Toward better metal flow control in electrohydraulic sheet forming by combining with electromagnetic approach

Abstract

Electrohydraulic sheet forming is a high-velocity manufacturing process, which utilizes a pressure pulse induced by underwater electrical discharge to plastically shape metals. It has attracted wide interest for its potential to shape metal materials with poor formability. Such advantages can be exploited by combining this process with the conventional stamping process or by using it solely. In both cases, the dominant deformation mode is stretching, implying substantial thinning of sheet metal. The goal of this paper is to improve the material flow control in electrohydraulic sheet forming. A controllable drawing deformation mode is introduced into the electrohydraulic sheet forming process by using a radial inward pulsed Lorentz force at sheet edge induced by an electromagnetic coil, which can substantially enhance the draw-in of the sheet flange. The flexible combination of the stretching deformation and the introduced drawing deformation allows active control of the high-velocity material flow behavior, thus enabling much better control of the final forming quality. About 20 % improvement of the forming height limit is observed from the experimental results. Furthermore, a numerical model is established to better understand the process mechanism, and the critical roles of the amplitude and the action timing of the radial inward Lorentz force are identified.