Design Method of Die Geometry and Pass Schedule by Void Index in Multi-Pass Drawing

The concept for die-geometry design is shown to suppress void growth in multi-pass drawing. First, the void index to evaluate the void fraction in multi-pass drawing was newly proposed based on the well-known equation to predict the fracture limit in cold working. Using finite element analysis, the influence of die geometries on the void index was investigated and it was clarified that the extra-low-angle die is effective whatever reduction in area is adopted. Moreover, dies were designed to have the effect of suppressing void with the minimum die length. A series of experiments was then carried out that successfully verified the numerical results.