Towards Salomon's hypothesis via ultra-high-speed cutting Ti-6Al-4V alloy

Cutting temperature is a crucial factor in high-speed machining processes. In 1931, Dr. Carl Salomon proposed the fascinating hypothesis that the cutting temperature increases with the cutting speed to a critical point and then decreases as the cutting speed continues to climb, which provides a successive impetus for developing high-speed machining technology. Despite extensive studies over the past several decades, Salomon's hypothesis has not been fully verified. In this study, a unique measuring technique was developed, which combines a light gas gun-based ultra-high-speed cutting setup with an infrared detector-based high-speed transient temperature measuring system. Using this technique, the cutting temperatures for the most typically difficult-to-cut and widely used Ti-6Al-4V alloy are measured over a broad spectrum of cutting speeds ranging from 7.5 to 212.6 m/s. The experimental results show that the measured temperature at the tool tip first increases with increasing cutting speed to a critical point of 125.2 m/s and then decreases as the speed continues to increase, providing solid evidence for the Salomon's hypothesis. We further reveal that the tool temperature decreases at ultra-high cutting speeds stems mainly from less heat generation in the primary shear zone and more heat convection by high-speed chip flow.