Effect of strain mode and blank orientation on waviness for paint appearance of automotive outer panels

Abstract

Paint appearance is an important requirement for outer automobile panels. Since the last decade automotive manufacturers started reducing paint thickness to address environmental concerns. As a result, the surface roughening of steel substrate due to stamping becomes a critical factor for paint appearance. Although much research work has been conducted on surface roughening, limited research has been focused on waviness and stamping conditions in the pressing of highly formable sheet steels. In this work, the effect of strain mode and blank orientation on waviness evolution has been investigated. It was found that strain mode has a strong influence on waviness, in addition to strain magnitude. Also, the relative orientation of the applied major strain and the direction of the roughness profile relative to the rolling direction affects waviness. When surface waviness is compared at the same surface major strain, the waviness is highest in equibiaxial stretch, followed by plane strain tension in the rolling direction, and then plane strain tension in the transverse diction. When waviness is plotted against thickness strain, the waviness in plane strain tension stretched in the rolling direction is highest, independent of the roughness profile measurement direction. The waviness in equibiaxial stretching is almost the same as that in plane strain tension stretched in the transverse direction.