Wall thickness control in multi-stage hydroforming of multiwave seal ring with small diameter

Thinning rate is a crucial factor in forming quality of the thin-walled seal ring with complex features. To control the excessive thinning by altering the stress state during the material deformation, a new multi-stage three-dimensional (3D) hydroforming technology was proposed in this work. Based on the characteristics of the seal ring and the used superalloy strip, a multi-stage internal pressure forming process was established through finite element analysis (FEA) and forming experiment verification. In addition, the distribution of wall thickness in every stage was discussed. And the influence of the width of deformation zone and the pressure loading path in the cavity on the wall thickness of the part in each step was studied. Finally, the optimal forming parameters of each step that can achieve a stable state of metal flow were obtained. The experimental results demonstrated that the developed 3D hydroforming technology can accurately control the material flow in the multi-stage forming of the multi-wave seal ring with small-diameter and ultrathin wall thickness. For the optimized parameter combination, the blank dimensions of deformation zone are 8 mm in the first step and 18 mm in the second step, while the pre-bulging pressure is 9 ~ 12 MPa and the maximum pressure is 100 MPa in the two steps.