Research On Upsetting-Rolling-Hydroforming Process Of Mulity-Way Tube And Microstructure Evolution

Lightweight is one of important means to save energy and reduce environment pollution in the fields of automotive and aerospace industires.Therefore,advanced manufacturing technology is taken more seriously to achieve the lightweight.Complex structural multi-way tube parts are of great significance in structural lightweight and are indispensable for energy conservation and emission reduction.At present,the multi-way tube parts are formed by casting technology.However,the mechanical properties and quality of tube parts are poor,which limits its application.When the multi-way tube parts are formed by stamping-welding technology,the production cost is hight with many forming processes.In addition,there are some defects such as welding slag and hole in the welding areas,which results in the the corrosion and leakage in the weld seam.Tube hydroforming is a widespread metal forming processes to manufacture the hollow structure parts.However,tube hydroforming to forming the multi-way tube is limited because the structure of tube parts is complex resulting in forming difficultly.A new forming method which is the combined upsetting-rolling-hydroforming loading is proposed in this work.An experimental setup was designed and built to achieve the combined upsetting-rolling-hydroforming loading during T-shaped tube and parallel double branched tube upsetting-rolling-hydroforming process.The deformation behavior was investigated using theoretical analysis,numerical simultioan and experiment under the T-shaped tube upsetting-hydroforming,rolling-hydroforming and upsetting-rolling-hydroforming.The microstructure evolution was obtained using Electron Backscattered Diffraction(EBSD)and Transmission Electron Microscope(TEM),and the hardness test was investigated.In addition,parallel double branched tube upsetting-rolling-hydroforming was investigated to reveal the deformation behavior of parallel double branched tube under the combined upsetting-rolling-hydroforming loading.The main content of this work was shown as following.(1)Compared to traditional tube blank,the local strength of tube could be improved to delay the thinning of wall thickness and prevent the occurrence of bursting,and the weight of tube part could be reduced using the variable thickness tube blank.The tube formability could be improved when the upsetting-rolling-hydroforming was used to manufacture mulity-way tube.The results show that the branch height of T-shaped tube could be increased by 15%and the thinning ratio could be decreased by 3%during T-shaped tube upsetting-rolling-hydroforming.The branch height of parallel double branched tube could be increased by 11%and the thinning ratio could be decreased by 2%during parallel double branched tube upsetting-rolling-hydroforming.(2)The response surface methodology was used to establish the mathematical models among loading parameters of upsetting-rolling-hydroforming and branch height,the maximum thinning ratio and return angel.The effect of internal pressure,axial feeding,rolling time and rolling angel on branch height,the maximum thinning ratio and return angel was investigated during the T-shaped tube upsetting-rolling-hydroforming.The mathematical models among dimension of variable thickness tube blank and branch height and the maximum thinning ratio was established and the effect of variable thickness tube blank on the tube formablity was investigated during the T-shaped tube upsetting hydroforming.The mathematical models among loading parameters of rolling hydroforming and branch height,the maximum thinning ratio and return angel was established during T-shaped tube rolling hydroforming.The effect of loading parameter of rolling hydroforming on the tube formablity was investigated.The mathematical models were verified to predict the relationship of objectives and design variables.(3)The deformation behavior of mulity-way tube was revealed during the upsetting-rolling-hydroforming.The numerical simulation was used to analyze the mulity-tube upsetting-rolling-hydroforming and obtain the stress and strain state,metal flowing and the variation of wall thickness for some specific locations.The reason for the improvement of formablity of tube parts were investaged under the combined upsetting-rolling-hydroforming loading.The result of numerical simulation was in good agreement with the experimental results.(4)The microstructure evolution during T-shaped tube upsetting-rolling-hydroforming was obtained to reaveal the microscopic mechanism of deformation.The result showed that the processes of grain refinement might result from the deformation-induced grain refinement.The coarse grains were refined and the fraction of low angel grain boundaries increased during the deformation.The dilocations piled up and arrays of dislocations that were tangled.The refined grains were generated with the increase of strain.(5)The hardness of tube was obtained during T-shaped tube upsetting-rolling-hydroforming.The brinell hardness on the top of branch was higher than that on the center of branch.The brinell hardness could be increased result from the work hardening and fine grain strengthening with the the increase of strain.The brinell hardness could be increased under the rolling loading.