Thickness improvement in non-homogeneous tube hydroforming of a rectangular component by contact sequence

Numerical simulation and experimental methods were conducted to study the non-uniform thickness during hydroforming of a rectangular cross-sectional component by using a bent tube, which is thickened inside and thinned outside. A method of changing the contact sequence of the tube to the die surface is proposed to improve thickness distribution of hydroformed part. There are four contact sequences, Side-and-Side (SS), Side-and-Fillet (SF), Fillet-and-Side (FS) and Fillet-and-Fillet (FF), that are proposed through the preform shape for a rectangular section. The effect of contact sequence on thickness distribution was studied. The results show that SF or FF contact sequence makes the fillet corner contact with the die surface first and suppresses the further thinning in hydroforming. On the contrary, SF or SS contact sequence makes the straight side of the bend inside contact with the die surface first and benefits the full deformation of the thickening region in hydroforming. Among them, the SF contact sequence is the best for the uniformity of thickness, and SF and FF contact sequences are useful to ensure the minimum thickness of the section and help to avoid cracking defects. On the basis of it, two contact sequences, SS and FF, were applied to an instrument panel bar, respectively. There is a cracking defect in the circular section for the SS sequence, while there is no defect in the straight and circular sections for the FF sequence. And the sound part is successfully developed and applied to the assembly of the instrument panel bar of Chrysler 300C car in mass production.