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

A physical based friction model is presented to describe friction in full-scale forming simulations. The advanced friction model accounts for the change in surface topography and the evolution of friction in the boundary lubrication regime. The implementation of the friction model in FE software codes is discussed. Results show that friction coefficients vary in space and time, and depend on local process conditions such as the nominal contact pressure and the plastic strain in the sheet material. The advanced friction model is validated by two small-scale forming processes, proving the enhanced predictive capabilities of FE simulations. The moderate increase in FE computation time, compared to using a Coulomb based friction model, demonstrates the efficiency of the proposed friction model.