Leu-M

A review of the wire arc additive manufacturing of metals: properties, defects and quality improvement

Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Wire and arc additive manufacturing : Opportunities and challenges to control the quality and accuracy of manufactured parts

A review on wire arc additive manufacturing: Monitoring, control and a framework of automated system

The wire and arc-based additive manufacturing process applies arc welding technology; the wire material is melted by the arc discharge, and is then accumulated successively in this process. The wire and arc-based additive manufacturing process directly and locally adds material to the molten pool. By changing the material locally during the process, more than one kind of material can be used simultaneously in a single manufactured component. In this study, two kinds of dissimilar metal deposition were conducted. A combination used was a stainless steel and Ni-based alloy. Mechanical properties near the interface such as hardness and bond strength were investigated. As a result, it was found that the mechanical properties of the manufactured alloy were comparable to those of a bulk material. In addition, an additive manufacturing system and a torch path planning method for using more than two kinds of material were proposed. By using this method, highly functional shapes whose surfaces and inner structures are made of different material could be made.

Dissimilar metal deposition with a stainless steel and nickel-based alloy using wire and arc-based additive manufacturing

Material properties, such as porosity, tensile strength, and microstructure, of magnesium-alloy components fabricated using wire-and-arc-based additive-manufacturing techniques, which essentially represent a form of arc-welding technology have been examined. In the proposed method, the wire material is melted by arc discharge, and the molten metal is subsequently solidified and accumulated. Magnesium wire developed in this study facilitated fabrication of magnesium-alloy components using the said additive-manufacturing process. Subsequently, combinations of fabrication conditions, such as the welding current, torch feed speed, and cross feed of the torch, were explored, and suitable conditions for realizing a solid structure with fewer weld defects compared to those observed when using die-casting and other manufacturing methods, were determined. Tensile tests and microstructure observations were also performed to elucidate mechanical properties of magnesium alloy components fabricated via the said wire-and-arc-based technique. It was demonstrated that the fabricated object possesses sufficient tensile strength compared to the observed standard value of the bulk material. Furthermore, results from microstructure observations demonstrated that the higher the torch feed speed, the finer is the microstructure. Moreover, the observed microstructure at the boundary between the substrate and fabricated object was finer compared to that at the top layer.

Material-property evaluation of magnesium alloys fabricated using wire-and-arc-based additive manufacturing

Wire and arc additive manufacturing (WAAM) is an additive manufacturing (AM) technology that uses wire-form materials and arc discharges as the energy source. AM techniques can fabricate complicated shapes that cannot be obtained via conventional processing. Building lattice structures inside components enables weight reduction while maintaining high strength. Strut shapes must be constructed to form these lattice structures using WAAM. For fabricating strut shapes with high accuracy, the process parameters should be optimized. However, the relationship between layer geometry and process parameters is not clear. Therefore, in this study, struts were fabricated under various process conditions to investigate the influences of process parameters on the built object geometry. The results showed that fabrication of strut shapes depends on the heat input condition. Moreover, it was found that the arc discharge time had the highest influence on the layer height and diameter. The inclination angle of an overhanging shape had little influence on the dimensional accuracy of the built object. In addition, computer-aided manufacturing (CAM) system was developed for the fabrication of lattice structures, and the lattice structures were successfully built using WAAM. The build accuracy was measured using an x-ray computed tomography (CT) scanner; the deviation in the structures designed using the CAM system and the actual fabricated structures measured using the CT scanner was lower than approximately ±2.3 mm.

Layer geometry control for the fabrication of lattice structures by wire and arc additive manufacturing

The phagocytes in hemolymph of Halocynthia roretzi and their phagocytic activity in vitro were studied by electron microscopy. Hemocytes were ultrastructurally classified as follows: Large granular amebocytes (LGs), small granular amebocytes (SGs), eight types of vacuolated or vesicular cells, dense granular cells and lymphoid cells. The vacuolated or vesicular cells, V1-V8, were distinguished from each other by the size of vacuole and the nature of inclusions. The identification of phagocytic cells and possible targets were examined in vitro. Freshly collected hemolymph was incubated with latex beads (LB) of 1, 5, 26,um in diameter, SRBC, Escherichia coli or small pieces of tunic. Small granular amebocytes actively ingested all the particles except the 26,um-LB. They surrounded the tunic pieces and the 26/zm-LB. LGs ingested only 1 /um-LB. Their activity was, however, weaker than that of SGs. We could not find any phagocytosed particles in other hemocytes during a 30 min incubation. Furthermore, the plasma factor(s) that activated the phagocytosis to SRBC, did not influence that to the LB.

The phagocytes in hemolymph of Halocynthia roretzi and their phagocytic activity

In the wire and arc additive manufacturing process, the cumulative temperature increase caused by the repeated deposition process reduces the dimensional accuracy of the build structure. When the temperature of the build structure increases, the deposited metal width increases, while the height decreases. In this case, using a lower heat-input condition is effective because the temperature near the molten pool can be locally lower and the molten pool size can decrease. Thus, the height of the build structure can increase, and the uniformity of the deposited metal width can be improved. In this paper, a heat-input condition control system is proposed. This system controls the voltage—a heat input condition—which is applied from the welding power source according to the temperature of the build structure. The temperature of this structure is measured using a radiation thermometer during the deposition process. To determine the optimal voltage value, the relationship between the build structure temperature and the deposited metal shape is estimated by a numerical simulation. The optimal heat input condition is derived based on simulation results with varying preheat temperatures and heat input conditions. By using numerical simulations, the number of experiments can be minimized. To evaluate the proposed method, a thin-walled structure was built, and its profile was measured. The accuracy of the build was successfully improved by using the proposed method.

Takeyuki Abe

Papers

Dissimilar metal deposition with a stainless steel and nickel-based alloy using wire and arc-based additive manufacturing

Material-property evaluation of magnesium alloys fabricated using wire-and-arc-based additive manufacturing

Layer geometry control for the fabrication of lattice structures by wire and arc additive manufacturing

The phagocytes in hemolymph of Halocynthia roretzi and their phagocytic activity

Thermal sensing and heat input control for thin-walled structure building based on numerical simulation for wire and arc additive manufacturing