Optimization of forming accuracy and wall-thinning rate of three-wave bellows tube in axial pressurization-assisted electromagnetic hydraulic forming

Metal bellows are flexible tubular components characterized by multi-wave geometries, capable of accommodating deformation under bending moments, axial forces, and radial forces. These tubes are widely applied in instruments, pipeline displacement compensation, and aerospace engines. In the present study, high-precision forming of bellows was realized through electromagnetic hydraulic forming. Without axial pressurization, the forming accuracy of the middle corrugation was the lowest, and accuracy gradually improved with increasing discharge voltage. When the discharge voltage reached 7000 V, a die-fitting gap of 0.2 mm was observed. By applying axial pressurization-assisted electromagnetic hydraulic bulging process to the forming of three-wave corrugated tubes, full die filling was achieved at a discharge voltage of 6000 V. Compared with the non-axial-pressurization condition at 7000 V, the axial material flow was enhanced by 43.7%, while the wall-thickness thinning rate was reduced by 25.2%. The introduction of axial pressurization generated a higher level of axial compressive stress, which increased the axial compressive strain in the middle corrugation from 3% to 9%, thereby promoting axial material flow and improving formability. Microstructural characterization using electron backscatter diffraction (EBSD) revealed that axial pressurization effectively reduced the post-forming geometrically necessary dislocation (GND) density, decreased the average Taylor factor, and weakened the deformation texture intensity. These microstructural evolutions collectively enhanced the plastic flow capability of the material, resulting in improved deformation uniformity and higher forming accuracy. The present study provides new mechanistic insights into corrugated tube forming and expands the potential applications of electromagnetic hydraulic forming technology.