Certainly, the rake angle dictates the chip formation/flow direction, and also, the chip geometries are somehow different among the three cases. By examining the equivalent stress distributions in the affected zones, it can be found that the primary shear zone becomes more Quizartinib supplier distinguishable from the secondary shear zone when the rake angle changes from negative to positive. Also, the affected uncut zone ahead of the cutting tool becomes shallower when the rake angle changes from negative to positive. This indicates the severity of compression effect in the affected uncut zone. Figure 6 Chip formations and equivalent stress distributions in nano-scale polycrystalline machining for case C12. At the tool travel

distances of (a) 30, (b) 120, and (c) 240 Å. Figure 7 Chip formations and equivalent stress distributions in selleck nano-scale polycrystalline machining for case C13. At the tool travel distances of (a) 30, (b) 120, and (c) 240 Å. Similarly, the cutting force evolutions

are compared to illustrate the effect of tool rake angle. As shown in Figure 8a,b, as the tool rake angle changes from -30° to 0°, and then to +30°, both the tangential force F x and the thrust force F y decrease and the deduction of thrust force is more pronounced. The average F x and F y values are also calculated to make a more direct comparison. As shown in Table 5, with the -30°, 0°, and +30° tool rake angles, the average tangential forces are 412.16, 338.73, and 280.80 eV/Å, respectively, and the thrust force values are 353.59, 132.68, and 19.43 eV/Å, respectively. The ratio

of tangential force to thrust force, F x /F y , increases from 1.17 to 14.45 as the rake angle changes from -30° to +30°. Clearly, the more drastic compression effect between tool and workpiece induced by the negative rake angle causes much higher thrust force compared to the cases with zero or positive tool rake angle. As the rake angle becomes more negative, the thrust force learn more needs to increase more significantly compared to the tangential force to overcome the plastic deformation resistance of the work material under the tool tip. This result is consistent with the literature on conventional machining and nano-scale monocrystalline machining [35, 36]. Figure 8 Evolution of cutting forces for three cases with three rake angles. (a) Tangential force, F x  and (b) thrust force, F y . Table 5 Average cutting force values with respect to tool rake angle Case number Tool rake angle (deg) F x (eV/Å) F y (eV/Å) F x /F y C4 -30 412.16 353.59 1.17 C12 0 338.73 132.68 2.55 C13 +30 280.80 19.43 14.45 Effect of machining speed The effect of machining speed can be analyzed by comparing cases C4, C8, and C9, which employ the machining speeds of 400, 100, and 25 m/s, respectively. The chip formation and equivalent stress distribution for case C4 is already shown in Figure 3. Figures 9 and 10 depict the results of cases C8 and C9, respectively.