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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schematic of the stronger and weaker loading direction in 3D printed specimens, from Loh et al., (2020).. In terms of tensile properties, a UTS of 947.26 MPa was obtained from the specimen printed flat (i.e. laying on the build plate), while alower value of 440.15 MPa was obtained from the vertical specimens. Fractography was used to study the fracture surface, and the results show that while the flat dog bone presented a ductile fracture surface, the vertical one shows clear signs of delamination (Fig. 11. a) layouts used in Alkindi et al., (2021); b) fracture surface of specimen printed at 90° (vertical); c) fracture surface of specimen printed at 0° (horizontal); d) schematic of the stronger and weaker loading direction in 3D printed specimens, from Loh et al., (2020).), due to the poor adhesion between layers. Suwanpreecha et al. (2021), Henry et al. (2021), and Caminero et al. (2021) reached the same conclusion in their research about the tensile properties of specimens printed out with 17-4 PH and 316L metal powder. The mechanical properties obtained were strongly dependent on the layout, in contrast to the relative density that depends more on other factors. A comprehensive comparison is shown in Fig. 12. Comparison between different studies on the UTS of stainless steel specimens. Tosto et al. (2021) proposed a broad investigation on 316L and 17-4 PH parts, printed both with a horizontal and vertical layout. For 316L parts, a 100% infill percentage was used for the infill strategy, and the results show expectably that the vertical layout performed worst under tensile loading. It is interesting, on the other hand, to observe the mechanical properties of the 17-4 PH parts, printed with a different infill strategy, called closed triangular cell path. This strategy is proposed by the commercial system Markforged Metal X, which was used both by Tosto et al. (2021) and Galati et al. (2019). Being the infill density well belove 100%, there is almost no difference between vertical and flat layouts, which is indeed a significant result.

Fig. 12. Comparison between different studies on the UTS of stainless steel specimens

5.2. Comparison with other techniques MEAM is presented as an advantageous technique compared to other AM processes. The key advantage of this process is the uncomplicated and inexpensive printing phase. Even though the parameters optimization requires more investigation, as widely pointed out in the previous paragraph, the FDM process is well-known and widely explored which is an advantage. In comparison with other AM techniques, MEAM is faster, therefore is more suitable for rapid prototyping, small-scale production, or spare parts production. This is in contrast to other powder bed techniques, such as Binder Jetting, SLM, and EBM. In the three abovementioned techniques, the necessity of the powder bed is a huge item in the cost list. Metal powder is also reactive and dangerous, and the safety issues related to its use are considerable. Moreover, the unmelted powder is an additional issue. Another advantage of MEAM over SLM and EBM is the absence of a highly focalized power source, such as the laser or the electron beam. The advantage is in terms of both cost and safety. SLM and EBM printers are also equipped with sophisticated chambers to maintain a high temperature in the printing volume or a controlled atmosphere, which is in both cases complicated