A comparative study of hole-making performance by coated and uncoated WC/Co cutters in helical milling of Ti/CFRP stacks

Carbon fiber reinforced plastic (CFRP) and titanium alloy stacks are typical difficult-to-machine materials and often result in rapid tool wear, leading to a low drilling efficiency in aircraft assembling. Helical milling process has demonstrated its superior performance in making holes in these materials, but selecting a proper cutting tool is still a great challenge and little research has been carried out to investigate the effect of different coatings on tool performance. Therefore, in this paper, milling tools with and without coatings (diamond coating, TiAlN+AlCrN multilayer coating and TiAlN coating) were employed in helical milling of Ti/CFRP stacks. The cutting performance and the degradation mechanisms of these milling tools were investigated in details. It is found that, uncoated tools demonstrate the best cutting performance with lowest cutting force, highest hole quality, and slightest tool wear. Degradation of nitride-coated tools is due to the combined effects of increased roundness of cutting edge and the strong dependence of cutting performance on the tool sharpness. Diamond-coated tools showed the greatest degradation, which has been attributed to the low material ductility at tool cutting edge, weak adhesive strength between the coating and substrate, and the poor thermal resistance of the diamond coating.