A MACHINABILITY STUDY OF COATED INSERTS FOR TURNING TI-6AL-4V

Titanium (Ti) alloys are classified as difficult-to-machine materials due to low thermal conductivity, low modulus, and high chemical reactivity. In this paper, a Ti-6Al-4V alloy bar in a solution treated and aged (STA) microstructure is turned using uncoated carbide, two commercial multilayered coated carbides (Sandvik (R) MM1115 and MM11125), and several other advanced coated carbide tools with AlTiN, TiAlN, ZrN, BAM, and (AlCrSi/Ti)N coatings that were fabricated for this study. While coatings with increased hardness and chemical stability are expected to provide better protection against tool wear, coated inserts have not been successfully implemented in machining Ti alloys. A series of turning experiments was carried out while measuring the cutting forces using a dynamometer at three cutting speeds (61, 91, and 122 m/min), and the extent of tool wear on the inserts was assessed using Confocal Laser Scanning Microscopy (CLSM). Among the inserts tested, the (AlCrSi/Ti)N coated insert with a 7 mu m coating thickness provided the best performance compared to other inserts, but only at the cutting speed of 61 m/min.