Abstract
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.
Highlights
Due to the high strength-to-weight ratio, carbon fiber reinforced plastic/Ti alloy (Ti/Carbon fiber reinforced plastic (CFRP)) stacks are extensively used in the aircraft industry [1,2,3]
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 tools performance
In hole making processes for Ti/CFRP stacks, the low thermal conductivity, low deformation coefficient and high chemical reactivity of titanium alloys often result in severe tool wear [13,14], while the high hardness of carbon fibers in CFRP poses a great challenge to the tool durability [15,16,17,18]
Summary
Due to the high strength-to-weight ratio, carbon fiber reinforced plastic/Ti alloy (Ti/CFRP) stacks are extensively used in the aircraft industry [1,2,3]. In hole making processes for Ti/CFRP stacks, the low thermal conductivity, low deformation coefficient and high chemical reactivity of titanium alloys often result in severe tool wear [13,14], while the high hardness of carbon fibers in CFRP poses a great challenge to the tool durability [15,16,17,18]. According to the investigation of Mruphy et al [23], TiN coated and DLC coated tools produced higher thrust forces and lower diameter accuracy compared with uncoated tool in machining of carbon-epoxy composites. Qin et al [14] found diamond coated tool produced serious coating flaking in helical milling of Ti alloys and it is not recommended for the hole making process of Ti alloys. The associated cutting forces, hole qualities and tool wear are investigated systematically and the detailed tool degradation mechanisms are discussed
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