Strain distribution at the transition from bent to unbent regions in tube rotary draw bending: an in-situ, real-time measurement study

In tube bending processes, accurate control of springback is of crucial importance as this affects the dimensional accuracy of the final product and overall equipment efficiency. The distribution of stress and strain during bending is one of the most fundamental issues determining the springback magnitude of the product. In conventional analyses of rotary draw bending, the deformation behaviour along the bending direction is normally assumed to be uniform for constant-radius bends, following the contour of the die configuration. In practice, however, the stress-strain distribution is non-uniform, particularly at the transition between the bent and unbent regions of the formed component. The distribution makes a significant contribution to springback and its variations, especially for low bend-angle components. This research focuses on exploring the strain distribution at the end transition of the bend of aluminium tubes in rotary draw bending. An experimental test setup for strain measurements with a strain gauge glued to the unbent area has been designed and conducted to measure the strain distribution during bending. The characteristics of non-uniform strain distribution during tube bending, including the evolving transition behaviour at the transition between bent and unbent areas, are studied. The results enhance the understanding of deformation characteristics of bent tubes, and contribute to improved physically-based models and springback control routines in industrial practice.