The wear resistance characteristics of pogo-pin plungers with different tip geometries were investigated through repeated touchdown tests. Five types of geometries were evaluated: three crown types (60°, 70°, and 90°), a round type, and a cone type. Touch down tests were conducted at an overdrive of 200 μm, 3 Hz, for 100,000 cycles. Contact resistance and contact force were measured in real time, and wear behavior of top plunger of the pogo-pins was analyzed through microstructural and surface observations. Crown-type plunger exhibited superior initial contact characteristics, but showed significant resistance increases after repeated tests, particularly the 70° crown type. In contrast, the round type maintained the most stable contact resistance. Contact force remained nearly unchanged, indicating that resistance variation was mainly caused by wear. Microstructural analysis revealed severe wear in crown types, while round and cone types showed relatively mild wear. Although crown types effectively removed oxide layers, increased wear and non-uniform contact led to degraded contact stability. These results indicate that round-type plungers provide more stable and reliable performance under repeated contact conditions.
This study aims to clarify the effects of electrode surface patterning and upper-lower electrode combinations on nugget morphology, heat balance, and electrode contamination behavior in aluminum resistance spot welding (RSW). As the use of aluminum increases with the growing demand for electric vehicles and lightweight body structures, issues such as heat imbalance, asymmetric nugget formation, and rapid electrode degradation arise due to its low electrical resistivity and high thermal conductivity. To address these challenges, the influence of electrode patterning on heat balance was analyzed through both SORPAS simulations and experimental evaluations. Simulation results showed that electrode patterning altered the initial current density distribution and reduced early-stage heat generation, leading to delayed nugget initiation and decreased nugget growth. When identical patterns were applied to both electrodes, the reduction in nugget height was more pronounced on the upper sheet with lower bulk resistance. Experimental cross-sectional analysis confirmed the same tendency, and the asymmetric patterning combination with a weak pattern applied to the upper electrode and a strong pattern applied to the lower electrode produced the most balanced nugget geometry. In addition, consecutive spot welding tests and dynamic resistance measurements revealed that the asymmetric patterning combination exhibited the slowest progression of electrode contamination and the latest onset of sticking, maintaining stable resistance behavior during repeated welds. These results demonstrate that applying asymmetric electrode patterning, considering material properties and bulk resistance differences, is more effective for improving heat balance and extending electrode life in aluminum RSW than symmetric pattern application.
The rapid expansion of electric vehicles and energy storage systems requires lithium-ion batteries with simultaneously high energy density and reliability. In this regard, the joint between the copper (Cu) current collector and the Cu tab becomes a critical determinant to represent cell performance and safety. However, Cu exhibits low absorptivity under infrared ray lasers and high thermal conductivity. These material characteristics disturb stable keyhole formation and molten pool flow, which result in weld defects. Relevant studies proposed high-power green and blue lasers, beam shaping, and spatial beam oscillation; however, they remain limited to provide the fundamental process knowledge enabling stable and persistent use of infrared ray lasers, which have been widely installed in production lines. This study presents the empirical analysis to characterize laser welded joints between Cu tabs and multi-layered foils in the infrared ray laser. In this study, welding tests are conducted on a joint of a Cu tab and multi-layered foil using a TruDisk 8000 infrared disk laser. Design factors are tab thickness (0.4, 0.5, 0.6 mm), foil thickness (5, 6, 8 ㎛), and the number of foil layers (5, 10, 20). Weld performance is evaluated through bead appearance inspections and tensile shear strength (TSS) tests. The maximum TSS for 5 layer stacks is measured, wherein a peak strength of 10.79 kgf is achieved with a combination of a 0.5 mm tab and 6 ㎛ foil on a 20-layer stack. The experimental results provide fundamental knowledge to correlate design factors with the joint strength in Cu foil-tab welding assembly.
In this study, the bonding characteristics of 100 μm diameter micro solder balls were comparatively analyzed according to the bonding process. Laser-assisted bonding (LAB) and vacuum reflow were applied, and an additional reflow process was conducted to simulate actual package assembly conditions. Accordingly, four bonding conditions were evaluated: LAB, LAB followed by reflow, vacuum reflow, and reflow followed by reflow. Cross-sectional microstructures were observed, and the thickness of intermetallic compounds (IMCs) was analyzed. In addition, shear strength measurements and fracture surface analyses were performed. The IMC thicknesses were 0.7, 2.3, 2.5, and 3.0 μm for LAB, LAB followed by reflow, vacuum reflow, and reflow followed by reflow, respectively. The shear strengths were 536.0, 520.3, 504.7, and 512.2 mN for the respective bonding conditions, showing no significant difference. Fracture analysis revealed that failure occurred within the solder matrix in all samples, indicating that the mechanical properties of the solder dominated rather than the interfacial strength. These results confirm that the LAB process is suitable for micro solder ball bonding applications and that it can effectively suppress IMC growth under multiple reflow conditions.
