Effects of the tool geometry, cutting and ultrasonic vibration parameters on the cutting forces, tool wear, machined surface integrity and subsurface damages in routing of glass-fibre-reinforced honeycomb cores

Honeycomb structured materials have been increasingly used for high-load applications; however, machining of the highly elastic honeycomb cores is still facing challenges from tool wear issues and degraded machined surface integrity. In this work, experimental evaluations were carried out in routing glass-fibre-reinforced honeycomb cores under the parametric control of tool geometries (straight and helical flutes), vibration amplitude (0–12 μm) and cutting speeds (30–120 m/min) in a full factorial design. The recorded cutting forces, cutting temperatures, tool wear and the machined surface integrity indicators were statistically tested and discussed, with their main effects and interactions. Executive findings indicated that the helical-flute routers in the oblique cutting produced lower cutting forces; in contrast, the straight-flute routers in the orthogonal cutting produced lower cutting temperatures. Moreover, the flank wear of the straight-flute routers decreased with the amplitude; whereas the flank wear of the helical-flute routers increased with the amplitude. The use of ultrasonic vibration-assisted energy would reduce propagations of cracks and pull-out fibres, compared to using conventional machining. Additionally, the internal damages such as out-of-plane cracks and fractures were characterised by their width and area via computed tomography scans. When routing at a high cutting speed (~90 m/min), the superimposed assisting energy coupled with the straight-flute routers could adversely convert the minor delamination into severe out-of-plane cracks. Causes and the underlying mechanisms are all discussed and detailed.