MULTI-OBJECTIVE OPTIMIZATION OF CNC MILLING PARAMETERS FOR ENHANCED MACHINING PERFORMANCE: MATERIAL REMOVAL RATE AND SURFACE ROUGHNESS OF EN8 STEEL USING RESPONSE SURFACE METHODOLOGY

Abstract

The present work investigates the multi-objective optimization of CNC milling parameters for EN8 medium-carbon steel with the aim of enhancing material removal rate (MRR) while reducing surface roughness (Ra). Five process variables spindle speed, depth of cut, cutter feed, step over, and coolant concentration were varied using a three-level factorial design comprising 12 experiments on a vertical CNC machining centre. MRR was evaluated from weight loss and machining time, whereas Ra was measured using a surface profilometer. Second-order models developed through Response Surface Methodology showed excellent agreement with experimental data (R² > 0.999). Analysis of variance indicated that depth of cut and step over predominantly influence MRR, while step over and cutter feed significantly affect surface roughness. Interaction effects, particularly between depth of cut and step over, and cutter feed and step over, were found to be substantial. Multi-response optimization using a desirability approach yielded an optimal setting of 3500 rpm spindle speed, 0.36 mm depth of cut, 1707.07 mm/min feed, 53.33% step over, and 8% coolant concentration. This combination provided a high MRR alongside acceptable surface finish. The study establishes a reliable framework for balancing productivity and surface integrity in CNC milling of medium-carbon steels.