Study On Effect Of Shot Peening On Bending Fatigue Strength Of 18CrNiMo7-6 Gear

Benefitting from the high transmission efficiency, large range of transmission ratio and velocity, gear is widely used in mechanical transmission. Frequently, gear bear a great load in transmission and bending fatigue strength of gear is the key performance indicator in the gear transmission, therefore it is vital to make a gear bending fatigue strength test in gear’s design and safety usage. Shot peening enable to import residual compressive stress, so a reasonable shot peening can improve the life of the workpiece. At present, a lot of research is done to improve gear’s service life at home and abroad. However, there is no completely quantitative relation between the shot peening process and the performance of workpiece. The selection of shot peening parameters mainly rely on the experience of designers and the effect is poor. It is meaningful to enhance the gear’s bending fatigue life by researching the influence of different shot peening processes on gear’s bending fatigue life. Based on the domestic level of heat treatment and shot peening process in the present, this research takes series of shot peening on 18CrNiMo7-6 gear, then acquires the gear’s bending fatigue strength by tests and draws its R-S-N curve. The Bending fatigue life and the ultimate bearing capacity in different shot peening processes is compared. Finally we research the influence of different shot peening processes on the evaluation index in surface integrity. Study topics include:First, special clamp for the gear bending fatigue tests is designed. The problem in calculation of the root bending stress is discussed.Then, bending fatigue test is taken with P9 series of gear. The minimum test points is determined by t distribution theory and the data is matched by the theory of mathematical statistics. Next, the result is inspected by K-S test and the R-S-N curve is obtained in different reliability. Based on above, we acquire the gear’s ultimate bearing capacity.Third, gear bending fatigue contrast test in 8 different shot peening processes is taken. We compare the life in different processes via group comparison method and screening method, then compare the gear’s ultimate bearing capacity by equal-slope method. Test shows: the combination shot peening gear owns the highest bending fatigue lifeFinally, the influence of different shot peening processes on the evaluation index in surface integrity is researched. Test shows: a. root surface roughness decrease with the increasing of shot peening intensity in large shot. On the contrary, root surface roughness increase with the increasing of shot peening intensity in little shot. It is helpful to reduce the surface roughness through improving shot peening coverage. b. Shot peening can significantly increase the residual compressive stress in the tooth root surface and it is helpful to increase the residual compressive stress through improving shot peening coverage. The residual compressive stress in the tooth root surface is increasing with the higher Shot peening intensity. Compared to the conventional shot peening, combination shot peening can obviously increase the residual compressive stress. c. Shot peening has little influence in hardness for surface-hardened gear. d. Shot peening can refine the grain near the surface of the gear.