Influence of milling modes and tool postures on the milled surface for multi-axis finish ball-end milling

Abstract

This work concentrated on the machined surface properties produced by the multi-axis ball-end milling process in order to enhance the high-performance application of multi-axis ball-end milling technology. The cutting speed of the engaged cutting edges and machining characteristics under various inclination angles were analyzed. The effects of inclination angles on the machined surface hardness, residual stresses, surface textures, topographies, and roughness were investigated under up-milling and down-milling conditions. Under up-milling condition, the machined surface hardness with regard to various tilt angles are larger than the ones under corresponding lead angles, and the variations of surface hardness with increasing lead angles are not apparent. In down-milling condition, double-peaks shape appears in the changing curve of surface hardness with increasing tilt and lead angles. The residual stresses present the overall trend of firstly increasing, then decreasing, and finally increasing with the increasing tilt angle from −45 to 45°. The surface residual stresses in both feed and cross-feed directions firstly decrease, and then increase with the increasing lead angle. Under both up-milling and down-milling, the compressive residual stresses significantly appear at the tool inclination angles near 0° due to extrusion action of the cutting edges close to tool tip and the low effective cutting speed. For down-milling condition, the surface textures are approximately parallel with the feed direction when using tilt angles with large values, and are approximately perpendicular to feed direction under varying lead angles. The apparent machining marks under negative tilt angles with relatively larger absolute values and obvious regular surface patterns corresponding to positive tilt angles could be observed. More surface pits and burrs and circular arc textures probably appear under small tilt angles and lead angles near 0°.