Mechanism analysis on reducing pressure of tube hydroforming through preform

Pressure for tube hydroforming of lightweight parts is usually determined by the radii of bulgy corners because the pressure for forming a small corner is much higher than other positions. Therefore, it is a key problem how to reduce the pressure for forming the corner with a small radius in tube hydroforming. Stress distribution and deformation mechanism of the corner on a hollow component during hydroforming is analyzed by classical mechanics and finite element method. For tube hydroforming of hollow component with polygonal sections, a rectangular cross-section is regarded as an example and researched. A method to reduce the pressure through preforming a petal-like cross-section is presented and its mechanism is analyzed. A calculated equation of key parameters of the preforming contour is given and an experiment is carried out to verify the method. The theory is meaningful for hydroforming of tubular parts with bulgy small-radius corners under lower pressure.