OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 Introduction Advances in additive manufacturing (AM) technology have expanded its application areas, and AM is becoming a viable option for producing fully functional metal parts [1–3]. In fact, metal AM is currently being applied in various industries [3–5]. One of the AM methods is Wire and Arc Additive Manufacturing (WAAM). Among all the existing AM methods, WAAM is known to be a relatively low-cost method that provides the highest surfacing rates [1–5]. Using this technology, the surfacing process is carried out in the open air using a robotic arm with a fi xed welding torch, with a localized shielded area [5–15]. An important challenge in ensuring the structural integrity of WAAM components is to evaluate the impact of the welding processes integrated into the WAAM technology on the mechanical and fracture properties compared to those obtained from the as-deformed material. WAAM technology enables the creation of parts with complex topologically optimized geometries with internal cavities that are impossible to form using traditional manufacturing processes. However, in most cases, the tight tolerances and strict surface integrity requirements cannot be achieved using stand-alone AM technologies. Therefore, WAAM parts usually require some post-processing to meet the requirements related to surface fi nish, dimensional tolerances and mechanical properties. Most of the literature on additive manufacturing describes the integration of AM with post-processing technologies into single- or multi-tool processing solutions, commonly referred to as hybrid AM. Most of the work devoted to additive manufacturing integrates AM with post-processing technologies into single- or multi-setup processing solutions, commonly referred to as hybrid AM. Hybrid AM has become a very attractive proposition for the industry, which has increased the amount of R&D work [5–15] aimed at developing this direction. The combination of additive and subtractive methods off ers a possible method to overcome this inherent problem of the process. It is also important to understand, and has been shown in numerous studies [10–18], that AM parts may contain voids or pores due to trapped gas or incomplete fusion during the printing process, which can weaken the structural integrity of the component. The works [4–9] point to an example that has been implemented in the Shape Deposition Manufacturing (SDM) process at Stanford University and the Controlled Material Buildup (CMB) process developed at IPT Aachen. In these processes, each layer is applied as a near-net shape using a thermal spray process, essentially laser cladding. The layer is then further shaped by CNC milling to the net shape before the next layer is added. In SDM processes, the top and side surfaces of each layer are machined and then protected by adding a copper support structure. This support structure is then removed using an etching process when the part is complete. In the work [4], the authors developed a similar approach, 3D welding and milling, using WAAM instead of laser cladding for faster and more cost-eff ective surfacing of individual beads. In the 3D welding and milling process, conventional gas metal arc welding is used to surface individual beads next to each other. Depending on the welding parameters such as speed and power, the bead thickness varies from 0.5 to 1.5 mm. When applying a layer, its upper surface is machined to obtain a smooth surface of a certain thickness for further application. Combining this process with face milling gives a clear advantage in setting the layer thickness from 0.1 to 1.0 mm. Once the deposition and face milling sequence is completed, a surface fi nishing treatment is applied in the same setup to remove the remaining steps on the surface and improve the near-net shape accuracy of the metal part. Until now, the mechanical properties and microstructure of WAAM carbon steels have not been comprehensively characterized. To fi ll this gap in knowledge, the authors of [19–22] conducted a comprehensive series of tensile tests on plates made of normal and high-strength WAAM steel; the microstructure of both steel grades was also investigated. In the works [23, 24], the fracture toughness of deposited walls made of low-carbon steel was investigated, and the advantage of the WAAM method was demonstrated. Some applications of the WAAM process are summarized in [22, 23] regarding the welding heat source used by the researchers. Some researchers have tried to use the gas metal arc welding (GMAW) process [23, 24] for WAAM as the main deposition tool due to its advantages such as relatively low metal spatter, independent control of
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