A Case Study on Effect of Subsequent Operations on Shot Peened Crown Wheel Pinion (Hypoid Gear Set) & Compressive Residual Stress Analysis

The prime function of crown wheel pinion is to receive the power from transmission & distribute to two-wheel ends. Doing so these members will experience the tremendous bending fatigue. Shot peen is the one of the latest technology used to improve the bending fatigue of the CWP [1]. In this particular case- six CWP are taken for the study to understand the effect of the operations after shot peen process. Three Samples are named as batch A, another 3 samples are named as batch B. Both the batch CWP are shot peened. Then as a regular production practice the batch A CWP are process through hard turning ➔ Abrasive lapping ➔ Hot lubriting (manganese phosphate) ➔ Fully finish ready for assembly. Then both the batch A & batch B samples are taken for residual stress analysis using X-Ray diffraction technique. The measurement location is 50 microns below the surface. The results tabulated, found that batch A samples shows decrease in Residual stress relatively to batch B. This evident that post operations after shot peen process reduces the induced compressed residual stress. This phenomenon is due to material crystal lattice relaxed to original orientation or few of them change over to new orientation, particularly d spacing & angle [2]. The drop in residual stress was approx. 10 to 15% at depth of 50 Micron from the surface. Residual stress drop is not to zero because post operations are not strong enough to nullify the induced compressive residual stress. The study shows that abrasive lapping & hot lubrite operation reduces the induced shot peen compressive residual stress to some extent which could lower the root bending fatigue life of the CWP.