dc.description.abstract | Sapphire substrates possess unique mechanical properties, including hardness and brittleness, and therefore, they are particularly challenging to process using conventional mechanical machining methods, especially in terms of microfabrication. In the current study, a microhole fabrication technique involving electrochemical discharge machining (ECDM) was developed to enable fabrication of sapphire substrates at tens of microns scale. A cylindrical tool electrode made of tungsten carbide with a diameter of 40 μm was used, and magnetic field assistance was implemented. A series of experiments were then conducted to identify a means of improving the quality of the tens of microns scale microhole fabrication. This study conducted a single-factor experimental analysis of the effectiveness of using ECDM with magnetic field assistance to fabricate microholes on sapphire substrates. The influences of several machining parameters, including voltage, feed rate, duration time, duty factor, and rotational speed, on the quality characteristics of the microhole fabrication on sapphire substrates were investigated. The quality characteristics included the inlet and outlet diameters of the microholes and the wear of the tool electrode.
Generally, when ECDM is used to fabricate microholes at the tens of microns scale, the small gap between the tool electrode and workpiece is bad for the flow of electrolytes into the machining area near the electrode tip. This insufficient electrolyte flow prevents the formation of an insulating gas film, resulting in collisions between the electrode tip and the workpiece, which in turn leads to fractures and renders the ECDM of microholes on sapphire substrates infeasible. Therefore, in the current study, magnetic-field-assisted ECDM was used to fabricate microholes on sapphire substrates. According to the experimental results, when magnetic field assistance was used, the generated Lorentz force promoted electrolyte circulation and facilitated thinning of the insulating gas film on the surface of the tool electrode. Consequently, the capability and quality of ECDM for microhole fabrication on sapphire substrates at the tens of microns scale were improved. Through holes were successfully fabricated on sapphire substrates with a thickness of 50 µm. When the optimal combination of machining parameters was used, including a voltage of 43 V, feed rate of 1/8 µm/sec, duration time of 20 µs, duty factor of 30%, and a rotational speed of 100 rpm, microholes with average inlet and outlet hole diameters of 78 and 41 μm, respectively, were fabricated. | en_US |