Process parameter optimization for CNC ball end milling of AISI 1020 prosthetic foot molds

Computer numerical control (CNC) ball end milling of prosthetic foot molds requires a balance between machining efficiency and surface quality because productivity-oriented parameters may reduce cycle time but deteriorate the mold surface. This study developed a process window for finishing a two-piece AISI 1020 prosthetic foot mold by considering computer aided manufacturing (CAM) estimated machining time and arithmetic mean surface roughness (Ra) simultaneously. A Taguchi L27 orthogonal array was used to evaluate stepover, feed rate, and axial depth of cut. Machining times for the upper and lower mold halves were estimated using Mastercam 2025, while Ra was measured experimentally using a contact stylus profilometer. Signal to noise (S/N) ratio analysis and analysis of variance (ANOVA) were used to determine factor effects, followed by desirability function optimization with equal response weights. Stepover was the dominant factor, contributing 52.9869% and 52.7903% to the CAM estimated machining time of the upper and lower mold halves, respectively, and 81.7726% to Ra. The fastest machining condition was obtained at s = 0.45 mm, f = 800 mm/min, and ap = 0.40 mm, whereas the best surface finish was obtained at s = 0.15 mm, f = 300 mm/min, and ap = 0.20 mm. The best compromise was achieved at s = 0.30 mm, f = 800 mm/min, and ap = 0.30 mm, with D = 0.8768, Ra = 2.368 μm, Tupper = 13.221 h, and Tlower = 12.197 h. This setting reduced Ra by 58.2% compared with the fastest condition, with only a moderate machining time penalty. The proposed framework provides an application-specific decision approach for CAM-based freeform mold finishing.