Fabrication of precise micro-holes on quartz substrates with improved aspect ratio using a constant velocity-feed drilling technique of an ECDM process

In the present study, a detailed experimental investigation is carried out on a constant velocity-feed drilling technique of an electrochemical discharge machining (ECDM) process to fabricate micro-holes on quartz substrates. First, cylindrical micro-tools of four different diameters (145 µm, 195 µm, 300 µm and 400 µm) with varying tool feed rates (TFRs) (0.3 µm s⁻¹–1.9 µm s⁻¹) are considered to study their influence on the precision of fabricated micro-holes while using a 30 wt% NaOH solution as an electrolyte, a machining voltage of 30 V and an initial working gap of 5 µm. Minimum micro-hole diameter and overcut were achieved at a TFR 0.8 µm s⁻¹ for the cylindrical tools of all diameters. Considering 0.8 µm s⁻¹ as an optimal TFR, the influence of tool shape on the quality metrics was investigated using a spherical shaped tool electrode having a ball diameter of 145 µm and a spindle diameter of 90 µm. A micro-hole realized using the spherical shaped tool shows that the entrance diameter, entrance overcut, central diameter and central overcut are reduced by 12%, 29%, 28% and 67% respectively as compared to that realized using a cylindrical tool for the same process parameters. Micro-holes with improved precision and aspect ratio are achieved without using cost intensive equipments, feedback mechanisms, coated tools and tool rotation. (paper)