Understanding Nanoscale Ductile Mode Cutting of Brittle Materials by Molecular Dynamics Simulation
lass, ceramics, tungsten carbide and silicon wafers are brittle workpiece materials. Traditionally, they are machined by grinding (a random fracturing process on the microscale), which creates a damaged layer full of microcracks on the machined workpiece surface. In a research project in
the Department of Mechanical Engineering, a potentially revolutionary technology for fracture-free cutting of brittle materials, known as nanoscale ductile mode cutting (NDMC), has been successfullydeveloped. In this technology, the stock material on the workpiece is removed layer by layer at the nanoscale with a tool having nanoscale edge radius. Experimental observations have shown that the critical condition for NDMC is the extremely high compressive stress in the chip formation zone. This is established by using a tool with nanoscale cutting edge radius when the thickness of the undeformed chip is smaller than the cutting edge radius.
To get a better understanding of the underlying science of NDMC, a molecular dynamics simulation system has been developed. This allows understanding the chip formation and cutting mechanisms in this process at the atomic level (Figure 1).
Two significant findings have been made through our molecular dynamics simulations.
Firstly, it was found that cracks could readily form in the chip formation zone when cutting brittle materials (Figure 2(a)). This has been related to the tensile stress state in the chip formation zone (Figure 2(b)). The condition of ductile mode cutting of brittle materials is without crack formation as shown in Figure 2(c). Our results show that when the tool edge radius is smaller than a critical value and the undeformed chip thickness is smaller than the tool edge radius, only compressive stresses are present in the chip formation zone (Figure 2(d)).
Another interesting finding is that in NDMC of brittle single crystals, dynamic hard particles which are atom groups with significantly shorter bond lengths (Figure 3), would be formed, removed and reformed in the chip formation zone. These hard particles, in turn, may cause micro/nano groove wear at the tool flank. Experimental confirmation of the wear grooves at the tool frank has been obtained in NDMC of single crystal silicon wafer with single crystalline diamond tools. An example of this is shown in Figure 4.
Contact person
Assoc Prof XP Li
Tel: 65163429,
Fax:67791459
E-mail: mpelixp@nus.edu.sg
