Study of the performance of PCBN and carbide tools in finishing machining of Inconel 718 with cutting fluid at conventional pressures

Abstract

Inconel 718 is a nickel-based superalloy widely used in the aerospace industry, nuclear plants and gas turbines due to the exceptional mechanical properties and resistance to corrosion at elevated temperature. For these reasons Inconel 718 have a low machinability due to the high temperatures that appear in the cutting area in addition to the wear caused in the tools as abrasion, chemical affinity, diffusion, flank and notch wear. Carbide and recently Polycrystalline Cubic Boron Nitride (PCBN), are the cutting tool materials used in finishing operations of nickel-based superalloys. This paper focuses on the comparative analysis of carbide and PCBN tools in finishing operations on Inconel 718 using cutting fluid at conventional pressure (7.5 bar). Experimental tests were performed at different cutting speeds, feed rate and depths of cut depending of the cutting tool. PCBN tools were used at speeds within the range of 250-300 m/min, feed between 0.1 and 0.15 mm/rev and depth of 0.15mm. Carbide tools are not used at such speeds because of their lower hardness at high temperature. Speeds five times lower than those were used for PCBN (50-70 m/min), the same feeds (between 0.1 and 0.15 mm/rev) and a depth of 0.25 mm were used. Tool life and machined surface has been analyzed with the aim of studying the viability of these tools in finishing conditions of Inconel 718. The results indicate that PCBN tools have a shorter life in minutes than carbide tools; however, the machined surface by cutting edge is larger at higher cutting speeds, so PCBN tools are an interesting alternative in this type of machining.