Effect of mandrel position on bending quality in the rotary draw bending process

The mandrel plays a critical role in supporting tubes within the bending region during tube bending operations. This research explores the impact of varying mandrel positions on bending quality. Therefore, both experimental and finite element analyses were conducted for five different mandrel positions. The study focuses on bending of AA6061-W (water condition) tubes with an outer diameter of 50.8 mm and a wall thickness of 0.889 mm, bent to a radius of 101.6 mm. Conducted experiments revealed ovality values ranging from a minimum of 0.83% to a maximum of 1.81%, depending on the mandrel position. Furthermore, minimum wall thickness measured on the outer side of the tube was 0.686 mm. Additionally, wrinkle and bump formations of varying densities were observed on the tube material, corresponding to different mandrel positions. Results indicate that the mandrel position has a direct effect on the severity of thinning, ovality, bump, and wrinkle formation. The ovality increased as the mandrel was pulled backwards. Finally, the same defect types were detected at similar regions for both finite element and experimental studies which they are in accord.