Welding in the World最新文献

Laser cladding is a surface modification technique used for repairing and enhancing substrate materials by depositing powder layers with a laser beam. This study investigates the effects of laser power, scanning speed, and heat input on the porosity, microhardness, microstructure, residual stress, and thermal behavior of Metco 42C martensitic stainless steel powder deposited on FGS600-3A ductile cast iron used in sheet metal forming molds. Characterization was conducted using optical microscopy, SEM, EDS, digital image processing, thermal imaging, and residual stress measurements via XRD and ESPI methods. The cladding zone exhibited a columnar dendritic martensitic structure, with coarser dendrites observed at high heat input (316.67 J/mm) compared to low heat input (78.57 J/mm). Increased heat input significantly affected porosity, with pore formation mechanisms including gas entrapment, lack of fusion, balling effect, and thermal contraction. Microhardness variation was attributed to carbon diffusion from the substrate, with a peak hardness of 946 HV0.05 in the transition zone. Residual stress analysis revealed compressive stress dominance at high heat input and tensile stress at low heat input. Thermal analysis indicated a peak temperature of 1771 °C in the first cladding layer, which also exhibited a higher risk of cracking. These findings highlight the influence of heat input on the mechanical and microstructural properties of the cladding, providing insights for optimizing laser cladding processes in industrial applications.

Moving from traditional thermomechanical processing to additive manufacturing (AM) of precipitation hardening (PH) stainless steels has introduced unexpected differences in the heat treatment response that produce wide variation mechanical properties. Changes in powder compositions and AM processing conditions have been identified as the primary causes since they produce different as-deposited microstructures within the same alloy system. In PH grade stainless steels, differences in nitrogen composition have been identified as the major contributor. For example, with low nitrogen levels on the order of 0.01 wt%, large ferritic grain structures with small amounts of a high temperature delta-ferrite existing along the grain boundaries are produced. On the other hand, high nitrogen levels on the order of 0.1 wt% or greater result in large amounts of retained austenite (81 vol.%). Higher required aging temperatures for the high nitrogen alloys has also been identified and evaluated so specific aging heat treatments can be selected based on the material composition and targeted properties. It is clear that aging heat treatments must be adapted to incoming material composition. To adequately adjust the heat treatments, a composition-based approach which guides appropriate aging parameters to control changes in copper precipitation as well as retained austenite stability is developed based on thermodynamic and empirical results. While nitrogen content varies significantly and has been the primary focus, these analyses and heat treatments are based on the entire composition.

Deep learning approach involving a convolutional neural network (CNN) has been developed to perform semantic segmentation in captured real-time images of the weld pool and determine the weld penetration status in real-time during activated TIG welding (A-TIG). A robotic welding machine with a CMOS camera attached to the welding torch was employed to capture real-time images of the weld pool. Welding experiments were conducted by varying the current from 90 to 300A in steps to achieve various levels of weld penetration depth in the range of 2–10 mm. The above weld penetration range has been categorised into four classes of weld penetration status. A CNN model with VGG 16 architecture has been applied as an encoder in the U-Net framework for weld pool image classification. The accuracy of classification was 99% and the model execution time was 90 ms in a computer for prediction in a single frame of the image. To reduce the model execution time further, a few lightweight architectures were chosen as encoders for the U-Net model and their performance was compared. Among them, the most accurate EfficientNet-B0 was chosen for real-time implementation. The developed model was executed in real-time to predict the weld penetration status in NVIDIA Jetson Nano embedded hardware. The classification accuracy determined for the four classes was found to be in the range of 94 to 98% for the validation experiments. The execution time was found to be reduced to 55 ms for prediction of the weld penetration status in a frame of weld pool image.

The applicability of additive manufacturing (AM) of duplex stainless steels has been limited by the complex thermal history causing an imbalance of ferrite and austenite in the as-deposited material. Laser-beam directed energy deposition with wire (DED-LB/w) presents a promising solution when combined with solution annealing. This study utilizes a specially developed 3Dprint AM 2205 and a conventional ER2209 wire to continuously build cylindrical components. Metallographic examination was conducted using light optical microscopy (LOM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and electron microprobe analysis (EPMA). While high deposition rates were achievable, excessively high wire feeding rates led to continuous areas of fine grains in the deposited beads. These regions, identified as partially molten wire, were sometimes associated with lack-of-fusion, porosity, and solidification cracking. Optimized parameter settings enabled efficient melting of the wire, producing defect-free deposits, and eliminating partially molten wire residues. Solution annealing effectively dissolved intermetallics and homogenized the microstructure, resulting in a more uniform phase distribution.

The distribution of residual stress and accurate deformation prediction in wire arc additive manufacturing (WAAM) and subsequent cutting components were crucial for practical application. This study focused on simulating titanium alloy walls manufactured by WAAM to analyze thermal and residual stress distributions. Subsequently, the blade shape of the WAAM wall was subjected to cold cutting conditions using the finite element method. The residual stress and deformation of WAAM were studied under various cutting directions. WAAM and cutting components were scanned and analyzed using the Calibry Nest scanner. The findings reveal that in the middle line of the deposition cross-section, residual compressive stress emerges after 18 layers, and the distribution of longitudinal residual stresses follows a "tension–compression-tension" pattern. In cutting direction from the middle to both sides, the deformation of the components is effectively controlled by a narrower residual stress range. As the number of deposition layers increases, the deformation in the width direction rises to a maximum of approximately 0.2 mm. Cold cutting alleviates thermal and residual stresses induced during the WAAM process, reducing substrate deformation.

