Measurement and analysis of the geometric characteristics of microholes and tool wear for varying tool-workpiece gaps in electrochemical discharge drilling

•The effect of the T-W gap on the microholes formation by the ECDD is reported.•A T-W gap of 10–30 µm for NaOH and 5–20 µm for KOH electrolyte must be maintained.•The required T-W gap depends on the electrolyte type and its concentration.•Microholes size initially increases and then reduces with further gap increment.•Depth of the microholes and tool wear decreases with an increasing gap. In the last decade, the Electrochemical Discharge Drilling (ECDD) has emerged as an alternative to conventional laser ablation to create blind and through-holes in non-conductive materials such as fused silica, quartz, and glass workpiece. The initial tool electrode and workpiece (T-W) gap play a vital role in microhole formation and tool wear. Therefore, an experimental investigation into the effect of the initial T-W gap with different machining time and electrolyte concentrations on the blind microhole formation in the glass and tool wear in the velocity-feed ECDD is reported. The microholes having superior surface quality and lower overcut were fabricated with KOH electrolyte and lower concentration. A novel numerical model based on inverse heat flux reduction for varying initial T-W gaps was studied for the first time. The obtained experimental results were compared to the numerical results predicted with the finite element based numerical simulations. The opening size of the microholes increased up to a critical T-W gap and then decreased with a further increase in the gap. The critical gap is found to be 20 µm and 10 µm for NaOH and KOH electrolyte, respectively. The depth of the microholes was the maximum at a zero-gap condition; however, the tool wear was severe. The highest average depth of 175 µm was obtained at 30 wt% NaOH for the machining time of 60 s. Tool wear tends to be decreasing with increasing the T-W gap. The least average tool wear of 9 µm was observed for 20 wt% KOH electrolyte for machining time of 60 s. The experimental results indicated that the conventionally used gravity-feed mechanism is not suitable from the tool wear point-of-view, and a particular initial T-W gap should be maintained during the ECDD process. The T-W gap between 10 and 30 µm for the NaOH electrolyte and 5–20 µm for the KOH electrolyte is recommended.