The application of surface integrity index to comprehensively evaluate the surface machining quality of spiral bevel gear is of great significance to improve the grinding surface machining quality of spiral bevel gear. Surface integrity includes not only surface micro morphology, surface roughness and other micro geometric characteristics, but also the composition of physical and mechanical properties in the surface layer, such as residual stress, work hardening, metallographic structure change and so on.
In 2005, Wang Guicheng and others experimentally studied the effects of surface grinding methods and cooling conditions on the surface hardened layer of Non Hardened Steel 40Cr and 45 steel, as well as the microstructure and change law of the hardened layer of surface grinding 65Mn steel, and simulated and predicted the grinding temperature field and the hardened layer thickness of the workpiece under different grinding parameters by using the finite element method.
The simulation results of grinding surface microstructure at room temperature are compared with the crystal structure of test results, as shown in Figure 1. The good consistency between the simulation results and the measurement results shows the credibility of the grinding hardening simulation results, which provides a basis for the analysis of the main influencing factors of grinding hardening layer.
(b) Crystal phase structure diagram of sample workpiece side surface
In 2008, Chen Wuyi and Zhang Hongxia studied and analyzed the grinding variation law of titanium alloy with SG grinding wheel. The research shows that the grinding burn of TC6 titanium alloy will occur when the grinding temperature exceeds 600 ℃. When the grinding burn is serious, the workpiece surface is also accompanied by cracks roughly perpendicular to the grinding direction. When the workpiece is burned, the metallographic structure of the surface layer of the material will change significantly, α The increase of the particle size of the phase has a certain inhibitory effect on the physical and mechanical properties of the titanium alloy, as shown in Figure 2 below.
(b) Surface metallographic structure of grinding burned workpiece
In 2010, Ming xingzu of Central South University found that 20CrMnTi material reached the critical condition when the grinding temperature reached more than 600 ℃ and the depth of metamorphic layer was more than 0.2 mm. At this time, grinding burns of different degrees would occur. During quenching burn, the microhardness of tooth surface is higher than that of normal grinding surface, and the maximum depth of burn is about 0.5 mm. The microstructure near the surface of quenching burn area is more acicular martensite + residual austenite + a small amount of carbide; The microstructure of the lower part of the quenching burn zone (close to the tempering burn zone) is martensitic ferrite + retained austenite, which is a hypoeutectoid zone. In case of tempering burn, the hardness is lower than that of normal grinding surface, and its structure is troostite and sorbite, as shown in Figure 3.
(b) Microstructure of the lower part of grinding quenching burn zone
(d) Histological characteristics of sorbite in burn area after tempering
In 2013, Kong Xianghan established the roughness model of the grinding tooth surface of spiral bevel gear along the grinding direction of the grinding wheel and perpendicular to the grinding direction of the grinding wheel by analyzing the formation mechanism of the grinding tooth surface roughness profile of spiral bevel gear, the morphology of the grinding wheel and the motion track of the grinding wheel grain, and according to the position and relative motion relationship between the grinding wheel and the grinding gear workpiece on the machine tool.
In 2014, Li Fei and Ming xingzu of Hunan University of technology detected and analyzed the surface metallographic structure characteristics of spiral bevel gear after grinding through experimental detection methods. The results showed that after grinding, the metallographic structure of the surface of spiral bevel gear was mainly acicular martensite, accompanied by a small amount of carbide precipitation and residual austenite, and the structural composition of the core was mainly plate-like low-carbon martensite, as well as a small amount of ferrite and bainite, As shown in Figure 4. Then the influence of different process parameters on the surface microstructure of spiral bevel gear is analyzed by orthogonal test. According to the range analysis, it is concluded that the grinding performance reaches the best when the grinding depth AP = 20 µ m, vs = 35.2 M / s and VW = 4.4 M / min.