# Additive Manufacturing of Ceramic Reference Spheres by Stereolithography (SLA)
## 4 Results and Discussion  
For the 18 spheres that were measured and analyzed, a nomenclature (Figure 10) was necessary to identify them according to their shape (B--bullet, M--mushroom), infill (ultimately only two types: F--with internal support, E--without internal support), orientation  
Figure 8: Thermal evolution in the debinding process. Figure 9: Sintering stage configuration and time vs. temperature diagram. (U--pole up, D--pole down), diameter in mm (20), wall thickness WT in mm (1, 2), and position on the tray (1, 2, 3). Additionally, to validate the process and conduct a metrological analysis that allowed for the evaluation of the influence of the proposed design variables, two parameters were evaluated: one dimensional (the diameter) and one geometric (the form error). The results for the diameter values (Table 4) of the different spheres measured by contact with the CMM ranged from 20.033 mm, measured on the sphere M_E_U_20\(2\)1 (artifact with mushroom geometry, without internal support, oriented upwards, \(\mathcal{O}\)20 mm, 2 mm wall thickness, in position 1 on the tray), to 19.916 mm, obtained on the sphere B_F_U_20\(1\)2 (artifact with bullet geometry, with internal support, oriented upwards, \(\mathcal{O}\)20 mm, 1 mm wall thickness, in position 2 on the tray). Thus, the diameter range was 117 \(\upmu\)m, with the average diameter of all spheres being only 9 \(\upmu\)m below the nominal value (Figure 11). Considering the arrangement of the different artifacts on the print trap, it can be observed that among the three possible positions, the intermediate position (position 2) always registers the smallest diameter values. It should also be noted that the values farthest from the nominal diameter, indicating the greatest contraction, correspond to the artifacts with the thinnest walls (1 mm) and internal support (B_F_U_20\(1\)2 and M_F_U_20\(1\)2). On the other hand, the average diameter of the spheres in position 3 deviates only 2 um from the nominal diameter, with the values being closest to the nominal. Additionally, when examining the values corresponding to position 1, it is noted that in all cases, the values are always above the average diameter of all spheres (19.991 um) and even above the nominal value. Regardless of the design variables and considering only the position on the print trap, it is significant to see the V-shaped distribution of all artifacts, which indicates the influence of the artifact's position. Regarding geometric quality, the data obtained for the form error (Table 5) shows a behavior similar to that of the diameter. The intermediate position (position 2) records, for all artifacts, the smallest value among the three measured for each type of artifact (the same V-shaped distribution). In this case, the smallest value, 69 um, was obtained for the artifact M_E_U_20\(2\)2 (artifact with mushroom geometry, without internal support, oriented upwards, \(\mathcal{O}\)20 mm, 2 mm wall thickness, and in position 2 on the tray), while the largest form error, 178 um, was recorded for the artifact M_F_U_20\(1\)3 (artifact with mushroom geometry, with internal support, oriented upwards, \(\mathcal{O}\)20 mm, 2 mm wall thickness, and in position 1 on the tray). In this case, the range of form error measurements is 109 um, while the average value of all form errors measured by contact is also slightly above one-tenth of a millimeter, 118 um (Figure 12). It is also observed that the highest geometric quality, with the smallest form errors, is recorded when the artifact walls are 2 mm thick, in both bullet (B) and mushroom (M) configurations. This clear dependency on wall thickness is even more pronounced when the artifact is manufactured without internal support, such that the model M_E_U_20_2 exhibits the smallest form error, as previously mentioned.