In addition to chemical composition, metallurgy, and welding parameters, the intensity of restraint is one of the key variables influencing solidification cracking (SC). Due to their high strength-to-density ratio, many modern lightweight steel constructions increasingly rely on high-strength steel. Given the theoretical framework of solidification cracking theory, tests tend to focus on the effects of strain rate. Externally restrained tests have provided valuable insights into solidification crack susceptibility. In practice, most welded structures are self-restrained; therefore, self-restraint tests more accurately reflect real-world applications. By varying the plate thickness in controlled thermal severity (CTS) tests conducted on S1100 QL, it was possible to adjust the intensity of restraint on fillet welds at a high level. Testing was performed using four different filler wires for gas metal arc welding (GMAW), including three solid wires and one metal-cored wire. Additionally, two sets of welding parameters were evaluated. High arc energy (U × I/welding speed) and increased welding speed were found to be more prone to solidification cracking compared to the parameter set with lower arc energy and welding speed. The results indicate a correlation between increasing restraint severity and a higher incidence of solidification cracking.

The document presents a comprehensive investigation into the fatigue strength assessment of welded fasteners, specifically bolts and nuts, used in various engineering applications. A fatigue strength assessment approach using a structural stress concept is established, accounting for the influence of mounting pre-loads and residual stresses from the welding process. With the developed approach, the fatigue strength of all investigated variants can be assessed with a scatter of 1:2. The experimental investigations showed that an early decrease in pre-load forces negatively affects the fatigue strength. While pre-load forces can enhance fatigue strength, a reduction in pre-load during service loading must be avoided to ensure a safe life.

This review paper explores the advancements and applications of gas tungsten arc welding (GTAW) for magnesium alloys, which are increasingly utilized in aerospace, automotive, and biomedical industries due to their high strength-to-weight ratio and excellent corrosion resistance. However, welding magnesium alloys presents significant challenges, including high reactivity with oxygen and hydrogen, hot cracking, porosity, and thermal distortion. While conventional GTAW methods provide satisfactory results, they often fall short in meeting the stringent requirements of high-precision applications. Recent innovations, such as pulse-modified and hybrid GTAW techniques, show great promise in addressing these challenges by improving heat input control, reducing defect formation, and enhancing mechanical properties. Key factors such as the choice of shielding gas, filler materials, and heat input control are critical for ensuring high-quality welds. Furthermore, advancements in artificial intelligence, real-time monitoring, and automation are poised to enhance the accuracy and efficiency of GTAW, making it a more reliable option for industrial applications. The paper also highlights future trends, including the integration of GTAW with additive manufacturing, which could expand its use in renewable energy, biomedical implants, and lightweight structures. This review demonstrates the transformative potential of GTAW for advancing the use of magnesium alloys in various high-performance industries.

Metal-cored (MCW) and flux-cored (FCW) wires are widely used for welding low-carbon (C) steels in structural applications, offering higher productivity but generating more welding fumes than solid wires. Growing awareness of the health risks associated with respirable particles has intensified the focus on fume composition. While proper fume extraction and personal protective equipment (PPE), such as helmets with breathing apparatus, are essential, modifying wire composition can help reduce harmful emissions. Manganese (Mn), a key alloying element in C-steels, and their corresponding welding consumables have been linked to neurological effects, prompting stricter occupational exposure limits (OELs) to protect welders. This has driven demands for low-Mn-emission welding consumables. This study evaluates two newly developed seamless low-Mn-emission products, one MCW (MCW-LMn) and one FCW (FCW-LMn), by comparing their fume and Mn emission rates (Mn_mg/s) to those of standard seamless and folded wires under varying welding parameters and shielding gas compositions. At equivalent parameter settings, the newly developed wires produced comparable fume levels but achieved Mn emission reductions of 25–70% for MCW-LMn and 60–85% for FCW-LMn.

Brazing hybrid joints of additively manufactured and conventionally produced components made of IN718 opens new application possibilities for additive manufacturing processes, such as PBF-LB/M, in industrial production processes. The combination of hybrid structures enables cost-effective production of large-volume parts with complex features. In this work, the differences between hybrid and conventional joints are analysed, due to the different microstructure of additive manufactured IN718 compared to bulk material. The differences in the microstructures lead to different diffusion paths of the elements from the molten braze alloy along the grain boundaries and to different wetting behaviors. This has a significant effect on the microstructure and the mechanical properties of the joints. To investigate the effect of the microstructure of PBF-LB/M base materials on the brazing of IN718 with the braze alloy VZ2177, vacuum brazing with varying dwell time has been employed to manufacture joints of the bulk material and hybrid joints, consisting of additively manufactured and bulk IN718. Due to the phosphorus in the filler metal, brittle phases in the center of the brazing zone have formed in both joint types. With increasing brazing, the width of the brazing area grew. In the hybrid joint, a strong formation of IMC phases could be observed at the PBF-LB/M side of the joint leading to a higher hardness, which was more pronounced at longer brazing times. The increase in hardness was accompanied with a crack formation that was located near the PBF-LB/M-side only in those hybrid joints with long brazing time and occurred most probably due to stress relief during cooling.