Enhancing the electromagnetic forming performance of thin-walled sheet metal via a thicker driver: Forming behavior and experimental validation

Abstract

Abstract This paper proposes an innovative electromagnetic forming approach for die-forming of sheet metal parts with a low thickness-to-diameter ratio (0.25%), in which an additional driver sheet was used to improve the forming behavior. Numerical simulations reveal that the conventional EMF method fails to prevent wrinkling defects in thin-walled sheet metal forming, with the severity of wrinkles increasing as the voltage rises. These wrinkles reach a maximum height of 11.3mm and result in inadequate workpiece adherence to the die. To address these challenges, a novel technique is introduced that effectively suppresses wrinkling by enhancing the interaction between the driver sheet and the workpiece. Through a comprehensive evaluation of forming efficiency and wrinkle suppression, an optimal driver sheet thickness of 3mm is determined, minimizing wrinkling to 0.67mm. Compared to the conventional EMF method, the proposed approach yields a fuller and more accurate forming results, closely conforming to the die contour. The process window is defined by analyzing two fundamental process parameters: blank holder force (FBHF) and discharge voltage (Vd). The deformation history of the driver sheet EMF is examined for a high forming quality case with Vd = 12kV and FBHF = 8 kN, resulting in 1.41mm die-fitting gaps. A comparative experimental study demonstrates the effectiveness of the driver sheet EMF technique in producing deep-cavity workpieces with superior forming accuracy. The results include a maximum die-fitting gap of 1.41mm and a maximum wrinkle height of 0.67mm. The proposed driver sheet EMF method exhibits enhanced flexibility and efficiency compared to the conventional EMF, particularly in manufacturing extremely thin-walled sheet metal parts.