This study presents a comprehensive review of thermal-fluid modeling techniques for welding processes based on computational fluid dynamics (CFD), with a particular focus on FLOW-3D and FLOW-3D WELD. Welding processes involve complex multiphysics phenomena including heat transfer, fluid flow, phase transformation, and vaporization, which significantly affect weld quality and defect formation. This review summarizes key numerical models such as free-surface tracking using the volume-of-fluid (VOF) method, heat source modeling for arc and laser welding, multiple reflection models for laser keyhole processes, and recoil pressure models. Furthermore, various welding processes?including conduction mode welding, keyhole laser welding, laser-arc hybrid welding, arc welding, beam oscillation welding, and dissimilar metal welding-are discussed to highlight the applicability of CFD-based simulations in predicting molten pool behavior, temperature distribution, and defect formation. Industrial applications in automotive, shipbuilding, and electronics industries are also reviewed to demonstrate the practical usefulness of these techniques. Despite significant advancements, several technical limitations remain, including challenges in multiphysics coupling, uncertainties in high-temperature material properties, and high computational cost. Future research directions are proposed, emphasizing the development of high-fidelity models, integration of multiphysics and multiscale approaches, incorporation of artificial intelligence for process optimization, and implementation of digital twin technologies. Overall, CFD-based welding simulation is expected to play a crucial role in advancing high-precision and high-efficiency manufacturing processes.
The AL-DGFVE232B-T6 alloy, a high-strength 7000-series aluminum alloy, is widely used in lightweight structural applications due to its low density and excellent mechanical properties. However, Gas Metal Arc (GMA) welding can degrade its mechanical performance and soften the microstructure, particularly in the heat-affected zone (HAZ), making post-weld heat treatment necessary. In this study, 8 mm-thick AL-DGFVE232B-T6 plates were GMA welded using X- and Y-groove configurations, followed by four artificial aging treatments and one natural aging condition. Tensile strength, hardness, and microstructure were evaluated to assess the effect of each condition. The results demonstrated that the mechanical properties and microstructural features varied with heat treatment, and a post-weld heat treatment condition showing relatively improved property recovery was identified within the investigated range.
The effect of welding position on the mechanical properties of high-strength low-alloy steel weld metals was investigated with an emphasis on low-temperature impact toughness. Welding was performed in horizontal (2G) and vertical-up (3G) positions using two filler wires with different alloying element contents. For the lower-alloying-content weld metals, the higher heat input associated with the 3G position promoted the formation of grain boundary ferrite and Widmanst?tten ferrite, while acicular ferrite remained the dominant phase, resulting in a pronounced reduction in impact toughness. In contrast, for the higher-alloying-content weld metals, excessive bainite formation in the 2G position led to a significantly reduced impact toughness, whereas a refined acicular ferrite microstructure developed in the 3G welds, yielding the highest impact toughness.
Fillet welds are extensively employed in ship hull structures. Under cyclic loading, fatigue cracks are prone to initiate and propagate at both the weld toe and root due to incomplete penetration, root gaps, and local stress concentrations. However, for weld-root fatigue assessment, the Effective Notch Stress (ENS) method requires detailed notch modeling, significantly limiting its practical applicability. To address this limitation, this study proposes a fracture mechanics-based Fatigue Crack Growth (FCG) framework incorporating a “virtual initial flaw” concept, enabling life predictions equivalent to those of the ENS method. The equivalence between the two approaches is formulated, and predictive equations for the virtual flaw size are derived as functions of plate thickness and weld leg length. The framework was validated using T-type specimens and excavator welds, demonstrating excellent agreement with ENS results, showing a deviation in fatigue life of less than 10%. Furthermore, integrating this FCG framework into a direct analysis-based hull weld design confirmed that the weld leg length could be optimized from 9.5 mm to 8.0 mm while maintaining structural integrity. Consequently, by introducing a fracture mechanics-based fatigue design framework, this study provides a comprehensive methodology applicable to both design-stage fatigue evaluation and in-service structural integrity assessment.
