Performance evaluation and loading path design in tube hydroforming of multi-convolution metal bellows

This study investigates performance evaluations of stainless steel bellows with three distinct cross-sectional profiles through finite element analysis (FEA) and loading path designs in tube hydroforming of multi-convolution bellows. At first, a series of static tests, including bending, stretching, and compression, are simulated to evaluate the stiffness and equivalent stress distribution of the three-profile bellows. The results indicate that the flat-bottom bellows exhibit lower stiffness and internal stress, suggesting enhanced fatigue resistance and deformation capacity. Subsequently, loading path designs for internal pressure and movable die feeding in tube hydroforming of multi-convolution bellows are conducted. To obtain bellows satisfying the geometrical and dimensional specifications, allowable internal pressure ranges are achieved for simultaneous and sequential feeding modes. Simulation results are also used to optimize the forming parameters and die structure. Finally, to validate the simulation outcomes, a custom-designed hydroforming machine is developed. Experiments of tube hydroforming of seven-convolution bellows are conducted. Experimental values of thickness distributions and convolution heights of the formed bellows for different forming pressures are compared with simulation results. The maximum deviation in peak height of the formed bellows between the simulations and experiments is less than 5.1%. Those research results provide valuable insights into the geometric design of bellows and the loading path design in tube hydroforming of multi-convolution bellows.