New process design for reduction of springback by forming with alternating blank draw-in

Abstract

Abstract Ultra-high-strength steels (UHSS) offer exceptional opportunities in car body manufacturing regarding the improvement of passenger safety as well as the reduction of total vehicle weight. However, springback represents a serious problem when forming such sheet metal materials. In this context, a new approach that can be used for significant reduction of springback was developed at Institute for Metal Forming, University of Stuttgart (IFU). The uniqueness of this approach is the alternating draw-in of blank during the deep drawing process. This paper shows research results regarding the influence of tool radii on springback by forming with an alternating blank draw-in of this kind. In these investigations, an ultra-high-strength steel sheet of the grade DP 980 was used. Firstly, a finite element (FE) analysis was conducted for a hat channel part geometry using the simulation code LS-Dyna. In order to describe the material behaviour in simulation as exactly as possible, additional tests were provided for determining the strain level dependent change of the elastic modulus as well as Bauschinger effect parameters of the used sheet material. Initial simulation results showed that use of smaller tool radii generally lead to reduced springback amount when forming with alternating blank draw-in. In order to validate these simulation results, experimental work was carried out with the same geometrical and technological parameters as in simulation. Afterwards, the part shape deviations occurred in the experiments were measured by using the optical measurement system GOM ATOS 5M. At the end, the simulation results were compared with the experimentally obtained results and a satisfying consistency was found.