Machinability of Titanium Alloy 6246 in Drilling Using TiAlN PVD Coated Carbide Insert Tools

Machinability is a measure of how easy a material to be machined. It can be assessed in some aspects: surface roughness and surface integrity of the machined parts, cutting speed, forces that work during machining or energy consumption, tool life, and chips formation. This article describes the machinability from tool deterioration perspective of titanium alloy 6246 by drilling with TiAlN PVD-coated carbide tools. Taguchi L18 was employed to design the experiments, with five parameters influenced the tool deterioration with mixed levels of parameters of 2 and 3. The tool deterioration was grouped into 3 categories: built-up edge (BUE), delamination, and chipping. Every drill bit was used for single drilling and then observed with SEM from flank and rake view. Wear was not found in this research, however, the tool delamination and tool chipping was evidenced, even if drilling depth was only 10 mm. Tool experienced built-up edge in the outer blade, inner blade and at the chisel. This BUE can be seen at both views, i.e. rake and flank sides. BUE is the most dominant deterioration and inevitably in drilling this alloy, regardless of the parameters applied. Tool delamination may occur during mechanism of peeling off the BUE. While chipping was related to higher feed rate, that may relate to high MRR. Data analysis using Minitab 19 shows that combination of drilling without cooling, 45 mm depth, cutting speed of 27 m/min and feed rate of 0.08 mm/min would result in the best performance of TiAlN tool for drilling Ti6246 heat treated 870oC then followed by water quenching.