## 3 Results and Discussion  
### Analysis of Flat Insert and Produced Samples  
After the production of the samples, all the inserts exhibited cracks along their cross-sections (Figure 4a) due to the high pressure involved in the micro injection moulding process and the brittle behaviour of the resin. A test conducted on the inserts used to produce a single sample showed that these cracks appeared after the first shot. This damage, however, seems to have no impact on sample production because the insert is well blocked inside the master plates of the steel mould and remains compact inside its housing. Furthermore, the surface morphology analysis (Section 2.3) showed how the moulding cycle affected the insert cavity. Figure 4 presents the evaluation of the cavity surface flatness for the V00 and V90 inserts before and after sample production (Figure 4b,e). Both bulk inserts maintain flatness in the range of 30 \(\upmu\)m, while at the end of the moulding cycle, a convex behaviour of about 100 \(\upmu\)m is observed on the surface of both, with the minimum in the centre for V00 (Figure 4c) and close to the running gate for V90 (Figure 4e). This variation in surface flatness highlights the viscoelastic nature of the insert polymer. During the moulding cycles, cavity pressure induces the compression of the insert, increasing its stress levels and leading to permanent deformation, as found by [46]. The interval main plot of S\({}_{\text{a}}\) and S\({}_{\text{z}}\) in Figure 5 shows no significant roughness evolution for both inserts before and after the moulding cycle. Figure 4: Analysis of insert flatness variation before and after moulding cycles. The results of the visual inspection of both inserts with the V00 and V90 flat surfaces are shown in Figure 6. The absence of sample flash is the result of the improved design discussed in [50] (Figure 6a). Moreover, Figure 6 shows that for both insert geometries tested, the wax residuals (the support material for material jetting) are removed and entrapped in the PMMA (Figure 6b) immediately after the production of the first sample. Samples produced from the V90 insert geometry show a surface sign (Figure 6c): a zone with a parabolic shape. This sign starts to be visible around the 15 th sample produced and also shows the flow front of molten polymer during the filling phase. Comparing this sign with the measure of V90 insert flatness in Figure 4e, it seems to correspond with the area where the deflection of the insert begins to be higher. Figure 5: Analysis of insert roughness evolution before and after moulding cycles. The results of the sample shape and thickness are summarised in Figure 7. It can be seen that the produced samples have a thickness higher than the designed one of 0.8 mm, with a decreasing trend along the filling direction (Figure 7a) for almost both V00 and V90 inserts (Figure 7b). This variation can be attributed to the higher effect of the injection pressure on the first part of the cavity and the viscoelastic behaviour of the resin insert, resulting in a higher compression of the insert and, consequently, a variation in sample thickness. The analysis of the surface roughness of the 1 st and 50 th samples produced with the V00 and V90 insert configurations (Figure 8) showed an improvement in the surface roughness of all samples, especially for those moulded with the V90 insert (from 50 \(\upmu\)m to about 40 \(\upmu\)m). The orientation of the inserts on the print plate significantly affects the quality of the samples in terms of surface roughness and geometry. The V90 inserts have a bottom surface cavity belonging to the y-z plane, allowing the layering effect found in the z direction on each part produced by additive processes (Figure 6c). Moreover, the layering weakens the mechanical properties and leads to higher deformation of the insert, resulting in parts with decreasing thickness. By contrast, the V00 inserts, with the cavity on the x-y plane, guarantee smoother parts with more regular thickness (Figures 7b and 8a).