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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1. Introduction Material Extrusion Additive Manufacturing (MEAM) has been recently used to produce metal and ceramic components. Numerous terms are adopted in the literature and it is usually shortened with the acronyms MEAM or MEX. It refers commonly to the process in which a part is printed through the FDM technique using a special composite filament, which contained metal or ceramic powder in a polymeric matrix. The polymers are subsequently removed in a debinding process, and the metal powder densifies during the sintering process. Nevertheless, the term MEAM is sometimes used with a wider meaning, referring to all the extrusion-based additive manufacturing techniques, independently of the material used. According to the standard ISO/ASTM 52900, material extrusion (MEX) is the process in which material is selectively dispensed through a nozzle or orifice . Therefore, regular Fused Deposition Modeling (FDM) is sometimes considered a material extrusion technique, as well as Direct Ink Writing (DIW) and Semi-solid Metal Extrusion and Deposition (SSMED) for metals (Ramazani et al., 2022). The present review paper is specifically focused on the MEAM technique above outlined, inspired by the FDM technique. To denote this process, numerous abbreviations have been used. Some general terms are MEAM-HP (high-filled polymer), SDS (Shaping, Debinding, and Sintering); SFF (Solid Freeform Fabrication); ADAM (Atomic Diffusion Additive Manufacturing); EAM (Extrusion-based Additive Manufacturing); and PDS (Printing, Debinding, and Sintering). More specifically, for metals, FDMet (Fused Deposition Modeling of Metals); MF3 (Metal Fused Filament Fabrication), or BMD (Bound Metal Deposition) have been used. If ceramics are involved, FDC is mostly used (Fused Deposition of Ceramics), CEAM (Ceramic Extrusion Additive Manufacturing); or also CEM (Composite Extrusion Modeling). The metal production is mainly investigated, in particular, stainless steels 316L and 17-4 PH. However, Titanium (Shaikh et al., 2021; Singh et al., 2020, 2021; Thompson et al., 2021), Copper (Dehdari Ebrahimi et al., 2018), Tungsten, and other hard metals (Abel et al., 2019; Bose et al., 2018; Lengauer et al., 2019) were also processed to assess the feasibility of this MEAM-HP technique. Hereafter, the process overview is presented. In Section 2 some of the feedstock preparation main issues are shown. Afterward, in Sections 3 and 4 the shaping phase and the post process are thoroughly described, with a focus on the main parameters involved. Finally, Section 5 and 6 collect some examples of studies related respectively to the production of stainless steels components and other metals. As mentioned above, the process is composed of several phases: the first phase is the shaping , in which the component is printed in a regular FDM printer, extruding a high-filled polymer filament. The mentioned filament is a compound of a considerable amount of metal powder dispersed in a polymeric binder. In Table 1 it is shown that the average volume fraction of the solid infill in these types of filament is usually around 60%. The possibility of using a regular FDM printer is a key advantage in the process. The shaped part after FDM process is commonly referred to as green part. In the second phase, debinding, the part is processed to remove the polymeric binder. After the debinding, the part is called brown part , it consists of packed metal powder and it has no significant mechanical properties. The final part, sometimes referred to as silver part (Kurose et al., 2020), is obtained after the sintering process. It consists of a thermal cycle in which the metal particles bond together, and a dense metal part is obtained. To the best of authors’ knowledge, the first appearance of MEAM dates back to late 90s. Agarwala et al. (1996) used both FDC and FDMet techniques to produce ceramic and metal parts. They were able to process silicon nitride, fused silica, piezoelectric ceramics, stainless steel, tungsten-carbide, and alumina. After a properly developed post process, the material properties such as porosity and density were observed to be comparable with other conventionally manufactured parts, encouraging further studies on the topic. Lately, Wu et al. (2002), compared the accuracy of stainless steel parts obtained with the so-called Solid Freeform Fabrication technique with silicone molded parts. More precision and complexity were achieved with additive manufacturing. In a previous work by Wu et al. (1999), preparation of the feedstock material was also investigated, covering the characterization of the 17-4 PH SS powder and the filament extrusion. Since then, MEAM has gained popularity due to its potential. Moreover, the patent on the FDM process has recently expired (Kuotsoan et al., 2014; Lee et al., 2015; Mueller, 2017), encouraging the research on the topic of FDC and FDMet in the last years