A novel eccentric lapping machine for finishing advanced ceramic balls

Abstract

Advanced ceramic balls are used extensively in hybrid precision ball bearings and show advantages in high speed, high temperature, high load and hostile environment. Finishing these balls with high quality, good efficiency and low cost is critical to their widespread application. A brief review of the methods for finishing ceramic balls is presented. The design of a novel eccentric lapping machine for finishing advanced ceramic balls is described. The kinematics of eccentric lapping is analysed and discussed, the symbolic expressions for the ball spin angular speed, omega (b), ball spin angle, beta, and ball circulation angular speed, omega (c), are derived and numerical solutions are plotted. Two kinds of hot isostatically pressed (HIPed) silicon nitride ball blanks (13.25-13.50 mm in diameter) were lapped and polished to 12.700 mm using this machine. A maximum material removal rate of 68 mum/h was achieved at the lapping step, which is much higher than by the traditional concentric lapping method. The polished ball surface roughness, R-a, value is 0.003 mum, and the ball roundness is 0.08-0.09 mum, which is above grade 5 and close to grade 3 of the precision bearing ball specification. This machine can be used as a prototype to develop a larger-scale machine for production.