Investigating the effect of mixed alkaline electrolyte (NaOH plus KOH) on the improvement of machining efficiency in 2D electrochemical discharge machining (ECDM)

Since the microchannels have a vital role in microelectromechanical systems (MEMS), microfluidic and lab-on-a-chip devices, the surface quality, material removal rate (MRR), and geometrical accuracy of microchannels should be controlled well. The electrolyte nature is one of the dominant and important factors that affect the accuracy and performance of electrochemical discharge machining (ECDM). In this contribution, two alkaline electrolytes, NaOH and KOH, were mixed in equal proportion. It was observed that using NaOH + KOH mixed electrolyte at 15 and 25 wt% concentrations provides more electrical conductivity than KOH and NaOH separately at the same concentrations. It results in the fabrication of deeper microchannel with sharper sidewalls compared to KOH and NaOH, while its surface quality is preserved as well. Also, using 25, 30, and 35 wt% mixed electrolyte, due to higher viscosity compared to KOH, improved the surface quality of channels up to 35, 42, and 36%, respectively. Analyzing the waveform of the current response of various electrolytes showed that the microchannel with poor MRR and surface quality will be fabricated in the presence of salt electrolytes due to the generation of very low energy and unstable electrochemical sparks. In another part of the experiments, scanning electron microscopy (SEM) images and energy-dispersive X-ray (EDX) analysis of the tungsten carbide (WC) tool used in different electrolytes showed that the tools used in NaOH and NaNO3 had more severe wear compared to KOH and mixed electrolyte. Also, at the applied voltages of 50 V, the tool erosion was more serious compared to tool erosion at 35 V.