Research on flattening behavior of wrinkled 5A02 aluminum alloy tubes under internal pressure

Control of wrinkle for its utilization in tube hydroforming process is a challengeable subject up to now, because wrinkle was always considered as one of the tube’s defects from the traditional view. In order to investigate the flattening behavior of wrinkles in the calibration stage, the wrinkled 5A02 aluminum alloy tubes, obtained under different internal pressures with same amount of axial feeding, were used as the preformed samples for the hydroforming under higher internal pressure of 15 p_s (p_s represents the initial yield pressure of tube). The effect of internal pressure during wrinkling process, as well as the axial feeding, on the flattening behavior of wrinkles was investigated and discussed. It has been found that the wrinkles can be flattened completely when the wrinkling internal pressure is 1.8 p_s. Furthermore, when the axial feeding ratio is reduced from 80 to 75 %, the wrinkling internal pressure range for fractured wrinkles in calibration stage will be enlarged backward to 1.2 p_s, but the pressure range for useful wrinkles can be improved forward to 1.6 p_s. In addition, the fitted Gauss function for every wrinkle was integrated in order to compare its area with the corresponding area of die cavity, so as to reveal the flattening behavior of the wrinkles. It is shown that the wrinkles are easier to be flattened completely without any dead wrinkles when the surface areas of left and right wrinkles are smaller than their die cavity, and the surface area of middle wrinkle is bigger than its die cavity.