A new approach on the determination of ease of machining by EDM processes

Recently, the ease of machining a workpiece by electrical discharge machining (EDM) processes has been determined by lambda.theta theory, which is the product of the thermal conductivity (lambda) and melting point (theta) of the workpiece in relation to the machining time. This paper presents a fundamental study of the total energy of discharge pulses required to machine different workpiece materials, and a new theory, referred to as lambda.theta.rho theory, is proposed, where rho is the electrical resistivity of the workpiece. Unlike the lambda.theta theory, the lambda.theta.rho theory includes the electrical resistivity of the workpiece material, because it involves the electric current transfer to create the discharge pulse. Using discharge pulse count monitoring, it was also revealed that the machining time cannot be used as a parameter to measure the ease of machining, since it is affected by many complications such as adhesion, cavitations, and short-circuiting. Parameters that are independent of machining complications are introduced in order to measure the ease of machining; the total energy of discharge pulses, discharge pulse number, average discharge pulse energy, discharge pulse density, and tool electrode wear. The results show that the coefficient of correlation for each parameter from the lambda.theta.rho theory is much higher than the lambda.theta theory. Thus, the lambda.theta.rho theory is better than the lambda.theta theory in determining the ease of EDM processes. (c) 2008 Elsevier Ltd. All rights reserved.