Numerical and experimental investigation on thermo-mechanically induced residual stress in high-speed milling of Ti-6Al-4V alloy

The machining-induced residual stress, which significantly influences the machined part's service performance and geometrical stability, is considered an essential indicator of surface integrity. The intermittent cutting process and the consequences of thermo-mechanical and microstructural phenomenon accompanying white layer formation, which directly influences residual stress distribution of the workpiece, make the milling process different from turning process. Therefore, a comprehensive understanding of residual stress distribution mechanism within the milled part is essential. The current study presents a numerical and experimental approach for in-depth residual stress prediction in the milled part of Ti-6Al-4V alloy. First, a simplified milling model was proposed based on J-C constitutive model and J-C failure criterion. Secondly, the proposed model was verified regarding cutting forces, cutting temperature, and chip morphological characteristics. An excellent correlation was obtained between the simulated and experimental results for given analogous milling conditions. Thirdly, the workpiece was allowed to cool down to room temperature for stress-strain relaxation. Finally, the effect of the white layer on residual stress distribution and the relationship between nano-hardness and residual stress were analyzed and discussed. It was found that residual stress was tensile when no white layer was detected on the machined surface, and the nature of residual stress becomes compressive with the formation of a white layer. This study can provide an in-depth understanding of residual stress distribution within the milled part and the fatigue life of the component's services performance.