Numerical Analysis of Arc Plasma Temperature in EDM Process Based on Magnetohydrodynamics.

Abstract

In this paper, the temperature of the arc plasma and the arc extinguishing time in the electrical discharge machining (EDM) process are calculated based on the magnetohydrodynamics (MHD)approximation. The temperature of the arc plasma determines the heat Flux at the surface of a workpiece which serves as the main heat source in melting and vaporizing of the workpiece. The arc extinguishing time, which must be shorter than the pulse interval, is closely related to the stabiliy of the machining process and hence the machining rate of the process.In cases for which local thermodynamic equilibrium can be assumed, the plasma is described as continuous matter, and the MHD equations are solved by the finite difference method to detemine the distributions of current density, Fluid velocity and temperature. The calculated results show that almost all of the discharge energy is equally distributed into anode and cathode, and that the energy transfer is mostly determined by the heat conduction but not affected by convection or radiation. Further more it is also found that the plasma is extinguished within a few microseconds after the current supply is ceased for each discharge pulse.