The micro-hole machining of quartz wafers depends on photolithography techniques akin to those used in semiconductor fabrication. These methods present challenges due to high equipment setup costs, large space requirements, and environmental pollution risks. This research applies ultrasonic vibration assistance in electrochemical discharge machining to create an array of micro-holes on quartz wafers. In the experiments, a self-prepared tungsten carbide micro-electrode array served as the tool electrode. This electrode was a 2 × 2 square array, with needles measuring 30 × 30 μm. A series of experiments was conducted to investigate the effects of various machining parameters, including working voltage, feed rate, duration time, duty factor, and ultrasonic power level, on the characteristics of the micro-hole array. The characteristics included average hole diameter and through-hole surface morphology. The experimental objective was to achieve a through-hole diameter of 80 μm with an accuracy of ±8 μm. During the electrochemical discharge machining, suitable ultrasonic vibrations can thin the insulating gas film coating on the electrode surface, resulting in a more uniform gas film. As the insulating gas film’s thickness decreased, so did the critical voltage needed for the electrochemical discharge machining, reducing the hole’s diameter expansion. The ultrasonic vibration assistance can enable the satisfaction of the dimensional accuracy requirement. The experimental results indicate that ultrasonic vibration assistance can effectively improve the processing capacity and reduce sample fragmentation. A working voltage of 44 V, feed rate of 1 μm/6 s, duration time of 30 μs, duty factor of 30%, and ultrasonic power level of 1 resulted in better inlet and outlet surface morphology without outlet fragmentation. Moreover, the average diameters of the inlet and outlet were roughly 80 μm while meeting the through-hole diameter of 80 μm with accuracy of ±8 μm.

The main purpose of this study was to develop observation techniques and processing technology for the electrochemical discharge machining (ECDM) of sapphire wafers. To measure the effect of gas-film thickness, discharge-spark conditions, and droplet sliding frequency on machining quality and efficiency in ECDM, this research utilized high-speed cameras to observe the gas film thickness and formation of the gas film during ECDM. Additionally, this study observed the machining-gap phenomena during ECDM. The formation mechanism and machining characteristics of the gas film were understood through experiments. The machining parameters included the liquid level, working voltage, rotation speed, and duty factor. This study analyzed and discussed the effect of each machining parameter on the gas-film thickness, current, electrode consumption, and droplet sliding frequency. Moreover, this study aimed to obtain optimized machining parameters to overcome the difficulty of machining sapphire. The experimental results indicated that utilizing a high-speed camera to capture the phenomena between electrodes during electrochemical discharge could effectively observe the gas-film thickness and the coverage of the gas film. A higher bubble coalescence rate enhanced the machining capability and reduced the lateral discharge. Therefore, this study could obtain better machining-hole depths through observation and analysis to improve gas-film stability and machining capability. This study demonstrated that a liquid level of 700 µm, a working voltage of 48 V, a duty factor of 50%, and a tool electrode rotational speed of 200 rpm could achieve a hole depth of 86.7 µm and a hole diameter of 129.5 µm.

In the process of Electrochemical Machining (ECM), the electrolyte renewal is likely to be poor as the machining gap is too narrow, so that the machining accuracy and surface quality are influenced, especially in the electrochemical trepanning of special structures, such as the rectangular groove with inner cylinder. As the flow field in the machining gap is difficult to be uniform, the machining quality is low and the cylindrical taper angle is large. Based on the abovementioned difficulties in ECM process, this study used ECM with mask and ECM with tool sinking, as well as the methods with and without ultrasonic vibration assisted sidewall-insulated electrodes, to conduct a comparative experiment on the electrochemical trepanning of rectangular groove with inner cylindrical structure for SUS304 stainless steel cylindrical workpieces. This study also discussed the effects of different ECM trepanning processing methods on the quality characteristics, such as cylindrical taper angle and surface morphology. The research results showed that in comparison to the ECM with mask, ECM with tool sinking had a smaller cylindrical taper angle and better surface morphology. When the ultrasonic vibration assistance was used for ECM with tool sinking, the uniformity of the flow field was improved. The electrolyte pressure changed rapidly in the processing area with the ultrasonic vibration assistance, resulting in pumping effect and cavitation effect, both of which disturbed the electrolyte, and promoted the renewal of the electrolyte in the machining gap. As a result, the resistance within the machining area is reduced, a smaller cylindrical taper angle was obtained, and the flow marks at the bottom of the rectangular groove were significantly reduced. Moreover, the surface morphology and surface roughness of the rectangular groove with inner cylinder after processing were better.

This study investigated the characteristics of a microtool used in electrochemical microdrilling under conditions with and without magnetic field assistance. The experimental results indicated that charged ions and the direction of bubble movement were affected by the Lorentz force under the condition with magnetic field assistance, forming a vortex to promote electrolyte renewal. Reaction products and heat generated by the machining process were effectively discharged. The zone affected by stray current corrosion and microhole expansion were also reduced.