Tool wear evolution and chip formation of the Ti-6Al-4V end milling under cryogenic cooling and minimum quantity lubrication conditions

Chip formation is dependent on the machining environment and is a major factor representing machining characteristics. This paper experimentally investigates the influence of cryogenic cooling and minimum quantity lubrication (MQL) on chip formation during titanium milling and their effects on tool wear and cutting force. Chip segmentation, shear angle, grain size, and compositions were evaluated according to the tool wear evolution. An application of cryoMQL strategy, which means the use of cryogenic cooling and MQL simultaneously, delayed the time of chip serration; serrated chips appeared at long machining distances compared to the dry machining. Then, the cryoMQL machining increased the shear angle and decreased grain size and oxygen atomic percentage. The phenomena represented occurrences of effective cooling and lubrication and reduced the tool flank wear length and the resultant force by 56.5% and 13.5%, respectively, compared to dry condition. The improvement in machinability was more remarkable in the cryoMQL condition than in the condition where cryogenic cooling and MQL were separately applied.