Numerical evaluation of transient thermal loads on a WEDM wire electrode under spatially random multiple discharge conditions with and without clustering of sparks

摘要

Thermal load on wire electrode under randomly located multiple discharge condition is the most important consideration for predicting wire breakage in wire electrical discharge machining process. Sometimes the discharges form clusters as observed experimentally by different researchers and may occur because of inadequate evacuation of the debris generated during each discharge. Formation of clusters is more likely in thick work pieces. Clusters are spread randomly along the wire while sparks in each cluster too are random. Such clustering of sparks enhances the intensity of thermal load on the wire. In the present investigation, a one-dimensional explicit finite-difference thermal model is proposed for estimating the transient temperature distribution along the length of the wire under the conditions of randomly located spatial sparks with and without the formation of clusters. While each of the electric discharges is simulated as a volumetric heat source present within the wire over the discharge channel width, which in turn is calculated from the available literature, the successive sparks and cluster of sparks are located on the wire by means of a random function. The predicted values of maximum wire temperatures indicate the degree of wire rupture risk, which has been found to be different for short and long elapsed times. Accordingly, random pulse and clusters models are suggested for predicting thermal loads while machining thin or thick work pieces, respectively. The effects of work-piece height, power input, pulse frequency, duty factor, wire velocity, wire diameter, and the convective heat transfer coefficient have been reported. The one-dimensional thermal models may be used for setting rules of selection for an expert system for the safe operating conditions of wire electro-discharge machining.