1. The thickness of the outer wall of the bending deformation zone of the profile becomes thinner;

2. The thickness of the inner wall of the stretch bending deformation zone of the profile increases and wrinkles;

3. Cross section shape distortion;

In the process of profile stretch bending, springback is an important factor to be considered in die design. The springback of profile after stretch bending has a great influence on its final forming. The springback is mainly manifested in the overall unloading springback and trimming springback. When the springback exceeds the allowable value, the forming defects will affect the geometric accuracy of tensile bending parts. In order to control the springback of parts with large bending radius after forming, stretch bending forming process can be adopted to make the formed parts have reasonable calibration allowance and reduce the workload of manual calibration. If the rebound of the part is too large, manual calibration cannot be carried out, resulting in scrapping of the part. Therefore, springback is an important factor affecting and restricting the forming of stretch bending die and stretch bending part.