Research On Forming Process Of Front-end Skin Of EMU

With the rapid development of economy,the fast-paced life has led to the problems of urban traffic congestion,energy crisis and environmental pollution.Because of the advantages of energy conservation,environmental protection,high safety,good comfort,huge transport capacity,rail transit not only can relieve traffic pressure,but also can alleviate the energy crisis and environmental pollution.So the development of rail transit has received much attention.For the advantages of low density,high specific strength,good plastic,easy processing and good corrosion resistance,aluminum alloy can meet application requirements of components and reduce the weight of components,so aluminum alloy has been widely applied to the railway.However,the defects consist of insufficient stretching,wrinkle,crack,springback,severely restrict the application of aluminum alloy components.In recent years,more and more people have optimized the process parameters by the numerical simulation method to control forming defects of aluminum alloy components,which has promoted the application and development of aluminum alloy components.This paper took the front-end aluminum alloy skin of EMU as the research object,the forming process was analyzed by finite element simulation software –Auto Form.The problems such as insufficient tension and springback of the skin were studied,and the control methods were put forward.Finally,the experiment was done,and the skin with good quality and high precision was formed.The main research and conclusions are as follows:(1)For the characteristics of twisted structure,large size,and bad rigidity,the skin forming by 4mm thick aluminum alloy sheet has been easy to appear the insufficient stretching,which seriously affected the quality of the skin.By optimizing die parameters and process parameters,the flow resistance of the sheet was increased,thereby reducing the insufficient tension area of the skin,but the effect was not obvious.Finally,according to the structural characteristics of the skin,setting the variable strength drawbead has better controlled the defect insufficient stretching of skin.(2)Because of large springbck and poor contour accuracy,the skin could not meet the precision requirement.The effect of die parameters and process parameters on springback of the skin was studied by the orthogonal test method.The results showed that optimizing die parameters and process parameters could control springback of the skin,and the maximum springback value reduced from 6.48 mm to 2.5mm.Finally,the springback compensation analysis of the skin was done.The sprigback of skin was the smallest,when the springback compensation coefficient was 1.2,and the maximum springback value was 0.74 mm,which fully met the accuracy requirements.(3)Based on the data of die surface after springback compensation,the die was developed and manufactured,and then the forming experiment was done.The contour precision of test pieces was tested in the special detection tool.The surface of test pieces was well fitted with the surface of detection tool,and the maximum clearance was 0.85 mm.The test pieces with smooth surface,good quality,fully met the requirements of actual production,which it has verified the correctness of the simulation results and provided important guidance for the actual manufacturing.