Cutting performance and surface integrity of hardened GCr15 bearing steel in laser-ultrasonic vibration-assisted turning

Hardened GCr15 bearing steel is an important engineering material for bearing applications, where high dimensional accuracy and surface integrity are required. Nevertheless, the high hardness of the material makes efficient machining difficult and often leads to accelerated tool wear and deterioration of the surface quality. To address these challenges, a systematic comparative investigation was conducted on the cutting performance and surface integrity of hardened GCr15 bearing steel under conventional turning (CT), ultrasonic vibration-assisted turning (UVT), laser-assisted turning (LAT) and laser-ultrasonic vibration-assisted turning (LUVT). The roles of ultrasonic amplitude and laser power in determining the surface integrity were further evaluated. The results reveal that UVT and LAT can enhance machining performance through intermittent cutting and thermal softening, respectively, whereas LUVT can synergistically couple these two mechanisms to achieve improved cutting performance and surface integrity under the conditions investigated in this study. Compared with CT, the UVT, LAT and LUVT can reduce the maximum flank wear by approximately 20.2%, 36.9% and 58.3%, and the surface roughness by 15.7%, 21.4%, and 42.9%, respectively. Moreover, surface defects including lateral material flow marks, oxide formation, scratches, tearing marks, and micro-chip adhesion are more effectively suppressed under the LUVT condition. In addition, both ultrasonic amplitude and laser power can significantly influence surface roughness and surface hardness, while subsurface microstructural observations indicate that these parameters also affect the depths of the plastic deformation and refined layers. These findings suggest that the surface integrity characteristics, including surface morphology, roughness, hardness and subsurface microstructural features, depend on the balance between thermal softening and vibration-induced deformation. The present study demonstrates that the improved cutting performance and surface integrity of hardened GCr15 bearing steel achieved by LUVT arise from the synergistic contribution of ultrasonic vibration and laser preheating, suggesting the potential of LUVT for future applications in the machining of hardened bearing steels.