallyinthere-searchesofnewmaterialsandprocesses.Inthetradi-tionalcastingtechnology,theevaluationofthemold-fillingabilityiscarriedonbymeasuringthemaximumfillinglengthofaspiral-linespecimen；however,thisevaluationislimitedforcastingmaterials,mouldma-terials,pouringtechnologiesandformingmethods.Henceinspecialcastingprocesssuchassqueezecasting,semisolidmetalcasting,lostfoamcastingandsoon,itisanewproblemtoevaluatethemold-fillingabilityofalloymelt.S.M.Xinginvestigatedthemold-fillingabilityofsemisolidalloyinthemoldwithmanyholesofdifferentdiametersunderapressure,andproposedatheoreticalformulaofthefillinglength11.Recently,JulioAguilar2designedameandersampleofAZ91alloywithalengthof2420mmtoevaluatethefillingabilityofalloysinthedie-castingprocess.Becausethereisnotanavailableformulatopredictfillinglength,thisevaluationmethodisnotconvenientinengineering.T.J.Zhang3investigatedtherelationshipbetweenmagneticfluxdensityandinputvoltageaswellasdistance,andfoundthatthemold-fillinglengthofthemeltincreasesrapidlywiththeincreaseoftheaveragemagnetic-fluxdensity,andCorrespondingauthor:HaiyingZhang,E-mail:thattheuppersteelmoldissuperiortotheuppergyp-summold.Moreover,inresearchingonhighpressurediecasting,S.Kulasegaram4,Z.Liu5,andClearyPaul6studiedthemold-fillingabilityofalloysbysimulations.E.N.Pan7studiedtheeffectsofpour-ingtemperature,coatingthicknessetc.onthemold-filingabilityoflostfoamA356alloy,thecalculatedflowlengthbasedonamodifiedEPCFlow-Solidificationequationshowedagoodagreementwiththeexperimentalresults.Theevaluationmethodofmold-fillingabilitymainlyincludesthreetypes,ex-perimentalevaluation,theoreticalcalculation,andsimulation.Theexperimentalevaluationmethodisabasiconebecauseofitsintuitionaleffects,butitislimitedfortheexperimentalconditionsandisdifficultforpopularuse.Thesimulationmethodisnotcon-venientinengineeringthoughitismoreexactthantheexperimentalmethodingivenconditions.However,thetheoreticalcalculationmethodcanbeusedcon-venientlytopredictthefillingabilityofvariousalloysinvariousprocesseswithoutanyspecialequipment.Squeezecastingisanewformingtechnologythatisexpectedtobewidelyusedinthefuture.However,thefillingabilityofalloymeltintheprocessisnotclear.Studiesevaluatingthemold-fillingabilityofalloymeltinsqueezecastingarefew.Inthisarticle,ex-perimentalevaluationandtheoreticalcalculationarecombined,andamathematicalmodelforcalculatingmold-fillingabilityisobtained.H.Y.Zhngetal.,Evaluationofthemold-fillingabilityofalloymeltinsqueezecasting612.Experimentalevaluationofthemold-fillingabilityinsqueezecastingBasedonspiral-linespecimeningravitycasting,aspecialspiral-line-specimenmoldisdesigned(showninFig.l),whichisusedforexperimentalevaluationofthemold-fillingabilityofalloymeltinsqueezecasting.ThemoldismadeofH13steel.Itsconstruc-tionmainlyincludesthreeparts,theuppermold,thelowermold,andthepunch.Fittedontheglide-pieceoftheformingdevice,theuppermoldhasanAr-chimedesspiral-linecavitywithatotallengthof1350mm.Thelowermoldisfittedontheworktableoftheformingdevice；itsmold-cavityisthecylindricalpressingchamber.Inthesidewallofthepressingchamber,thereisarunnerthatconnectswiththeAr-chimedesspiral-linecavity.Thepunchconnectswithmold-fillingpistonoftheformingdevice.Theformingdeviceisthedouble-actionhydraulicpresseswhichhasthefunctionssuchasmold-locking,mold-filling,ejecting,andmold-fillingvelocitytransiting.Theprocessparameterssuchasmold-fillingpressure,pressingvelocity(mold-fillingvelocity)etc.canbesetandtheexperimentaldatacanbesavedautomaticallybyacomputercontrollingsystem.Theformingtypeisinverted-extrusioninwhichthealloymeltinthecyl-indricalchamberispressedintotheArchimedesspi-ral-linecavitythroughtherunnerinvertedtothepunchmovingdirection.3Fig.2.Archimedesspiral-linespecimen.Aftermelting,alloymeltispouredintothecylin-dricalchamberofthelowermold,theuppermoldmovesdowntooclosetothelowermoldunderahy-draulicpress.Then,thepunchdropsnearthealloysurfacewithafastvelocityandthenpressesthealloymeltwithaslowvelocityintotheArchimedesspiral-linecavity.Keepingasettime,theuppermoldde-tacheswiththelowermold,andtheArchimedesspi-ral-linespecimenisobtained(showninFig.2).Fi-nally,thelengthsoftheArchimedesspirallinesaremeasured.3.Mathematicalevaluationofthemold-fillingability3.1.DatapreparationThegeometricaldimensionsofthepressingcham-ber,therunnerandthespiral-linecavityareshowninFig.3.Fig.1.Spiral-line-specimenmold:1-thepunch:2-theuppermold:3-thelowermold:4-thepressingchamber.diFig.3.Schematicdiagramofthemold.1-thepunch:2-thepressingchamber:3-therunner；4-thespirallineDuringthemold-fillingprocessinsqueezecasting,thereexiststwotypesofforces:oneisthedrivingpowersthatforcealloymelttoflowtotheArchimedes62J.Univ.Sci.Technol.Beijing,Voh13,No.1,Feb2006spiral-linecavity；theotheristheresistantpowerswhichblockoffflowingandcausethepressurelosing.Whenthedrivingpowersarelessthantheresistantpowers,alloymeltwillstopfilling,andthefillinglengthreachesthemaximumlengthL,simultane-ously.Thedrivingpowersmainlyincludethemold-fillingpressureprovidedbythepunchandthegravityofalloymelt.Itisconsideredthatthegravityisfarlessthanmold-fillingpressurethatcanbeignored.Theresistantpowersmainlyincludethefrictionre-sistanceandthepartialresistance.Hencetheconditionsforkeepingalloymeltfillingcanbedescribedbythefollowingequation:P2F(1)wherePisthemold-fillingpressureandFisthetotalresistanceofthefrictionresistanceandthepartialresistance.Insqueezecasting,alloymeltcanberegardedasastable,incompressibleviscousfluid.Thatistosay,thealloydensitypisaconstantinthefillingprocess.Supposetheviscositycoefficientofalloymeltvkeepsaconstantinthewholemold-fillingprocess.Thepressureprovidedbythepunchinthepressingchamberisnamedasmold-fillingpressureP.Themovingvelocityofthepunchisregardedastheaver-ageflowiligvelocityVofalloymeltinthepressingchamber(namedasmold-fillingvelocity).Basedonthecontinuousequationoffluid,theaveragevelocityofalloymeltintherunnerisVo=AV/Aoandtheav-eragevelocityofalloymeltinthespiral-linecavityisVl=AV/Al,whereA,Ao,Alarethecross-sectionareaofthepressingchamber,therunner,andthespiral-linecavity,respectively.Supposethewholepressingchamberispouredwithalloymeltatthebeginning,themovingheightofthepunch(thedescendheightofalloymeltinthepressingchamber)isHandconsequentlythelengthfilledspirallineisL.Basedonthemassconservationlaw,therelationshipofHandLisHZ-A1LA3.2.Frictionresistance(1)Frictionresistancegeneratedfromthealloymeltflowinthepressingchamber.WhentheReynoldsnumberislessthan2300,theflowingstateofalloymeltisregardedasalaminarflow,andwhentheReynoldsnumberismorethan4000,theflowingstateisregardedasaturbulentflow.Otherwise,theflowingstateisatransitionalflowstateinterveninglaminarflowwithturbulentflow.TheReynoldsnumberofthealloymeltflowinthepress-ingchamberisRe=VDlv,whereDisthediameterofthepressingchamber.Ifitisalaminarflow,thefrictionresistancecoefficientist1=641Re8.Basedonthemomentumtransmitequationofthein-compressibleviscousfluid,thefrictionresistanceinthepressingchamberisHpV202ReD02313.6HpV2-313.6HpvVFl=9.8t1-=-(34Ifitisaturbulentflow,thecoefficientoffrictionS,sothefric-0.129-0.129resistanceiscl=Re0.2-fVD)O(UJtionresistanceisIHpV20.632HpV2-0.632HpV2F1=9.8&-=-D2D.(,),.12(3b)(2)Frictionresistancegeneratedfromtheflowofalloymeltintherunner.Similarly,theReynoldsnumberofthealloymeltflowintherunnerisRe0=VoDo/v=AVDo/Aov,whileDoisshownintheFig.3.TheReynoldsnumbervarieswiththedifferenceoftheflowvelocityandtherunnerdimension.Sotheflowingstateisalaminarfloworaturbulentflowunderdifferentconditions.Ifitisalaminarflow,thecoefficientoffrictionresis-tanceist2=641Re0=64Aov/AVDo,andhencethefrictionresistanceisHpVo2-313.6Hp(AV)2-313.6HApvVF2=9.852-Do2ReoDoAo2AoDo2(44Ifitisaturbulentflow,thecoefficientoffriction,therefore-I0.129resistanceisl2=-Reoo.12AVD.thefrictionresistanceis-F2=9.852,-HpVo2=_0.632Hp(AV)DO2Reo0.12DoAo20.6328pA2V0.12AVDo(3)FrictionresistancegeneratedfromthealloymeltflowintheArchimedesspiral-linecavity.H.Y.ZhangetaL,Evaluationofthemold-fillingabilityofalloymeltinsqueezecasting63AccordingtothedimensionoftheArchimedesspi-ral-linecavity,themaximumofd/D1isonly0.1,dandD,areshowninFig.3,sothecoefficientofpartialresistanceisverylittle,thealloymeltflowintheAr-chimedesspiral-linecavityisregardedastheflowinthedirectpipeandthepartialresistanceisignored.TheReynoldsnumberisdenotedasRel=Vldlv=AVd/Alv.Thecoefficientoffrictionresistanceforalaminarflowist3=/Rel=64A1v/AVd,thereforethefrictionresistanceisLpV12d2Re,dA12Ald313.6LP(AV)-313.6LApvVF3=9.853-=-(54Ifitisaturbulentflow,thecoefficientoffriction-resistanceist3=-0129,andhencetheRelo.fAVd)12frictionresistanceis-F3=9.853I-LpV12=-0.632Lp(AV)2d2Re10.2dl0.632LApV3.3.PartialresistanceWhenalloymeltflowsfromthepressingchambertotherunnerandthentothespiral-linecavity,thepartialresistanceisgeneratedfromthemomentumlosingcausedbychangesinflowvelocitydirectionandinflowspace.Whentheflowingstateisaturbu-lentflow,theresistancelosingincreasesproportion-allywiththesquareofaveragevelocityandisshowninthefollowingequation8:whereKPartisthecoefficientofpartialresistance.Whenthemeltflowfromthepressingchambertotherunner,thecoefficientofpartialresistanceisasshowninthefollowing