Dae-Won Cho

Automated welding processes have become increasingly critical in the shipbuilding, automotive, and aerospace industries. Precise weld seam tracking is essential for reliable automated welding, as torch misalignment causes weld defects and significant variations in bead geometry. In this study, fillet welding experiments using flux-cored arc welding (FCAW) were performed under 15 conditions comprising five torch offset levels (−2, −1, 0, +1, +2 mm; positive values denote displacement toward the vertical plate) and three welding speeds (6.0, 7.5, and 9.0 mm/s). Twelve characteristic points were extracted from three bead cross-section zones—the vertical penetrated zone, horizontal penetrated zone, and bead surface zone—and predicted using a nonlinear exponential regression model. All regression coefficients were statistically significant at the 95% confidence level. Piecewise cubic Hermite interpolation (PCHIP) was subsequently applied to reconstruct smooth two-dimensional bead profiles from the predicted feature points. Quantitative validation of the primary leg-length parameters (L_V and L_H) yielded low prediction error (RMSE below 0.7 mm and MAE below 0.5 mm) across all tested conditions. The proposed algorithm runs in under 1 ms and is therefore well-suited for real-time integration into seam-tracking control systems.

This study investigates the laser welding characteristics and mechanical properties of the Can-Cap butt joint in 600 mm ultra-large prismatic batteries, which are emerging as next-generation electric vehicle (EV) and energy storage system (ESS) platforms. To overcome the high reflectivity and thermal conductivity of aluminum alloys, a green laser with a wavelength of 515 nm was utilized to weld 0.7 mm thick Al3003-H14 sheets. The effects of welding patterns (straight and wobble) and scanning speeds on the weldability, cross-sectional defects, microstructural hardness, and tensile strength were experimentally evaluated. Precise joint alignment was achieved using the Auto Position Alignment (APA) function of the laser scanner. Optical microscopy of the etched cross-sections revealed that both patterns produced sound, fully penetrated weld beads free of internal porosity and hot cracks. Vickers hardness depth profiles indicated that the fusion zone (WZ) exhibited the highest hardness due to rapid-cooling-induced microstructure refinement, with the straight pattern showing higher hardness than the wobble pattern due to its faster cooling rate. Tensile testing demonstrated that the tensile strengths of the straight and wobble patterns reached 84.1% (138.8 MPa) and 77.1% (127.3 MPa) of the base metal, respectively. The straight pattern exhibited a 9.1% higher tensile strength compared to the wobble pattern, which is attributed to the narrower bead width, reduced heat-affected zone (HAZ), and higher joint hardness of the straight path. These experimental findings provide baseline datasets to validate computational fluid dynamics (CFD) melt pool simulations and advance intelligent laser autonomous manufacturing frameworks.

In welding and additive manufacturing processes, thermal behavior significantly affects process quality and structural performance due to the use of localized heat sources. While finite element analysis (FEA) and computational fluid dynamics (CFD) have been widely used to analyze thermal and fluid phenomena, conventional heat source models such as the double ellipsoidal model often require complex parameter optimization and fail to fully capture asymmetric or variable weld pool geometries under different welding conditions. In this study, a novel heat source model, termed the traveling steady pool (TSP) model, is proposed to address these limitations. Unlike conventional models where the heat input is centered around the arc or laser, the proposed model treats the stabilized molten pool itself as the source of heat transfer through its lower boundary. By analyzing bead cross-sections and molten pool lengths from high-speed camera images, the pool shape is approximated using simple first-order polynomials, enabling the construction of a simplified TSP (S-TSP) model without relying on CFD. The model was implemented in FEA and applied to welding under various tilt angles (0°, 15°, 30°, 45°). Results demonstrate that the S-TSP model accurately reproduces the fusion zone (FZ) and heat-affected zone (HAZ), offering a practical and efficient alternative for thermal analysis and weld quality prediction in complex welding environments.

Many industries, such as automobile, aerospace, heavy industries, etc, have been interested in welding automation due to cost reduction and improving productivity. For welding automation, seam tracking plays an important role for the quality of welds. If the seam is misaligned, it can cause troubles such as weld defects and poor appearance. Most of previous studies have analyzed the influence on the bead shape and weld defects by current, voltage, welding speed, but there is lack of research regarding the effects of misaligned seam, called offset. Thus, in this study, fillet welds were conducted with flux-cored arc welding, which has high welding efficiency and low cost. To find out the guideline of offset, various offsets were intentionally applied to the welding experiments, and the changes in bead shape were observed and weld defects were detected for various combination of offset and welding speed. In addition, the grades of weld defect in each condition were evaluated by ISO 5817, which illustrates the international standard of weld defects. Based on the results, the guidelines of offset was suggested to avoid weld defects.

The autogenous manual gas tungsten arc welding (GTAW) process was used for cladding austenitic stainless steel 316L using a single pass with various contact tip-to-work distances (CTWDs). Immersion and electrochemical tests were used to evaluate the corrosion resistance of the welded specimens, and a microstructural analysis was conducted to investigate the chemical composition of the molten pool and the heat-affected zone of welding. The key findings of this study indicate that the corrosion resistance improved under a CTWD of 5 mm due to the optimal distribution of ferrite and a refined microstructure. Additionally, the highest hardness was observed in specimens with a CTWD of 3 mm, attributed to the increased ferrite content in the weld metal. As the CTWD increased, the ferrite fraction decreased, and the hardness also diminished. However, in the CTWD 7 mm case, the higher heat input influenced the microstructure and molten pool shape significantly through the Marangoni effect, resulting in a lower corrosion resistance. These results suggest that optimizing the CTWD can enhance the corrosion resistance of welded 316L stainless steel.

This study investigated how welding affects the thermal deformation of square cells produced for casks, which are dry storage containers for spent nuclear fuel. We aimed to minimize structural deformation by utilizing STS316L as the material for the square cells. We explored a method of subdividing the square cells and joining them through butt welding. Keeping the upper plate thickness constant, GTA butt welding was conducted while varying the column’s wall thickness, followed by measurement with a laser vision sensor. The heat conduction and thermal strain were then calculated using a finite element analysis (FEM). Both experimental and analytical results confirmed that there was significant thermal deformation in the cases of thick-walled columns due to variations in heat conduction distribution, with the resulting deformation patterns depending on thickness.

Various studies are being conducted on underwater cutting using lasers for nuclear power plant dismantling environment. The depth of pressure vessels for most reactors is more than 10 m. When cutting a structure contained in a reactor with 10 m or more depth, pressure is applied, and the shape of the cut due to the cutting gas in this environment needs to be identified. Though several studies exist on laser cutting of stainless steel underwater, laser cutting research in pressurized underwater environment is insufficient. This study investigated the relationship between the cutting kerf width and the assistant gas flow at a depth of 10 m or more in underwater environments. Laser cutting was performed on 80 mmt stainless steel in a pressurized underwater environment. The conditions for obtaining sound cut surface quality were derived by analyzing the kerf shape and roughness of the test piece according to the assistant gas pressure. Additionally, the relationship between the kerf width and the assistant gas flow was established by visualizing the flow of gas through Schlieren analysis and by analyzing the shape of the drag line according to the kerf width and assistant gas flow.