About a new method to enhance the productivity of die sinking EDM

Abstract

In order to control the EDM inter-electrode gap, the regulation is usually done indirectly by measuring the ignition delay or the average gap voltage, and the axes positions of the machine are adjusted accordingly.The machine efficiency strongly depends on the performance of this gap width controller.The problem in the procedure described above, lies in the comparably slow response time of the machine mechanics, in the tens of millisecond range, with respect to the discharge frequency, which is in the kHz range. The machine mechanics cannot follow it, therefore the performance of the machine is affected in terms of material removal rate, electrode wear, and surface quality.However, adapting the electrical discharge parameters can be typically 1000 times faster than moving the machine axis.This paper shows how it is possible, by adapting in real time the ignition voltage of every pulse to the gap width, to realize a sort of electronic servo system. Additional generator parameters are adjusted for every pulse as a function of the gap width, such the pulse interval etc. Moreover, the mechanically coupled servo system, and the electronic one complement each other.Experimental results show a remarkable increase of the discharge frequency and consequently of the material removal, without penalizing the other technological results, i.e. the inter-electrode gap, the workpiece roughness, the tool electrode wear.