Enhancing forming accuracy in aluminum alloy variable-diameter tubes through dual-coil controllable electromagnetic forming

High-accuracy forming of aluminum alloy variable-diameter tubes imposes strict requirements on force field design. Although electromagnetic forming has shown unique advantages in enhancing the formability of aluminum alloy materials, its shortcomings lie in the single and difficult-to-adjust force field, which limits its application in variable-diameter tubes. To address this challenge, a novel dual-coil electromagnetic forming approach with good controllability of force field is proposed. Numerical simulations and experiments are both conducted to showcase the superiority of this approach in forming variable-diameter aluminum alloy tubes. The results demonstrate that the forming accuracy of AA6061-O variable-diameter tubes has significantly improved compared to a traditional single-coil system, in which the maximum die-fitting gap is reduced from approximately 2 mm to less than 0.22 mm. Furthermore, it is identified the force field produced by the single-coil system causes a local cavity gap between the tube and the die, which adversely affects the forming accuracy. In contrast, the improved force field produced by the dual-coil system facilitates bottom-to-top deformation of the tube, thereby avoiding undesirable cavity gaps and achieving high forming accuracy. Importantly, the dual-coil forming system offers significant controllability of the Lorentz force field by adjusting the coil discharge, making it suitable for variable-diameter tubes of different sizes without changing the coil structure. This work represents a substantial advancement in controllable tube forming, offering a new approach to force field design and holding promise for extensive applications in the forming of variable-diameter tubes.