Process Design for Multi-stage Elliptic Cup Drawing with the Large Aspect Ratio

Abstract

Finite element analysis of multi-stage deep drawing processes is carried out for the tool shape design of the elliptic cup drawing with the large aspect ratio. A multi-stage inverse finite element scheme is developed and applied to the complicated tool design problem of three dimensions for rapid estimation of the initial blank shape and the strain distribution. The inverse analysis calculates intermediate blank shapes and thickness strain distribution at each forming stage with the aid of a sliding constraint surface concept. A direct finite element method is then carried out to inspect the failure such as tearing and wrinkling during forming more accurately. The direct analysis incorporates with shell elements for an elasto-plastic finite element method with the explicit time integration scheme by using LS-DYNA3D. The deep drawing process of an elliptic cup with the large aspect ratio consists of four deep-drawing stages in which the cylindrical cross section at the first stage of drawing is changed to the elliptic shape gradually. Due to the difference of the drawing ratio between the major and minor axis, non-uniform metal flow is expected to cause wrinkling and severe extension. The irregular contact condition between the blank and the die also induces non-uniform metal flow to cause tearing and wrinkling. This paper reveals such unfavorable mechanism in elliptic cup drawing and suggests some guidelines on the design modification in the process and the tool shape.