Numerical and experimental study of end-milling process of titanium alloy with a cryogenic internal coolant supply

Cryogenic machining is an environmentally friendly process; liquid nitrogen (LN2) is sprayed onto cutting tool to reduce cutting temperature, increasing tool life. Cutting temperature and force were numerically predicted during cryogenic assisted milling with an internal coolant-assisted tool holder (internal cryogenic milling) for Ti-6Al-4V alloy. The influence of LN2 on the material temperature throughout the machining was estimated; a numerical model to simulate the initial temperature of work material was discussed by consideration of LN2 injective mechanism. A modified Johnson-Cook model including the cryogenic temperature range was adopted to model material plasticity. The predictive models were validated based on side-milling test. The predicted values captured the trend of experimental result; the minimum and maximum temperature errors were 0.1% and 8.6%, and those for the cutting force were 0.2% and 34.4%. Moreover, comprehensive experimental studies for the cutting temperature, cutting force, chip morphology, and chip composition were performed to understand the effect of cryogenic cooling condition. In internal cryogenic milling, the cutting temperature and force tended to be lower than dry machining. Based on the morphological analysis of the generated chip, the coefficient of sliding friction at tool-chip interface under the internal cooling was reduced by 21.4% as compared to the dry condition.