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Additive manufacturing of metals is actively being researched due to its potential for mold modification and cost savings. However, producing smooth aluminum parts with directed energy deposition (DED) using welding heat flux presents material restrictions and challenges. While research has focused on developing cold metal transfer (CMT) with minimal heat input, its application can be costly in industry. To address this issue, we checked over a DED process using pulsed variable polarity (VP) gas metal arc welding (GMAW), which, for the first time, reduces costs compared to CMT. Optimal parameters were determined via experimentation, with deposition efficiency (DE) used to evaluate post-processing loss and deposition performance. Tensile tests were conducted to verify the mechanical properties of deposited specimens, and microstructure analysis was performed. In this study, method achieved a stable deposition tendency with an electrode negative ratio of 18% under the welding conditions of an ER4043 Ø1.2 electrode wire, 120 A, 21 V, 80 cm/min, a shield gas flow rate of 20 L/min, and bead-on-plate position. By varying the layer-by-layer velocity throughout the deposition process, a maximum DE of 82.56% was achieved, resulting in lower post-processing loss than CMT with suppressed anisotropy in the material. Tensile test data and microstructure inspections confirmed isotropic behavior. For the first time in the field of study, this research proved that deposition process by VP-GMAW is cost-effective compared to CMT. [ABSTRACT FROM AUTHOR]

Conductive polymer composites (CPC) have been remarkably developed, demonstrating their potential in various applications such as sensors, wearables, and even the field of biomedical. Furthermore, the recently attracted multi-material additive manufacturing (MMAM) technology indicates the potential for expansion into a wider range of applications. However, the characteristics studies of printable composites are still in progress, and this implies that the applicability of composite materials is limited in the near future. It is also necessary to consider an investigation of conductive composites with unexplored wide ranges of filler contents. CPCs are easier to print when the conductivity filler content is low. On the contrary, increasing the conductivity filler content to enhance electrical conductivity leads to a decrease in polymer characteristics, making it challenging to print. In this study, TPU (thermoplastic polyurethane)/MWCNT(multi wall carbon nanotube) filaments incorporating relatively high content MWCNT were manufactured. The filaments were extruded by the melting mixing method and the printing characteristics were discussed using fused filament fabrication (FFF). It was confirmed that TPU/MWCNT filaments with a maximum MWCNT content of 20% could be produced, but printing was limited to 15% MWCNT content. As the MWCNT content increases, the nozzle temperature also needs to be increased to avoid print quality reduction. Additionally, the electrical and mechanical properties of the printed TPU/MWCNT composites were investigated. [ABSTRACT FROM AUTHOR]

Homogeneous and heterogeneous PAW (plasma arc welding) experiments were conducted to obtain weld beads with tensile strength of 100% or more compared to that of the base metal in lap joint fillet welding of CP (complex phase) 780 MPa grade high strength steel sheet. Homogeneous and heterogeneous welding mean welding technic without and with welding wire in each. Common basic welding parameters of both homogeneous and heterogeneous PAW wire were applied, including welding speed of 21 cm/min, arc length of 3.5 mm, weaving amplitude of 3 mm, work angle of 30°, and Ar 99.99% shielding gas with 12 L/min. In homogeneous PAW, the optimized additional welding conditions were a welding current of 90 and 95 A, push angle of 20°, and weaving frequency of 5 Hz. The fracture strengths of all the samples were less than that of the base metal, and all fractures occurred at the weld bead fusion zone due to insufficient reinforcement. In heterogeneous PAW, the optimized additional welding conditions were a welding current of 125 A, push angle of 0°, weaving frequency of 4 Hz, and wire feed speeds of 1.53 and 1.38 m/min. Moreover, the welding wire was fed from behind the arc. The fracture strengths of all the samples were greater than that of the base metal, and fractures occurred at the base metal or fusion zone boundary. The reason for higher tensile in heterogeneous PAW wire is deduced as the large cross-section area of reinforcement provided by the welding wire comparing to homogeneous welding. It is well known that small radius of welding heat source clearly produces narrow heat affected zone. Therefore, the PAW produces relatively narrower heat affected zone, then resulted as fully enough strength of weldment. This is another reason of the current achievement. [ABSTRACT FROM AUTHOR]

Toxic fission products, such as cesium (137Cs) and iodine (129I) are of great concern because of their long half-lives and high solubility in water. The simultaneous removal of Cs and I using a single adsorbent is an area of increasing interest. In this study, MXene/silver nanowire (AgNW) composite was synthesized through physical mixing and employed for simultaneous removal of iodide (I−) and cesium (Cs+) ions from contaminated water. The MXene/AgNW composite demonstrated excellent adsorption capacities of 84.70 and 26.22 mg/g for I− and Cs+, respectively. The experimental data supported the hypothesis of multilayer adsorption of Cs+ owing to the inter-lamellar structures and the presence of heterogeneous adsorption sites in MXene. The interaction between I− and the AgNW involved chemisorption followed by monolayer adsorption. MXene/AgNW composite material exhibited promising results in the presence of competitive ions under extreme pH conditions. Thus, synthesized composite materials holds promising potential as an adsorbent for the remediation of radioactive liquid waste. [ABSTRACT FROM AUTHOR]