With increasing interest in improving indoor lighting comfort and energy efficiency, the development of lightweight and multifunctional decorative materials has become important. In this study, a polyester organza fabric-polyester mesh was fabricated using a direct thermal welding method to adjust an indoor atmosphere. Different colors of organza fabric and polyester mesh were welded under various temperatures ranging from 320 to 480 °C, and their mechanical strength, visible light transmittance, and color rendering were analyzed. Brighter organza colors exhibited higher visible light transmittances, while these values decreased with multi-stacking of organza fabrics. The combination of different colors of organza fabrics produced forty-eight novel colors. Increasing welding temperature enhanced polymer chain entanglement between organza fabric and polyester mesh, achieving a maximum joint strength of 10.25 MPa. The direct welding of organza fabric and polyester mesh is lightweight, flexible, and enables color diversity, therefore it can be a good candidate material for lighting and shading to adjust indoor atmosphere.
In this study, the effect of W content on the microstructure and impact property in TIG welded joint of reduced- activation ferritic/martensitic (RAFM) steels was investigated. For this purpose, two types of RAFM steels with different W contents and filler wires of the same composition were prepared. After TIG welding, a post-weld heat treatment (PWHT) was performed at 730 ℃ for 1 h. Microstructures of the weld metals were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The weld metal with low W content (1.2 wt.%) consisted of tempered martensite and precipitates of intergranular M23C6 and fine MX within the laths. An increase in W content caused the formation of δ-ferrite and the coarsening of M23C6 carbide. Mechanical properties of the weld metals were evaluated by Vickers hardness and Charpy V-notch impact tests, indicating that the impact properties of the weld metal decreased significantly with an increase in W content. Finally, the relationship between microstructure and mechanical properties in the weld metal was discussed.
This study examines the microstructural evolution and mechanical properties of medium-thickness DP980 advanced high-strength steel subjected to simulated welding thermal cycles. Gleeble simulations reproduced the thermal histories of coarse-grained (CG), fine-grained (FG), intercritical (IC), and subcritical heat-affected zone (SCHAZ) subregions. Microstructures were analyzed by scanning electron microscopy (SEM), and X-ray diffraction (XRD), while Vickers microhardness and Charpy impact tests were performed at room temperature and -40 ℃. Results showed that CGHAZ and FGHAZ developed polygonal prior-austenite grains and lath martensite, yielding higher hardness and toughness than the base metal. In contrast, ICHAZ contained a heterogeneous mixture of ferrite, martensite, retained austenite, and martensite-austenite (M-A) constituents, which led to significant toughness loss at both temperatures examined. The SCHAZ contained tempered martensite within ferrite and showed only moderate changes in impact energy. Although overall trends were similar, impact toughness decreased further at -40 ℃. These findings highlight the critical role of intercritical microstructures in governing toughness and emphasize the need to control welding parameters to suppress detrimental M-A formation in DP980 steel.
Colored and colored-infrared (IR) hybrid laser technologies have recently gained attention as promising alternatives to conventional IR sources for welding highly reflective metals such as aluminum and copper. These emerging technologies are particularly relevant to electric-vehicle battery manufacturing, power-electronic packaging, and high-precision joining of conductive materials, where conventional IR lasers often face absorption and stability limitations. This review summarizes developments in blue (450 nm), green (515-532 nm), and colored-IR hybrid systems, focusing on their welding characteristics and absorption behavior. Blue and green lasers exhibit improved energy coupling, enabling deeper penetration and wider bead formation at reduced power levels, whereas IR lasers often suffer from unstable keyhole behavior and spatter formation that degrade weld quality. Hybrid systems have shown additional benefits in stabilizing keyhole formation by preheating the surface with visible light and maintaining deep penetration with IR radiation. Influence of differences in energy density, beam size, emission mode (pulsed vs. continuous wave), and experimental setup were also discussed in relation to their impact on welding behavior, aiming to clarify why colored lasers exhibit superior performance over IR lasers for highly reflective materials. Although existing studies remain limited in providing quantitative comparisons, this review was intended to enhance understanding of the underlying mechanisms and to offer insights for optimizing future laser welding processes.
This study examines the effects of Mo, V, and Nb additions on the metallurgical and mechanical behavior of austenitic Fe-Mn-Al-C lightweight steels and their heat-affected zone (HAZ), with a particular focus on κ-carbide precipitation behavior. Microstructural characteristics and mechanical properties, including tensile behavior and Charpy V-notched impact toughness, were evaluated for both the base metal and simulated HAZ specimens, produced using a Gleeble thermal simulator. Metallurgical analyses revealed that the addition of Mo, V, and Nb effectively suppresses κ-carbide precipitation during welding thermal cycles by increasing the thermodynamic barrier to κ-carbide formation and/or by consuming carbon through competitive carbide precipitation, thereby mitigating the degradation of impact toughness in the HAZ compared to the base metal. However, since a small amount of κ-carbide still formed during the welding thermal cycle, tensile fracture occurred in the base metal rather than in the HAZ, indicating localized strengthening of the HAZ as each HAZ was locally strengthened by κ-carbide precipitation. These findings demonstrate that controlled alloying and steelmaking strategies can enhance the weldability and mechanical reliability of austenitic lightweight steels, while highlighting the importance of balanced alloy design to achieve optimal performance under welding conditions.
