Refined Friction Modeling for Simple Upsetting

A refined model for friction in lubricated simple upsetting processes which takes account of the different lubrication regimes which may occur at the workpiece/tooling interface is developed. The refined friction model considers not only the full film situation but also the mixed and boundary lubrication condition. The load carrying capacity of the lubricant in the mixed lubrication regime is evaluated by using the average flow model to treat the influence of surface roughness on lubricant flow. The mechanics of asperity contact is governed by a semi-empirical boundary model in which the plastic deformation of the workpiece is considered. The lubricant film thickness is then determined by using a shooting method to ensure that the interface pressure is partially supported by the asperity contact and partially supported by the lubricant film. The refined friction model is then combined with a rigid-plasticity finite element code to analyze the simple upsetting processes. Numerical results using the coupled codes such as the distribution of the friction stress and normal pressure, the geometry and surface topography of the deformed workpiece are compared with previous numerical and experimental investigation under different lubrication conditions. The simulation results are in good agreement with the experimental data.