Deformation characteristics in hydro-mechanical forming process of thin-walled hollow component with large deformation: experimentation and finite element modeling

The automobile exhaust manifold regularly has a multi-valved shape that used to be formed by the combination of stamping and welding. The current study intended to investigate and develop a tube hydro-mechanical forming (THMF) process to form an integral automobile exhaust manifold that has the characters of large deformation and small corner. It included three stages such as pre-forming stage, die-forming stage, and calibration stage. In addition, the non-feasibility of one-step hydroforming process was proved by FE modeling and experimental for the target component. An optimal loading path was obtained through the principle of dichotomy for pre-forming stage and die-forming stage, corresponding to the maximum thinning ratio of 19.7% and 13.27% respectively. The variation of stress and strain states were analyzed for the whole process. As a consequent, the thickness distribution exhibited a V-shaped along axial direction at each stage, while a fluctuated distribution after die-forming was presented along radial direction in the multi-valved area. For the final component, a maximum thinning ratio of 28.53% and the large deformation above 60% obtained from FE modeling kept a reasonable agreement with that achieved from experiments. It showed that THMF has advantages of not only decreasing the internal pressure but also improving the formability of tube.