Effect of grinding wheel speed on self-sharpening ability of PCBN grain during grinding of nickel-based superalloys with a constant undeformed chip thickness

Abstract

Cubic boron nitride (CBN) superabrasive wheels are of great potential in grinding of difficult-to-machine metallic materials. The grain wear and its evolution directly determine the sharpness of the grinding wheels, and therefore greatly affect the grinding efficiency, surface integrity and the tool life. In order to effectively control the grain wear, the present work is aimed to elucidate the wear behavior difference of polycrystalline CBN (PCBN) abrasive grains and conventional CBN grains, and meanwhile analyze the influence of grinding wheel speed (ranged from 20 to 120 m/s) on the PCBN grain wear. The wear behavior was also quantitatively characterized based on the fractal theory. Results obtained show that the self-sharpening ability of PCBN grain is superior to CBN grain considering the fractal dimension and specific grinding force. The radial wear and specific grinding force with the grinding wheel speed of 120 m/s increase severely by 29.6% and 117.3% compared with that of grinding wheel speed of 80 m/s, which is in accord with the change of fractal dimension. When considering the wear evolution behavior of PCBN grains, a critical grinding wheel speed, e.g., 80 m/s, could be determined. If the grinding wheel speed is above 80 m/s, the grain macro-fracture wear happens rapidly; however, if it is below 80 m/s, the grain micro-fracture wear increases with increasing of the grinding wheel speed. According to the finite element analysis, the micro-fracture of the PCBN grain is mainly caused by the intergranular fracture of the grain, while the attritious wear is due to the wear of the grain cutting edge.