High Speed Machining of Inconel 718 with High Pressure Coolant Focusing on Material Structures of CBN Tools

Abstract

Recently, cubic boron nitride (CBN) cutting tools and high pressure coolant (HPC) have garnered significant attention for high performance machining of difficult-to-cut materials, such as nickel-based super alloy, Inconel 718. In this study, the cutting performance of a low-CBN-content (L-CBN) cutting tool, which is known as a suitable CBN material structure for the high-speed machining of Inconel 718, is investigated under the HPC conditions. The experimetntal results show that, although crater wear is significantly suppressed as the coolant pressure increases, the combination of high cutting speed and high pressure coolant causes severe thermal cracking on the tool rake face of the L-CBN cutting tool. Hence, we evaluate the cutting performance of high-CBN-content (H-CBN) cutting tool which has smaller coefficcient of thermal expansion, compared with the L-CBN cutting tool. A series of cutting experiments shows that changing the material structure of the CBN tool effectively suppressed thermal cracking and that the H-CBN tool is a highly promising option for the high performance machining of Inconel 718.