A simple model to estimate the thermal loads on an EDM wire electrode

Abstract

The wire-cut electro-discharge machining (EDM) process is used in industry for the production of devices such as punches, dies, stripper-plates of very hard metals and alloys and suchlike. However, the frequent occurrence of rupture of the wire is one of the most serious production constraints in EDM wire cutting. The phenomenon restricts the cutting speed, increases the machining time and affects the surface finish and accuracy adversely. The probable causes leading to wire rupture and failure under thermal load, failure through short-circuiting and wire vibration, the most important among these being the thermal load. It is, therefore, necessary to be able to predict wire failure under excessive thermal loads so that this situation can be avoided in actual operation and the performance efficiency thus improved. The main objective of the present work is to determine the temperature distribution in the material of the wire and thereby to predict failure due to thermal load. In the present work, a simple computational model is developed which will give the temperature values for varying magnitudes of parameters, viz., input power, pulse-on time, wire velocity and wire diameter. It is hoped that the optimum control of these parameters will help in preventing thermal failure, thus obtaining better utilisation of the process. A finite-difference thermal model to predict the temperature distribution along the wire for the wire-EDM process in the zone of the discharge channel is proposed. The power is presumed to be dissipated in a single spark through a volumetric heat source present within the wire over the discharge channel width, which, in turn, is calculated from the available literature. The temperature distributions are calculated by varying the values of different pertinent parameters: input power (50–300 W), pulse-on time (10–200 μs), wire velocity (0.5–10 m/min) and wire diameter (0.1–0.3 mm).