This study compared the mechanical properties of the NAB (Ni-Al-bronze) material fabricated using wire arc additive manufacturing (WAAM) technology with those of the cast NAB. Using a CMT (cold metal transfer) welding process, this study analyzed the bead shape for six welding conditions, determined an appropriate bead shape, and fabricated a square bulk NAB material using the bead shape. For a mechanical properties comparison, the study obtained two test specimens per welding direction from the fabricated bulk NAB material, and compared those with the cast NAB materials. In the tensile test, the deposited NAB material showed significantly better results than the cast NAB; furthermore, the deposited NAB material showed better performance than the cast NAB material in the Vickers hardness test, impact test and wear test. In addition, the deposited NAB showed anisotropy depending on the welding direction, and showed high tensile strength, hardness and shock absorption in the longitudinal direction of the welding line.

With the rise of electric vehicles, the use of battery modules, which are key units that drive vehicles, is increasing. The battery housing is the final form of a battery system mounted on electric vehicles, and is generally made of aluminum alloys, located at the bottom of the vehicle. The aluminum housing has a special shape to accommodate the battery module and is produced by welding extruded panels. This study applied friction stir welding (FSW) to weld 2.5 mm thin aluminum plates in order to improve the weldability and productivity. To increase productivity, we compared the mechanical properties after performing experiments under various FSW conditions. As a result, it was possible to derive speed-enabling welding conditions that can improve productivity without decreasing tensile strength. Deformation occurred in the structure during welding, causing gaps in the structure. Since these gaps have a significant influence on the degradation of mechanical properties after welding, the welding deformation at each step of welding must be calculated and reflected in the process. This study used the inherent strain method to calculate the deformation of each step of welding to apply automatic welding, and reduced the analysis time to 1/30 compared to the thermal elasto-plastic analysis method. Finally, this study verified the validity of the analysis method by comparing the experimental results with the numerical results using the inherent strain method.

Estimating the thermo-elasto-plastic deformation by arc welding through finite element analysis has been used in various industrial fields. The Goldak heat source model is one of the most important and widely used models in finite element analysis, and its parameters are estimated based on the results of previous studies and tests. Part I of this study focused on the adequate heat source model, and the study for the welding deformation with the moving heat source will be done on the latter research. This study used the parameters of Goldak’s heat source model, weld efficiency, and the location of the heat source as design variables, and defined the Heat Affected Zone (HAZ) boundary line of Bead on Plate (BOP) welding as the target. BOP welding was performed using SS400 plates, the HAZ boundary line was determined based on examining the shape of the cross-section, and the optimization condition was that temperature inside the boundary line exceeded 727 °C while the temperature outside the line did not exceed 727 °C during the welding process. During this process, a multi-island genetic algorithm (non-linear global optimization method) was used to obtain the optimal results out of 1000 candidate groups, in which the HAZ boundary was similar to the experimental results. Applying a global optimization algorithm to determine the parameters of the most important heat source model to analyze welding deformation is significant, and this may be applied in various industrial fields that use welding including shipbuilding, aviation, and machinery industries.

The welding process, which accounts for about 60% of the shipbuilding process, inevitably involves weld deformation. Considering this, productivity can be significantly increased if weld deformation can be predicted during the design phase, taking into account the fabrication order. However, the conventional welding deformation prediction method using thermo-elasto-plastic analysis requires a long analysis time, and the welding deformation prediction method using equivalent load analysis has a disadvantage in that the welding residual stress cannot be considered. In this study, an inherent strain chart using a solid-spring model with two-dimensional constraints is proposed to predict the equivalent strain. In addition, the welding deformation prediction method proposed in this study, the equivalent strain method (ESM), was compared with the ship block experimental results (EXP), elasto-plastic analysis (EPA) results, and equivalent load analysis (ELM) results. Through this comparison, it was found that the application of the equivalent strain method made it possible to quickly and accurately predict weld deformation in consideration of the residual stress of the curved double-bottom block used in the shipyard.

The wire arc additive manufacturing (WAAM) process used to manufacture aluminum parts has a number of variables. This study focuses on the effects of the heat input and the current and voltage ratio on the deposition efficiency. The effects of the heat input and current and voltage ratio (V/A) on the bead geometry were analyzed, depending on the cross-sectional geometry of the deposition layers, for nine different deposition conditions. The deposition efficiency was also analyzed by analyzing the cross-sectional geometry of the thin-wall parts made of aluminum. The heat input range was about 2.7 kJ/cm to 4.5 kJ/cm; the higher the heat input, the higher the deposition efficiency. The maximum deposition efficiency achieved in this study was 76%. The current and voltage ratio was used to quantify the portion of voltage (V) in the total heat input (Q), and the effect on the bead geometry was analyzed. As the portion of voltage in the quasi heat input decreased by about 10%, it was found that the deposition efficiency was decreased by 1% to 3%.

As the environmental regulations on ship emissions by the International Maritime Organization (IMO) become stricter, the demand for a ship powered by liquefied natural gas (LNG) is rapidly increasing worldwide. Compared to other materials, high-manganese steel has the advantages of superior impact toughness at cryogenic temperatures, a low thermal expansion coefficient, and a low-cost base material and welding rod. However, there is a limitation that the mechanical properties of a filler material are worse than those of a base material that has excellent mechanical properties. To solve these shortcomings, a basic study was performed to apply fiber laser welding with little welding deformation and no filler material to high-manganese steel. The relationship between laser welding parameters and penetration shapes was confirmed through cross-section observation and analysis by performing a bead on plate (BOP) test by changing laser power and welding speed, which are the main parameters of laser welding. In addition, the welding performance was evaluated through mechanical property tests (yield strength, tensile strength, hardness, cryogenic impact strength) of a welding part after performing the high-manganese steel laser butt welding experiment. As a result, it was confirmed that the yield strength of a high-manganese steel laser welding part was 97.5% of that of a base metal, and its tensile strength was 93.5% of that of a base metal.