薄板冲压成形时表面质量状态的分析

以薄板冲压为例，在冲压成形缩条情况下，根据希尔理论利用有限元法分析成形件的表面状态，得出了计算有的条件和方法，为薄板在冲压成形时产生表面不规则变形的分析提供了理论依据。

ANALYSIS OF SURFACE DEFLECTION OF SHEET METALS DURING PRESS FORMING

Hill's criterion of uniqueness used for analyzing the deflection of sheet metals during press forming can not be applied to most cases since it could contact the die. Therefore, the following method is proposed to characterize the deflection. Deflections of sheet metal are caused by shear stress in the out of plane direction, such that the development of surface deflections can be easily detected when shear stress is observed using deformation analysis during press forming. In this paper, the relationship between the results of deformation and bifurcation analyses is represented by numerical examples using Mindlin's shell theory. It is revealed that the proposed method can determine the approximate bifurcation limit and the mode of the deflection of sheet metal, where initial imperfection of the configuration with a reasonable value should be assigned to sheet metal. Criteria to evaluate the deflection caused by a lack of bifurcation must also be established.