# Experimental Study on Micro-Grinding of Ceramics for Micro-Structuring
## 3 Results
### 3.1. Machining Characteristics of Zirconia
Considering the grinding force increment in Figure 5, it is possible to infer that the tool with a larger edge radius produced with a larger capacitance resulted in a higher minimum uncut chip thickness, enhancing the ploughing effect with smaller chip formation, and also resulting in a higher grinding force [28; 29]. Using a micro-tool with a diameter of 200 \(\upmu\)m, the grinding characteristics of zirconia were investigated with respect to the tool feed rate, depth of cut, and rotation speed. Figure 7 shows that as the feed rate increases, the grinding force increases, and the grinding marks are clearly evident in the photographs in Figure 8. Considering the increase in the roughness of the machined surface in Figure 7, it can be assumed that as the tool feeds, the cusp grows, leaving a clearer grinding mark. Figure 9 shows the 2D and 3D profiles of the surfaces. Figure 5: Comparison of normal force (Fz) at different feed rates of tools fabricated using working capacitances of 1000 and 100,000 pF. Figure 6: **(a)** Effect of the working capacitance on the tool edge radius (\(r_{e}\)) and SEM images of the edge fabricated with capacitances of **(b)** 1000 pF and **(c)** 474,000 pF. Figure 7: Influence of the feed rate on the normal force (Fz) and roughness of the machined surfaces (tool diameter: 200 \(\upmu\)m, depth of cut: 10 \(\upmu\)m, rotation speed: 30,000 rpm). Figure 8: SEM images of the cutting marks on the grooves for different tool feed rates: (**a**) 50 \(\upmu\)m/s, (**b**) 200 \(\upmu\)m/s, and (**c**) 400 \(\upmu\)m/s (tool diameter: 200 \(\upmu\)m, depth of cut: 10 \(\upmu\)m, rotation speed: 30,000 rpm). Experiments were performed by changing the depth of cut to confirm the size effect depending on the edge radius. By using a tool with a capacitance of 10,000 pF, an edge radius of 9.2 \(\upmu\)m was obtained. Figure 10 shows the force component in the feed direction (Fx) increased for depths of cut of 10 \(\upmu\)m or higher. This means that the side surface of the tool participated in machining when the depth of the cut was larger than the edge radius. Figure 10: Effect of the depth of cut on the grinding force components. Figure 9: 2D and 3D surface profiles of the grooves for different tool feed rates: (a) 50 \(\upmu\)m/s, (b) 200 \(\upmu\)m/s, and (c) 400 \(\upmu\)m/s. From Figure 11a, the experimental results indicate that with a depth of cut of 10 \(\upmu\)m or more, the surface roughness of the machined surface increased. As shown in Figure 11b, some defects were observed on the surface at 15 \(\upmu\)m.  
Figure 12 shows the decrease in the normal force according to the tool's rotational speed. As the rotational speed increased, the unit material removal volume and the grinding force decreased. The roughness of the machined surface was reduced from 30 nm to 18 nm in Ra. Figure 11: (**a**) Effect of the depth of cut on the roughness of machined surfaces. (**b**) SEM images of the surfaces. Figure 12: Normal force (Fz) and surface roughness obtained by varying the rotation speed of the tool. Figure 13 shows the spiral structure on the surface of zirconia machined by micro-grinding. The structure had 600 \(\upmu\)m in width and 300 \(\upmu\)m in height. The machining conditions used were the following: feed rate of 100 \(\upmu\)m/s, depth of cut of 10 \(\upmu\)m, and rotation speed of 30,000 rpm. Figure 14 shows the SEM images of the chips obtained during the grinding of zirconia. They consist of a lot of debris or particles of 1 \(\upmu\)m or sub-micron size.