Friction modelling in sheet metal forming simulations for aluminium body parts at Daimler AG

Tribology plays a key role in the production of high-quality car body parts. In forming simulations, often a constant value for the friction coefficient is used, which limits the overall simulation accuracy. In reality, friction depends on the pressure distribution, forming velocity, interface temperature, plastic strain, type/amount of lubrication and the surface topography of both the sheet and the tooling. The simulation accuracy, and therefore the prediction of the formability of complex geometries, can be improved significantly by taking all these parameters into account. This paper presents a selection of results for 2 aluminium cases: 1 scientific part conducted at the IFU Stuttgart and 1 complex body part from Daimler AG. Simulation results have been validated by experimental results to show the influence of friction on e.g. part quality, draw-in and spring-back. Results show that friction modelling becomes increasingly important in the stamping process of aluminium parts, and that the overall simulation accuracy increases when accounting for the actual tribological conditions in stamping. (paper)