Surface Layer Characterization of Shot Peened Gear Specimens

Abstract

The production of gear components includes numerous manufacturing operations, which are carried out to ensure proper surface characteristics. Shot peening is one of the surface finishing processes used for transmission components like gears to improve their fatigue behavior. Shot peening increases the compressive residual stresses on the surface, and the procedure also reduces the amount of retained austenite in the surface layer. In addition, shot peening has an influence on other mechanical properties, such as surface roughness and surface hardness. An experimental design was conducted with varying shot peening process parameters, like coverage density and intensity, to alter the surface layer of 13 transmission gear specimens. The correlation between shot peening parameters, Barkhausen noise (BN) features, and X-ray diffraction residual stress measurement was studied. Linear correlation was found between residual stress and shot peening parameters. The relationship between residual stress and BN root-mean-square was not evident but was revealed by taking the ratio of BN measurements at different frequencies. Additionally, BN features, such as peak position, coercivity, and integral area, were found to have a linear trend with the intensity. Along with the aforementioned measurements, other material characterization measurements were also taken. The shot peening coverage density was observed to have a linear relationship with surface roughness values, while an intensity of over 0.6 mm A was noticed to affect the surface hardness. The results obtained can be used in the determination of suitable shot peening parameters to achieve a surface with desired residual stress and other surface properties.

Determination of the optimal coverage for heavy-duty-axle gears in shot peening

“…5, the surface roughness Ra of SP5 is about 21.28% less than that of SP1, whereas the reduction is about 7.15% for Rz. It is revealed that proper increase of coverage can reduce the surface roughness of gear tooth flanks, and the results are compatible with that of other literature [10,17,34,39].…”

“…Such damages created by overlapping of peening dimples and surface plastic deformation can often be found around the hobbing marks or between dimple boundaries, which could cause premature crack initiation on tooth flanks. Some researchers also got the similar SEM characterization observations on other materials [10,[41][42][43][44][45][46][47]. To conclude, it is inevitable that defects generate on the peened surface of gears as clearly seen in the SEM images.…”

“…Fig. 6(a-c) shows very few microscalings on the peened gear surface [10,40]. More notably, Beyond the coverage of 1000%, the population of tooth surface microscalings goes up, the surface layers begin to peel off, and the pallings occur on the peened gear surface as shown in Fig.…”

“…In addition, shot peening can induce tiny indentations on the tooth flank as very small oil reservoirs which help to promote lubrication, reduce wear, spalling, scoring and lower operating temperature by reducing friction [6][7][8][9]. Shot peening can eliminate the tool marks left by machining and reduce the stress concentration on gear tooth flanks [10]. Surface abnormal layer can be reduced by shot peening [11].…”

“…However, the coverage variation range is not wide in Inoue's study. Santa-aho et al [10] studied the effect of shot peening on the tooth surface roughness of 17NiCrMo6-4 carburized gear through scanning electron microscope (SEM) characterization experiment. The results showed that increasing the shot-peening intensity and coverage density at the same time could reduce the surface roughness when gears were harder than the shots used in the experiment.…”