Process Analysis And Experimental Study For Granule Medium Bulging Of AA5083 Tube

Internal high pressure forming technology has drawn greater attention and became a main manner to manufacture hollow structure parts as the increasing development of automobile and aviation industry.A series of excellent properties,such as low density and high strength,make light alloy be used widely in automobile and aviation industry bringing a improvement of fuel economy and less environmental pollution.In this paper,AA5083 sheet is chosen as the study material which is unable to be strengthened by heat treatment.The constitutive relation related to temperature and strain rate is built by hot unidirectional tensile test.The theoretical forming limit diagram(FLD)at different temperature is created by M-K theory.The fracture appearance of sheet is also observed to analysis the mechanism of fracture failure.The hot unidirectional tensile test shows that the best processing temperature of this material is 190?.At 190?,the influence of weld zone on the property of whole tube is studied by hot ring tensile test,hardness testing and metallographic test.Ultimately,according to the characteristics of hot granule medium bulging technology,outer friction coefficient testing between granule medium and sheet,radial pressure coefficient testing of granule medium and pressure transfer property testing of granule medium are designed and conducted at high temperature.Basing on those tests,the pressure-transfer model for granule medium is created at different temperatures,punch forces and boundary conditions.Taking free bulging tube and hexagon cross-section tube as examples,the stress and strain characteristic at the pole of free bulging region,any point in free bulging region,corner region and straight wall region of hexagon cross-section are analyzed.The plastic mechanical models are also respectively created for those points and regions above.By solving the models,the analytic calculation method for stress,strain and thickness in every region—free bulging region,corner region and straight wall region—of tube can be obtained in any stroke of the forming process,and the contraction amount of tube end varying with the expanding of bulging diameter also can be obtained.NMG simulation model is created at the best forming temperature to analysis the effect of load path including punch force and end feed on process results such as tube thickness,bulging profile,tube end constriction and the principal strain path of feature point.Process test is conducted to verify the simulation model.The thickness distribution and bulging region profile of tubes obtained in different load paths is very close to the forecasted result of simulation with a maximum error of 5%.That is to say the NMG simulation model is accurate.The comparison between calculating and testing results shows that the thickness theoretical analysis for hexagon cross-section tube is accurate in straight wall region but exists little errors in corner region.The main reason is that the uniform deformation assumption can not describe the characteristic of corner filling process accurately.This problem need to be studied further.The forming quality of tube is effected by the matching relationship of tube feed and punch force.The analysis for appearance of fracture in forming process shows that fracture occurs because deformation reaches the forming limit when the tube end is free,while excessive wrinkle also can bring fracture when the tube end is forced by the punch force.