Electrochemical discharge machining (ECDM) is a spark-based micromachining method especially suitable for the fabrication of various microstructures on nonconductive materials, such as glass and some engineering ceramics. However, since the spark discharge frequency is drastically reduced as the machining depth increases ECDM microhole drilling has confronted difficulty in achieving uniform geometry for machined holes. One of the primary reasons for this is the difficulty of sustaining an adequate electrolyte flow in the narrow gap between the tool and the workpiece, which results in a widened taper at the hole entrance, as well as a significant reduction of the machining depth. In this paper, ultrasonic electrolyte vibration was used to enhance the machining depth of the ECDM drilling process by assuring an adequate electrolyte flow, thus helping to maintain consistent spark generation. Moreover, the stability of the gas film formation, as well as the surface quality of the hole entrance, was improved with the aid of a side-insulated electrode and a pulse-power generator. The side-insulated electrode prevented stray electrolysis and concentrated the spark discharge at the tool tip, while the pulse voltage reduced thermal damage to the workpiece surface by introducing a periodic pulse-off time. Microholes were fabricated in order to investigate the effects of ultrasonic assistance on the overcut and machining depth of the holes. The experimental results demonstrated that the possibility of consistent spark generation and the machinability of microholes were simultaneously enhanced.

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Electrochemical discharge machining (ECDM) is an effective spark-based machining method for nonconductive materials such as glass. The spark generation in ECDM processes is closely related to the electrode effects phenomenon, which has been explained as an immediate breakdown of electrolysis due to the gas film formation at the electrode surface. The initiation of the electrode effects is mainly influenced by the critical current density, which is dependent on several parameters such as the wettability of the gas bubble, surface conditions of the electrode and hydrodynamic characteristics of the bubbles. In ECDM processes, precise control of the spark generation is difficult due to the random formation of the dielectric gas film. In this study, a partially side-insulated electrode that maintained a constant contact surface area with the electrolyte was used for the ECDM process to ensure that a uniform gas film was formed. Visual inspections indicated that the side-insulated tool provides new possibilities for describing the exact geometry of a gas film by inducing single bubble formations. Experiment results demonstrated that ECDM with a side-insulated electrode immersed in the electrolyte generated more stable spark discharges compared to non-insulated electrodes. Microchannels were fabricated to investigate the effects of the side insulation on the geometric accuracy and the surface integrity of the machined part.