PSI - Issue 79

Déborah de Oliveira et al. / Procedia Structural Integrity 79 (2026) 248–258

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1. Introduction The additive manufacturing (AM) process for metals has been extensively studied and is becoming a viable alternative to traditional manufacturing methods for metallic components, such as casting, machining, and forming. In this context, Gisario et al. (2019) discussed the various benefits, challenges, and emerging trends of using additive manufacturing within the aerospace industry. AM can represent significant advancements in fuel efficiency and, consequently, in emissions reduction, due to the ability to produce components with more complex geometries and reduced mass. Gisario et al. (2019) cites the study by Tomlin and Meyer (2011), who achieved a 32% weight reduction in an optimized component produced via additive manufacturing when compared to its original counterpart. There are many different AM methods being studied, having specific results on the part, a widely applied is the PBF (Powder Bed Fusion) process, which operates by distributing a layer of metal powder over a movable platform, which is then selectively melted by a heat source (typically a laser or electron beam). The build platform moves vertically to enable the layer-by-layer construction of the part. Another method that stands out is the DED (Directed Energy Deposition) method, that functions through the direct injection of powder or wire into the substrate, with different heat sources (Bhavar et al., 2014; DebRoy et al., 2018). Processes that use powder as feedstock are capable of producing components with superior surface finish and fine detail resolution due to the small particle size of the powder, whose morphology and size are critical parameters. Wire-based techniques employ a variety of heat sources and offer several advantages over powder-based processes, such as higher material deposition rates and the capability to fabricate larger parts (DebRoy et al., 2018). Other additive manufacturing techniques differ significantly in that they do not utilize powder, wire, or conventional heat sources. One example is ultrasonic additive manufacturing (UAM), patented by Dawn (2003), which uses a vibrating sonotrode that applies axial force to thin metal foils, promoting solid-state bonding. Since no melting occurs in UAM, it may be advantageous depending on the application (Hehr and Norfolk, 2019). Another example is the friction-based additive manufacturing process, known as friction freeform. Similar to UAM, this method does not involve melting. Instead, a consumable rod is rotated while pressed against a stationary substrate, generating frictional heat and causing localized plastic deformation and wear of the rod, resulting in the deposition of successive layers (Dilip and Janaki Ram, 2013). The Wire Arc Additive Manufacturing (WAAM) process offers certain advantages over powder-based methods, primarily due to the lower cost of wire feedstock and its suitability for larger deposits. Key wire-arc technologies are GMAW (Gas Metal Arc Welding), GTAW (Gas Tungsten Arc Welding), and PAW (Plasma Arc Welding). GMAW operates by forming an electric arc between a consumable wire electrode and the substrate, using a protective gas (either inert or active) to prevent contamination and oxidation during melting (DebRoy et al., 2018). Williams et al. (2016) highlighted several benefits of this process: relatively low machine costs, the capacity to fabricate large-scale parts limited only by robotic reach, an open architecture allowing parameter customization (e.g., heat source, material), and high deposition rates of 1–4kg/h. Xiong et al. (2015) studied the influence of deposition parameters (speed, current, thermal input) on bead geometry using 1.2 mm copper-clad steel wire and identified current (100–180A) as the most critical factor. In a later study, Xiong and Zhang (2014) utilized a vision sensor at 90° to monitor torch–top-surface distance in real time, achieving ±0.5mm control through adaptive deposition and platform movement. Li, Han, and Zhang (2021) applied WAAM-GMAW to repair a coal-mining gear using 1.2mm abrasion resistant steel wire (RMD545), scanning the damaged gear, generating toolpaths, and restoring it in 150minutes, then finishing by machining. To further improve GMAW, CMT (Cold Metal Transfer) was invented by Fronius in 2004, refines the process by mechanically controlling droplet transfer to reduce heat input and spatter (Prado-Cerqueira et al., 2017). In CMT, contact between wire and molten pool triggers a servomotor to retract the wire, mechanically severing the droplet. This cycle repeats continuously (Furukawa, 2006). Variants include CMT+P (pulse-enhanced droplet rate), CMT Advanced (variable polarity), CMT Pulse Advance, and CMT Dynamic (Srinivasan et al., 2022). CMT+P increases deposition rate but may introduce pores due to thermal input. CMT Advanced, combining polarity alternation, reduces porosity. Zhang et al. (2018) reported denser Al ‑ 6Mg walls. Fang et al. (2018) corroborated these findings with Al5183, noting lowest porosity in CMT Advanced, while CMT+P produced the highest. Besides presenting promising results, it is important to make sure that the parts will present no, or reduced, defects to allow their application (Barroqueiro et al., 2019). The part will be submitted to high thermal gradients (Kumar et al., n.d.), resulting in microstructural variations (Zhai et al., 2022), different hardness in the same part (Da Costa et al.,