Research On Ceramic Ball Lapping And Sphere-Shaping Mechanism With Rotated Dual-Plates Machine

Over the past decade, ceramic balls have become important components in advanced bearings, and are successfully used in hybrid bearings (ceramic balls and steel races). Silicon nitride, especially, is considered as the most promising material for high speed, high temperature and high precision bearing for jet engine, high precision machine tool and apparatus because of its desirable properties.To overcome limitations in traditional lapping process, such as low precision and efficiency, low uniformity and stability of process, a new type of high efficiency lapping method for high precision ceramic ball, Rotated Dual-Plates (RDP) lapping, is developed in this paper. Under RDP lapping mode, two down plates are driven to rotate respectively in designed speed combination to achieve better uniformity of lapping trace distribution on ceramic ball surface, which will improve lapping accuracy and sphericity error correcting rate. RDP lapping method involving ball kinestate, lapping trace distribution, sphere-shaping mechanism, ball surface wear, high efficiency material removal technology, and optimization of lapping parameters are studied in this paper.In this paper, lapping trace distribution on ball surface is studied with observing the marked point on the ball surface, and 3D simulation of lapping trace. A uniformity valuation method for lapping trace is also put forward, and the uniformity requirements and satisfying degree under RDP lapping mode are discussed.To study the'size selection'of ceramic balls in lapping process, mechanisms of sphere error correction, unifying process of ball size, ball sliding against plates and impaction between balls are studied. The influence of loading system, lapping parameters and lapping tools on sphere-shaping process is also discussed with experiments and theory analysis.The wear mode of ceramic balls involved in the lapping process is also investigated in this paper. Abrasion tests are performed with different grit size, loads and slurry concentrations on a ball-plate wear test apparatus. To improve the material removal rate of ceramic balls, a fixed abrasive lapping technology employing fine diamond abrasive and photosensitive resin is used to replace traditional free slurry lapping in rough stage.To figure out a better process for ceramic ball under RDP lapping mode, Taguchi method is applied to optimize lapping parameters to obtain the better MRR, sphericity and surface finish. Influence of parameters involving, including load, speed, and slurry concentration is discussed and the optimum lapping conditions are figured out.In the final part of this paper, a high efficiency lapping process developed in this paper for high precision ceramic ball is introduced. In this process, fixed abrasive lapping technology is adopted to improve MRR of ceramic ball in rough lapping, RDP lapping technology is employed to improve ball precision and consistency in semi-finishing stage, and CMP (chemical mechanical polishing) technology is used to obtain high surface quality in finishing. Fine sphericity (0.05μm), surface finish (Ra 5nm) and batch diameter variance (0.10μm) are obtained, and the total lapping time is reduced to 1/2~1/3 of traditional lapping process.