Grinding of Steels with Cubic Boron Nitride (CBN)

An investigation is reported on grinding of steels with resin bonded cubic boron nitride (CBN) wheels with various operating parameters, wheel compositions, truing and dressing methods, and workpiece compositions and heat treatment. During grinding, the forces were generally found to decrease from extremely high peak values at a progressively slower rate tending toward an apparent steady state. Surface finishes became much rougher during this transient. SEM examination of wheel surfaces indicated that high initial forces are due to flattened grain tips generated by wheel truing, and that subsequent force reduction is due to sharpening (reduction in flattened area) by grain pullout and fracture. The ultimate degree of sharpening depends mainly on the removal rate which, if sufficiently big, results a wheel with almost no flattened areas. In this case, the specific energy is independent of the removal rate (no size effect), which can be attributed to the influence of the CBN cutting point morphology on plowing phenomena. Likewise the surface finish is also insensitive to removal rate, and spark-out provides no significant surface finish improvement. A wire brush dressing technique was developed to avoid high initial forces.