The In-Process Dressing Characteristics of Vitrified Bonded CBN Grinding Wheels

When grinding carbon steels, creep-resistant materials, and other metals such a titanium, cubic boron nitride (CBN) has become recognized as the preferred choice over Al₂O₃ and SiC. The succes or failure of the grinding process with CBN lies in the mechanical dressing of the wheel because mechanical dressing is accompanied by very large stresses that distort the grinding wheel and deflect the grinding machine. One recent approach is to true the CBN wheel mechanically and then dress the wheel during the actual grinding manufacturing process. This work observes the dressing of vitrified bonded CBN during the actual like cycle in the production process of steel bearings. Scanning electron micrographs of CBN wheel surfaces are related to surface topography measurements of both wheel and bearing using a Tallysurf machine. In addition, the compositions of the wheel surfaces were checked using the SEM x-ray spectrography facilities. In-process dressing was determined to comprise three distinct stages: the primary or initial dressing, the secondary occurring during steady-state grinding, and finally the tertiary stage after which dimensional tolerance is lost. It was found that the life characteristics of the CBN wheel are quite different than current theories predict. Instead of the limitation of grinding being due to work material loading of the wheel and subsequent dulling of the grains, it was found that the CBN grains remain unchanged and a wear process occurs in the matrix material until the grains fall out and the wheels lose their dimensional tolerance.