# Conformal 3D Material Extrusion Additive Manufacturing for Large Moulds
## 4 Discussion  
The previous section describes a practical application of the methodology proposed in this research on a manufacturing machine to produce small prototypes of moulds and sandwich structures.  
In particular, by customising a desktop FFF system, it was possible to build and validate a hybrid manufacturing framework capable of producing different types of objects where both traditional and additive manufacturing processes coexist. A unique machine with an extrusion head, typical of AM technology, and a standard milling tool, has been used. The resulting prototypes demonstrate the possibility of further increasing the design-to-manufacturing workflow by deleting some tedious steps that should be accomplished manually by expert workers.  
The traditional G-code structure of AM machines is based on the philosophy of a 2.5D deposition of new material, which limits the applicability of LM objects in structural applications. Moreover, high surface roughness is a typical drawback of LM techniques; thus, 2.5D deposition should be avoided in the manufacturing of moulds. The first sample we produced to validate the desktop hybrid machine functionality--described in Section 2.2--confirms this challenging aspect. However, the G-code of FFF machines can be easily modified to achieve a conformal material deposition, as demonstrated with the FFF desktop machine case study. Therefore the proposed methodology uses a 3D spatial material deposition along conformal paths by converting instructions typical of traditional manufacturing processes into AM language, a methodology that has never been reported in the literature before. Thus, several operations, such as external coating or release agent  
Figure 12: Large-scale mould finishing: (**a**) rough milling to remove exceeding external clay; (**b**) accurate milling for surface finishing.  
deposition, can be automated. A customised procedure coded in software is at the heart of the methodology. The second sample test in the previous section validated the approach with encouraging results. Indeed, the cumbersome stair-step effect, typical of LM, is completely removed. Moreover, the methodology demonstrates that the milled mould can be easily reused for other manufacturing cycles without operator-dependent processes.  
This approach can be easily reproduced and applied for different tasks, as Figure 1 suggests: sandwich structures, simple moulds, or moulds and AM CFRP (Carbon Fiber Reinforced Plastic) lamination. New materials are developed for AM FFF machines, such as carbon filament, metal wires, and nylon based wires, so several combinations of materials for moulds and parts can be set.  
The extension of the methodology from the test with the FFF machine to the larger AM-CNC hybrid proved feasible. Indeed, results demonstrate that a precise material deposition and a significant decrease in the human workload can be obtained. The goal of this research has been successfully achieved by obtaining a well-machined, waxed, and polished large-scale mould: a dramatic reduction of the need for human involvement has been noticed. 3D spatial wax deposition seeks to create highly polished and smooth surfaces while limiting the handcrafting of the mould by technicians and potential damage to the external surfaces of the mould due to wrong machining operations.  
In all applications in which external surface continuity is crucial, such as the mould of hulls in marine and aerospace engineering, single-piece large-scale moulds could be easily produced thanks to the proposed methodology.