Analytical, experimental, and numerical analysis of the electromagnetic tube bulging process

Electromagnetic forming is a high-velocity process that uses electromagnetic forces to deform materials; however, the relationships among stored electrical energy, useful forming work, wall thinning, and forming efficiency still require quantification in experimental tube-bulging applications. In this study, aluminum AA6061 tubes were bulged using a six-turn expansion coil at 11, 13, and 15 kV with a two-bank capacitor system. The process is analyzed using an energy-balance formulation, measured discharge-current waveforms, experiments, and a coupled electromagnetic-structural finite element model developed in LS-DYNA. Increasing the discharge voltage from 11 to 15 kV increased the peak current from 102.62 to 139.94 kA, the current density from 4.14 to 5.40 GA/m 2 , the magnetic field from 2.40 to 3.32 T, and the Lorentz force from 9.70 to 17.50 GN/m 3 . The tube deformation increased, but severe wall thinning occurred at the bulge center, where the minimum thickness decreased from 1.8 mm in the undeformed tube to 0.6 mm at 15 kV. The energy analysis showed that the total transferred energy increased with voltage, while only a limited fraction was converted into useful plastic deformation; therefore, forming efficiency and thickness retention must be considered together while selecting the discharge condition. The numerical model is validated against experimentally measured bulge profiles, and the maximum error in bulge diameter remains within 2.3%. Energy analysis indicates that only a portion of the stored energy is effectively transferred to deform the tube. The remaining energy is dissipated within the system due to losses such as resistive heating and energy conversion inefficiencies.