An analysis of ironing limit in sheet metal forming

Ironing is drawing of hollow bodies through an ironing ring, with an inner tool (punch) pressing against the bottom of workpieces such as cups or cans to reduce the wall thickness of deep-drawn cups or cans. This process is currently applied widely in industries requiring more accurate wall thickness tolerance and better surface brightness of final products. In this paper, an analytical equation incorporating Hill's non-quadratic yield function is proposed to analyze stress states in the deformation zone of ironing process, and to compute limit ironing reduction ratios (LIRs) under various ironing conditions. The material considered is a tinplate for the production of steel D&I can. Forming variables include material anisotropy, friction coefficients and entrance angles of ironing die. The computed results are compared with those from both experiments and a finite element analysis.