Milling Parameters for Surface Finish, Material Removal Rate, and Cutting Force Using Taguchi and Response Surface Methodology

This paper presents a systematic experimental investigation into the optimisation of CNC end milling process parameters for EN31 alloy steel using the Taguchi L9 orthogonal array design, Analysis of Variance (ANOVA), and Response Surface Methodology (RSM). Three machining strategies — conventional, climb, and high-speed milling — were evaluated at three levels of spindle speed (2000, 3000, 4000 rpm), feed rate (100, 150, 200 mm/min), and axial depth of cut (0.4, 0.8, 1.2 mm) using a TiAlN-coated solid carbide four-flute end mill. Response variables measured include surface roughness (Ra), material removal rate (MRR), and main cutting force (Fc). Signal-to-Noise (S/N) ratio analysis identified the optimal parameter combination as spindle speed 4000 rpm, feed rate 100 mm/min, axial depth of cut 0.8 mm, using climb milling strategy. ANOVA revealed spindle speed as the most significant factor with 43.1 percent contribution to surface roughness, followed by feed rate (28.6 percent) and milling strategy (16.2 percent). RSM second-order models predicted all three responses with R² greater than 0.96. Climb milling reduced surface roughness by 39.4 percent and cutting force by 21.8 percent compared to conventional milling. Confirmation experiments validated predicted optimal values with errors below 4.8 percent.