Investigation of ultra-high speed cutting mechanism by considering tool-chip friction property and inertia force derived from chip formation

摘要

The friction angle at the tool-chip interface, which is analysed using the cutting force measured, tends to rise as the cutting speed increases when the cutting speed is in a higher speed range. In order to elucidate a reason of the rising of the analysed friction angle, this study examined the temperature at the tool-chip interface and the chip formation mechanism by performing the orthogonal cutting experiment of a pure lead with a cutting speed of from 1 m/s to 140 m/s using an air-gun type of cutting tester developed. The temperatures at the tool-chip interface directly measured reach the melting point of the pure lead when the cutting speed is beyond 100 m/s. Hence, the true friction between the tool material and the chip material, as the tribological property, must lessen under such a high-speed cutting condition, because a thin molten metal layer will form at the tool-chip interface. Under the ultra-high speed cutting condition where the cutting speed is beyond the plastic wave speed of the workpiece material, the chip formation mechanism changes so that the chip width will widen extremely. Widening of the chip width changes the direction of the inertia force originated from the change in momentum occurring in the shear zone. Considering the change in the direction of the inertia force figured out that the analysed friction angle inevitably rises. The analysed friction angle no longer expresses the true friction property in such high-speed cutting conditions. This study deduces that the thrust force as well as the principal force will keep increasing regardless of the true friction property between the tool and chip materials under the ultra-high speed cutting condition.