High tolerance plasma arc cutting of commercially pure titanium

The quality of cuts performed on titanium sheets using high tolerance plasma arc cutting (HTPAC) process was investigated under different process conditions. A 5 mm thick sheet of grade 2 commercially pure titanium was cut using several feed rates in the dross-free feed rate range and with the adoption of oxygen or nitrogen as cutting and shielding gases. When oxygen was used as cutting gas higher feed rate and geometry attributes (unevenness and kerf width) of better quality were achieved due to the oxidation reaction. The quality features of the cutting edge of HTPAC of commercially pure titanium were integrated with considerations on microstructural features related to the formation of a wide layer severely affected by plasma-induced thermal cycle and by interaction with the cutting gas. In fact, all cutting edges displayed an external layer of oxide, under which a thin layer of oxygen-enriched α-case was noticed for cuts performed with oxygen. The thickness of the total heat affected zone (HAZ) overcame 1 mm for all the cuts in nitrogen and for the slowest cut in oxygen. Temperature measurements during the passage of the torch defined the thermal cycles of the cutting process in several locations of the sheet. These are characterised by high heating rates (above 2000 K/s within the HAZ) and low cooling rates (150-580 K/s within the HAZ). An analytical model was applied to simulate the thermal effects of the material interaction with the torch in the case of slow cuts with oxygen. A comparison between predicted thermal cycles, experimental measurements and microstructural observations confirmed the reliability of the estimation in terms of extension of microstructural modifications.