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The Impact of Torsion on the Bending Curve during 3D Bending of Thin-Walled Tubes - A Case Study on Forming Helices

Chassis or cabin designs in the transportation sector are currently manufactured out of several single structural elements. To save handling steps and energy intensive joining processes and furthermore support lightweight design, bending processes can be used that offer the direct production of structural parts that incorporate the functionality of several single elements. In recent years, several processes for the kinematic bending of three-dimensional tubes and profiles have been developed. Additionally, three-roll push bending has gained in importance in manufacturing three-dimensional tubes. In this kinematic process, three-dimensional bending is achieved by continuously changing the bending plane relative to the workpiece during the forming process. Several studies exist that investigate the mechanisms that lead to three-dimensional bending contours. These were, however, based on the generation of empirical models, e.g. characteristic maps. Up until now, no analytical model exists, which describes the process of bending three-dimensional tubes in a comprehensive manner, especially taking into account tube torsion. In the following case study, the tube rotation needed to produce helices is measured and compared to helix radii and helix height. The results were subsequently used to set up an analytical model, which, first of all, describes the tube rotation needed to produce the torsion of the investigated helices and, more importantly, can be generalized to describe the tube rotation needed for the torsion of arbitrary bending curves.