Abstract
Strengthening of pressed components has recently been reqired to husband natural resources and save energy. Unfortunately, any strengthening of sheet metals generally causes a decrease in their ductility and formability. Therefore, it is very important to find out the optimum forming conditions. In the present study, the optimum conditions for increasing the critical forming depth in pure stretch forming are clarified, using several punches with an ellipsoidal profile, seven kinds of sheet metals and four kinds of lubricants. The optimum punch profile and the optimum frictional coefficient for increasing the critical forming depth were found by both numerical analysis and experiments. In addition, it was confirmed that the critical forming depth could be increased by applying a low friction lubricant (PTFE and Bright stock) to the central region of the punch and a high friction lubricant (Rosin) at the outer region.
