Friction mechanisms during stamping of zinc electrocoated sheets for car body panels

Abstract

This work was carried out on electrolytic zinc coated steel sheets, and was aimed at understanding and justifying the onset of fractures found in some samples during real stamping of automotive parts. For comparison purposes, a set of samples obtained from zinc coated steel sheets that showed lower friction values was also analysed. Samples that failed by fracture show values of coefficient of friction under BL conditions higher and unstable. This behaviour can be justified by differences in the original surface topography and by a different evolution of the real surface ratio Sc, in contact with the tools. Coils with surface topography having lower values of material ratio in the Abbot-Firestone curve, that is, with higher values of Rpk and lower values of Mrl, contribute to maintain low values of Sc under boundary lubrication conditions and to guarantee stable and low friction coefficient values, allowing correct stamping.