## 3 Results and Discussion
### Cutting Force  
Cutting forces were measured while machining the two cross-sectional shapes, as described in Section 2.3. Then, the specific cutting pressure was calculated from the measured cutting forces. Figure 9a shows the cutting force measured during the experiment in Section 2.3 versus the MRR (material removal rate), and Figure 9b shows the specific cutting pressure calculated based on the cutting force versus the MRR. The experimental results showed that the cutting force of the V-shaped cutting cross-section was slightly larger than that of the trapezoidal cutting cross-section, even though the material removal rate was the same. Additionally, the specific cutting pressure calculated based on the cutting force was slightly larger. Figure 8: Illustration of the shape error of three microstructural patterns: (**a**) trapezoidal cross-sections, (**b**) rectangular cross-sections, and (**c**) triangular cross-sections. Since the machining speeds of the two cases were the same, it is conceivable that the machining cross-sectional area is the same if the material removal rates are the same. Figure 10 shows the length of the cutting edge according to the change in the cross-sectional area for the two cross-sectional shapes. When the cross-sectional area of the cutting was the same, the length of the cutting edge for the V-shaped cross-section was shorter than that for the trapezoidal one. Thus, the chip thickness of the trapezoidal cross-section was smaller than that of the V-shaped cross-section in this study. In general, the cutting force is expected to be larger when the chip thickness is smaller [23; 24; 25; 26; 27]. This is very true if the cross-sectional shapes to be cut are very similar or the same. The experiment results in this study were not consistent with those in previous works due to a slight difference between the shapes of the trapezoidal and triangular cross-sections. The difference in the cutting forces in this study might be expressed by considering the formation and deformation of a chip in two machining processes. Figure 10: Cutting edge length. Figure 9: Measured cutting force and specific cutting pressure: (a) cutting force, (b) specific cutting pressure. Tables 1 and 2 show the change in the width of the cross-section before and after machining for the two cross-sectional shapes. Figure 12\(b\) is a value calculated from a machining condition and a tool shape, and Figure 12\(b^{\prime}\) is a value measured from an SEM image of the chip. In the case of the trapezoidal cross-sectional shape, the width of the chip generated after machining was larger. In the case of the V-shaped cross-section, the width of the cross-section of the chip generated after machining was smaller than the width of the cross-section before machining when the depth of cut was 5 \(\upmu\)m. When the depth of cut was 10 \(\upmu\)m, the width of the chip generated after machining was larger, but the difference was smaller than that in case of the trapezoidal cross-sectional shape. Figure 13 shows an enlarged view of part of the SEM image shown in Figure 11b. A close look at the V-shaped combs generated by the triangular-shaped tool shows that the wrinkled areas in the oblique direction to the V-shaped combs appeared intermittently (as indicated by the dotted arrow). From the results, it can be seen that there was a chip flow in the center around the vertex of the triangular-shaped tool in the shear deformation process to generate the chip. The flow of this type of chip has also been mentioned by [PERSON] et al. [10]. To summarize the cutting force experiments, the plastic deformations of the chips for the two machining processes were different, even if the cross-sectional areas to be cut for the two processes were the same. A V-shaped cross-section resulted in a more complex shape change in the chip formation than the trapezoidal cross-section. Correspondingly, the required cutting load for the V-shaped cross-section was higher than the trapezoidal cross-section.