Modeling Mixed Lubrication Friction for Sheet Metal Forming Applications

Abstract

Accurate modeling of friction is important in Finite element (FE) analyses of forming processes. Friction behavior depends on various parameters such as local contact load, surface topographies of sheet metal and tool, their material properties and the lubrication condition. In a typical deep drawing process, mixed lubrication condition is common, meaning that a lubricant can influence the coefficient of friction. Friction in the mixed lubrication regime is governed by the direct asperity contact as well as the hydrodynamic pressure developed by the lubricant. Local hydrodynamic pressure is also influenced by surface topography in addition to the lubricant amount and other process parameters. Direct numerical implementation of a measured surface topography in FE simulations is impractical due to the enormous computational effort. In this study, the overall frictional behavior in mixed lubrication regime is determined with the main objective to incorporate real measured surface topography in an efficient manner. An average Reynolds equation is solved on global FE domain of the forming simulation to determine lubricant pressure. A coupled friction model combining the effects of lubricant pressure and direct asperity contact is implemented in the forming simulations.