Effect of mandrel-cores on springback and sectional deformation of rectangular H96 tube NC bending

To reveal the effect mechanism of mandrel-cores on springback and sectional deformation of rectangular H96 tube NC bending, the stress variation caused by using different numbers of cores are analyzed based on the finite element simulation as well as its relationship with the springback and sectional deformation. Results show that the flexible core causes larger tangential stress in the bending stage, which leads to larger springback. The frequency of repeated loading-unloading process of the tube increases with the increase of the core number, and the reloading process always keeps in plastic deformation range, so the varied elastic modulus effect and the Bauschinger effect are highly suggested to be considered to predict springback accurately. The retracting mandrel is an elastic process that will average and reduce the magnitude of stress, and the stress reduction nearly increases with the increase of the core number. The variation trend of sectional deformation is determined by both the tangential stress and the circumferential stress. In addition, the performances of the mandrel-core die and the PVC mandrel on the H-bending process are compared. It is found the mandrel-core die has advantage to prevent the width and height deformations of H-bend when compared with the PVC mandrel, and this phenomenon is absolutely opposite with that in E-bending process.