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20084TG376200804DissertationforthedegreeofMasterTHERESEARCHONFORMINGPROCESSESOFTITANIUMRINGPIPEWITHHIGHERSTRENGTHANDUNIFORMWALLTHICHNESSCandidate:ZhaoBinSupervisor:Prof.ZengWeidongProf.ZhaoYongqingAcademicDegreeAppliedfor:MasterofEngineeringSpecialty:MaterialsProcessingEngineeringDateofOralDefence:Apirl,2008UnitofDegreeConferred:NorthwesternPolytechnicalUniversityDateofDegreeConferred:2008-I-≥1000MPa360°360°≤180°Ti-26Ti-26Arrhenius)/137.103exp()]0146.0[sinh(e1737.57.79RT−⋅=σε&SuperformTi-26-II-36mm2mm124mm1.3040º8001.251.92mm/s108mmTi-26ABSTRACT-III-ABSTRACTTheringpipeoftitaniumalloywasusedinspecialworkpieceofspaceflight,aircraft,weapons,fossiloilandchemicalindustryetc,anditsringgascylinderhasaperspectiveuseinaerospaceindustryforitsexcellentpropertiesoflightweight,non-magnetism,corrosionresistance,crampedstructureandsoon.Formeetingtheprogressofspacecraftindustry,thereismorestrictdemandforringpipeoftitaniumalloy,forexample,thestrengthishigherthan1000MPa,theangularityisnear360°andauniformwallthicknessandhomogeneousstrengthweredemanded.Therefore,theformedstudyofthetitaniumringpipewithhigherstrengthanduniformwallthicknessisverynecessaryformeetthedemandofthemodernspacecraftindustry.Theuniformwallthicknesscannotbeobtainedusingordinaryformedcraftbecauseoftheconstraintconditionofbendingradiusandangularityfortitaniumringpiper.Byexperience,heatingpushingexpandingdiameterbendingdeformation(HEBD)wasthoughtafeasiblemethodforthetitaniumringpiperwithauniformwallthicknessandnear360°angularity.HEBDhasbeenwildlyusedintheproductionofsteelbentpiperwithaangularityoflowto180°,buttotheringpiperofhighstrengthtitaniumalloywithneat360°angularity,thereisnonanyreport.Becauseofthedifferencesbetweensteelandtitaniumalloy,therewillbesomedifficultyinformedprocess.Forexample,higherspecificstrengthoftitaniumalloycomparisontosteelwillleadtomoredifficultformation,andtheincreaseofbendingangle(from180°insteelto360°intitaniumalloy)willleadtogofferandbaduniformwallthicknessforworkpiece.Inthispaper,thefiniteelementanalysisandphysicsimulationaimingatHEBDofTi-26alloyringpiperwerefirstlycarriedout,afterthattheoptimizingworkingparameterswereusedtothepracticalformedcraft.TheresultindicatedthismethodisfeasibleforTi-26alloyringpiperwithuniformwallthicknessandbigbendingangle.Themainconclusioninthispaperisfollowing.AccordingtotheprocessingcharacteristicofHEBD,AkindofnewdesignedideaaboutHEBDwasputforward.TheArchimedeanspiralwithvariablecurvaturewasusedformakingdiebysimpleparameter.ThematerialconstantsofTi-26alloyshavebeenobtainedbyregressionanalysisrecordsafterthermocompressionexperiment.Theinfluenceofdeformationtemperature,strainrateandflowstressinhotdeformationprocessaredisclosed.AconstitutiverelationshipofABSTRACT-IV-thisalloyisformulatedatthree-phaseregionandaboveitBasedontheplatformoffiniteelementsoftwareSUPERFORM,Wehavegainthelawwhichringpipethicknessinfluencedbythedie’sparametersofexpandingdiameterratioandthebendingangle:Whentheexpandingdiameterratioislittle,thethicknessofringpipeinnerarcbecamethickanditofouter-arcbecamethin;withtheratioincrement,theuniformwallthicknessofringpipecanbeobtained.Increasetheratio,thethicknessofringpipeinnerarcbecamethinanditofouter-arcisinalterability.Whenthebendingangleissmall,pipethicknessisnon-homogeneous.Withtheangleincrease,thethicknessofringpipeinnerarcbecamethick.TheinfluenceofmainprocessparametersonringpipequalityhavebeendisclosedinHEBDprocess,includingdeformationtemperaturefield,pushingspeedandworkconditionofinductioncoil.Theresultsshowthat:(1)thethicknessanddiametersoftitaniumalloyringpipeinnerarcincreasesandbendingradiusdecreasewiththeincreasingoftheheating-temperature,butcrispappearwiththeexcessivelyhightemperature;(2)thelowpushingspeedmakethethicknesshomogeneousanddecreasingellipticityratioofcross-section.Thescalesofpitchouter-arcwerereducedandthethicknessofcross-sectionincreasewiththedecreasingofpushingspeed;(3)theformingprocessbecomeseasywiththedegreeofdiametersofinductioncoilandnumberofturnsincreases,buttheefficiencyofinductionheatingbecomeslow.Thehighstrengthtitaniumalloyringpipewiththesize:cross-sectiondiameter36mm,thickness2mm,intermediatediameter124mmhavebeenresearched.It’sbetterprocessing:thedieexpandingdiameterratiois1.30,thediebendingangleis40º,theprocessingtemperatureis800,thepushingspeedisbetween1.251.92mm/s,theinductioncoildiameteris108mmwithtwo-turnwinding.KeywordsTi-26alloy;ringpiper;heatingpushingexpandingdiameterbendingdeformation(HEBD);finiteelementsimulation-V-123Ti-26-VI-............................................................................................................................IABSTRACT................................................................................................................III...............................................................................................V..............................................................................................................11.1......................................................................