Ultra-precision grinding of bearing raceways is a common process for finishing the surface of bearing raceways. Finishing processes mainly include ultra-precision grinding, polishing, cross-linking, abrasive belt grinding, and finishing machine finishing. Ultra-precision grinding of bearing raceways is the final step in raceway grinding. The process involves using a microcrystalline abrasive wheel (whetstone) under good lubrication and cooling conditions (often using oil-based ultra-precision fluid), applying small pressure perpendicular to the workpiece's rotation direction. The workpiece rotates at a certain speed, while the whetstone simultaneously performs rapid, short reciprocating oscillations. The reciprocating oscillation trajectory of the whetstone maintains the same shape and contour as the bearing raceway cross-section. To obtain superior raceway microstructure quality, it is typically divided into two stages: rough ultra-precision and fine ultra-precision, using whetstones of different grits and different cutting parameters. Ultra-precision grinding of bearing raceways with whetstones can significantly reduce surface roughness, improve raceway profile and waviness, and eliminate internal structural stresses generated after grinding. After ultra-precision finishing, a compressive stress layer forms on the raceway surface, which helps improve the contact fatigue strength of the bearing raceway, enhances the oil film quality during use, and strengthens the raceway's corrosion resistance.
The quality of the rolling surface of the bearing rings directly affects the bearing's performance and service life. Grinding, due to its pursuit of production efficiency, typically involves large cutting volumes and is often affected by factors such as grinding machine precision, vibration, deformation, high temperature, and cutting parameters, making it difficult to directly achieve the final technical requirements of the raceway surface. Key quality indicators such as surface roughness, waviness, geometric accuracy, and the physical and mechanical properties of the surface layer still require finishing after grinding to meet bearing precision requirements. The main technological benefits of ultra-precision finishing include: reducing raceway roughness. During ultra-precision finishing, the oilstone mainly acts on the crests of the waviness, not the troughs. Under good grinding quality, the ultra-precision amount is generally 3~5μm. For heavy-duty bearings, the raceway roughness after ultra-precision finishing can be reduced to Ra0.25 or Ra0.4 or less. Reducing roughness helps slow raceway wear, reduce frictional resistance, and improve fatigue strength, thereby extending bearing life. Furthermore, lower roughness also improves corrosion and chemical resistance. Reducing raceway waviness: The oilstone makes surface contact with the raceway, and its contact arc is larger than the wavelength of the workpiece surface waviness. This effectively removes waviness peaks (eliminating only one-sided peaks, without affecting troughs), thereby reducing waviness and minimizing vibration and noise during high-speed bearing operation. Improving raceway shape profile: The oilstone reciprocates and oscillates according to the theoretical profile of the raceway cross-section. Through the grinding action of fine abrasives, it effectively corrects the local groove shape, improving it by approximately 30%. This helps optimize the stress distribution on the raceway and improves the bearing's load-bearing capacity. Forming an ultra-precision compressive stress layer on the raceway surface: The raceway surface after grinding often has a tensile stress layer with low hardness, making it prone to fatigue spalling. Ultra-precision grinding, through the reciprocating oscillation and pressure of the oilstone, generates residual compressive stress on the surface, resulting in a denser structure and enhancing the raceway's fatigue resistance and spalling resistance. Improving the quality of the oil film on the raceway surface: By removing surface peaks and reducing roughness, the oil film thickness and λ ratio can be increased, enhancing lubrication, reducing friction, and ensuring a stable oil film between the raceway and rolling elements. This helps to lower operating temperatures and extend service life. Improving raceway surface cleanliness: Lower roughness makes it less likely for wear debris and stains to remain, facilitating cleaning and thus improving the raceway's resistance to rust and chemical contamination, reducing wear, and further extending bearing life.