# Experimental Study on Micro-Grinding of Ceramics for Micro-Structuring
## 4 Conclusions  
In this study, grinding was performed using a micro-tool for high-hardness zirconia and alumina ceramics. Considering the size effect of micro-machining, the characteristics of the micro-grinding of ceramics were investigated by adjusting the working capacitance, tool feed rate, depth of cut, and rotation speed as parameters.  
In the grinding with the side surface of the tool, the increase in the working capacitance during tool fabrication by EDM caused a decrease in the normal force. On the contrary, the normal force in the machining of micro-grooves increased continually as the working capacitance increased. To determine the cause of the contrasting tendency, the edge radius of the tools was investigated in terms of the size effect in macro-machining.  
During the fabrication of the PCD tool, the edge radius was changed by adjusting the working capacitance. The larger the capacitance used to fabricate the tool, the larger the edge radius produced. Accordingly, the force acting on the tool manufactured with 1000 pF decreased by up to 50% compared to that of the tool with 100,000 pF.  
Next, the micro-grinding characteristics of zirconia were investigated. When the tool feed rate was increased by 50-400 \(\upmu\)m/s, the normal force increased in the range of 0.35-0.85 N, and a smooth surface with a surface roughness of at least 19 nm Ra was obtained at a feed rate of 50 \(\upmu\)m/s. As the depth of cut became larger than the edge radius of the tool, the proportion of the force in the feed direction increased, resulting in a larger number of defects. After grinding 1000 mm in length, the wear on the tool face was examined by SEM observation considering grinding force, surface roughness, and evident abrasion wear.  
Finally, micro-grinding of alumina was conducted and produced a partially smooth surface with some defects and failures. When increasing the feed rate in the range of 50-1000 \(\upmu\)m/s, the normal force increased up to 1.2 N, and the area where the fractures occurred widened. When the depth of the cut increased from 5 to 7 \(\upmu\)m, the area of the fractured surface increased. Based on the results of observation of the machined surfaces, the defects were classified according to their shape into raw material defects and intergranular fractures resulting from the breakage of grain boundaries.  
Figure 20: SEM images of defects on the machined surface of alumina: (**a**) defects caused by raw material pores and micro-pits separated with grinding chips and (**b**) intergranular fractures.  
**Author Contributions:** Conceptualization and methodology, B.H.K. and Y.N.; formal analysis, Y.N. and U.S.L.; writing--original draft preparation, Y.N.; writing--review, B.H.K.; supervision, B.H.K.; funding acquisition, B.H.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Technology Innovation Program (20010984) funded by the Ministry of Trade, Industry & Energy (MOTIE), Korea.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.