Foil-driver enabled method for electromagnetic forming of low-conductive metals: theoretical criterion, experimental validation, and forming applications

This paper proposes a novel criterion with greater generality for the effects of driver sheet thickness on the driving effects in the electromagnetic forming (EMF) for low-conductivity materials. The new criterion inspires a potential method of driver foil to expand the application range of driver sheet from sheet metal only to various shaped workpieces. In addition, the barriers of high cost and low flexibility in driver sheet applications can be avoided. In this paper, the detailed deduction of analytical modeling for EMF processes with driver sheets and the derived criterion from that are first introduced. Then, experiments and numerical simulations are performed to validate the generality of the criterion and the feasibility of driver foils, based on two different EMF processes. In the numerical modeling of the foil driving processes, a simplified model is proposed to avoid convergence issues caused by the unreasonable mesh size of the driver foil and to reduce the computation time cost. The experimental and simulation results show that a very small driver foil thickness of 0.115 mm can improve the maximum forming height of a Q160 steel sheet by about 200% in an electromagnetic sheet forming process, and a driver foil thickness of 0.295 mm can improve the average flanging angle of a Q160 steel circular hole by nearly 100% in an electromagnetic sheet flanging process. The characteristics of the driving effects with the driver foil thickness can be more accurately predicted by the proposed criterion compared with the existing criterion commonly used by researchers at present. The experimental and simulation results of a multi-step electromagnetic flanging process demonstrate the applicability of the driver foil in forming various shaped workpieces and controlling the spatial distribution of the Lorentz forces.