On finishing turning of Inconel 718 using WC and CBN cutting inserts under dry conditions

Innovative application fields, such as aerospace, require highly reliable materials to manufacture their components, as they frequently operate under harsh conditions, such as extremely hot and abrasive environments. Nickel-based superalloys are widely employed in these applications due to their outstanding mechanical properties, which they maintain over a wide temperature range. One of the most commonly used nickel-based superalloys is Inconel 718, which exhibits a yield strength of 550 MPa, remaining nearly constant up to 760 °C. However, the very high mechanical strength of Inconel 718, coupled with its low thermal conductivity, leads to limited efficiency during machining operations in terms of tool wear acceleration, shortening the tool life and negatively affecting the machined surface quality. Cubic boron nitride (CBN) inserts have proven effective in overcoming these issues, enabling high-speed machining while ensuring acceptable workpiece quality at the same time. This paper explores the performance of CBN inserts in finishing turning of Inconel 718, compared with the coated tungsten carbide (WC) tools currently used in industrial practice. The turning experimental campaign was conducted under flood and dry conditions to evaluate the feasibility of the latter as a more sustainable alternative when machining Inconel 718. The comparison was made in terms of inserts’ life curves and wear types, degree of surface roughness achieved on the workpiece, and required cutting forces. The main key findings are: (i) the CBN inserts are less affected by adhesive phenomena compared to the WC ones but suffer from end-of-life chipping; (ii) dry turning with CBN inserts combines good productivity and a better degree of surface finish with a lower environmental impact.