Determination of flow factors for the semi-analytical prediction of friction coefficients

Abstract

Friction conditions in sheet metal forming are mainly influenced by the surface topography of blank and tool, its mechanical properties and the properties of the intermediate medium, the lubricant. Aiming towards an analytical determination of friction coefficients for sheet metal forming, such factors should be included in suitable models and be weighted accordingly. In addition to the elastic–plastic deformation of the surface topography of the blank as a result of increasing nominal surface pressure, the influence of the lubricant can be considered using the Reynolds equation. In the present investigation, the flow factors of the elasto-hydrodynamic lubrication and mixed friction, which take into account the effects of surface topography and orientation, were calculated as a function of nominal surface pressure and nominal contact area in terms of plastically deformed surfaces. Asperity deformation is evaluated with a numerical contact model using the flow curve of base metal to calculate local contact forces.