Evaluation of the thermal characteristics in high-speed ball-end milling

In this paper, the thermal characteristics were evaluated in the high-speed ball-end milling of hardened steel (HRc 42). Experimental work was performed to find the optimal cutting environment to increase the tool life at a cutting speed of 210 m/min. Dry, wet and compressed chilled air at −9 and −35°C as the cutting environment were investigated. The implanted thermocouple technique was used for temperature measurement. A K-type thermocouple, implanted in a hole in the workpiece, was directly cut in order to measure the temperatures of the shear zone in the cutting process. The cutting temperatures were about 790, 350, 540, and 450°C in dry, wet, and compressed chilled air at −9 and −35°C, respectively. For the ball-end milling of hardened steel, the cutting environment for compressed chilled air at −9°C provided the best tool life among all the cutting environments. Although the wet condition had the most effective cooling, it provided the worst tool life.