The polishing process of advanced ceramic balls using a novel eccentric lapping machine
Abstract 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, and 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 hot isostatically pressed (HIPed) silicon nitride balls. In the initial polishing stage, the polishing load is demonstrated as being 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 on the ball surface from previous lapping processes should be avoided. The best polishing results achieved were surface roughness values of Ra of 0.003 μm and r.m.s. (Rq) of 0.004 μm, ball roundness of 0.08–0.09 μm. This proves that the novel eccentric lapping machine is also suitable for polishing advanced ceramic balls.
A Novel Eccentric Lapping Method with Two Rotatable Lapping Plates for Finishing Cemented Carbide Balls
Abstract—Cemented carbide balls are usually implemented in industry under the environment of high speed, high temperature, corrosiveness and strong collisions. However, its application is limited due to high fabrication cost, processing efficiency and quality. A novel eccentric lapping method with two rotatable lapping plates was proposed in this paper. A mathematical model was constructed to analyze the influence of each design parameter on this lapping method. To validate this new lapping method, an orthogonal experiment was conducted with cemented carbide balls (YG6). The simulation model was verified and the optimal lapping parameters were derived. The results show that the surface roundness of the balls reaches to 0.65um from 2um in 1 hour using this lapping method. So, using this novel lapping method, it can effectively improve the machining precision and efficiency of cemented carbide balls.
Magnetic fluid grinding of ceramic balls
Abstract Magnetic fluid grinding is a process capable of material removal some 10 to 25 times quicker than is lapping, for the finish manufacturing of ball bearings. It is fast because balls, driven through a viscous fluid, are caused to skid against a drive shaft at speeds which can reach 10 m/s. Material removal is by abrasive wear caused by grits embedded in the drive shaft. In this paper it is shown that there is an optimum fluid viscosity: too small a viscosity does not cause skidding; too large a viscosity, although it causes skidding, prevents effective action of the grits in the shaft. Results are presented for the removal of material from silicon nitride, zirconia and alumina materials, over periods of up to 90 min. Abrasion is by plastic processes for the first two materials and by fracture for the last. Initially, wear coefficients range from 0.06 to 0.6. For all three, removal rates reduce with time probably due to loss of grits and to deterioriation of the fluids.