Investigation on the edge forces in ball end milling of inclined surfaces

This work focuses on the analysis of the edge forces generated in ball end milling of hardened alloy 55NiCrMoV6 steel. The investigated forces consider the effects of friction, rubbing and ploughing mechanisms between the work piece and tool flank face during machining process. The primary objective of the paper concentrates on the determination of edge forces in the range of variable surface inclination angles and increasing tool wear. The proposed approach involves the measurements of instant cutting forces in machine coordinates (Fz, Fy, Fz). Subsequently, the measured forces are converted to the forces in the tool coordinates (Ft_av, Fr_av, Fa_av). In the next step, the Ft_av, Fr_av, Fa_av forces are expressed in function of average uncut chip thickness. In order to obtain the edge forces values, the extrapolation of forces in the tool coordinates to the zero uncut chip thickness is made. The investigations reveal that edge forces are strongly affected by surface inclination angle and progressing tool wear. The growth of the tool wear induced the monotonic increase in edge forces values. Nevertheless, in case of surface inclination angles α≥15° the influence of this factor on edge forces was low. It was also shown that cutting force estimation with the consideration of the variable edge forces is characterized by a higher accuracy than one based on constant edge forces. Therefore, the proposed method can be employed in the reliable calibration of specific force coefficients contained in mechanistic cutting force models dedicated to the finish ball end milling of sculptured surfaces.