Increasing Efficiency of Ti-6Al-4V Machining by Cryogenic Cooling and using Nanolubricants

摘要

Generation of high localized cutting zone temperatures leading to dissolution wear hinders machinability of Ti alloys using uncoated carbide tools and polycrystalline diamond (PCD) tools. In addition, the thermo-plastic instability exhibited by titanium alloys promotes serrated chip formation that causes fluctuations in the cutting forces leading to chatter and severe flank wear. This work considers two methods to mitigate these problems during cutting of Ti-6Al-4V, namely, cryogenic machining to influence chip segmentation, and the use of WS2 blended metal removal fluids (MRF) to influence interface coefficient of friction (COF). Cryogenic machining of Ti-6Al-4V at 45 m/min and 0.15 mm/rev led to easier fracture of chip segments due to decrease in toughness of the material. Analyses of fracture surfaces of the chips showed that the decrease in toughness was due to increased presence of shear ridges at low temperatures. The role of COF was determined using pin-on-disk experiments. Iterative tests of Ti-6Al-4V pins sliding against uncoated WC-Co disk showed that the addition of WS2 nanoparticles to MRF are capable of decreasing the interface COF lower than that under MRF lubricated conditions alone. Orthogonal machining of Ti-6Al-4V at a cutting speed of 29.5 m/min, feed rate of 0.4 mm/rev under dry conditions generated an average cutting force of 400 N. Under MRF + WS2 lubricated conditions, the average cutting force reduced to 190 N, which was 52% lower than dry conditions. The low COF values due to the MRF + WS2 lubricant reduces the interface temperature and thus aids in machining.