SUMMARY

This thesis studies scaling effects in specific cutting energy when micro-cutting ductile metals. This is achieved by performing unique experiments to isolate one force component, detecting direct evidence of material separation, and numerical modeling of chip formation incorporating ductile fracture. The cutting force is viewed as a combination of a constant component, and increasing and decreasing force components, the independent variable being the uncut chip thickness or thickness of material removed in orthogonal cutting. The constant force component is isolated by performing high rake angle orthogonal cutting experiments at high rake angles. To understand the source of this constant force component the chip-root is investigated by examining the chip-workpiece interface in a scanning electron microscope. Evidence of ductile tearing ahead of the cutting tool is clearly seen at both low and high rake angles, at high and low cutting speeds, in a range of uncut chip thickness values, with small and large edge radius tools, and in two materials OFHC Copper and Al-2024 T3. A finite element model of the cutting process that captures ductile fracture leading to material separation is implemented in Abaqus/Explicit. Material separation is modeled via element failure. The model is validated using cutting and thrust forces. As the thickness of layer removed is reduced, the energy consumed in material separation becomes important. Simulations show that the stress state ahead of the tool is favorable for ductile fracture to occur. The numerical model is used to study the difference in energy consumption between a sharp tool and a tool with a non-zero edge radius. In summary, the thesis shows conclusive evidence of ductile fracture leading to chip formation in micro-cutting of ductile metals. It also shows the importance of including this phenomenon in modeling the micro-cutting process and in explaining the scaling of the specific cutting energy.