Feeding path and movable die design in tube hydroforming of metal bellows

Feeding path and movable die designs are crucial to implement bellows manufacturing with an appropriate hydraulic pressure and make the products satisfy the required geometrical and dimensional specifications. In this paper, a tube hydroforming process combined with movable die designs is developed to obtain an appropriate forming range of the internal pressure and increase the thickness uniformity in the formed product. Two kinds of feeding types are proposed to discuss the effects of the feeding path and die design on the convolution heights and thickness uniformity in the formed bellows. A finite element simulation software “DEFORM” is used to analyze the plastic deformation of the tube within the die cavity using the proposed feeding types for three different shape bellows. Allowable forming ranges of internal pressures for sound products with required tolerances in geometry and dimensions using different feeding types are also investigated. Finally, tube hydroforming experiments of three-convolution bellows are conducted and experimental thickness distributions and convolution heights of the products are compared with the simulation results to validate the analytical modeling with the proposed movable die concept.