Analysis of transition corner formation in hydroforming of rectangular-section tube

The filling behaviour of a transition corner was investigated by theoretical analysis, experiment, and finite element method for a rectangular-section tube during the hydroforming process. The cracking mechanism of the transition region between the straight side and the corner was analysed. The expression of the limiting corner radius was given by way of mechanics analysis and the incremental strain theory. It has been shown that severe thinning deformation or cracking takes place first at the transition region because the effective stress increases gradually from the midpoint of the straight side to the transition point under the effect of friction on the straight side. The mechanism of limiting corner radius is that strain increment along the horizontal direction changes from a positive value to zero at a certain point along the straight side, near the transition point, and then no further material is fed into the corner. The forming pressure needed for the transition corner increases as the relative corner radius decreases during the corner filling process. Lubricant conditions have a significant influence on transition corner filling. The forming pressure needed for the transition corner is effectively reduced by improving lubrication conditions, so that a smaller limiting corner radius is achieved.