Wear of TiAlN and DLC coated microtools in micromilling of Ti-6Al-4V alloy

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The trend toward the miniaturizing of commercial and engineering products is inevitable. Micromilling is the most versatile process to shape microcomponents subtractively. One of the main areas that benefit from micromilling is medical, with titanium and titanium alloy being its most frequently used materials. The popular Ti-6Al-4V alloy has excellent combination of strength and toughness, combined with a great resistance to corrosion and oxidation. This particular alloy dominates other Ti alloys and is used in 50% of all titanium applications. Taking into consideration that this alloy is considered a difficult to cut material, this study investigates the machinability of Ti-6Al-4V in micromilling operations. The wear of micro tools (152.4 μm diameter) coated with TiAlN and diamond-like carbon coating (DLC) are investigated and compared against uncoated tools. The tests are performed on a four-axis CNC milling system with a 60,000 min−1 maximum spindle speed. The tools are tested under dry conditions and wet conditions using the minimum quantity of lubrication. It is used cutting speed of 9.6 m/min, feed rate of 0.1 μm/tooth and axial depth of cut of 10 μm. The test consisted of machining slots 4.2 mm long until the end of the tool life. The results show that edge radius rounding and flank wear are the main wear types. The wear is predominant on the secondary clearance face of the microtool when applying cutting fluid. The lowest tool wear is obtained with the DLC coated microtools under dry conditions, presenting a wear reduction of 640% and 267% when compared to TiAlN coated and the uncoated microtool, respectively.