In this work a finite element simulation is used for the hemispherical punch stretching test. The effect of strain hardening exponent, the original thickness of the sheet metal and the coefficient of friction between the punch and the blank on the formability of sheet metal are investigated. The results of this simulation are used to derive an empirical formula combining the simultaneous effect of the three parameters on the final thickness of the sheet. This formula is used to derive a numerical criterion which can be used in a separate finite element program for predicting the initiation and the position of localized necking. The effect of the three parameters on the level of the forming limit diagram is also investigated. An emphasis is put on the relation between the coefficient of friction and the strain path.

Keywords : Localized necking, empirical formula, strain path