Cutting Performance of SiAlON Ceramic End Mills in the High-Speed Milling of Inconel 718

To investigate the effect of spindle speed on the cutting response of solid SiAlON ceramic end mills during dry milling of Inconel 718, down-milling tests were conducted at 14,000, 16,000, and 18,000 r/min with identical nominal tool geometry, feed per tooth, and axial and radial depths of cut. Each tool completed a cumulative effective cutting length of 5 m. Cutting forces, temperature, and tool and chip morphologies were analyzed. Increasing the spindle speed from 14,000 to 16,000 r/min reduced the mean x-direction force by 10.7%, whereas the mean y- and z-direction forces increased. A further increase to 18,000 r/min raised the theoretical material removal rate by 12.5% but increased the mean z-direction force by 105.4%, relative to 16,000 r/min. The proportion of the recorded time above 900 °C reached 52.3%, accompanied by an increase in the mean resultant force during the middle and later stages of machining and more pronounced morphological irregularities at the end cutting edges. In contrast, at 16,000 r/min, the mean resultant force varied relatively little during these stages, and the end cutting-edge profiles remained relatively well defined. These findings indicate that, under the tested conditions, the productivity gains from increasing spindle speed should be evaluated jointly with multidirectional cutting loads, thermal conditions, and tool damage.