Effect of pre-stress on surface integrity in micro milling: Modelling and experimentation

Recent years have witnessed rapid growth in microscale manufacturing, particularly in the biomedical, electronics and aerospace industries. Therefore, it is required to improve the capabilities of micro-cutting processes such as micro-milling to generate intricate features with high surface quality. The surface integrity of the machined materials is influenced by the cutting conditions, tool geometry and material properties. The novelty of the proposed work is to improve the surface finish and compressive residual stress of the milled slot by tailoring the pre-compressive stress condition. Ultrasonic-assisted abrasive peening is used to tailor the residual stress and obtained grain refinement on the surface. The micro-milling is performed on the peened surface of Ti-6Al-4V, Al-6061, and OFHC-Cu to investigate the surface roughness and residual stress. A hybrid model is developed to estimate the surface roughness considering the effect of tool geometry, process parameters, size effect and workpiece microstructure. Induced residual stress at the machined surface is simulated through the finite element (FE) method. Moreover, the FE model simulated the minimal chip thickness and contact pressure at the flank face and is deployed as an input to the analytical model for estimation of surface roughness. The pre-deformed material by peening reduced the surface roughness by 35 to 42 % on different materials and improved compressive residual stress due to grain refinement. The predicted average surface roughness and residual stress are validated with experimental results.