The role of discharge plasma on molten pool dynamics in EDM

Abstract

Abstract Each discharge in electrical discharge machining (EDM) generates a plasma with a temperature of several thousands of degrees, which not only evaporates and melts the electrode material, but also applies forces on the molten pool. To determine the role of the discharge plasma on the molten pool dynamics, this study used high-speed photography technology and the finite element method (FEM) to investigate the discharge process. The observation results of the discharge process without an external magnetic field demonstrate that the randomly moving plasma caused the movement of the molten pool, which can have an influence on the removal of the molten material and the final crater topography. It is thought that the randomly moving plasma applied a moving pressure and a moving shear force on the molten pool, causing its movement. The discharge process was observed under an external transverse magnetic field, which indicated that under the action of the Lorentz force, the plasma did not move randomly but moved along the direction of the Lorentz force. The molten pool flowed along the trailing direction of the plasma, and large molten materials were removed from the molten pool along the same direction. The transverse magnetic field influenced the removal of the molten material and the movement of the molten pool by influencing the plasma which actually applied a pressure and a shear force on the molten pool. Finally, the simulation results demonstrate that under the action of the plasma pressure, the molten material was extruded from the molten pool, and the bulge around the discharge crater was generated gradually, forming a deep and bowl-shaped discharge crater with a static plasma and a shallower and larger diameter discharge crater with a moving plasma.