Improvement of machining characteristics with polarity-changed pulse in EDM processes

In this paper, a new type of discharge current waveform, named polarity-changed pulse, is proposed in order to improve the machining characteristics in the EDM process. The principle of the method is to alter the polarity so that a greater instantaneous removal rate of the workpiece can be obtained, since the removal rates of the anode and cathode change with the development of the plasma arc. The polarity of the workpiece is set to positive when the discharge takes place, and then the polarity is changed to negative at a certain time after the discharge ignition. At first the removal amount of the workpiece and the tool wear ratio with respect to the polarity-changed pulse were calculated on the basis of the experimental results obtained with the conventional pulse. The removal rate and tool wear ratio were then investigated when the polarity-changed pulse was used. It is found from both experimental and calculated results that the use of polarity-changed pulse can decrease the tool wear ratio and increase the workpiece removal rate.