| The rail train body uses curved parts made of aluminum alloy material to reduce the weight of body.In its manufacturing process,the stretch bending process is widely used due to its high forming precision and small springback.However,in the case of stretch bending manufacturing method,the aluminum alloy still have forming defects such cross-sectional distortion and springback.Therefore,the research on the stretch bending process of aluminum alloy is of great significance to the manufacture of rail trains in China.In this dissertation,aluminum alloy thin-walled profile used in rail trains with large size and L-section shape is taken as the research object,and the finite element simulation software ABAQUS is used to analysis the influence of process parameters on stretch bending process,improving forming accuracy by optimizing parameters and die.And the main work contents are summarized as follows:(1)According to the basic assumptions of mechanical analysis of stretch bending and the relationship between stress and strain increment,the calculation formulas of internal stress,strain and springback value during springback were derived,and the main influencing factors of springback after stretch bending were analyzed.According to the actual working condition of stretch bending process of the aluminum alloy profile,the finite element simulation model was established.The dynamic explicit algorithm and the static implicit algorithm of ABAQUS were used to simulate the stretch bending and springack process of the profile,respectively.The shape change of the aluminum alloy profile during the stretch bending and springback process were obtained.(2)Using the finite element model of aluminum alloy profile,the simulation with different uniform loads applied to the cover plate,the gaps between baffle and workpiece and the bending angles under per step were implemented.The influence of equivalent stress,equivalent strain and cross-sectional distortion of the aluminum alloy workpiece in stretch bending process and the equivalent stress,cross-sectional distortion and springback of the aluminum alloy workpiece in springback process were analyzed.The aluminum alloy stretch bending process of specific process parameters were simulated and tested.The reliability of finite element model was verified by comparing the simulation datas with the experimental datas.(3)According to the influence of process parameters on the forming results of aluminum alloy profiles,the orthogonal experimental method and range analysis were used to optimize the process parameters.According to the way of continuous shape modification of die in the actual working condition,combining with the idea of tangential method to accelerate the iterative root finding,the springback compensation of die surface was carried out,die’s curvatures were optimized.The results show that when the optimal process parameters are combined into the load 40kN,the gap 2mm and the angle 0.5°,the right curvature of die is 8.641×10-4 and the left curvature of die are 1.529×10-4 and 3.9×10-4,the maximum cross-sectional distortion of forming result is 2.72mm,the maximum contouring error between forming result and standard workpiece is 2mm.By comparing the original model and results after parameter optimization,it is found that the maximum cross-sectional distortion of workpiece is reduced by 57.2%and the maximum contour error is reduced by 60%.In this dissertation,the stretch bending process of aluminum alloy profile with large size,L-section shape and thin-wall used in rail trains is studied.The influence of process parameters on forming precision of stretch bending is analyed,and the process parameters and die are optimized.It provides technical support for the improvement of the forming precision of aluminum alloy bending parts. |
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