Analysis of Surface Roughness and Vibrations During Micro Ball End Milling with Various Ramping Directions

This study focuses on dependencies between the tool effective diameter and dynamics, as well as the machined surface quality obtained in the micro ball end milling of hardened steel with various ramping directions. As part of this research an analytical expressions of tool effective diameter in case of micro ball end milling of inclined surfaces have been formulated. Moreover, the micro-milling tests involving the measurements of accelerations of vibrations and machined surface roughness parameters were carried out. These tests included the micro ball end milling with surface inclinations of 15º in upward and downward ramping strategies. It has been found that distribution of tool effective diameter and cutting speed values in micro ball end milling with ramping strategies depend on tool nominal diameter, surface inclination and depth of cut in axial direction. The direction of ramping strategy significantly influences the surface roughness parameters values, as well as the amplitudes and power spectral density (PSD) charts of vibrations generated during micromachining process. The larger values of a measured process outputs were found during the downward ramping, which can be attributed to the lower values of cutting speeds distributed along the active cutting edge.