Cold Bulge Forming of Aluminum Tubes: Effects of Geometrical and Process Parameters on Formability and Thickness Variation in Bulged Tubes

Abstract

In this paper, cold bulge forming process of a tube made of aluminum alloy 6061 is performed experimentally using a solid medium polyurethane. The results of the bulged tube show that the bulge forming process can successfully form the 6061 aluminum tube without necking due to uniform compression of polyurethane medium. The results of thickness measurements prove that the thickness reduction in the formed tube after bulge forming process is less than 12%. In addition, numerical simulation of bulge forming process of Al-6061 tube is performed using ABAQUS finite element software. After validating numerical results with experimental measurements, the effects of geometrical and process parameters such as initial tube thickness, radius of die curvature, tube/die friction coefficient and bulge forming speed on thickness variations in the bulged tube are investigated for aluminum tubes made of Al-5052, Al-5083, Al-7072 and Al–Mg. Moreover, several numerical models are analyzed in order to study the residual stress and spring back of the bulged aluminum tubes. It is concluded that the residual stresses in the bulged tube after unloading step are approximately two times lower than the stresses at the end of loading step. It will be shown that by decreasing the bulge forming speed, friction coefficient between die and tube and initial thickness of the tube, better correlation can be seen between experimental and numerical results. The results show with an increase in the radius of die curvature, thickness of bulged tube at the end part converges to a constant value for all types of aluminum alloys.