A novel trapezoidal cross-section welding coil for electromagnetic pulse welding

Electromagnetic pulse welding (EMPW) is a high-strain-rate solid-state joining process in which a pulsed current in a working coil generates transient Lorentz forces that accelerate a flyer sheet toward a target sheet for impact bonding. For sheet welding, the H-shaped coil remains attractive for its compact layout; however, conventional rectangular conductors may underutilize electromagnetic loading under high-frequency discharge conditions. Here, a trapezoidal conductor cross-section is introduced for an H-shaped coil, and the conductor area is kept constant to isolate the geometric effect. A multi-physics finite-element model that couples the discharge circuit, transient electromagnetics, and structural dynamics is developed for Cu-Al sheet welding to compare rectangular, trapezoidal, and trapezoidal-rectangular designs. The numerical simulation results indicate that the trapezoidal cross-section produces the highest Lorentz-force density and increases the initial collision velocity from 338.16 m/s to 361.83 m/s. Based on the V c - β weldability window criterion, the model predicts that the effective weld width reaches 0.6089 mm, corresponding to a 19.72% increase over the rectangular coil, and a 10.91% increase for the trapezoidal-rectangular coil. From a practical perspective, this model-predicted improvement suggests that the predicted weldable region can be enlarged without increasing the input energy or the coil footprint, which is beneficial for high-current applications such as battery tab-to-busbar connections. These simulation results suggest that conductor cross-section tailoring is a feasible geometric design approach to improve the predicted weldability of H-shaped coils.