The Computer Simulation of Tribological Influence on Strain Path and Forming Limit in Punch Stretching of Sheet Metal

The purpose of this paper is to describe the principles and results of some numerical simulations of strain path and forming limit analysis in punch stretching operations which include the tribological influence by using a realistic friction model. Three tribological variables (i.e. the mean lubricant film thickness, tooling roughness, and workpiece roughness) are required for the simulation. The calculation of these variables using lubrication theory and related semi-empirical equations are described. The active lubrication regime and suitable friction model can be determined from the current local values of these tribological variables. Friction stress can then be computed from these variables combined with more traditional parameters such as pressure and sliding speed. The limiting dome height and variation of strain path are then predicted by using the coupled FEM and lubrication/friction model. The comparison between the calculated and measured results shows that the present scheme is efficient in computation and will provide a useful tool for industrial applications.