Modeling boundary friction of coated sheets in sheet metal forming

Abstract In forming processes, friction is a local phenomenon influenced by the contact conditions at the tool-sheet metal interface. A multi-scale friction model applicable for coated sheets is developed for the boundary lubrication regime which accounts for the physical behavior of coating and measured surface topographies of sheet and tools. The contact patches and therefore the real area of contact is determined at the tool-sheet metal interface for different contact loading conditions. A single asperity micro-scale ploughing model is adopted at each contact patch to determine the friction force from which the overall coefficient of friction is determined. The friction model is validated using different sets of lab-scale friction tests and cup drawing experiments on zinc coated (GI) steel sheets.