Correlation between Grinding-Induced Residual Stress State and Material Removal Rate

The knowledge of the residual stress state is of interest to the gear industry due to its critical role in avoiding fatigue failure mode. Since fatigue cracks are always nucleated and propagated under tensile actuating stresses, a suitable compressive residual stress state is desirable to decrease the total stress profile, by the superposing principle. Usually applied as the last process of the gear manufacturing chain, grinding provides both thermal and mechanical loads, from which residual stresses are induced. The intensity of such loads is associated with the material removal rate (MRR); however, it is not constant along the tooth profile, due to the complex kinematics of gear grinding process. The objective of this study is then the comprehension of how the variation of material removal rate along the tooth profile influences the grinding-induced residual stresses. Case-hardened steel discs were manufactured with different material removal rates, induced by varying grinding parameters. The ground surface integrity of such simplified samples was characterized in terms of residual stress state, topography, microhardness, and microstructure. ITA Geometry gear samples were manufactured with grinding parameters definition based on the disc grinding results. The characterization of the surface integrity state of the ground teeth was similar to the disc assessment and showed a good correlation regarding the material removal rate and the residual stress state along the tooth profile. Such results highlight that a strategic definition of grinding parameters by material removal rate can improve the residual stress state, leading to more reliable gear fatigue prediction.