Research On Surface Quality Of Precision Ceramicballs For Dual Roating Plates Lapping Mode

Silicon nitride (Si₃N₄) balls (hot pressed or hot isopiestic pressed) are being actively considered for high speed/high temperature precision bearing because of many superior properties, including lower density, higher hardness, higher elastic modulus (higher stiffness), lower thermal expansion coefficient, higher thermal and chemical stability and non-magnetic characteristics compared to the traditional steel balls. Surface quality is a key factor that plays an important role in service life, precision, noise and etc of ceramic ball bearing. In this paper, the surface quality and its effecting factors, lapping parameters optimizing method are investigated.The mode of material removal of ceramic balls during lapping process is investigated, and its influence on surface quality is discussed. Abrasion tests are performed with different grit size, loads and slurry concentrations on a ball-plate wear test apparatus, A wear-mode map, which defines the regimes for two-body abrasion or three-body abrasion dominating in the micro-scale abrasion test, is plotted. An empirical formula for the wear mode transition is adopted to calculate the transition point, which can then used to predict the wear mode in lapping process of silicon nitride ball.To study the influence of lapping parameters on surface quality, surface roughness, surface damage and surface residual stress under different parameters are measured. It is found that lapping load is the greatest effecting factors on surface quality, smaller lapping load is better to obtain fine surface quality.Taguchi method is applied to optimize lapping parameters to figure out better lapping process parameters for ceramic ball surface quality. The influence on surface quality (Ra,Rt) of lapping parameters including load, speed, and slurry concentration is discussed and optimized.CMP (Chemical mechanical polishing) technology is adopted to further improve the surface quality and reduce the surface damage. The resultant on ball surface after CMP processing is measured by XPS technology, and the theoretical prediction is approved. Fine surface of Ra 5nm for 05mm ball is obtained by CMP technology.