The grinding of tool steels-a comparison between diamond and cubic boron nitride

The performance characteristics of two grinding wheels, each containing one of the super-hard abrasives, diamond or cubic boron nitride, CBN, are found to be at variance when the wheels are used to grind a number of different hardened tool steel workpieces. Although each of the wheels contains metal-clad abrasive and is of the resinoid bond type, the diamond wheel is of a significantly softer grade and hence no attempt is made to compare the wheel performances on a straight quantitative basis. The results of plunge-type surface grinding tests indicate that CBN abrasive wears primarily as a result of mechanical wear processes whereas diamond abrasive suffers both mechanical and chemical attack by the workpiece material, the latter perhaps being insignificant when the carbon content of the steel is sufficiently high. The grinding force variations for the two wheels are found to be different in nature. Diamond grinding forces are found to increase during the early stages of grinding whereas forces associated with the use of the CBN wheel decrease from the initial values. Eventually, the forces appear to attain equilibrium values. The tangential components of the wheel force are much the same for diamond and CBN, but the radial component of wheel force, when grinding with diamond attains a value of some four times that for CBN abrasive. The surface finishes produced on the ground workpieces are measured but appear not to be simply related to the mechanical properties of the workpiece materials.