Experimental research on deformation and dimensional accuracy of rectangular-section tubular part during open die hydro-pressing process

To solve the problems involving in the open die hydro-pressing process, such as different corner radii and bigger dimensional deviation, an open die hydro-pressing process was proposed and an experiment was conducted on hydro-pressing process of DP590 steel tubular part with rectangular-section. The effects of pressing sequence and supporting pressure on cross-sectional shape and corner filling were discussed. An analysis was conducted to reveal the reason for uneven deformation of the section corners. It is illustrated that the values of corner radii of the tubular part are obviously different under the condition of one pressing step, and the corner nearby the fixed die is larger than that nearby the pressing punch. The reason is that a difference exists in the circumferential force between the four corners due to the existence of the friction, which results in the uneven deformation on the section corner zone. The deviation of the cross-sectional dimension can be effectively improved by multi pressing steps, but too great a number of pressing steps also reduces the forming efficiency. Under the condition of two pressing steps, a rectangular-section tubular part with high dimensional accuracy was obtained by a reasonable pressure loading path. Its relative corner radius is only 2.5, which exceeds the limiting value of that formed by conventional tube hydroforming.