Cold Stretch Bending Forming Technology For T8 Al-Li Alloys Profiles

Springback behavior of aircraft frames of the 2196-T8511 and2099-T83 Al-Li alloys in stretch bending was investigated at room temperatures. With this experience in mind, the status and progress in Al-Li alloys and stretch bending are reviewed, and mechanical property outlined.Firstly, to understand the origins of springback and improve its prediction, new displacement-controlled and force-controlled stretch-bending model were developed, and carried out. The model incorporates deformation and springback taking into account the effects of pre-stretch and post-stretch.Secondly, three new methods for designing general stretch-bending dies to produce a desired final part shape, taking springback into account, have been developed. In order to test the usefulness, a two-dimensional part shapes was subjected to die design. Considering the working principle of stretch wrapping machines, operating procedures, and control parameter setting, the jaw trajectory of arc-bending was established. Then the adjustment method for tension displacement was developed taking axial force into account.Lastly, to verify this method, stretch bending tests with various process parameters were performed on the two types of Al-Li alloys extrusions with T-section and Z-section. The predicted springback, as well as tendency, were in good agreement with the experimental results. The new compensation for springback has been confirmed by experiment to produce accurate die shapes and final part shapes with no trial-and-error and with few iterations.