PSI - Issue 41

Saveria Spiller et al. / Procedia Structural Integrity 41 (2022) 158–174 Saveria Spiller/ Structural Integrity Procedia 00 (2019) 000–000

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that a more intense extruding force is necessary to flow the material. Therefore, a higher extrusion temperature or lower speed rate has to be chosen. Finally, the morphology of the powder is relevant, with regular and spherical powder particles are suitable to achieve higher density (Singh et al., 2020). Once the binder and powder components are chosen, all the elements have to be combined homogeneously since agglomerations of powder make the filament brittle (Singh et al., 2020). Furthermore, if excess binder exists in some regions, the distribution of the voids after the debinding will be affected, with consequences on the shrinkage of the component during the sintering. Ultimately, the homogeneous compound is shaped in a filament, either using a capillary rheometer or a screw extruder (Agarwala et al., 1996). Typical diameters of the filaments are 1.75 and 2.85 mm.

Table 1 feedstock material characteristics from the literature

Mean powder size

Infill content

Sadaf et al. (2021) Kurose et al. (2020) Hassan et al. (2021) Thompson et al. (2019)

20-35 µm 10 µm 8.8 µm 17.7 µm 30-50 µm 12.3 µm

65vol% 60vol% 63vol% 55vol% 88wt% 55vol% 58vol% 63vol%

316L

Liu et al. (2020) Godec et al. (2020) Wu et al. (2002)

17-4 PH

22 µm

Suwanpreecha et al. (2021)

3.97 µm

3. The shaping phase As mentioned before, the first phase of the MEAM process consists in printing the part using an FDM printer. With such equipment, the filament is loaded in the unity called printing head, where it enters a heating chamber. The material is softened and pushed through the nozzle. The printing head follows on the building platform the path illustrated in the G-code (Gibson et al., 2021). In this way, the material is selectively deposited layer upon layer to build the part. The main process parameters of the FDM process are widely studied, and some examples are layer thickness, printing speed, nozzle temperature. Although FDM has been widely studied and optimal printing parameters were defined when dealing with polymers, using a high-filled one requires some adjustment to the standard setting of the printer. A good description of the process is presented in some reviews available in the literature. The one proposed by Gonzalez-Gutierrez et al. (2018) covers broadly the topic; some other comprehensive reviews can be found in the published works by Nurhudan et al. (2021), Rane, (2019), and Ramazani et al. (2022).

Fig. 4. Stair effect on the side of FDM printed parts (Loh et al., 2020)

One of the most relevant parameters is the layer thickness. It has an impact on both the external appearance of the components and on the mechanical properties. By choosing a thin layer height, it is possible to reduce the surface roughness and the stair effect, a common issue of AM, reaching better details accuracy. Rane et al. (2019) proved that layer thickness is the most significant parameter in the model designed to assess the surface quality of 316L