Bolts, round head with oval neck,Cup Head Nib Bolts,Cup Square Bolts Zhejiang XianChuang Auto Parts Co.,LTD , https://www.showstrong.com Bearing assembly quality hazard
Analysis of the causes of fragmentation and solutions
Figure 1 bearing metallurgical organization 
(a) Macro inspection 
(b) SEM scan 
Figure 3 Fracture section enlargement Conclusion
As an important part of bearing bearing life, the assembly of bearing assembly is affected by many factors, including the selection of bearing material, bearing installation design, manufacturing process and manufacturing precision. If the installation process and method of the bearing are improperly selected, it is easy to cause the inner ring to be damaged or the assembly is not in place during the bearing assembly process, which seriously affects the operating life of the rotating component. From a certain point of view, since the bearings are now gradually standardized in the design of various mechanical products, the influence of the installation and matching design precision of the bearing and the material selection and other ontology factors on the installation process are getting smaller and smaller, which can be neglected.
The front and rear hub bearings used by our company's front axle assembly are all tapered roller bearings. The bearing body material is GCr15. The main feature of this type of bearing is that it can carry a certain load, and the structure of adjusting the gap is easy to realize. The bearing installation method is installed in a cold state, and then the mounting sleeve directly hits the inner ring of the bearing until it is in place. From the point of view of product design, the inner bearing installation mainly adopts interference fit, the interference is 0.010~0.035mm, and the outer bearing is selected as transition fit. Since the machining accuracy of the mounting part generally tends to be the clearance control for the machining control, there is no problem with the outer bearing of the transition fit, but for the inner bearing installation with a small interference, the main risk is during the installation process. The inner ring of the bearing is broken. In this paper, the causes of the rolling bearing fracture during the assembly process of the front axle assembly are analyzed, which provides an effective improvement direction for the assembly process on site.
1. Bearing manufacturing precision
Assembly assembly line feedback: The bearing provided by a company continuously has the problem of internal bearing assembly fragmentation during the assembly process. After the assembly station is improved, the bearing fragmentation cannot be completely eliminated.
According to the metallographic examination report obtained by crushing and cleavage analysis, the heat treatment structure of the bearing itself is hidden needle martensite, which is consistent with the national standard, and no major defects are found (see Figure 1).
Macroscopic inspection of the fracture of the fracture bearing and SEM scanning of the bearing revealed that there were machining marks on the inner ring of the bearing (see Figure 2).
Figure 2 Fracture area cleavage
Further observation of the fracture site revealed that the two arc-shaped transitions were inconsistent in shape and that there was a source of cracks in one of the locations (see Figure 3). By consulting the product design, it is known that this part is required to maintain R3 ~ R5mm.
From the above bearing fracture analysis, the reason for the fracture of the bearing batch is that the bearing product has a tool mark in the key part of the manufacturing process, which leads to invisible crack in the heat treatment process of the bearing, and is further expanded in the subsequent grinding process. Since the bearing is an interference fit, our company is currently installed in a cold state, and the outside world must apply a large force to overcome the resistance to ensure the installation is in place. In addition, the positioning and guiding of the sleeve of the bearing itself are not accurate, and these factors are intensified. A one-time overload condition occurs in the inner ring of the bearing during assembly, which eventually leads to chipping of the bearing assembly.
2. Selection of installation methods
Assembly assembly line feedback: Using the 7312E bearing provided by a company, the bearing fragmentation phenomenon occurs continuously, and the fragmentation product is 3 to 5 pieces per shift. Since the shape of the fault is consistent with the previous batch, it was initially identified as the quality of the bearing itself, but it cannot be eliminated by improving the design of the station. By measuring the inner diameter of the bearing and comparing it with the bearing of another manufacturer, it is found that the inner diameter of the bearing produced by the company is generally lower, resulting in a interference of 0.005 to 0.010 mm larger than that of the other manufacturer. If the assembly is carried out according to the original assembly habits, it will inevitably lead to an increase in the probability of a one-time overload during the bearing installation process, and the proportion of the inner ring of the bearing is increased. After consultation with the technical department, it was decided to use the hot-packing process for assembly, which not only improves efficiency, reduces labor intensity, but also effectively avoids bearing cracking. At the same time, according to the interference demand set by the product, combined with relevant information, the bearing heat is combined. The temperature of the unit is controlled at 110 °C. Through subsequent practice, it is proved that the phenomenon of bearing fragmentation is effectively controlled after the hot charging process.
Through the on-site solution and analysis of the bearing assembly and chipping problems in this batch, it is necessary to adopt different assembly and installation methods to ensure the bearing installation for the bearing processing habits of different manufacturers. The assembly and installation method has a great influence on the subsequent assembly, especially the assembly work of the mass flow component assembly.
In summary, in addition to the problem of large bearing fragmentation during the bearing installation process, the machining accuracy of the bearing itself and the tolerance distribution range are also important factors. In the actual analysis process, it should be confirmed and solved according to the actual use situation, in order to achieve good results.