大尺寸铝合金件超塑成形尺寸精度控制数值模拟研究

Study of Size Precision Control of Super-plastic Forming on Large Size A-alloy Structure Based on Numerical Analysis

相对于冷冲压成形,利用超塑成形制造铝合金薄板零件具有许多优越性,实际加工中,由于模具材料和铝合金的热膨胀系数不同,成形后的零件在冷却到室温时与模具的收缩量亦不一样。对于火车车窗等大尺寸零件来说,为保证成形后产品尺寸在允许公差范围内,必须修正模具型面尺寸。传统的超塑成形模具设计仍基于冷拉成形模具的设计经验,采用"试错法"逐步修正,对于具有复杂曲面的零件,零件和模具的膨胀和收缩过程是非线性、多因素影响的,传统的方法颇为费时。采用非线性有限元软件MARC对火车车窗零件的超塑成形全过程进行了模拟分析,结果表明,利用有限元方法可以检验模具型面设计的正确性,从而实现对超塑成形精度的控制,可以有效提高模具设计效率,降低实际生产加工中的试模次数。

Compared to cold stamping of sheet, there is the superiority of making A-alloy sheet using super-plastic forming. In manufacturing, the shrinkage of the mold and the part is different when they are cooling down to room-temperature after forming, because of different coefficient of thermal expansion of the material between mold and A-alloy. For lager-size parts such as train windows, to ensure that the size of part is within the acceptance tolerance after forming, molding surface has to be correct. Trial-and-error method is used in the traditional mold design of super-plastic forming based on the experience of cold drawing. But for complex pans, the tradi- tional way is burdensome because shrinkage ＆ thermal expansion of mold and part are nonlinear and affected by many factors. In this paper, nonlinear finite-element analysis （FEA） software MSC. Marc is used to analyze the whole process of super-plastic forming for train window. The results show that the FEA simulation is a powerful tool to check the molding surface, and thus control the precision of super-plastic forming. It can improve efficiency of mold design, and reduce mold-test times efficiently in practical process.