| The rapid development of high-speed railway meets people’s demands of long distance, long time and continuous high speed running, bringing great convenience to our lives. For the characteristics of low density, high specific strength and stiffness, good impact resistance and higher corrosion resistance, aluminum alloy has become one of the main materials used in subway and high-speed train body structures. Nowadays, aluminum alloy has been the main material for all domestic high speed multiple units except CRH1. The wide use of aluminum profiles have promoted the rapid development of high speed multiple unit trains. However, confined by itself structures, the defects during aluminum alloy stamping process consist of inadequate stretch, wrinkle, crack and springback etc, which increase the difficulties of controlling parts quality and designing die, severely restricting the application of aluminum alloy parts in practical production. Therefore, the stamping forming process of aluminum alloy has been studied with finite element numerical simulation method, The laws of the parameters affecting the forming quality were got, which has great significance to improve the forming quality of aluminum al oy parts and design the stamping die.Based on the practical production examples, this paper takes the front-end three dimensional skin of C EMU as the research object, the stamping process wa s analyzed using finite element simulation method and the results were used to guide the actual production process of aluminum skin pa nels.Due to the thick sheet and distortion of space structure, aluminum skin panels had serious springback which resulted in poor contour dimension accuracy. Springback was the prominent problem in the production of skin panels. In this paper, two solutions that optimizing the process parameters and compensating die surface were studied to control the springback.Firstly, the theory of finite element numerical simulation, the constitutive relation of material, element type and numerical simulation algorithm were introduced etc. In addition, the finite element model was established based on the characteristics of skin panel and related theory.Secondly, the influence laws of process parameters on forming quality and springback results were analyzed and the formability control measures were proposed. The effects of drawbead, blank- holder force, die clearance, friction coefficient, die radius on forming quality and springback results of skin panels were analyzed. The simulation results showed that drawbead has great effect on the formability of skin panel, which could increase the resistance of materials flow and ensure all the parts of sheet be fully stretched; increasing blank-holder force could reduce springback, but there were crack defects when the large parameter was set; under the condition of no fracture defects on skin panel, the smaller die clearance was, the smaller springback amount was, but the smaller die clearance would make the sheet thin seriously; increasing the friction coefficient was beneficial to decrease springback of skin panel but would reduce surface quality of the part. In addition, the smaller die radius was helpful to control the springback of the skin panels, but it would seriously shorten the die service life when the die radius was too small.At last, the die surface was modified with compensation method and applied to practical production. According to the springback results, die surface was compensated in the corresponding node position with compensation coefficient 1.The compensated die surface was used to design the forming die and applied to practice. The detecting results of aluminum skin panels showed that springback was been effectively controlled, which met the accuracy requirements. The conclusions of this thesis have important significance for enterprises to make stamping process of aluminum skin panels and design the forming die. |
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