PSI - Issue 42

Saveria Spiller et al. / Procedia Structural Integrity 42 (2022) 1239–1248 Saveria Spiller/ Structural Integrity Procedia 00 (2019) 000 – 000

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MEAM advantages are incontrovertible. The process is uncomplicated and inexpensive, especially concerning the printing phase. It is also faster in comparison with other techniques, and suitable for rapid prototyping, small-scale series production, and spare parts production. In comparison to the PBF techniques, it entails fewer safety issues: for example, no focalized power such as a laser beam or electron beam is required, and no handling of the metal powder in the printing phase is necessary. The facilities required for PBF techniques are also more expensive and technically advanced. The main drawback of the technique is related to some issues with the resulting parts that need to be further investigated. For example, the residual porosity in MEAMed parts is usually significant in comparison to both conventional manufacturing and PBF techniques, which allow the creation of denser and stronger parts. The purpose of the present work is to extend the knowledge so far acquired about MEAM with stainless steel highly-filled polymers. A commercial 316L SS highly-filled filament was used (BASF Ultrafuse 316L). Simple specimens were printed using a commercial Prusa printer (Original Prusa i3 MK3S) to characterize the material and to preliminary optimize the process in order to print successfully tensile specimens. The post-processing was outsourced (Elnik Systems GmbH, Germany). Tensile tests were then performed on the sintered specimens and the results are shown in the following sections. Section 2 contains a theoretical description of the process. Section 3 describes how the printing procedure was carried out, from some preliminary trials to the print of the tensile specimens. Finally, Section 4 contains the tensile test results obtained in the present study. 2. The process 2.1. The shaping phase The shaping phase consists of the selective deposition of softened material through a nozzle. Usually, an FDM printer is used and the feedstock material is in the shape of a filament. The filament is pushed towards a heating chamber and extruded through a nozzle on the printing bed. In some studies, the feedstock material was in the shape of pellets or rods, but the filaments are more common (Gonzalez-Gutierrez et al., 2018). As mentioned before, several factors and parameters affect the quality of the green part, and, consequently, of the final part. Some parameters regard how the material is distributed on the platform, such as layer thickness, infill pattern, raster angle, and building direction. Those parameters have an impact on both the surface quality of the specimens and their structural integrity. The layer thickness for example affects the so-called stair effect depicted in Fig. 2a, which is an esthetic defect and a mechanical problem at the same time since cracks can easily propagate from these points, especially in the case of cyclic loading. The deposition path is also important to guarantee a better external surface, while the pores size, distribution, and morphology in the samples are dependent on the raster angle of the infill strategy (Damon et al., 2019). In Fig. 2b a specimen is depicted in which every layer has a rectilinear infill with an alternating raster angle of ±45°, which is, as well as 0°/90°, one of the most common infill strategies.

Fig. 2. a) the stair effect features on the 3D printed specimens and a zoom of potential crack initiation location along these features. b) schematic of the printing strategy and raster angle alternation. c) building directions