PSI - Issue 57

Dr.-Ing. D. Jbily et al. / Procedia Structural Integrity 57 (2024) 199–216 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

201

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Table 1. Characteristics of the test gear

Nominal gear geometry Normal module (mm)

Pinion

Gear wheel

m n

4.5

Normal pressure angle (degrees)

α z x

20

Number of teeth

16

24

Profile shift coefficient

+0.1817

+0.1715

Reference profile

ISO 53:1998 Profile A

ISO 53:1998 Profile A

Tip diameter (mm)

d a

82.4

118.3

Accuracy grade (ISO 1328)

Q

5

5

Facewidth (mm)

b a

18

14

Centre distance (mm)

91.5

Gear ratio

u

1.5

Profile and flank line modifications are introduced (Table 2) at the teeth of the studied gears.

Table 2. Tooth modifications

Micro-geometric modifications

Pinion

Gear wheel

Flank line crowning (µm)

35 50

0

C β

Tip relief value (µm) Type of Tip relief

50

C  a

arc-like 79.268

arc-like 115.448

Tip relief application diameter (mm)

d Ca

2.1. Material and treatments The material considered in this study is a carburized 18CrNiMo7-6 steel, which is subjected or no depending on the case study, to shot peening. A summary of the specimens used in this study, their manufacturing process and surface treatments are described below: • Reference gear (REF): the specimens are first cut and then heat treated (case hardened+quenched+tempered). After heat treatment, the gear teeth are ground to remove any irregularities that have occurred during cutting and heat treatment. • Shot peened gear (SP): REF + shot peened. The surfaces of teeth are shot peened to create residual compressive stresses in the surface layer. Shot peening is carried out using a nozzle device as shown in Fig. 1. Before all the test gears were shot peened, a test was performed on test gear to ensure that shot peening, under identical conditions, on a roller and on a gear led to the same results. Initially, the same shot peening called G2 with the same parameters and conditions as those applied to the rollers (Peyrac et al. (2017)) was used: UFS100, 6 bars, angle 60° (simple shot peening - 200% coverage). Performing this shot peening on the teeth results in identical residual stresses but unsatisfactory surface roughness. This is certainly due to the different geometry of a roller and a gear. It was therefore decided to modify certain parameters of shot peening process (pressure, incidence angle) without changing the media. Then, based on the analysis of the surface roughness and residual stresses measurements of the test gear, the most favorable parameters of this treatment were determined, which were later used during shot peening of the test gears. The shot