Role of tool-substrate gap in the micro-holes formation by electrochemical discharge machining

Electrochemical discharge machining (ECDM) is an efficient micro-machining technique for fabricating hard to machine materials such as glass, alumina, zirconia, etc. Glass based substrates have many applications in the field of MEMS and microfluidic systems. The tool-substrate gap is one of the important process parameters which affects ECD machining characteristics such as micro-feature overcut, width, depth, etc. The reported work investigates the effect of the tool-substrate gap on the ECD machining performance with NaOH and KOH electrolytes. A tapered tool with 130 µm average tip size was used to create blind micro-holes in glass substrate with varying tool-substrate gap and machining time. Numerical and experimental results showed a similar decreasing trend of the depth of blind holes as the tool-substrate gap increases. Higher overcut was observed in the case of a tool-substrate gap of 20 µm in the NaOH electrolyte and 10 µm in the KOH electrolyte. The maximum tool-substrate gap up to which machining happened was observed to be 60 µm and 30 µm in the case of the NaOH and KOH electrolytes, respectively. Tool wear was found to be higher when the tool was in physical contact and when the NaOH electrolyte was used for a machining duration of 60s.