Determination of pressure-dependent friction coefficient from draw-bend test and its application to cup drawing

Friction under lubricated conditions is known to depend on pressure, and experimental determination of this dependence has typically quantified pressure as a uniform value over the contact area. However, non-uniform pressure distributions at the contact interfaces of draw-bend tests have been reported from various experiments and simulations. A previous study by the authors had evaluated the conventional methodology, which assumes uniform pressure distribution to estimate friction coefficients from draw-bend friction tests, and has concluded that the conventional methodology is only valid for measuring an average friction coefficient over the pressure range, which exists in a specific draw-bend system. In this paper, a new methodology to determine friction coefficients from draw-bend friction tests considering the pressure non-uniformity is suggested. In the methodology, contact pressure maps obtained from simulations, instead of the uniform pressure assumption, are included in the analysis of test data to measure the pressure dependency of friction coefficient. The proposed method is applied to friction measurement of aluminum sheets with anisotropic mill-finish surface and friction coefficients were obtained as functions of contact pressure, sliding velocity and sliding direction. Lastly, the obtained friction data were implemented into a finite element code, and circular cup drawing experiments and simulations were performed to validate the methodology.