Jungho Cho

Laser-induced graphene (LIG) is a promising porous carbon electrode for flexible microsupercapacitors (MSCs), and defocusing is an established means of tuning its morphology. Here, a defocusing series was evaluated as a complete process-to-device chain with the CO₂ laser power and scan speed fixed at 5.0 W and 46 mm s⁻¹. A polyimide substrate was positioned 0–3 mm below the focal plane to produce laser-induced graphene fibers (LIGFs), LIG-1, LIG-2, and LIG-3. Increasing the defocusing distance lowered the peak fluence per pulse from 16.7 to 2.1 J cm⁻², transforming a fibrous network into porous LIG, an open-cell-like network, and a film whose smooth, oxygen-rich surface skin covered a porous interior. LIG-2 showed the lowest sheet resistance (15.3 Ω sq⁻¹), I_D/I_G ratio (0.29), and equivalent series resistance (78 Ω), delivering 2.88 mF cm⁻² at 0.05 mA cm⁻² and 97.4% retention after 2000 cycles. LIGF showed the lowest contact angle (12.1°), retained 57.3% of its capacitance at 0.25 mA cm⁻², and surpassed LIG-2 at ≥0.10 mA cm⁻². Both electrodes retained their cyclic voltammetry (CV) response under a single 180° bend. Thus, substrate-height adjustment tunes LIG morphology and rate-dependent MSC performance without changing laser power or scan speed.

In aluminum GMAW processes, moisture in the atmosphere is dissociated into hydrogen by the arc plasma, and the resulting hydrogen readily dissolves into the weld pool due to the high hydrogen solubility of aluminum. Although most of the dissolved hydrogen escapes to the atmosphere during solidification, a portion that fails to diffuse out becomes trapped within the weld and forms porosity. These pores are critical defects that can significantly degrade the mechanical performance of welded joints; therefore, cross-sectional analysis and various non-destructive testing (NDT) techniques are commonly used for inspection. However, cross-sectional analysis provides only localized information and is insufficient for evaluating defect distribution along the entire weld. Moreover, X-ray radiography often contains noise and irrelevant artifacts, making accurate quantitative assessment challenging.In this study, GMAW was performed on Al6061-T6 plates under conditions conducive to porosity formation, and X-ray radiographic images were acquired to capture defect information across the full weld region. MATLAB-based image processing techniques combined with a circular Hough transform algorithm were applied to quantitatively detect pore location, count, and diameter.

Adjustable ring mode laser has been increasingly adpoted for welding of aluminum leads and copper busbar in the manufacturing of lithium-ion batteries. Spatter generated during welding can penetrate into the cell and potentially cause performance degradation, internal short circuits, or even thermal runaway. To prevent such defects, it is essential to understand the motion characteristics of spatters at the moment of ejection. In this study, high-speed camera was employed to capture the spatter behavior, and the acquired frames were processed through image processing. Subsequently, spatters were tracked using a Hungarian algorithm based assignment method, enabling quantitative extraction of spatter size, speed, and ejection angle. The results provide dynamic behavior of spatter during adjustible ring mode laser spot welding of aluminum and copper.

Wire arc additive manufacturing (WAAM), which uses arc as a heat source during the direct energy deposition (DED) process, is a melting-based additive manufacturing process that melts metal wires using an arc and then deposits them layer by layer to create components. It has the advantages of fast production speed and low cost. The WAAM process is mainly performed using a cold metal transfer (CMT) welder capable of low heat input. In this study, the deposition efficiency was studied through a deposition experiment on ferritic stainless steel 436 material. The research method is as follows: first, the appropriate variables of the deposition process (Arc length, Pulse/dynamic, Z-offset, Cooling time) were evaluated and conditions were selected, second, the amount of post-processing loss and deposition performance were evaluated through the deposition efficiency, and third, the mechanical properties were verified through a tensile test evaluation using the deposited specimen, and the appropriate process conditions were selected to create pipes that can be used in industrial sites by multilayer deposition of ferritic stainless steel 436 material.

It is well known fact that the columnar grains in fusion zone make problems such as lower strength or crack initiation especially interface plane of columnar grains along longitudinal direction. Generally it is hard to make columnar grains in arc welding comparing to high power density welding method like laser or electron beam welding. However, it is found that lack of shield gas supply affects on the columnar grain growth and limited equiaxed grain generation in STS 439L arc welding. It is proved through comparing cross sections of weldment for lower shield gas feed rate, 5 LPM, and higher case, 20 LPM. Therefore, it is recommended to control the shield gas supply more strictly to prevent columnar grains and its induced defects in STS 439L arc welding as result.