Study on Micro-machining Mechanics Based on Direct SEM Observation (2nd Report)

This paper describes the dynamic behavior of crack and its role in the shear type chip formation process. In order to observe actual crack behavior during machining, direct SEM examination is carried out for 6-4 brass. The local strain analysis near the crack is also carried out to determine the crack nucleation and propagation mechanism. The crack nucleation is associated with the cavitation on the machined surface at a finite distance from the tip of the cutting edge. The crack grows into the material nearly in direction of maximum shear strain rate. After growing to be of sufficient size, it propagates along the shear band due to extreme shear strain concentration. The effects of cracking on the machined surface integrity and the cutting force characteristics are also discussed.