Springback and compensation of bending for hydroforming of advanced high-strength steel welded tubes

Bending springback plays an important role in hydroforming of curved hollow components, and the effect will be more apparent with the increase of the strength of the material. In order to predict and eliminate the effect of springback on hydroforming process, springback of DP590 welded tube was investigated in computer numerical control (CNC) bending process using theoretical analysis, numerical simulation, and experimental methods. The effects of the bending angles, the diameter-thickness ratio d/t, and the relative bending radius R/d on springback are studied, and the influence factor of the weld position is considered. The theoretical and experimental results show that the springback of the DP590 welded tube with 65 mm in diameter and 2.6 mm in thickness varies within the range from 4.0 to 4.9 % and the amount of springback is influenced by the tube diameter and thickness. The springback reduces from 7.0 to 3.5 % when the diameter-thickness ratio is increasing from 10 to 40. On the contrary, the springback increases from 3.7 to 7.2 % when the relative bending radius is increasing from 1.2 to 4.0. The effect of weld position on springback is very little, but it has a negative effect on defects of hydroforming and wall thickness distribution. It is liable to crack when hydroforming if the weld locates on the outside or neutral layer of the bend. Finally, springback rules and weld effect are applied to form a control arm. A sound part had been successfully manufactured to avoid flash and crack defects considering the appropriate springback compensation and weld position.