Numerical and experimental investigations into microchannel formation in glass substrate using electrochemical discharge machining

Microchannels formed in non-conductive substrates like fused silica, glass and quartz, etc, have wide applications in the field of micro-fluidic and lab-on-chip applications due to their optical transparency, chemical inertness, and biocompatible nature. Electrochemical discharge machining (ECDM) has emerged as a potential low-cost fabrication method to fabricate microfeatures in these materials, compared to conventional laser etching techniques. In this paper, numerical simulation and experimental fabrication of microchannels in a glass substrate using the ECDM based micromilling technique is demonstrated. Stainless steel needle as tool electrode is used in alkaline electrolyte medium. The effects of process parameters viz. tool feed rate, pulse frequency and machining voltage on material removal rate (MRR) and surface roughness (SR) of the microchannels were analysed. The experimental results showed that the MRR and SR increases with an increase in machining voltage and tool feed rate but reduces with an increase in the pulse frequency. Simulations using FEM-based model showed similar trends in MRR with that of experiments. A comparison between the cross-section profiles obtained by the experimental work and predicted profile by the numerical simulation showed some deviation between them due to the Gaussian heat flux assumption in the numerical model. Optical images showed that KOH performance is comparatively better than NaOH with respect to thermal damage and width of cut. Further, multi-objective optimization was performed using utility theory coupled with Taguchi's method to optimize the process parameters. Moreover, the capability of the ECDM process was demonstrated in fabricating various other micro-features such as sinusoidal channel, letter engraving, etc in a glass substrate, which can be extended to other brittle materials like quartz, fused silica, ceramic, etc.