# Design and Verification of a New Fixture for Machining of Porous Blocks for Medical CAD/CAM Systems
## 3 Results
On the basis of these results, it can be seen that FEM analysis showed overall good  
Figure 5: Distribution of Von Mises stress in the porous block for different preloads of 10 N, 35 N, and 50 N.  
Figure 6: Distribution of resultant displacements in the porous block for different preloads of 10 N, 35 N, and 50 N.  
Figure 7: Distribution of strain in the porous block for different preloads of 10 N, 35 N, and 50 N.  
results, with low distribution of stress and low displacement in the XYZ direction. This showed that the selected design should perform as intended and that it will support the porous block during its machining. After the FEM analysis, the next step involved manufacturing the designed fixture in order to test the concept and functionality of the device. According to the design, a PEEK disc with a fixed diameter of \(\mathcal{O}\)98.5 mm, and a thickness of 10 mm was used for manufacturing the fixture, along with steel 1 mm plates, silicone tabs, and all necessary fasteners. A fabricated and assembled fixture is shown in Figure 8.  
After the fixture has been fabricated, the next step involves testing in real conditions. Based on the requirements, a 3D model of bone graft was imported into MillBox CIM software, and a predefined machining strategy was selected by an operator. The only thing that was reduced from the predefined strategy was the spindle speed, due to the fragile nature of the workpiece, in order to prevent any breakage during CNC manufacturing (Figure 9a-c). Figure 9a shows the locating and clamping of the workpiece inside the fixture and fixture placement in the disc holder of the INTERDENT CC Power CNC milling machine. Figure 8: Fabricated fixture for porous block. Figure 9: Showing (**a**) locating and clamping of porous block inside the designed fixture and its placement in disc holder, (**b**) machining of bone graft, and (**c**) machined bone graft inside porous block. Figure 9b shows the machining process. During the machining process, the disc holder was rotated by 180\({}^{\circ}\) for machining of the workpiece from both sides, in order to obtain the full shape of the final bone graft. Also, water was used to wash away the debris during machining. Figure 9c shows the machined bone graft from the porous block. The machining process of bone graft from the porous block was supported by four 3 mm pins during machining (Figure 9c). After the machining of the bone graft was completed, the following step was to remove it from the porous block and clean it up. Figure 10 shows the manufactured bone graft and its placement on the 3D-printed upper jaw, for which it was originally designed. This step presents a quick verification that the manufactured graft actually fits in its designed place. Dimensional verification was conducted as the last step in order to verify manufactured bone grafts dimensional accuracy and also to check if any deviations occurred, such as accidental movement of the porous block during its machining, which would impact its accuracy. CAD Inspection analysis was performed. Figure 11a shows the measurement process of bone graft on a CMM where the inner side of the manufactured bone graft was 3D scanned. The bone graft was placed on a putty material, which was shaped based on its geometry, and this enabled the bone graft to maintain a fixed position during CMM scanning. Figure 11b shows the measurement results (obtained point cloud and reconstructed mesh 3D model), while CAD Inspection analysis in GOM Inspect software is shown in Figure 11c. Figure 11: Showing **(a)** CMM scanning of machined bone graft, **(b)** acquired point cloud and its mesh 3D model, and **(c)** CAD Inspection analysis. Figure 10: Manufactured bone graft and its placement on the upper jaw for verification. On the basis of CAD Inspection analysis, it can be seen that the deviations are in the range of \(\pm\)0.135 mm, while concentration is at around +0.015 mm. Some deviations in blue and red color can be observed as a result of material porosity.