The polishing process of advanced ceramic balls using a novel eccentric lapping machine

The finishing process of advanced ceramic balls can be divided into two steps. The first step is lapping in which most of the stock from the ball is removed at a higher material removal rate. The second step is polishing in which the required ball surface roughness, roundness, dimensional and geometric accuracy are achieved. In polishing, the abrasive particle size is ≤ 1 μm, and the load and speed are lower than lapping. A novel eccentric lapping machine is used for polishing HIPed (Hot Isostatically Pressed) silicon nitride balls. In the initial polishing stage, the polishing load is demonstrated most influential in the reduction of surface roughness value Ra. However, in the later polishing stages, the erosive process played a major role in the further reduction of Ra, although the high roughness peaks cannot be removed by erosive process alone. Experimental results also show that in order to achieve desired surface roughness value, the initial surface quality of the upper plate should be reasonably high, and deep scratches should be avoided to leave on the ball surface in previous lapping process. The best polishing results achieved were surface roughness values of Ra of 0.003 μm and rms (Rq) of 0.004 μm, ball roundness of 0.08~0.09 μm. This proves the novel eccentric lapping machine is suitable for polishing advanced ceramic balls as well.