# Design and Verification of a New Fixture for Machining of Porous Blocks for Medical CAD/CAM Systems
## 3 Results  
In regard to the current design of the fixture, FEM analysis was conducted. Figures 5-7 show FEM analysis results for Von Mises stress, displacement, and strain under three different preloads of 10 N, 35 N, and 50 N, respectively. \begin{table}
\begin{tabular}{c c c c c c} \hline
**No.** & **Operations** & **Used Tool** & **Spindle Speed (rpm)** & **Feed Rate (mm/min)** & **Total Machining Time (min:s)** \\ \hline \multirow{2}{*}{1.} & External rough & end mill, ball tip & \multirow{2}{*}{1000} & \multirow{2}{*}{1200} & \multirow{2}{*}{5:59} \\  & Milling (one side) & D = 2 mm, L = 50 mm & & & \\ \hline \multirow{2}{*}{2.} & External rough & end mill, ball tip & \multirow{2}{*}{1000} & \multirow{2}{*}{1200} & \multirow{2}{*}{10:54} \\  & Milling (other side) & D = 2 mm, L = 50 mm & & & \\ \hline \multirow{2}{*}{3.} & External finish & end mill, ball tip & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{15:46} \\  & Milling (one side) & D = 1 mm, L = 50 mm & & & \\ \hline \multirow{2}{*}{4.} & External finish & end mill, ball tip & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{20:15} \\  & Milling (other side) & D = 1 mm, L = 50 mm & & & \\ \hline \multirow{2}{*}{5.} & \multirow{2}{*}{Profile milling} & end mill, ball tip & \multirow{2}{*}{1000} & \multirow{2}{*}{500} & \multirow{2}{*}{20:31} \\  & D = 0.6 mm, L = 50 mm & & & \\ \hline \multirow{2}{*}{6.} & External rough & end mill, ball tip & \multirow{2}{*}{1000} & \multirow{2}{*}{600} & \multirow{2}{*}{21:13} \\  & milling of connectors & D = 0.6 mm, L = 50 mm & & & \\ \hline \end{tabular}
\end{table} 
Table 2: CNC milling parameters. Regarding the analysis, it can be seen that the stress analysis for the 10 N load is not very significant (4.856 \(\times\) 10\({}^{-2}\) MPa), however, some stress concentrations were found on the porous block on 35 N and 50 N load, and they are 1.700 \(\times\) 10\({}^{-1}\) and 2.428 \(\times\) 10\({}^{-1}\) MPa, respectively. This is noticed on the longer edge of the porous block inside the fixture (Figure 5). The resulting displacements (Figure 6) show that most of the displacement occurs at the center of the bone block, as expected, due to the concentration of forces there, it equals 1.269 \(\times\) 10\({}^{-4}\) mm and 1.813 \(\times\) 10\({}^{-4}\) mm for 35 N and 50 N, respectively. Insignificant displacement is noticed for the 10 N load, which was 3.627 \(\times\) 10\({}^{-5}\) mm. Strain analysis for all three sets shows similar trend results of 2.344 \(\times\) 10\({}^{-6}\), 8.203 \(\times\) 10\({}^{-6}\), and 1.172 \(\times\) 10\({}^{-5}\) for 10 N, 35 N and 50 N, respectively (Figure 7). It can be observed that with the increase in static preloads for all three different sets (10 N, 35 N, and 50 N), stress, displacement, and strain values are rising proportionally. Based on the detailed view, minor red areas were noticed on the longer edge of the porous block for stress and strain. By comparing the obtained results with the actual material's known stress limits in [34], it is concluded that the stress concentrations found in the FEM analysis, which reach a maximum of 2.428 \(\times\) 10\({}^{-1}\) MPa (for the 50 N load), do not approach critical levels. These values are significantly lower than the material's maximum stress capacity, ensuring that the porous block remains well within safe limits. Therefore, the stress concentrations observed in the analysis are unlikely to cause failure or excessive deformation of the porous block, confirming the structural integrity under the applied loads.