Friction modelling in sheet metal forming simulations: application and validation on an U-Bend product

The accuracy of sheet metal forming simulations strongly depends on, amongst others, friction modelling. The industrial standard is to use the Coulomb friction model with a constant coefficient of friction. However, it is known that the true friction conditions are dependent on the tribology system, i.e. the applied sheet material, coating and tooling material, the lubrication and process conditions. In this paper, an approach is presented for friction modelling in sheet metal forming simulations. The approach is applied to the forming of U-bend test parts for varying tribology systems as commonly used in the automotive indus-try. The friction conditions per system are described using a physically-based friction model included in the Triboform Software. Friction in the U-bend simulations are described as a function of local contact pressure, relative sliding velocity and straining in the sheet material. The simulation results are validated using U-bend forming experiments. It is concluded that the numerical prediction of the punch force magnitude is highly sensitive to friction. In addition to an overall improvement of the prediction accuracy of stamping simulations by including friction modelling, this approach enables to model friction and the effect of varying tribology systems on the final stamped part quality.