Stress model and evolution process of hot bulging wind turbine bearing rings with irregular cross-sections

As a core component of wind power equipment, the precision and mechanical properties of the wind turbine bearing are crucial in determining the service life. Stress serves as a key factor determining the fatigue life of large bearing rings. The hot bulging process is an effective manufacturing process for large bearing rings, especially in controlling the stress distribution uniformity. However, the evolution mechanism of stresses during the continuous hot rolling-bulging process of large bearing rings with irregular cross-sections remains unclear, which hinders the effective regulation of stress uniformity. Although the outer ring is a critical load-bearing component, it typically experiences different stress magnitudes and distributions compared to the inner ring in service. This study focuses on the hot rolling-bulging process of large-scale wind turbine bearing outer rings with irregular cross-sections. The proposed strategy aims to improve its geometric precision and stress uniformity. Based on elastoplastic theory, an analytical model for the hot bulging force of irregular cross-sections is derived first, and then a coupled finite element model incorporating rolling stress is developed. The results reveal that the strain in the ring exhibits a periodic wavelike distribution, with circumferential strain being the dominant component driving radial expansion. The two-stage characteristics of stress evolution during bulging demonstrate that the non-monotonic relationship between strain uniformity and bulging amount stems from the competition between material hardening and geometric softening. The average stress in the ring is reduced approximately 28% through the proposed multi-step rotational bulging strategy. This study elucidates stress evolution mechanisms and provides a validated process strategy for improving stress uniformity, thereby offering theoretical and technical guidance for improving in-service performance of large-sized bearing rings with irregular cross-sections.