Multi-scale friction modeling for sheet metal forming: The mixed lubrication regime

A mixed lubrication friction model is presented to accurately account for friction in sheet metal forming FE simulations. The advanced friction model comprises a coupling between a hydrodynamic friction model and a boundary lubrication friction model, based on the lubricant film thickness. Mixed lubrication interface elements are introduced to solve the governing differential equations. The interface elements have been implemented in FE forming software. Two deep-drawing applications are discussed to demonstrate the performance of the friction model. Results show friction coefficients that vary in space and time, and depend on external process settings like the amount and type of lubricant. A comparison with experimentally obtained punch-force displacement diagrams is made to prove the enhanced predictive capabilities of FE forming simulations.