Experimental and numerical analysis of a rectangular helical coil actuator for electromagnetic bulging

The electromagnetic sheet forming process for aluminum alloy sheets was studied experimentally and numerically with a rectangular helical coil actuator. The widely used planar spiral coils are associated with a low magnetic pressure at their center that imposes limitations on the shapes of sheet products. In order to generate a relatively uniform magnetic pressure, a rectangular helical coil is introduced with parallel wires covering the working area uniformly. Two approaches were used for the analysis. In the analytical modeling approach, the analytical expression for the magnetic pressure was obtained, assuming that the wires are equivalent to a current sheet. In the numerical modeling approach, a loosely coupled scheme was introduced to solve the electromagnetic and mechanical problems. The Maxwell equations were first solved for estimation of the magnetic pressure exerted on the workpiece ignoring any workpiece deformations. The magnetic pressure variation was then used as a boundary condition in the mechanical calculation for estimation of the deformation of the workpiece. For validation of the developed numerical model, a rectangular helical coil actuator was designed and tested to form a half ellipsoid with aluminum alloy sheets. The measured and predicted shapes of the half ellipsoid were compared. The effects of the coil design parameters for increasing the magnetic pressure are also discussed.