Experimental characterization of the reverse micro-electrodischarge machining process for fabrication of high-aspect-ratio micro-rod arrays

Abstract

High-aspect-ratio arrayed structures find application in the creation of deep blind holes used in ink-jet nozzles, air-bearings, etc. This paper focuses on the use of reverse micro-electric discharge machining (micro-EDM), to generate high-aspect-ratio micro-rod arrays. A micro-rod of 60 μm in diameter and a high-aspect-ratio of 33 is successfully fabricated using the process. An L8 orthogonal array is used to study the effect of gap voltage, capacitance, threshold, and feed rate on the process response variables. The measured process responses are dimensional accuracy (measured at various locations along the length of the micro-rod), zero error length, and surface roughness. Furthermore, the surface morphology and chemical composition at the root and tip of the generated structure are studied. Analysis of variance studies show that the statistically significant factors that influence response variables are the gap voltage and capacitance. The gap voltage is identified as the single most important factor governing the accuracy of the micro-rods at almost all locations. Analysis of surface morphology reveals that there are more craters at the tip of machined rods whereas, the area around the base is relatively smooth. Value of surface roughness varies from 1.6 μm Ra to 6.3 μm Ra under different experimental conditions. A variation in chemical composition is observed along the length of the rod. Plausible explanations are presented for the various phenomena observed during the reverse micro-EDM process.