Forming characteristics of a novel robot-based tube bending process

With the advancement of ‘Industrial 4.0’, industrial robots are becoming increasingly widespread. Thus, this study proposes a novel robot-based tube bending forming technology (RTBF) to increase the flexibility of manufacturing thin-walled complex-shaped tubes and to improve their quality. The forming mechanism and characteristics of the proposed technology are investigated using finite element modelling. Besides, the theoretical models for calculating the tube’s inner and outer sides’ equivalent stress are also presented. The obtained results showed that the bending die feeds in the tube axis direction while rotating in the novel robot-based tube bending forming, and the axial tensile stress T on the tube during the bending process is reduced. Comparing these results with the traditional rotary draw bending (RDB), the tensile stress and strain on the outer side of the bent tube and the thinning wall rate are both lower. On the other hand, the compressive stress and strain on the inner side of the bent tube and the wall thickening rate are higher in the robot-based tube bending process. The maximum cross-sectional distortion of a bent tube in the robot-based tube bending forming process remains unchanged with increasing bending angle and is always smaller than in the RDB process: the larger the bending angle, the more noticeable the difference. In summary, the robot-based tube bending forming technology significantly reduces the small diameter tube’s wall thickness and cross-sectional distortion.