Observation of Quantity of Bubbles in Electrical Discharge Machining Gap

In order to further improve the machining accuracy and machining speed of electrical discharge machining (EDMing), it is necessary to understand the gap condition during the EDMing process. In this paper, a new method of using ultrasonic waves to measure the gap condition is proposed. First, the possibility that the change in the quantity of bubbles existing in the gap between the electrode and the workpiece could be detected as a change in the attenuation factor of ultrasonic waves is confirmed through a fundamental experiment of the proposed detection method. Second, the method is applied to an actual EDMing process with several machining settings. From these experiments, the dissimilarity of the gap conditions under several EDMing processes is clarified and the fact that the gap is filled with bubbles for most of the machining period is confirmed. Third, a comparative experiment is conducted to investigate the influence of the amount of bubbles in the gap on machining efficiency. As a result of the experiment, it is ascertained that machining with a small amount of bubbles has higher efficiency than machining with a large amount of bubbles. These results provide useful information for constructing the most suitable EDMing control system for improving machining performance.