Heat Transfer Efficiency of Cryogenic-LN2 and CO2-snow and their application in the Turning of Ti-6AL-4V

Abstract

Owing to poor thermal conductivity, and high chemical reactivity of Ti-6Al-4V alloy at elevated temperatures, a lubri-cooling having superior heat transfer is benefic to apply to dissipate cutting heat and to improve the machinability. As conventional coolants are ineffective to prevent thermal damage and tool wear. Therefore, recent advanced cryogenic coolants such as cryogenic-liquid nitrogen (LN2) and carbon dioxide (CO2-snow) are hypothesized to mitigate the set objectives. In this experimental study, a static workpiece plate was sprayed to compare their heat transfer coefficients. Furthermore, the machining performance of cryogenic coolants was evaluated in the turning of Ti-6Al-4V in terms of tool wear, cutting force, surface roughness, and chip curl diameter. For this, experiments are conducted at a constant cutting speed of 120 m/min, a feed rate of 0.1 mm/rev, the coolant injection flow rate of 350~450g/min, and a depth of cut of 2.5 mm to clarify their effect on the process. The outcome analysis of this work showed the overall less tool wear, cutting forces, surface roughness, with maximum chip curl diameter under CO2-snow cooling followed by cryogenic-LN2 and dry condition. In summary, CO2-snow showed promising outcomes and a superior heat transfer effect warrant its implementation in the aerospace industry.