Characterization and Reclamation of Machining Swarf Generated by Superabrasive Grinding of Ceramics

Abstract

This work examined the particle size of machining swarf generated during superabrasive grinding of silicon carbide, tetragonal zirconia polycystal and alumina workpiece materials. Grinding trials were carried out at surface speeds of 9.35 m/s, 19.7 m/s, 28.0 m/s, 37.9 m/s and 48.7 m/s for 40/50 120, 220, 320, and 600 wheel grit number diamond abrasive wheels. Swarf particle distributions were determined with laser light scattering analysis and related to machining parameters. Silicon carbide swarf examined show a tendency toward bimodal particle distributions at low surface speeds and low wheel grit designations, with increasing surface speeds and higher wheel grit designations resulting in finer mean particle sizes due to a shift of particles from the coarse to the finer peak. Mean particle size trends correlated linearly with both surface speed and the abrasive particle size in the grinding wheel ranging from 3.36µm at 9.34 m/s using a 40/50 grit number wheel to 0.67µm at 48.7 m/s using a 600 grit number wheel. Grinding of the tetragonal zirconia polycrystal material using a 600 grit number wheel at a surface speed of 48.7 m/s generated a mean particle size of 1.18µm. Observation of the tetragonal zirconia polycrystal swarf by SEM showed definite indications of plastic deformation based on the similarity of its chips with machining chips of ductile materials. Increased plasticity during abrasive interactions with the workpiece is believed to be the cause of the increase in mean particle size relative to silicon carbide swarf ground using identical machining parameters Industrially generated alumina grinding waste was also characterized and analyzed to determine the potential for reclamation and reuse. The grinding swarf displayed a particle distribution with a mean particle size of 1.15µm. This powder was cleaned, pressed into a pellet and then sintered at 1500 , with two other pellets hot pressed at a temperature of 1500 and 1600 at a pressure of 40ksi. These sintering trials resulted in a range of densities from 81.1% and 93.7% of the theoretical density of alumina.