# Experimental Study on Micro-Grinding of Ceramics for Micro-Structuring
## 2 Experimental Setup  
Table 1 shows the hardness of several hard materials, including ceramics. Cemented carbide (WC-Co), a common material used in commercial micro-tools, has a degree of hardness similar to that of alumina. Therefore, micro-tools made of cemented carbide suffer from severe tool wear while processing ceramic materials. In contrast, because the  
hardness of PCD is 3-5 times higher than that of alumina and zirconia, PCD is a suitable tool material for ceramic processing.  
The fabrication of micron-sized PCD tools by grinding is a difficult and time-consuming process. Since polycrystalline diamond grains were sintered with cobalt binder, bulk PCD is electrically conductive. Therefore, electrical discharge has been widely used for manufacturing micron-sized PCD tools [22; 23; 24; 25; 26]. To manufacture the micro-tool, a 500-\(\upmu\)m thick PCD layer is brazed to the end of a cemented carbide material with a diameter of 1000 \(\upmu\)m. The grain size of PCD was 10 \(\upmu\)m. In our experimental setup, micron-sized PCD tools were machined by WEDG [19]. WEDG is similar to wire EDM, but a metal wire electrode is fed along a wire guide in WEDG. In this study, a brass wire of 200 \(\upmu\)m in a diameter was used as a wire electrode and EDM oil was used as a dielectric fluid to minimize the discharge gap. A resistor-capacitor (RC) generator circuit was used to generate the discharge. The resistance was 1 \(k\Omega\) and the working capacitances of 1000 pF to 478 nF were used. The applied voltage was 100 V.  
After WEDG, the tools were moved to a microgrinding system, where a ceramic workpiece was installed, as shown in Figure 1. As shown in Figure 2, two kinds of grinding processes were tested: side-grinding and groove-grinding. For the side-grinding, a circular tool with a diameter of 800 \(\upmu\)m was used as shown in Figure 3a. For the groove-grinding, however, unstable machining may occur because of a grinding chip can be stuck between the tool and the workpiece during machining. To avoid this issue, a micro-tool with a D-shaped cross section and an inclined bottom surface was manufactured, as shown in Figure 3b. Tables 2 and 3 show the machining parameters for the side-grinding and groove-grinding, respectively.  
Figure 3: SEM images of PCD grinding tool: (**a**) cylindrical tool and (**b**) inclined D-shape tool.  
\begin{table}
\begin{tabular}{c c} \hline \hline Tool material & PCD \\ Tool shape & circular tool of Ø 800 \(\upmu\)m \\ Workpiece material & Zirconia \\ Rotation speed (rpm) & 30,000 \\ Feed rate (\(\upmu\)m/s) & 250 \\ Radial depth of cut (\(\upmu\)m) & 5 \\ Axial depth of cut (\(\upmu\)m) & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Machining parameters for the side-grinding.  
Figure 2: Schematic of (**a**) side-grinding and (**b**) groove-grinding.  
A high-speed spindle was equipped on the \(Z\)-axis of the precision stage, and the grinding force was measured using a dynamometer (9256C, Kistler Instrumente AG, Winterthur, Switzerland) on the X-Y-axes stage. The roughness of the tool and the machined surface were acquired using a laser confocal microscope (OLS5000, Olympus Corp., Tokyo, Japan). The magnification of an objective lens was 100\(\times\). A tilt removal and Gaussian filter were applied for the surface roughness measurement. Experiments and measurements were repeated three times for each parameter.