Wire and arc additive manufacturing (WAAM) produces thin-walled parts superior to other additive manufacturing methods, because of its high efficiency, good compactability, and low cost. However, the WAAM accuracy is limited by its large heat input. Here, 0.8 mm 316L stainless steel welding wire is deposited via speed cold welding to form 30-layered thin-walled samples, with 2 mm thickness, and up to 65 mm height. The effects of three process parameters (the bottom current mode, scanning speed, and cooling time) on the deposition process stability, macro morphology, structure, and mechanical properties are studied. In the experiment, the probability density curves of electrical parameters of sample #GRBC-30 cm/min-10 s on the third and tenth layers were narrower than other samples, which implied a more stable process. The three process parameters mainly affect the deposition morphology and have a minor performance effect. The hardness and tensile properties mainly depend on the deposition direction. Gradual, layer-by-layer current reduction improves the bottom molding and performance, and the deposition efficiency, and stabilizes the process. Scanning speed enhancement or cooling time reduction destabilizes the end formation, reduces the effective deposition rate, and slightly degrades the performance. All deposited samples are distinctly anisotropic, but satisfy the industrial standard. Overall, deposition in speed cold welding mode, with 10 s cooling time, 30 cm/min scanning speed, and gradually reduced bottom current exhibits good stability, and the molding efficiency and mechanical properties are optimal.

Wire and arc additive manufacturing (WAAM) has advantages of high efficiency and low cost. However, different welding current processes lead to different heat input and repeated heating treatment during the deposition process, which has an influence on the forming and performance. In this study, 30 layers of reciprocating depositions for 316L stainless steel were carried out by speed cold and speed arc welding processes, and the morphology, effective deposition rate per power, microstructure, and properties of depositions were compared. The outcomes indicated that different welding current processes make different shaping appearances, and the effective deposition rate per power of speed cold welding is 15.2% higher than that of speed arc welding. The microstructures of depositions are columnar crystals; however, the higher power of speed arc welding leads to the coarse structure, and the enhanced thermal cycle and preheating effect produce a uniform hardness and 4.9% higher tensile strength, but lower toughness than those of speed cold welding. Due to the direction of deposition, the tensile strength of depositions by two processes has obvious anisotropy that can reach to 8.18% and 13.3%, respectively.

Arc additive manufacturing based on gas metal arc welding (GMAW) can decrease the cost and increase the efficiency of manufacturing large-sized components. In this paper, a double-arc additive manufacturing process for stainless steel 316L (SS316L) based on GMAW that does not use more power than the single-arc process is proposed. In addition, this study compared single- and double-arc additive manufacturing processes by analyzing the morphology, microstructure, and mechanical properties. The results indicate that with the same power, the deposition rate of the double-arc process was 1.25 times higher than that of the single-arc process. Further, the increased number of welding wires and the induced stirring of the molten pool produced finer grains. In addition, the average Vickers hardness and tensile strength of the double-arc sample were 0.6% and 3.5% higher than those of the single-arc samples, respectively, while the elongation was 0.34% lower, and the tensile properties had a similarity of over 90% with those of the SS316L wire.

Cold metal transfer (CMT) additive manufacturing (AM) is widely used for its efficiency and low cost, in order to improve the efficiency the manufacturing,this study carried out CMT arc modes and interlayer cooling time depositions, and researched deposition stability, roughness, microstructure, and properties. Moreover, as the tensile anisotropy was a significant characteristic of arc AM, this study conducted tensile fracture metallographic test, and revealed the tensile anisotropic mechanism. The results showed that CMT mode was the most stable process, and CMT Plus Pulse (CMT+P) mode with an alternating of CMT and pulse processes had a finer grain and bigger hardness. Although an interlayer cooling time refined the grain size, it also increased the deposited time and roughness. Then, deposition efficiency of CMT+P continuous deposition was up to 87.9%, which realized the forming efficiency. The tensile fracture metallographic test indicated the deformed columnar grains were widened by horizontal stretching, and then the fracture occurred at the grain boundaries. However, no obvious grain deformation occurred under the vertical tension, and the columnar grain boundaries were the weak link of tensile fatigue. Thus, horizontal tensile strength with more grain boundaries was smaller than the vertical one.

Serious heat accumulation limits the further efficiency and application in additive manufacturing (AM). This study accordingly proposed a double-wire SS316L stainless steel arc AM with a two-direction auxiliary gas process to research the effect of three parameters, such as auxiliary gas nozzle angle, auxiliary gas flow rate and nozzle-to-substrate distance on depositions, then based on the Box–Behnken Design response surface, a regression equation between three parameters and the total score were established to optimized parameters by an evaluation system. The results showed that samples with nozzle angle of 30° had poor morphology but good properties, and increasing gas flow or decreasing distance would enhance the airflow strength and stiffness, then strongly stir the molten pool and resist the interference. Then a diverse combination of auxiliary process parameters had different influences on the morphology and properties, and an interactive effect on the comprehensive score. Ultimately the optimal auxiliary gas process parameters were 17.4°, 25 L/min and 10.44 mm, which not only bettered the morphology, but refined the grains and improved the properties due to the stirring and cooling effect of the auxiliary gas, which provides a feasible way for quality and efficiency improvements in arc additive manufacturing.

Cold metal transfer (CMT) has been widely used in metal additive manufacturing for its low heat input, less splashing and high efficiency. Wire feeding speed and travelling speed are important processes that affect morphology in CMT deposition. This study optimized the forming process of 30-layer stainless-steel part deposited by double-wire and double-arc CMT plus pulse (CMT+P) process, and investigated the effect of the ratio of wire feeding speed to travelling speed on deposition morphology. The results show that asynchronous arc striking and extinguishing can improve the forming. Moreover, the deposition molding is affected by the interaction of heat input and heat accumulation. With the similar ratio of wire feeding speed to travelling speed and the similar heat input, increasing the wire feeding speed can increase the heat accumulation and the width of sample, and decrease the height. The optimum process interval of wire feeding speed to travelling speed ratio and heat input is 3.9–4.2 and 70–74.8 J/mm, respectively. Although the increasing heat accumulation makes grain coarse and slight decreases mechanical property, the highest deposition rate can be up to 5.4 kg/h, when wire feeding speed and travelling speed are 5 m/min and 120 cm/min, respectively, and the tensile strength and elongation rate of which can reach the basic standard requirements for stainless-steel forgings.