Deformation behavior in boss forming with small punch/die diameter ratio

Sheet metal parts with bosses or small pins can be manufactured by half blanking. This paper focuses on deformation in small boss forming on a sheet metal by half blanking at small punch/die diameter ratios of 1–1.8. In the case that the boss diameter is less than the sheet thickness, the boss height became lower than the depth of punch penetration at a punch/die diameter ratio of 1. The mechanism of decrease in the boss height and countermeasures to the problem were investigated through the FE analysis. The results showed that the boss height was improved up to the same level as the depth of punch penetration by both increasing punch/die diameter ratio and applying an appropriate blank holding force. The boss height was also affected by the material ductility and a higher boss was formed for the not-annealed sheet under the same forming conditions. The punch/die diameter ratio did not make a big difference in the mean punch pressure although a larger force was needed by using a larger diameter punch.