Experimental research on vibration assisted EDM of micro-structures with non-circular cross-section

In micro-electrical discharge machining (EDM) of micro-structures with non-circular cross-section, the machining efficiency may be extraordinarily low due to the difficulties for dielectric liquid to flow and discharged debris to be removed out of the narrow discharge gap. To improve the machining efficiency and accuracy, the method of assisting workpiece vibration was introduced into such micro-EDM process using the tool electrodes with non-circular cross-section or array structures. The micro-amplitude vibration of workpiece was realized by applying high-frequency sine-wave voltage to drive a piezoelectric (PZT) actuator. A number of machining experiments were designed and carried out by changing the frequency and the amplitude of vibration at different discharge parameters. The experimental results showed that the effective discharge ratio increased obviously due to the assisting high-frequency vibration. Moreover, the increase of the effective discharge ratio also increased the spark explosive force, which could accelerate the dielectric liquid circulation and debris removal during the EDM process assisted with workpiece vibration. Therefore the machining stability, the machining accuracy and efficiency of the micro-EDM process are improved. The machining efficiency increased 18 times and the dimension accuracy improved by 10.5 mu m when using a tungsten electrode of empty set 175 mu m at the vibration frequency of 6 kHz and the amplitude of 3 mu m. In this study, the emphasis is laid on the effects of assisting workpiece vibration with gap servo control on the EDM performance of micro-structures. Furthermore, the process principle of the effects is analyzed to explain our experimental results. The experimental data and the process analysis suggest that higher frequency vibration helps to acquire higher machining efficiency, and good machining effects can be obtained when the vibration amplitude is set nearly equal to the discharge gap. (C) 2008 Elsevier B.V. All rights reserved.