Tool wear characteristics and their effects on nanoscale ductile mode cutting of silicon wafer

Nanoscale ductile mode cutting of single crystalline silicon is a very promising technology for fracture free machining of silicon wafers. In the technology, the tool edge radius is required to on nanoscale for the ductile chip formation mode. Therefore, one of the main concerns with the implementation of such a technology is the tool wear and its effect on chip formation mode. In this study, the variation of tool geometry due to tool wear and its influence on the nanoscale ductile mode cutting of silicon wafer with single crystalline diamond tools is investigated and analyzed. The tool shape and cutting edge radius before and after cutting are measured using a non-destructive nano-indentation method. Variations of the cutting forces with tool wear during cutting are also investigated. It is found that the tool cutting edges undergo two processes simultaneously. One is the wear of material on the tool main cutting edge, which increases the main cutting edge radius, but leaves the shape of the main cutting edge unchanged, enhancing the conditions for ductile mode chip formation. The other one is the generation of nano or micro grooves at the tool flank, which forms sub-cutting edges of much smaller radii on the main cutting edge. As the grooves become deeper and deeper, the sub-cutting edges extend towards the tool rake face ultimately becoming the dominating cutting edge of much smaller radius. In such a way these sub-cutting edges tend to change the cutting mode from ductile to brittle.