ECONOMIC EVALUATION OF CERAMIC END MILLING TOOLS FOR ROUGH MILLING OF BLISKS MADE OF INCONEL 718

High-pressure compressor stages in modern aero-engines are commonly designed in the integral blisk ("blade-integrated disk") configuration, due to their advantages regarding weight, blade density and freedom in airfoil design over conventional blade-disk assemblies. These components consist of thin-walled airfoils with high-aspect ratios, which result in a large weight percentage of the workpiece to be removed before achieving the final part. Because of their complex shape and tight dimensional tolerances, most of the machining is done by the conventional cutting technologies turning and milling. Thereby, first near-net-shape blanks are turned and then the blades are milled with end milling tools. As operating temperatures in the compressor section are rising to reach higher engine efficiencies, blisk components are increasingly made of heat-resistant superalloys (HRSA) such as Inconel 718. Machining processes for these components made of difficult-to-cut nickel-based alloys exhibit low productivity and high tool wear, which can be attributed to the conventionally used cemented carbide tooling. Innovative ceramic cutting materials such as SiAlON can be produced in the form of end milling tools and offer the potential to increase the productivity in the time-consuming roughing operation significantly. Due to the high hardness at elevated temperatures, the cutting velocity v(c) can be increased by a factor of 20 when using ceramic end milling tools compared to conventional strategies with cemented carbide. However, these innovative cutting tools are rarely applied in series production, which may be due to their high costs compared to cemented carbide tools. This study, therefore, aims at evaluating the economic potential of SiAlON end milling tools for roughing operations of blisk components made of Inconel 718. To reach this goal, a blisk milling process was designed and executed with both tool configurations, tool wear and machining times of all operations were measured and tool life as well as machine costs are evaluated.