## 4 Discussion
### Manufacturing  
Once printed, the mold sections were sanded and then sealed with a fast-curing, wet layup epoxy resin system. This was by far the most time-consuming step of the manufacturing process, mainly because of the complex internal shapes of the mold. The inside of the resin infusion passageways and the shear web fixture could not be sealed. This was sufficient to provide a good vacuum seal for the VARIM process but did lead to other issues. The resin was drawn into the internal cavities of the 3D prints (see Figure 9), leading to a significant increase in the resin required for the infusion. Based on estimates from an assumed fiber mass fraction for the VARIM process, the total mass of the fiberglass, and the volumes of the internal mold cavities, the part absorbed almost three times as much epoxy as was calculated to be required. Because of this, better sealing methods are required for 3D-printed molds with hard-to-reach, complex geometries and design features. Techniques such as vapor smoothing with acetone [26] may be very useful for this type of application, but will require stricter controls when applied on a larger scale. More research is required in this area. Hands-on manufacturing of the conceptual design provided a true understanding of which design features were particularly beneficial for the manufacturing process. The segmented mold construction was simple to implement and would be beneficial for transportation or on-site manufacturing of large components. In fact, it made sealing the harder-to-reach areas of the mold easier while it was still segmented. Integrating the root fasteners also worked as intended, as well as the integrated shear web fixture. The premade shear web was easily inserted and sealed into the mold for infusion. On a larger scale, more considerations would need to be made for the thickness taper and hydrodynamic twist of the tidal turbine blade. Both the integrated root fasteners and shear web features proved to be incredibly useful, removed time-consuming steps from the manufacturing process, and eliminated the need for costly, defect-prone adhesive bonding steps. The only design features that proved to be a hindrance were the integrated resin passageways. As described earlier, it was not possible to seal the inside of them, which led to excessive resin uptake. In this case, they were not worth the additional design and manufacturing effort, although their presence was useful for providing resin flow around the shear web. Despite the disadvantages, this research has demonstrated that it is possible to implement integrated resin passageways as a 3D-printed design feature. They may still become useful for other more complex composite geometries in the future, wherein accurate resin flow is critical. Final finishing of the blade section was a critical step in the manufacturing process. It was already understood that this was where the novel internal molding process would be at a disadvantage to traditional female molding techniques. Overall, the finishing process was not much more time-consuming than is typically required for a tidal turbine blade based on past manufacturing experience in the CoMET, but other issues were uncovered. The spar caps needed a substantial amount of material removed to meet the designed hydrodynamic surface geometry. This would be detrimental to the integrity of a full-scale blade structure. Great care also needed to be taken around the trailing edge region to avoid grinding through the skin plies to the mold surface. In light of these issues, the grinding and sanding process could be accounted for in the design process. Low-cost \"sacrificial\" plies, such as chopped-strand mats could be included in the composite layup design, so that the critical skin and spar cap plies would not get damaged by the finishing process. Figure 10 shows some visible out-of-plane waves in the composite around the root of the blade section that were not removed during the final finishing process.