Micro-fracture variation and grinding performance of PCBN superabrasive grains in high-speed grinding

Abstract

Abstract In this work, a finite element analysis model of micro-fracture of polycrystalline cubic boron nitride (PCBN) superabrasive grains based on Voronoi diagrams was established to study the fracture behaviour during the single-grain high-speed grinding process of Inconel 718 nickel-based superalloys. The profile evolution of grain was predicted by iterating the profile of fractured grain and analysed by combination with the experimental results. The effects of internal stresses and microstructure of PCBN grain on grain fracture were investigated. The profile evolution and chip formation process of PCBN grain due to micro-fracture were analysed, and the effect of micro-fracture on the grinding performance of PCBN grain was studied. Results showed that the main fracture modes of PCBN grain were micro-fracture near cutting edges and crack propagation inside the grain. Tensile stress was the main internal affecting factor of the fracture behaviour and led to more consumed volume than compressive stress. The microstructure of PCBN grain hindered the stress transfer and made the grain susceptible to cracks and micro-fractures. The number of cutting edges involved in the cutting process varied due to micro-fractures. The balance between the difficulty in chip formation and energy loss could only be reached when the percentage of fractured regions ranged from 40% to 50%. Micro-fracture changed the profile and sharpness of PCBN grain, thereby forming a ‘passivation-sharpening’ cycle.