Effect of Bending Method on Tube Hydroforming

Abstract

We studied the effect of the bending method on the hydroforming of a tube in a subsequent process, using experiments and the finite element method. Two bending methods, rotary draw bending and intrusion bending, were investigated. A tube was bent into an S shape by each bending method, and a hydroforming test was carried out with the same hydroforming die. The wall thickness distribution was measured after the hydroforming. The wall thickness of the tube was smallest on the compression side when it was bent by the rotary draw bending method and on the tension side or the intermediate side when it was bent by the intrusion bending method. In both bending cases, burst occurred on the intermediate side during axial feeding. In rotary draw bending, a burst occurred on the compression side or at the R stop nearby. However, in intrusion bending, burst did not occur on the compression side but occurred on the R stop nearby during the final increase of internal pressure. Intrusion bending left a larger hydroforming allowance than rotary draw bending. This is because the wall thickness after intrusion bending was greater than that after rotary draw bending.