Investigation on Corner Filling Process in Hydroforming of Thin-Walled Aluminum Alloy Tubular Part with Polygonal Sections

Bursting at the corner during calibration stage is a popular failure mode in hydroforming process of tubular part with polygonal sections. Bending of thin-walled tube is also a big obstacle for hydroforming process, especially for aluminum alloy tube. In this paper, a thin-walled aluminum alloy tubular part with polygonal sections was hydroformed with the step of hydro-bending, preforming and hydroforming. The influence of internal pressure during bending was discussed. Corner filling process of a symbol section was analyzed, such as filling sequence, corner shape changing and thickness distribution. The corner with less expansion ratio contacted the die first and thickness reduction is smaller. Bursting occurred in the corner with big expansion ratio. If the corner is located in the outer side of bending arc, danger of bursting is more severe. The key factor is to maintain a sound shape for the section before calibration to keep the expansion distribution evenly. [doi:10.2320/matertrans.MF201114]