Improvement of Cylindrical Deep Drawability in Hot Stamping

Deep drawability of steel sheets in hot stamping was investigated. In the case of deep drawing with a conventional die, the forming limit was significantly lower because the temperature of the sheet metal at the flange part decreased during the forming and the flow resistance increased. Therefore, the blank holding method to avoid temperature decrease at flange part of sheet metal was studied. In this study, application of gap supports and forming without blank holder were investigated. In the former method, the gap supports made clearance at the flange part. In the latter method, the blank holder was located at the lower dead point from the beginning of forming and the flange part of the blank was free during forming. The forming limit in both cases was improved as compared with that in the conventional blank holding method. For the application of gap supports, the limiting drawing ratio was also evaluated. In this experiment, the maximum value of limiting drawing ratio was 1.71.