Improvement of material flow in tube hydroforming by advanced sealing methods

In this paper, two advanced sealing methods are proposed to enhance the formability of aluminium alloys in the tube hydroforming process. These methods are aimed at omitting friction force at the contact area between the tube and the die in the feed region and facilitating the material flow to the deformation region. The advanced sealing methods are numerically and experimentally examined against the conventional sealing method by conducting the free bulge test on AA6063 aluminium tubes. The deformation mechanics are deeply analysed in the principal strain space to identify the influence of the sealing methods on deformation paths. In addition, the effectiveness of the advanced sealing methods is evaluated under different lubrication conditions and contact lengths in the feed region. Results show that in the advanced sealing methods compared to the conventional one, the thickness in the feed region does not increase and the necking occurs in larger in-plane strains, leading to a higher bulge height. Results also allow concluding that a higher bulge height is formed using the second advanced sealing method, in which the tube is pressurized from both sides in the feed region. Thus, the advanced sealing methods are recommended for tube hydroforming of aluminium alloys with low formability.