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Abstract Functionally graded surfaces — surfaces with properties that are engineered to have spatial variations — have numerous applications such as micropumps, auto-mixers, and flow control for lab-on-chip devices. Manufacturing of functionally graded surfaces is an increasingly important topic of research. This study investigates the feasibility of creating a functionally graded surface during channeling of borosilicate glass by the electrochemical discharge machining (ECDM) process. The ability to create surface roughness gradients in microchannels during the machining process was demonstrated by modifying the input voltage, tool feed rate, and tool rotation speed. Microchannels with graded surface roughness having Ra values ranging from 0.35 to 4.07 μm were successfully machined on borosilicate glass by ECDM. Surface profiles were obtained via a stylus profilometer, and roughness values were calculated after detrending and applying a Gaussian filter. To demonstrate the process versatility, micro channels with increasing and decreasing Ra values were machined, one increasing from 1.43 μm to 4.07 μm, another decreasing from 3.29 μm to 1.10 μm. To demonstrate the process repeatability, a micro channel with similar surface roughness on both ends and a lower Ra value in the center was created. In this channel, the Ra value at the start is 0.35 μm, reducing to 0.24 μm, then rising again to 0.38 μm in the final section. 

Electrochemical discharge machining (ECDM) is an emerging micromachining method to drill advanced non-conductive materials such as Hexagonal boron nitride (hBN). Physical contact of micro tools with work material could cause machining inaccuracies, excessive tool wear, and even tool breakage. In this study, a control system based on monitoring the force generated by the ECDM gas film has been developed to achieve non-contact machining of ECDM by dynamically adjusting the tool feed rate. The accuracy of the control system was verified by accelerometer and Fast Fourier Transformation (FFT) data. In the modules, it was found that a non-contact machining process requires the FFT amplitude to be lower than 42 V for a 1200 rpm tool rotation. The experimental results show consistent micro-holes with an average diameter of 650 µm and less than 20 µm error in the overcut achieved using this control system. 

Micromachining of glass has gained importance due to numerous applications of glass in microfluidics, optics, electronics, and biotechnology industry. Electrochemical discharge machining (ECDM) is an emerging nontraditional process which has the potential for micromachining of glass with minimal surface damages. Material removal during the machining of glass by ECDM involves thermal machining by electrical discharges between the tool and the gas film. The energy of these discharges is influenced by the gas film characteristics and affects the machining results. In this study, a combined approach of finite element simulation and experimentation is used to study the ECDM process to understand the impact of gas film characteristics on the overcut in machining. The multiphase simulation setup incorporates a combined electrochemical system of glass and electrolyte. The changes in the gas film characteristics due to the variations in the level of electrolyte and the corresponding changes in the overcut are studied. It was observed that the gas film thickness increased with an increase in the level of electrolyte and the gas film stability showed an opposite trend. This resulted in an increase in the overcut in the machining with the increase in the level of electrolyte. This trend observed in the simulation was validated with experimentation.