The root cause of grinding burn is grinding heat, so reducing grinding heat is the key. First of all, appropriate grinding wheels should be selected. At present, CBN and TG grinding wheels have been widely used because of their good thermal stability, hardness and strength, and low grinding temperature; Secondly, select a suitable grinding depth to ensure that the rough grinding feed is not more than 0.03~0.05 mm and the fine grinding is not more than 0.01~0.02 mm, and reasonably distribute the grinding allowance of spiral bevel gears; Third, pay attention to the cooling control during the grinding process of spiral bevel gears. The cooling should be fully enough to take away the grinding heat in time. In addition, shot peening after carburizing and quenching uses a large number of high-speed moving shot particles to impact the surface of the workpiece, causing the surface of the workpiece to be squeezed, causing cold plastic deformation, and forming surface compressive stress. This compressive stress will offset part of the tensile stress on the surface, reducing the probability of subsequent spiral bevel gear grinding cracks.
1) The tooth top hardness of cracked spiral bevel gear is 61~62 HRC, which can meet the technical requirements of 58~62 HRC.
2) The pitch circle of the uncracked tooth surface (concave surface) and the cracked tooth surface (convex surface) of the tooth-shaped sample are far away from the pitch circle of the crack, the surface hardness and microstructure meet the technical requirements of the drawing, and there is no grinding burn feature; However, at the root of the uncracked tooth surface and the root of the cracked tooth surface close to the crack, there are obvious hardness “bow” phenomenon and incomplete secondary quenching phenomenon above Ac1 point, which are consistent with the characteristics of grinding tempering and grinding burn.
3) The surface temperature of the crack on the convex surface of the tooth-shaped sample exceeds the Accm point due to grinding heat and is re-quenched. The hardness of the surface white zone is abnormally increased, with the maximum hardness of about 820 HV0.1. The black zone that has been tempered and softened due to grinding heat is located in the vicinity of the white zone, with the minimum hardness of about 486 HV. The depth of the crescent-shaped white and black burn zone is about 0.9 mm, showing typical grinding burn characteristics; Although the carbon and nickel content in the non-carburized part of the spiral bevel gear center is higher than the upper limit of GB/T 3077-2015, this is not the main reason for the arc crack on the tooth surface. The tooth surface crack is mainly caused by grinding burn.
4) The grinding process of the carburized and quenched spiral bevel gear should avoid grinding burn as much as possible. The grinding heat can be reduced by selecting appropriate grinding wheel, controlling the feed amount of rough grinding and fine grinding, reasonably distributing the grinding allowance, and strengthening the cooling control. In addition, strong shot peening can also increase the residual compressive stress on the surface of the spiral bevel gear, and offset the impact of a part of the tensile stress.