Influence of cold rolled surface structures with undercuts for interlocking joints on bending processes

Abstract. Lightweight design is one of the methods to reduce CO2 emissions and optimize energy efficiency in the transportation sector. The main motivation of this study arise from weight reduction through multi-material design with the materials commonly used in the automotive industry, steel and aluminum. Metallurgical bonding of steel and aluminum carries the risk of forming brittle intermetallic phases. Hence, new joining techniques such as joining by forming or casting are promising for these multi-material components. Previously, a hybrid component method was presented using channel-like surface structures with undercuts on a steel sheet created in a modified cold rolling process. In a subsequent high-pressure die casting, the channels were filled with aluminum melt, forming an interlocking connection as it solidified. As automotive components demand increased complexity, the bending of the structured sheet before casting was investigated. This study aims to analyze how the surface structure affects the bending process. Numerical simulations and experiments were used to investigate the effect on the maximum bending force, the resulting bending angle and springback. Therefore, the parameters bending angle, bending radius, and the lateral or longitudinal orientations of the channel structure on either sides of the bend were taken into account. The results showed a strong influence of the lateral and longitudinal orientation on the maximum bending force. Furthermore, a minor effect of the bending radius on the force and springback was found.