Some Effects on EDM Characteristics by Assisted Ultrasonic Vibration of the Tool Electrode

摘要

It is well known that electrical discharge machining (EDM) is a machining method that does not affect the hardness of the material being processed. The EDM method is widely used for the finish machining of metal molds, for which materials having a high degree of hardness is used. However, the EDM method has a disadvantage in that the machining speed is remarkably slow compared to other machining methods. However, if the discharge energy is increased, the quality of surface finish is decreased. For this reason, it is difficult to machine a finished surface. In order to improve machining characteristics while using the same discharge energy, it is important to homogeneously disperse the discharge, so as to increase the rate of normal discharge, and to discharge the machining dust that accumulates between the electrode and workpiece. However, it is difficult to generate a constantly normal discharge in EDM. What is worse, the more deeply a hole is machined, the more difficult it is to remove the machining dust that accumulates between the electrode and the workpiece. A concentrated discharge tends to occur locally because of the presence of machining dust between the electrode and workpiece. This concentrated discharge has an adverse effect on the surface finish Also, it creates a big problem, namely a bridging contact is generated between parts. In order to avoid generating such a concentrated discharge or abnormal discharge, it is necessary to disperse the discharge appropriately. In this study, we investigate EDM characteristics by using assisted ultrasonic vibration of the tool electrode as a method of overcoming the problem. The result showed that the machining speed was increased several times by using assisted ultrasonic vibration of the tool electrode. The method proved to remarkably effective in increasing machining speed even if the amplitude of the ultrasonic vibration was 1 μm. Furthermore, the rate of normal discharge increased by applying ultrasonic vibration. In particular, this method yielded a beneficial effect in finishing conditions. This is expected to produce a better effect under conditions of finish machining when there is a small gap between the electrode and workpiece. In particular, occurrences of abnormal discharges, such as a concentrated discharge, decreased since the electrode tool was forcibly separated from the workpiece. Machining wastes are positively removed as a result of the tool electrode working with a "pumping action." In particular, when applied to deep-hole machining, this method is extremely effective in machining deeper holes.