Experimental Evaluation of Innovative Tools for Ti-6Al-4V Turning

Titanium alloys, mainly because of their poor thermal conductivity, need to be cut at relatively low cutting speeds, with obvious negative consequences on the profitability of machining. An important amount of research activities has been done in order to increase productivity in titanium machining operations: high performance coatings and innovative technologies to improve inserts resistance to wear represent promising solutions. In this work, the cutting performance in Ti6Al4V rough turning of an innovative TiAlN coating obtained by Physical Vapor Deposition (PVD) magnetron sputtering and the effects of a Deep Cryogenic Treatment (DCT) have been experimentally investigated and a statistical analysis of the results has been performed. Typical commercially available inserts (TiAlN-AlCrO coated) have been used as a benchmark. Preliminary hardness and thermal conductivity measurements tests have been performed on the three types of tool to determine the differences caused by the different coatings and thermal treatment. The experiments have been conducted using a full factorial design in order to statistically evaluate, using ANOVA, the significance of the input factors on the process most interesting outputs. tool life and other variables of interest with different process parameters. The considered input factors are type of insert, cutting speed and feed rate. The analysed responses are average flank wear, surface roughness, cutting forces, coefficient of friction and chip morphology. The results show that even if friction coefficients are lower for standard tools, innovative inserts exhibit a higher resistance to wear. Taylor’s law parameters of PVD coated tools, with and without DCT have been determined, clearly showing that cryogenically treated tools present higher resistance at higher cutting speeds, mainly due to their superior hardness. In conclusion, it appears that relevant improvements of productivity or profitability of titanium turning can be obtained if an advanced PVD coating, deposited by magnetron sputtering is used on tungsten carbide inserts and if deep cryogenic of the inserts is performed afterwards.