The liquid metal embrittlement (LME) susceptibility of Zn-1.5Al-1.5Mg coated dual-phase (DP) steel with Ni pre-plating was investigated during resistance spot welding. Microstructural analysis revealed primary Zn phases with binary and ternary eutectic structures, where Mg and Al were selectively distributed. The Ni pre-plating layer (~2.5 mm) promoted the formation of Fe-Ni-Zn and Ni-Fe intermetallic compounds, which were associated with LME crack initiation. Diffusion-assisted phase evolution, combined with thermal and mechanical stresses, is suggested to degrade interfacial integrity. These findings highlight the role of Ni pre-plating in LME susceptibility and provide insights into the detrimental role of Ni pre-plating in Zn-Al-Mg systems and suggest careful consideration in coating design.
In this study, the orientation-dependent solidification behavior of CMSX-4 single-crystal superalloy welds was systematically investigated using phase-field simulations. A multiphase-field model implemented in MICRESS, coupled with CALPHAD-based thermodynamic and mobility databases, was employed to simulate weld solidification under gas tungsten arc welding (GTAW) conditions. The numerical model was validated by comparing the simulated primary dendrite arm spacing (PDAS) with experimental observations, showing good agreement. Initial crystallographic misorientations of 0° and 15° were introduced to represent epitaxial single-crystal and high-angle polycrystalline solidification, respectively. The results reveal that, although the mushy zone range remains nearly identical for both orientations, the morphology and continuity of residual liquid at the terminal stage of solidification differ significantly. For the epitaxially grown condition (0°), residual liquid is distributed in a discontinuous droplet-like form due to early dendrite arm coalescence. In contrast, high-angle misorientation (15°) delays dendrite coalescence, leading to the formation of continuous liquid films enriched with solute elements such as Hf. This continuous liquid film provides an effective pathway for crack initiation and propagation, resulting in a substantially higher BTR. These findings demonstrate that the solidification cracking susceptibility of single-crystal superalloy welds is governed primarily by the morphology of residual liquid during the final stage of solidification rather than by the mushy zone range itself. The present study provides a mechanistic framework for understanding BTR variation in single-crystal superalloy welds and offers critical insights for controlling epitaxial growth and improving weldability in repair welding and additive manufacturing applications.
This study investigates the arc characteristics and process stability of Cold Metal Transfer (CMT) welding for fabricating copper (Cu) overpacks of spent nuclear fuel disposal canisters. Applying arc deposition processes to pure Cu poses significant challenges due to the material's high thermal conductivity, which inherently induces arc instability. To address this, the influence of shielding gas composition (100% Ar vs. 75% He - 25% Ar) on arc physics, metal transfer regularity, and bead geometry was systematically analyzed. In the pure argon (Ar) environment, the arc exhibited an expanded bell-shape with erratic root wandering, resulting in a random and unstable nature of metal transfer with a high Vilarinho regularity index (IVsc) of 0.43 and excessive spatter generation. Conversely, the addition of 75% helium (He) induced a strong thermal pinch effect, constricting the plasma into a highly regular and stable columnar arc morphology. This morphological change effectively anchored the arc root, significantly improving process stability with a reduced IVsc of 0.17 and eliminating current overshoot-induced spatter. Consequently, the He-rich condition produced beads with superior dimensional uniformity compared to the irregular deposition observed under pure Ar. These findings demonstrate that utilizing the thermal pinch effect via optimized shielding gas is critical for overcoming the intrinsic instability of Cu-Fe system, providing a fundamental basis for high-quality canister fabrication.
