Combined rotary draw tube bending and hydroforming: thickness recovery and defect optimization

The demand for bent hollow parts, particularly those with larger diameters and smaller bending radii, has significantly increased in industries such as automotive, energy, and aerospace. However, manufacturing these components presents substantial challenges, primarily due to the risk of defects such as wrinkling or cracking caused by excessive wall thinning. This study investigates the combined manufacturing process of Rotary Draw Tube Bending (RDTB) followed by Tube Hydroforming (THF) to address these challenges. Through numerical simulations and experimental validation, the process parameters of both forming techniques, as well as key defects including wrinkling, wall thickness reduction, and die filling rate, were thoroughly examined. The findings reveal that excessive thinning in the extrados during RDTB is mitigated during the subsequent THF operation. Similarly, excessive thickening in the intrados during RDTB is counteracted by the stretching and thinning effects of THF. The results demonstrate that the proposed process, with optimized parameters, enables the production of high-quality elbow parts, confirming the method's effectiveness and its potential as a reliable manufacturing solution for complex elbow geometries.