Effect of the minimum quantity lubrication in high-speed end-milling of AISI D2 cold-worked die steel (62 HRC) by coated carbide tools

The objective of this paper is to compare the tool performance of Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N coated carbides end-mills deposited by hybrid coating method, using flood coolant(wet), dry and minimum quantity lubrication (MQL) conditions in the high-speed machining of AISI D2 cold-worked die steel (62 HRC). Superhard Ti-Al-Si-N films, characterized as a nanocomposite nano-sized (Ti,Al,Si)N crystallites embedded in amorphous Si3N4 matrix, was successfully synthesized on WC-Co substrates by a hybrid coating system of arc ion plating(AIP) and sputtering method. The hardness of Ti-Al-Si-N film increased with incorporation of Si, and had the maximum value ~ 48 GPa at the Si content of 8 at.%, respectively. The values of tool wear for coated tools were evaluated under a high-speed cutting condition using vertical high-speed machining center (Makino, V-55). It is found that cutting under flood coolant condition results in the shortest tool life due to severe thermal cracks while the use of MQL leads to the best performance. MQL is beneficial to tool life both in the Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N coating tools. This conclusion proves the feasibility in the high-speed machining of high-hardened materials for industrial applications.