Effect of the lubrication between the tube and the die on the corner filling when hydroforming of different cross-sectional shapes

This paper presents an experimental study on corner filling in the tube hydroforming process. A single-step tube hydroforming process was retained based on pure expansion hydroforming with the conjunction of only internal pressure loading. Several hydroforming experiments were performed with differently shaped dies, such as a square, a rectangular, a trapezoidal, and a trapezoid-sectional die. The distribution of thickness was studied under both dry and lubricated conditions. The main results revealed that thinning occurred in the transition zone, between the corner radius and the straight wall, for both the square and rectangular dies. However, for the trapezoidal and trapezoid-sectional dies, the thinning took place in the sharp zone. The use of Teflon as a lubricant between the die and the tube led to significant changes in terms of thickness distribution and the reduction of thinning. For each of the various dies that were used, it was found that the lubrication of the contact tube/die offered a more uniform thickness for the final hydroformed product.