In the contemporary shipbuilding industry, the construction of Liquefied Natural Gas (LNG) carriers represents a pinnacle of high-value manufacturing that demands extreme precision. The fabrication of membrane-type containment systems, such as Mark III and NO96, relies heavily on the lap-joint welding of thin corrugated plates made of STS 304L or Invar alloy. Recently, the imperative for welding automation has intensified due to the critical shortage of skilled welders and the stringent requirements for gas leakage prevention. However, the application of Laser Vision Sensors (LVS) for seam tracking has been hindered by specular reflection, intense arc interference, and mechanical interference from clamping devices. This study aims to systematically evaluate the seam recognition performance of an LVS-based system under these adverse conditions. A robotic welding system integrated with a coaxial LVS module was constructed to conduct experiments on STS 304L corrugated lap joints. The influence of optical and geometric parameters, including laser power and camera angle, on the quality of acquired laser profiles was analyzed quantitatively. To enhance robustness, the sensor’s logarithmic gain settings were optimized to mitigate interference from TIG arc under varying heat inputs. The results demonstrate that a 200mW line laser at a 50-60° camera angle provides the highest height-difference detection resolution for lap joints. Finally, this research confirms the optical feasibility of LVS in LNG tank fabrication and suggests future directions for hybrid or AI-enhanced sensing solutions.
The Sn-3.0Ag-0.5Cu (SAC305) solder, widely used in the electronics industry, exhibits excellent wettability and mechanical stability. However, its relatively high melting point of 217 °C can cause thermal damage and interfacial delamination during repeated reflow processes. As an alternative, the Sn-58Bi solder, with a low melting point of 139 °C, has attracted significant attention. Sn58Bi solder is cost-effective and shows favorable mechanical properties and wettability. Nevertheless, its high Bi content (58 wt%) leads to brittleness and the formation of coarse Bi-rich phases, which degrade joint reliability. To overcome these limitations, a hybrid solder structure combining Sn58Bi and SAC305 has been proposed, allowing the integration of the low processing temperature of Sn58Bi with the mechanical robustness of SAC305. However, conventional reflow soldering still involves a high thermal load and long processing time, which result in excessive energy consumption and accelerate intermetallic compound (IMC) growth and warpage. To address these issues, this study adopts intense pulsed light (IPL) soldering, which utilizes the photothermal effect of a Xe flash lamp as an alternative process. The IPL process enables localized heating within a few seconds to induce solder melting and bonding, allowing the formation of a thin IMC layer with precise temperature control. In this study, Sn58Bi solder paste was printed on Cu pads, and SAC305 solder balls were mounted on top to form a hybrid joint structure. The joints were then fabricated using both reflow and IPL soldering processes, and their microstructural and mechanical properties were compared according to the process conditions. As a result, the IPL process produced a thinner IMC layer than reflow soldering and, although it exhibited slightly lower shear strength, the increased shear displacement indicated improved ductility of the joints.
In this study, a process monitoring approach was developed to collect and analyze in-situ data during the Ti64ELI laser powder bed fusion (PBF) process. Real-time images of each layer and corresponding energy mapping data were obtained using a built-in high-speed camera system. The results demonstrated that excessive heat input regions, observed as red dots in energy maps, were associated with over-melting and structural collapse in the upper layers. Mechanical testing of six specimens fabricated under identical process parameters (laser power: 450 W, scan speed: 1,500 mm/s, layer thickness: 50 ㎛) showed average yield strength of 906 MPa, ultimate tensile strength of 997 MPa, and elongation of 12.3%, consistent with the typical range for Ti64ELI additively manufactured alloys. However, specimens with locally concentrated energy input exhibited reduced elongation due to uneven heat distribution. These results confirm that energy distribution and geometric instability during the AM process have a significant effect on mechanical properties. The captured layer-wise images and energy mapping data were studied as monitoring technology capable of analyzing defects that may occur during the process and predicting quality in the 3D printing process.
The demand for reliable dissimilar metal joining is growing with the miniaturization and high-performance needs of modern industries. Brazing between copper (Cu), with excellent thermal conductivity, and stainless steel (STS), with superior corrosion resistance, is widely used in heat exchangers and piping. However, a stable Cr2O3 oxide layer on STS reduces filler wettability, causing incomplete bonding and defects. To solve this problems, a flux-free Ag-Cu-Sn-P filler metal was developed. Phosphorus (P) was added to remove oxides and promote interfacial reactions, and Sn was used to adjust the melting range and reduce solidification defects. Alloys with different Ag and P contents were fabricated and evaluated for microstructure, wettability, and Cu-STS joint strength. Analysis revealed phases of Ag-Cu, Cu3P, and Cu3Sn, with P addition increasing the Cu3P fraction. Alloys containing 5wt.% P showed superior spreading, and joints produced with these alloys had higher tensile strength than commercial BCuP-5. These results highlight the potential of Ag-Cu-Sn-P alloys as cost-effective, flux-free fillers that improve bonding and reliability in Cu-STS dissimilar joints.
