Multi–criteria optimization of cutting parameters during dry computer numerical controlled milling of martensitic stainless steels 410 and 420 using grey relational analysis

This study optimized cutting parameters for dry computer numerical control milling of martensitic stainless steels (410/420) using grey relational analysis and identified the optimal parameters as a spindle speed of 1500 min −1 , a depth of cut of 0.3 mm, and feed rate of 30 mm/min, achieving a balanced reduction in R a (0.62 μm– 0.66 μm) and F c 164 – 200 N) and with a balanced temperature of 44 – 48 °C. Analysis of variance revealed that the depth of cut was the dominant factor, contributing 57 % (martensitic stainless steel 410) and 62 % (martensitic stainless steel 420) to the grey relational grade variance. This was followed by the feed rate (27 % and 25 %, respectively) and the spindle speed (12 % and 10 %, respectively). The intermediate spindle speed of 1500 rpm softened the cutting zone, reducing F c and R a . Normal probability plots confirmed residual normality, validating the reliability of the experiment. Surface plots revealed peak grey relational grade values at a medium spindle speed and a low depth of cut/feed. Scanning electron microscope is employed for tool wear analysis. This study shows that parameter synergy, rather than individual adjustments, is essential for multi‐objective optimization in hard‐to‐machine steels.