The role of transversal ultrasonic vibration and tool geometry on surface integrity and fatigue performance in drilling of Al-Li alloy

Advanced hole-making technology is crucial and important in the aviation industry. In this study, we proposed a new drilling method that combines transversal ultrasonic vibration with tool blunt geometry, and validated it through experiments on Al-Li alloys. In the paper, we investigate the cutting performance in ultrasonic peening drilling (UPD) of Al-Li alloy, under the condition of single-factor blunt tool geometry and optimized multi-factor blunt tool geometry. The blunt cutting tool significantly increases the cutting force, while the ultrasonic vibration decreases the cutting force and torque. Moreover, compared to the standard tool in conventional drilling (CD), the multi-factor blunt tool in UPD reduces surface roughness by 47.6% and increases deformation thickness, microhardness, and residual compressive stress by 5.89 times, 25.4%, and 136.8%, respectively. Electron backscatter diffraction (EBSD) analysis demonstrates that the multi-factor blunt tool in UPD induces a substantially machined affected zone with a thickness of 165 μm, exceeding twice the affected zone produced by the standard tool in CD. Finally, the multi-factor blunt tool in UPD enhances the fatigue life by 189.8%, with the fatigue source shifting from the chamfered area to the hole subsurface. These results indicate that the combination of UPD and multi-factor blunt tools provides a promising hole-making approach to achieving deeper reinforcement and longer fatigue life.