When the main drive system of the CNC milling machine is used for soil work, it is precisely because the gears, bearings and other components undergo an excitation response, and they are transmitted and radiated inside the system. The vibration force increases and the noise increases. How to control the bearing noise of the CNC milling machine? 　

　1. Control the quality of the inner and outer rings. In the main drive system of the malfunctioning milling machine, all the bearings rotate in the inner ring and the outer ring is fixed. At this time, if radial deflection of the inner ring occurs, it will cause unbalance during rotation, resulting in vibration and noise.

　　 If the outer ring of the bearing has poor matching hole shape and position tolerance, radial oscillation will occur, which will destroy the concentricity of the bearing components. If the end faces of the inner ring and the outer ring have a large lateral runout, it will also cause the inner ring of the bearing to be skewed relative to the outer ring. The higher the accuracy of the bearing, the smaller the aforementioned deflection and the smaller the noise.

　　 In addition to controlling the geometric deviation of the inner and outer rings of the bearing, the waviness of the inner and outer ring raceways should also be controlled, the surface roughness should be reduced, and the surface of the raceway should be strictly controlled during the assembly process. It is impossible to reduce the vibration and noise of the bearing. It is found through observation that when the waviness of the raceway is dense wave or sparse wave, the contact points of the rolling elements are obviously different when rolling, and the vibration frequency caused by this is very different.

　　2, control the matching accuracy of the bearing, the hole and the shaft. In the main drive system of the malfunctioning milling machine, the bearing should be matched with the shaft and hole to ensure that the bearing has the necessary radial clearance. The better value of the radial working clearance is determined by the fit of the inner ring on the shaft and the outer ring in the hole, and the temperature difference between the inner ring and the outer ring in motion. Therefore, the selection of the initial clearance in the bearing is of great significance to control the noise of the bearing. An excessively large radial gap will increase the noise in the low-frequency part, while a smaller radial gap will increase the noise in the high-frequency part. Generally, it is better to control the gap at 0.01mm.

The matching form of the outer ring in the hole will affect the noise propagation. A tighter fit will improve the sound transmission, thereby increasing the noise. An over-tight fit will force the raceway to deform, thereby increasing the shape error of the bearing raceway, reducing the radial clearance, and also leading to an increase in noise.

　　Only the proper fit of tightness can dampen the vibration of the outer ring by the oil film at the contact between the journal and the hole, thereby reducing noise. In addition, the shape and position tolerances and surface roughness of the mating parts should meet the requirements of the selected bearing accuracy class. If the bearing is tightly installed on a shaft with inaccurate machining, the shaft error will be transmitted to the inner ring raceway of the bearing and manifested in the form of higher waviness, and the noise will increase accordingly. The control of the bearings of the CNC milling machine can be carried out through the above methods.