Super-finishing Using Fine cBN Stone to Achieve Nano-mirror Surfaces on Hardened Steel

One of the goals of this study is to obtain nano-mirror surfaces on SUJ2 (J IS) hardened steel. We clarified the causes of drop-out of abrasive grains that increase surface finish (roughness), paying attention to the crossing angle between abrasive grain paths. We have developed an ultra-low-pressure method for obtaining a finer finish in super-finishing using vitrified bonded cubic boron nitride (cBN) abrasive stones. This is a finer finish with very little or no stock removal, less than ordinarily occurs in a conventional process using aluminum oxide or silicon carbide stones. We have fabricated a prototype super-finishing machine that provides stable ultra-low pressures by means of an air slide. Super-finishing was attempted using ultra-low pressures (less than 0.1 MPa) with cBN abrasives averaging less than 8 mum in diameter. As a result, super-finishing with a processing pressure of 0.02 MPa could be achieved using fine-grit cBN. The study demonstrated that a surface finish on the nano-order can be obtained under ultra-low-pressure conditions.