| Abstract | The application of the tube hydroforming process for the manufacture of aerospace components is relatively new and challenging due to the limited formability of high strength alloys used for aerospace applications. A multistep forming process, including intermediate heat treatment steps, has been proposed as a viable solution for increasing the hydroformability of these alloys. Interrupted free expansion tests were used in this study to emulate the multistep forming. Initially, free expansion tests were performed up to the burst point to determine the maximum pressure. An automated 3D deformation measurement system, ARAMIS®, was used to measure the strain distribution along the tube length as well as to measure the bulge height (expansion) as a function of time. Based on the strain distribution results obtained from ARAMIS®, a pause pressure corresponding to about 80% of the burst or maximum pressure was selected as the interruption point of the free expansion test in order to apply a softening heat treatment to restore the formability of the material. After this free expansion and softening cycle, the tube was then hydroformed up to the burst point.The results indicated that the inclusion of an intermediate heat treatment before the second forming step increased the expansion from 9.5 mm to 12 mm, a 26% increase. Interestingly, in addition to the higher expansion, the pressure required to reach a specific level of expansion was reduced by half due to the softening effect of the intermediate heat treatment and thinning of the tubes from the first forming step. |
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