Die-sinking micro electrical discharge machining of deep narrow groove arrays using self-sharpening sandwich electrodes

Based on the theorem of die-sinking micro electrical discharge machining (EDM) with a composite material electrode (CME), this study proposed to use two high wear rate electrode foils to bond and clamp a low wear rate electrode foil, and stack them to produce a sandwich electrode that could be reused, in principle. This sandwich electrode was used to machine deep narrow groove arrays by EDM. The two sub-electrodes on the outer side rapidly wore out during processing. Therefore, the width and depth of the processed narrow groove were determined by the middle sub-electrode with a low wear rate. While processing the deep narrow groove, the discharge grinding of the sandwich electrode was adaptively completed to avoid the extremely thin low wear rate sub-electrode being exposed for too long, making it unstable or even damaged. Based on this principle, a sandwich electrode composed of Cu foil and H62 brass foil was fabricated. Taking the example of machining a narrow groove array with a spacing of 300 μm on high-speed steel workpieces, the optimal open circuit voltage, pulse frequency, and Cu foil sub-electrode thickness for EDM were studied. Based on this, deep narrow groove arrays with depths exceeding 2.1 mm and aspect ratios greater than 13 were machined. A self-sharpening model of the sandwich electrode was established based on the die-sinking micro EDM theorem with CME. Through simulation iteration, the process of self-sharpening and rapid convergence of narrow groove top cup shape into microstructures was studied.