Improving Forming Accuracy of Variable-Diameter Tube by Electromagnetic Forming Using Segmented Coil

Electromagnetic forming (EMF) has shown considerable promise in lightweight alloy tube manufacturing industry. However, the generated force field falls short of meeting the stringent forming accuracy requirements for variable-diameter tubes. To solve this, this paper proposes an EMF process using a novel coil structure, named as segmented coil, to improve the forming quality of tubes. The design and implementation of coil, as well as the deformation behavior of tubes, are discussed. Results show that a multi-layer solenoid coil can generate excessive force on the upper portion of the tube, thus causing an undesired gap between the coil and tube that is unfavorable for forming performance. In contrast, when employing a segmented coil, the force applied to this section is mitigated, allowing the tube to fit into the die from bottom to top and achieving a maximum die-fitting gap of no more than 0.1 mm. Besides, it is found that the forming accuracy increases with increasing discharge energy, and an optimal coil structure exists when the discharge energy is fixed. This work showcases the considerable flexibility of the segmented coil in controlling the Lorentz force distribution and tube deformation behavior. These findings hold significant implications for expanding the applications of EMF technology.