The experiments of wire arc additive manufacturing (WAAM) with general pulsed gas metal arc welding (GMAW) machine were performed to optimize process parameters. As optimized conditions, 140A welding current, 34 V welding voltage, 40 cm/min welding speed, and 15 mm contact tip to work distance (CTWD), were selected. Welding current and voltage affected heat input. Lower deposition, short circuit mode, and spatters were obtained by insufficient heat input. The melting of previous layer and lower height were obtained by excessive heat input. Welding speed and CTWD affected surface state and arc stability. Unsound surface and bead shape due to short circuit mode and spatters were observed in slow welding speed and short CTWD conditions. Arc instability were also observed in fast welding speed and long CTWD conditions. With the optimized process parameter, curved propeller shape blade was manufactured by the change of robot arm teaching point. It can be considered that the desired sufficient quality was obtained due to curved shape. [ABSTRACT FROM AUTHOR]

In GMAW (gas metal arc welding) of Zn (zinc)-coated steel sheets, defects such as pores occur in the weld due to trapped Zn vapor. To solve this problem, we investigated the pore-free welding condition using conventional solid wire. We verified through experiments that the combination of 20% CO2-Ar shielding gas and DCEP (direct current electrode positive) polarity has a higher pore-free performance than other combinations. A higher performance of pore-free welding was obtained by reducing the CTWD (contact tip to work distance) and using ER70S-3 wire. In conclusion, the optimized welding conditions at 10 mm overlap, 80 cm/min welding speed, and 30° work angle are 160 A arc current, 20 V voltage, 15 mm CTWD, 10° push angle, DCEP polarity, 20% CO2-Ar shielding gas with 20 L/min flow rate, and ER70S-3 wire type. For flow pattern analysis, a high-speed camera with blue laser was used, and it was observed that a longer weld pool and smaller droplets could improve the efficiency of Zn vapor emission. With ER70S-3, a longer weld pool can be obtained, as it has a lower viscosity due to lower percentages of Si and Mn in its composition. [ABSTRACT FROM AUTHOR]

Recently, the development of material technology for application to wearable devices has been promoted. In particular, as core technologies for e-skin, Internet of Things, and AI robots, studies on flexible circuits required for connection and operation between devices are attracting attention. In this study, an epoxy-based flexible electrical conductor (EFEC) that can be applied to flexible circuits was developed. It was made by mixing a 2-µm Ag flake, epoxy resin, epoxy hardener, and IPA at a ratio of 50:10:5:5. Flexibility can be achieved by adjusting the ratio of the epoxy base and hardener. IPA, a volatile solvent, was added to lower the viscosity of the epoxy, and Ag flakes were added to increase the electrical conductivity. It was dispersed with a sonicator and magnetic stirrer for overall resistance uniformity. A specific resistance of 2.85 × 10 - 3 Ω cm was measured. Through scanning electron microscopy and energy-dispersive X-ray spectra analyses, the cause of the low resistance was identified. In addition, 100% strain was achieved in all cases through the tensile test and resistance deviation results. Among them, the lowest resistance deviation was confirmed in CASE 4. Although the specific resistance of the EFEC was approximately 10 times higher than those of electrically conductive adhesives (ECAs) ( 3.6 × 10 - 4 Ω cm ), it could efficiently be used as a conducting material. ECAs become brittle after hardening. However, we observed that the EFEC exhibited flexibility and that hardening did not proceed even after an extended period. Therefore, the applicability of the EFEC's flexible circuit was confirmed by securing high electrical conductivity and flexibility. [ABSTRACT FROM AUTHOR]

Resistance spot welding is widely used in automobiles and ships, and especially, it accounts for 70% of the body welding process. However, resistance spot welding is limited when welding the closed structure of a vehicle body. As welding is performed by placing a spot gun in a closed structure, a passage is required for the insertion of the spot gun. This passage is called a "passing hole", and the structural design of the passing hole and the cover that is installed to block the passing hole is complicated, resulting in durability problems as the weight of the vehicle body increases. This study aims to develop a plasma arc spot welding (PASW) process that can replace resistance spot welding. "Part 1 - Development of Plasma Arc Spot Welding Process" determines whether this process can replace the resistance spot welding process through experiments by adjusting the existing process variables of the plasma arc welding process as well as additional process variables. The experimental results of applying the PASW process are then applied to the development of a finite element analysis model for predicting the fracture strength of the PASW process in Part 2. [ABSTRACT FROM AUTHOR]

When the welded part of a vehicle body is considered in an analysis model, the accuracy of the analysis varies depending on whether the welded part is assumed to be a simple rigid body or if its characteristics are included. Particularly, when assuming a simple rigid body, the accuracy of the stress result may be insufficient, resulting in a large error. In this study, titled "part 2-development of finite element method (FEM) analysis model for predicting fracture strength", a commercial welding simulation program, MSC Simufact welding software, was used to create a finite element method analysis model that includes the material characteristics of the welded part, and the analysis accuracy was determined in comparison with the experimental results presented in part 1. The analysis results showed satisfactory results with an error rate of 0.03%. Thus, the fracture strength and fracture position of the welding specimen could be confirmed using the FEM analysis model. Additionally, assuming that the welded part in spot welding has a simple geometric-shaped structure, a simplification spot welding model was created to determine whether it can replace the plasma arc spot welding experiment and pass the tensile shear test. [ABSTRACT FROM AUTHOR]