During gear grinding, the surface layer structure of the gear will change, that is, grinding burn. The reason is that the grinding temperature is high, up to 1500-1600 ° C, and the temperature of the workpiece surface layer is more than 9000 °. This temperature exceeds the phase transformation temperature of steel, so grinding is easy to cause burn problem. Especially when grinding hard tooth surface, the temperature in the grinding area is higher and burns are more likely to occur. In scraping, burns do not exist.
The residual stress of surface layer can be divided into residual tensile stress and residual compressive stress. It is generally considered that for parts with residual tensile stress, the surface layer or near the surface layer is easy to form crack source during use. Under the action of external load and environmental medium, the crack will further expand and eventually lead to failure. Therefore, it is an effective way to improve the service life of parts to try to obtain beneficial surface residual stress.
There are three reasons for the generation of residual stress in the surface layer: cold plastic deformation caused by cutting force, hot plastic deformation caused by cutting heat, and metallographic structure change. The surface residual stress during gear grinding is mainly caused by the hot plastic deformation caused by grinding heat, while the influence of cutting force and metallographic structure is very small; Moreover, the thermal plastic deformation caused by grinding heat has added the residual tensile stress of surface products, so the residual tensile stress is mostly formed on the tooth surface after grinding. When the residual tensile stress exceeds the strength limit of the material, cracks will occur. The research shows that during scraping, the residual stress of the gear surface layer is mostly residual compressive stress. This helps to improve the wear resistance and service life of the gear.
Compared with scraping and grinding, in addition to the above advantages, it also has the advantages of good flexibility and less machine tool investment. Therefore, when eliminating the heat treatment deformation of, the scraping process of hard tooth surface is of certain significance not only from the quality of tooth surface, but also from the aspects of machining efficiency and cost.