## 5 Validation: Design for Additive Manufacturing and Multi Jet Fusion
### Additive Manufacturing Process: Printing an Innovative Fan  
Additive manufacturing is based on eight steps that are independent from the technology used. Let us apply the following phases to the fan:  
CAD: All processes, even non-additive ones, start with the definition of a mathematical model on a CAD software. This has the function of describing the object geometrically. We already have the 3D model of the fan, previously designed.  
STL (standard triangulation language) convert: This file is a simple way to describe an object geometrically. The STL extension discretizes the solid model into a series of triangles as it happens for the meshes (elements in the FEA analysis). Moreover, sometimes it is required to repair STL file because triangulation is not accurate. Using Autodesk Netfabb, it is possible to manipulate STL files.  
1. File transfer to machine: Once the STL file has been created, it can be directly sent to the AM. It is the machine itself that translates the STL file into G-Code. At this point, it is possible to analyze the fan by CAM software and to optimise the process. The following picture (Figure 17) shows a wall thickness test that depicts which surface can be damaged during printing. The green surface means that the walls are thick enough. Finally, on the CAM software, it is possible to simulate the whole process and understand which are the critical phases.
2. Machine set-up: Once all tests are passed, it is possible to set up the machine. In this case, the picture shows how many layers were generated and the total height of the print. Moreover, the machine display shows also the layout of components during machining. It is possible to print objects one inside the other without compromising the final result (space optimization). Before analyzing the printing process, it is important to understand the difference between lattice structure and full structure of the innovative fan. During the case study, both structures were printed.  
Before applying the lattice structure, the total volume of material was 67.08 cm\({}^{3}\). Then, by introducing the lattice structure, the weight changed to 39.06 cm\({}^{3}\), saving almost 30 cm\({}^{3}\) of material used.  
1. Build: The images on the right (Figure 18) show a thin layer of powder placed on the working area and the image below shows the application of transforming agents and energy to merge  
Figure 17: Wall thickness test.  
powder particles together. It is clear from the image the difference between the lattice structure (white arrow) and full structure (black arrow).
4. Remove: After the printing process, which lasted 6 h and 21 min, the build unit is transferred to the processing station for the cooling and cleaning of the components (Figure 19). The components are initially totally immersed in the powder that needs to be recovered. The recovered material ends up in a cardboard container, ready to be reused in the subsequent processing.
5. Post-process: Finally, there were several post-processing available, but to limit costs, only sandblasting was performed. This machine allows inserting the pieces from the left side and handling the compressed air and sand nozzles for complete cleaning (Figure 20).
6. Final product: Finally, the two variants were produced. Externally they look the same (Figure 21). However, the left one is printed using a full structure, whereas the right one is printed using a lattice structure.