Influence of Turning Conditions on Force, Surface Roughness, and Cylindricity of C45 Steel

Achieving high surface quality and geometric accuracy while minimizing cutting forces remains a major challenge in precision machining. This study experimentally investigates the influence of cutting speed, feed rate, and depth of cut on cutting force, surface roughness, and geometric deviations during dry CNC turning of C45 medium-carbon steel. Experiments were performed on a HUNOR PNC721 CNC lathe using a Taguchi L9 orthogonal array with cutting speeds of 130, 150, and 180 m/min, feed rates of 0.10, 0.20, and 0.30 mm/rev, and depths of cut of 0.5, 1.0, and 1.5 mm. Cutting force, surface roughness (Ra and Rz), cylindricity (CYLt), roundness (RONt), and straightness (STRt) were evaluated using precision measurement systems. Analysis of variance (ANOVA), Pearson correlation, and regression analysis were employed to assess machining performance. The results revealed that depth of cut accounted for 70.69% of the observed cutting-force variation, with mean force increasing by approximately 58.0% as depth of cut increased from 0.5 to 1.5 mm. Cutting speed exhibited the largest contributions to Ra (32.32%) and Rz (39.88%), while feed rate accounted for 55.29% of cylindricity variation. A strong positive correlation was identified between Ra and Rz (r = 0.929, p < 0.001). Although ANOVA factor effects were not statistically significant at the 5% level, the findings demonstrate the importance of considering multiple machining responses when selecting cutting conditions. This study provides experimental insights supporting process planning, surface quality improvement, and geometric precision in C45 steel turning.