Machined surface integrity of inconel 718 in high-speed dry milling using SiAlON ceramic tools

Abstract

The surface integrity of complex engineering components has a major effect on their mechanical properties. Recently, modern ceramic tools have demonstrated themselves as potential candidates for high-speed machining of heat-resistant superalloys, delivering a substantial increase in productivity. The results of previous studies showed that after surpassing a cutting speed of 800 m/min, the cutting forces experienced a sharp decrease accompanied by a reduction in tool wear. However, in such applications, extreme temperature and mechanical loads are generated at the cutting zone, implying a possible negative influence on the machined surface integrity. In this study, numerous characterizations have been performed to evaluate the different aspects of inconel 718–machined surface integrity after face milling with SiAlON cutting tools at the range of 900 m/min. Since the cutting conditions are remarkably far from those experienced during conventional cutting, the results are also compared to those obtained during conventional milling of inconel with a commonly used commercial coated carbide tool. Results showed that the milling process induces tensile residual stresses as high as 2 GPa on the machined surface while generating an unwanted white layer with a thickness of around 1 μ and a relatively rough surface with Ra = 4.5 μm as compared to surfaces machined with conventional carbide tools at Ra = 2.2 μm. No major work-hardening effect was observed. Nevertheless, imperfections were observed to be contained within a thin sub-layer of the workpiece, suggesting that the ceramic tools can be used for roughing processes provided further finishing operations performed to remove the damaged layer.