Influence of Shear Cutting Process Parameters on the Residual Stress State and the Fatigue Strength of Gears

Abstract

Shear cutting is used for manufacturing various parts ranging from e.g. simple washers to complex gears. The latter are typically subjected to cyclic loading and fail foremost due to fatigue damages. Hereby, the parts lifetime is mainly determined by: the geometry, the applied load, the material, the hardness, the roughness and the residual stress state. While numerous research works deal with the influence of the process parameters on the hardness and the parts geometry, the influence of the process parameters on the residual stress state and on the resulting fatigue strength has not been investigated in detail, yet. In an earlier publication, suitable shear cutting techniques, which allow to achieve a high amount of clean-cut and a favorable residual stress state were compared. In this paper, the influence of the process parameters on the residual stress state and the resulting bending fatigue strength are addressed. To simulate the bending stress occurring in the tooth root, C-shaped specimens were manufactured by different blanking techniques. The die-clearance and punch and die edge radii were varied with these blanking techniques. After measuring the cut-surface geometry, the hardness distribution and the surface roughness, the fatigue strength was determined in a pulsating test rig. By carrying out residual stress measurements using x-ray diffraction and simulating the material flow behavior using the Finite-Element-Method, basic mechanisms, which are influencing the residual stress state and the resulting bending fatigue strength, were identified and will be presented and discussed in the paper.