Sustainable Milling of Ti-6Al-4V: Investigating the Effects of Milling Orientation, Cutter's Helix Angle, and Type of Cryogenic Coolant

Ti-6Al-4V, the most commonly used alloy of titanium, possesses excellent mechanical properties and corrosion resistance, which is the prime reason for the continual rise in its industrial demand worldwide. The extraordinary mechanical properties of the alloy are viewed as a hindrance when it comes to its shaping processes, and the process of milling is no exception to it. The generation of intense heat flux around the cutting zones is an established reason of poor machinability of the alloy and unacceptably low sustainability of its machining. The work presented in this paper attempts to enhance sustainability of milling Ti-6Al-4V by investigating the effects of milling orientation, cutter's helix angle, cutting speed, and the type of cryogenic coolant and lubricant on the sustainability measures, such as tool damage, cutting energy consumption, process cost, milling forces, and work surface roughness. It was found that micro-lubrication is more effective than the two commonly used cryogenic coolants (carbon dioxide snow and liquid nitrogen) in reducing tool wear, work surface roughness, process cost, and energy consumption. Furthermore, down-milling enormously outperformed up-milling with respect to tool wear, work surface quality, and process cost. Likewise, the high levels of cutter's helix angle and cutting speed also proved to be beneficial for milling sustainability.