Deformation Behaviour in Boss Forming by Sheet Extrusion

Sheet metal parts with bosses or small pins can be manufactured by sheet extrusion or half blanking with a negative clearance. The purpose of this study is to understand the forming behavior of the boss with a small punch/die diameter ratio. Two kinds of pure aluminum sheets of 2 mm thick were applied and a boss of 1 mm in diameter was formed on the sheet. In the case without a blank holder, increase in a punch/die diameter ratio caused local thickening around the boss and the boss height became lower than that expected. By applying appropriate blank holding force, the boss height was rather improved, nevertheless it didn’t reach the ideally calculated value. The error of the boss height became larger when increasing in a punch/die diameter ratio and when using the annealed material.