Cutting Mechanism of Superfinishing by Fine CBN Stone

The paper deals with some features in cutting mechanism of superfinishing by vitrified bonded fine cubic boron nitride (CBN) stones as applied to hardened bearing steel and their applications for optimizing stone structures and operating conditions. Comparative tests among the equivalent stones of CBN, diamond, aluminum oxide abrasives are carried out. In contrast with the performance by conventional stones in which break-off and loading take place purposely, the CBN stones show stable cutting performance with little tendency to wear and spall on cutting edges. This higher cutting capability, on the other hand, inevitably tends to be associated with rougher surface finish. Along with cutting experiments under the widely ranged operating conditions, carefull SEM observations are executed on the stones and chips removed. To sustain high cutting performance with acceptable surface finish, CBN stones with finer grit size than that employed in conventional ones are recommended to use under the conditions which ensure a stable cutting and fine finish acceptable with little loading by providing suitable small channels on the bond for easy chip removal. The conditions recommended are lower stone pressure, high peripheral speed and a certain optimal inclination angle.