Contour bevel gears are the essential components for the transmission of motion between intersecting and staggered axes with the advantages of good meshing performance, smooth transmission, high bearing capacity, low noise, etc. They are widely used in automotive, engineering machinery, aerospace, mining, metallurgy, petroleum and other industrial fields. The quality of the machined surface has a significant effect on the matching accuracy, wear resistance, fatigue resistance, corrosion resistance and transmission performance of contour bevel gears. The manufacturing accuracy of contour bevel gears directly affects the transmission efficiency, noise, motion accuracy and service life of the machine. Its true tooth surface morphology is complex, such as machine tool rigidity, cutterhead installation errors and cutting parameters. It restricts the machining accuracy of contour bevel gears seriously. Therefore, it is of great practical significance to study the surface quality of contour bevel gears.
Scholars around the world have conducted different degrees of research on the quality of machined surfaces. Han et al. [
1] proposed a central composite surface design method based on response surface methodology and established a regression model for the surface roughness of honing workpiece gears. Khalilpourazary et al. [
2] studied the surface roughness of the processed spur gears and found that the arithmetic surface roughness value of the spur gears manufactured with a lubricant containing alumina nanoparticles during the hobbing process was decreased. Ming et al. [
3] established an equation for the residual height to improve the surface quality of the face gear and modified the grinding surface roughness model of the face gear. Pathak et al. [
4] used the surface finish, microstructure, and microhardness to evaluate the surface quality of bevel gears, and they found that honing gears can improve the surface quality of gears and reduce the transmission noise of the machine. Michalski et al. [
5] found that the roughness height and roughness spacing were smaller for the tooth point surface than for the root surface after hobbing. Klocke et al. [
6] performed a metallographic test on surface defects of gear hobbing, they investigated the effect of the tool and process design on dry hobbing surface defects by comparing the appearance of surface defects and characteristic values generated by the gear hobbing. Han et al. [
7] quantitatively analyzed the three-dimensional morphological data of tooth surfaces for two gear finishing processes, grinding and honing, and found that the grinding process could obtain smaller roughness and higher geometric accuracy compared to the honing process, but the residual stresses of the honing process were smaller than those of the grinding process. Zheng et al. [
8] proposed an algorithm, which takes the insert run-out errors into consideration, for the roughness of the face-milling spiral bevel gear. Simon [
9] proposed a new hobbing model that determines the deviation between machined and theoretical tooth surfaces of spur and helical gears, which can be used to improve the microscopic surface morphology of spur and helical gears. Hassanpour et al. [
10] conducted milling tests on 4340 alloy steel, they used response surface methodology to investigate the influences of different cutting parameters on surface roughness, morphology, microhardness, white layer thickness, and surface chemical composition. Mao et al. [
11] proposed a tooth grinding method by variable velocity generation machining of variable speed of conical wheels, and it can reduce surface roughness and shorten grinding time remarkably by comparing with the uniform generation machining method. Lin et al. [
12] used the roughness profilometer to obtain the measurement data of the tooth profile and formulated the theoretical geometric model of the involute cylindrical gear tooth profile based on the parameters of the tested gear. Bin et al. [
13] established a mathematical model for grinding disk wheels based on the principle of CNC grinding by the generating machining method for face gears, considering the influence of grinding wheel morphology and contact deformation during the grinding process. Ma et al. [
14] carried out theoretical analysis and experimental research on the surface roughness of the hard tooth surface gear after shaving. They found that the surface roughness of the gear is smaller than that of the general hobs, and decreases with the increase of the negative rake angle of hobs. Gao et al. [
15] conducted gear hobbing experiments by selecting different hobs, top edge fillet radius, and hob edge shapes for hobbing experiments. They analyzed the influence of different factors on tooth surface roughness. Li et al. [
16] obtained the results of effectively reducing the tooth surface error by automatic identification of tooth surface error and feedback correction of machine tool motion parameters. Wang et al. [
17] discretized the tooth surface and gave the radial and normal vectors of the discrete points of the tooth surface according to the mathematical model of the curved bevel gear, and established the expression of the tooth shape error of the modified tooth surface at the discrete points concerning the theoretical tooth surface.
In summary, scholars around the world have conducted research on the machined surface quality of external cylindrical, flat, and standard cylindrical gears and other parts. There are few studies on the machined surface quality of contour bevel gears. Therefore, this paper takes the contour bevel gear as the research object, analyzes the forming process of the machined surface roughness of the workpiece by the generation machining principle of the contour bevel gear. The dry milling experiment of contour bevel gears is carried out, dry milling experiment of contour bevel gears is conducted to study the effect of cutting speed and feed rate on the surface quality of machined surface roughness and surface morphology by single factor method, and to analyze the surface defects of the machined surface by EDS; XRD is used to compare the diffraction peaks of the microscopic grains of the machined surface and the substrate material, and the effect of cutting parameters on the microhardness of the machined surface is studied through work hardening experiment. The above research results not only provide a basis for the optimization of the surface quality and process parameters of contour bevel gears but also have a certain reference value for the research on the machining accuracy and transmission efficiency of contour bevel gears.