Factors effecting on the roundness of the inner raceway of rolling bearings

The raceway roundness of the inner ring of a rolling bearing is an important quality index, which directly effects on the working accuracy, stability and service life of the bearing. The main factors effecting on the roundness of the inner ring raceway are as follows:

1. The inner ring raceway’s grinding is divided into semi-finishing or finishing processes. They usually play a decisive role in the roundness of the inner ring raceway of the finished product. In addition to the accuracy and dynamic characteristics of the grinding process system, the roundness of the inner ring raceway grinding is closely related to the grinding process parameters. It has been valued by many scholars and conducted a lot of research, which greatly improves the roundness of the grinding inner ring raceway by the way of improving precision of the grinding process system and the dynamic characteristics. The grinding process parameters have become the main factor effecting on the roundness. Therefore, it is great significance to study the influence of the grinding process parameters on the roundness, and reasonably select the process parameters to ensure the roundness of bearing raceway, so as to realize the optimization of the optimization of grinding process parameters of the bearing raceway. 

2. Grinding feed rate of bearing inner ring groove. Usually, the inner ring raceway is processed by the cutting-in grinding method by changing the feed speed. The grinding cycle operation can be divided into four stages: rapid approach of the workpiece, rough feed, fine feed and no feed grinding. The main factors effecting on the roundness of the grinding bearing raceway can be summarized as:

(1) The accuracy of the process system during the grinding process. This depends on the precision of the grinder and the positioning principle, structural parameters and accuracy of the fixture:

(2) The dynamic characteristics of the process system. Especially the balance state of the grinding wheel: during the wheel dressing and grinding process, the unbalance of the grinding wheel will cause forced vibration, due to the difference between the relative position of the dresser and the grinding wheel when the dresser dressing grinding wheel and that of the workpiece and the grinding wheel during grinding, as well as the difference in the rigidity of the process system under these two different situations, causes the vibration to bring about the surface of the ground workpiece to be non-round ,the grinding process parameters will affect the contact stiffness between the grinding wheel ,and the workpiece, the wear process of the grinding wheel and the damping characteristics of the process system vibration, thus affecting the vibration characteristics of the grinding process ,finally reflected in the geometry (i.e. roundness) and other surface qualities of the ground workpiece.

(3) Elastic deformation of the process system. This will lead to the reproduction of the original error of the workpiece. By analyzing of the variation rule of the geometric error of the workpiece in the grinding cycle shows that the reflection of the geometrical error of the workpiece after grinding mainly depends on the rigidity of the process system, the grinding process parameters, and the wear speed of the grinding wheel and original error of the workpiece. Considering the above influencing factors when the rigidity and dynamic characteristics of the process system are constant (especially the grinding wheel must be well balanced), the roundness error of the grinding workpiece mainly depends on the grinding process parameters, so the test data of the grinding roundness ,some important parameters can be selected important parameters from multiple process parameters through stepwise regression modeling, and regression equations can be gradually introduce to establish the optimal regression equation for the relationship between grinding roundness and process parameters.

3. Vibration of the machine tool caused by unbalanced grinding wheel or other factors. This will seriously affect the roundness of the ground workpiece. Keeping a good working condition of the machine tool and a good balance of the grinding wheel are the prerequisites for the application of the roundness mathematical model fitted above. In addition, different grinding wheel hardness, organization, abrasive grain size and abrasive types, as well as different coolant composition, will have a certain impact on the roundness of grinding.