Multi-objective precision optimization of μ-ECM performance for Hastelloy C-22 using hybrid AHP–MOORA analysis

Hastelloy C22 is a nickel-based superalloy utilized in chemical processing, aero engines, and pollution control equipment. Electrochemical micromachining is a suitable process for addressing the formidable hardness of nickel alloys, alongside the challenges of miniaturization. However, achieving a precise surface finish and dimensional characteristics in the microchannels of chemical reactors and microfluidic channels presents a potential avenue for this research. In this study, Hastelloy C22 was machined using a brass tool of 500 µm under two electrolyte combinations, namely sodium chloride (NaCl) + sodium nitrate (NaNO 3 ) and sodium bromide (NaBr) + sodium nitrate (NaNO 3 ). Two sets of Taguchi's L9 runs were employed to derive the machining performance with applied voltage, electrolyte concentration, tool feed rate, and duty cycle as input variables. The output responses considered in this study include material removal rate, surface roughness, radial overcut, and taper angle. The results of the analysis of variance showed that variations in voltage and duty cycle are statistically significant factors impacting the output responses. The results from the analytical hierarchy process (AHP)–MOORA (multi-objective optimization by ratio analysis) method showed that the best results from the NaBr and NaNO 3 mixture produced surface roughness (0.176 µm), taper angle (23.47°), material removal rate (0.0366 mm 3 /min) and radial overcut (0.418 mm) comparably better than those using the NaNO 3 + NaCl mixture. Using a combination of NaBr and NaNO 3 has shown to provide synergistic effects that work to provide superior control of the dissolution and surface refinement of Hastelloy C22.