Manufacturing of bent tubes with non-uniform curvature and cross-section using a novel hydroforming die: experimental, finite element analysis, and optimization

Producing non-uniformly curved tubes with sharp corners using the common experimental methods in hydroforming process is difficult. A common approach is to increase the internal pressure as high as possible; which may lead to excessive thinning and fracture on the corners of the tubes. To manufacture this type of tubes, the current study has proposed a new hydroforming die to perform such a process by taking two general steps: initial bulging and forming. The proposed die facilitated with two movable bushes is able to produce bended stainless steel tubes with non-uniform curvature and cross-section. To find the optimum pressure and axial feed profiles, finite element simulations were performed, and the results were validated with experiments. The main advantage of this die is that by moving the bushes inside the die cavity, the friction between die and bushes can be reduced considerably while axial feeding is provided properly, leading to produce a tube with a uniform thickness distribution and maximum achievable corner filling.