Understanding the self-sharpening characteristics of polycrystalline cubic boron nitride super-abrasive in high-speed grinding of Inconel 718

Abstract

This study aims to understand the self-sharpening characteristics of the polycrystalline cubic boron nitride (PCBN) super-abrasive grains in high-speed grinding of Inconel 718. Comparative single grain grinding operations by separately using the brazed PCBN and conventional CBN abrasive grains are carried out. An in-depth analysis on the grain fracture morphologies and the workpiece scratch profiles during grinding are provided. The cutting mechanism and the material removal difference induced by the PCBN and conventional CBN grain fracture behaviour during grinding are revealed. The obtained results indicate that, the PCBN abrasive grain tends to intergranular fracture during grinding, which not only leads to the grain micro-fracture behaviour but also provides plenty of micro cutting-edges of microcrystalline CBN particles to participate in the grain cutting process. The surface roughness of the workpiece scratch grooves produced by the PCBN abrasive grain is 0.30 μm in average, which is 0.10 μm higher than that produced by the conventional CBN abrasive grain. This is mainly attributed to the additional cutting effects of the outcropped microcrystalline CBN particles on the PCBN grain fracture surface in the actual grinding process, and the additional grain cutting effects on the workpiece materials contribute to the self-sharpening characteristics of the PCBN. Finally, a mechanical analysis model of the single abrasive grain in grinding is also developed to provide a more comprehensive understanding on the self-sharpening mechanism of PCBN, and the established mechanical model can be correctly demonstrated by the calculated grinding force ratios in the single grain grinding operations.