The effect of tool posture on surface integrity during ball-end milling

This study investigated the effect of tool postures on cutting performance and surface integrity during ball-end milling. Firstly, a cutter-workpiece engagement (CWE) model was constructed from the perspective of cutting microelements, and the impact of tool posture changes on the CWE was analyzed. Through ball-end milling experiments, the influence of tool posture on cutting force and surface integrity was investigated. The results showed that under the same tool inclination angle, the cutting time under the tilt posture was about 30% shorter than that under the lead posture, and the material removal process was more concentrated, leading to higher cutting forces and component forces compared to the lead posture. Under the lead posture, when the cutting edge passed through the final reserved area of the CWE, the cutting process was stable with fewer surface defects. At this stage, the number of cutting microelements participating in cutting and the material removal were small, resulting in lower cutting force and minimal tool deformation, thus making the pit features on the workpiece surface more pronounced. In contrast, under the tilt posture, due to the chip separation effect, more surface defects appeared at the edges of the pits. The number of cutting microelements and the material removal were larger, significantly increasing the cutting force, leading to intensified tool deformation and weakening the pit features on the workpiece surface. The increase in tool inclination angle caused an increase in radial cutting force, which enhanced the extrusion effect of the tool on the workpiece surface, increasing surface plastic deformation, and thereby improving the surface microhardness and residual compressive stress. Under the same tool inclination angle, the larger radial force and vertical downward velocity component of the cutting microelements under the tilt posture led to an increase in the plastic deformation thickness on the workpiece surface, and the microhardness and residual compressive stress values were higher than those under the lead posture. Overall, the lead posture provided better surface quality and more consistent surface integrity as the tool inclination angle increased.