Effect of Strain Rate and Friction on Formability According to Major Deformation Modes in Sheet Metal Forming

The effects of strain rate and friction on the formability of the steel sheet are studied according to the three major deformation modes that are widely used in the industry. Experiments for circular cup stretch, plane strain stretch, and circular cup drawing are carried out at two speeds of 3 SPM and 30 SPM for SGACUD 0.7 t and DP 590 1.0 t steel sheets. The corresponding finite element simulations are carried out. A constitutive equation, which is a function of strain and strain rate, is used to account for the effect of strain rate on flow stress in the finite element analysis. The formability is evaluated using the polar effective plastic strain (PEPS) forming limit diagram. An experimental equation that takes the sliding velocity into account is utilized in this study. In conclusion, the effects of strain rate and friction are clearly understood; finite element analysis by using the constitutive equation to consider strain rate, and also the friction coefficient model according to the sliding velocity, can be effectively used to predict the formability as forming speed changes for the three deformation modes.