Welding in the World最新文献

Challenges in terms of reliability still surround thermal measurement methods in welding processes. However, the temperature distribution within the weld pool can provide important resources for understanding behaviors and explaining phenomena. This work aims to study the effect of gravity on the temperature distribution within the weld pool under different welding positions using an in-house developed equipment. First, a combination of optical settings and a calibration procedure were established. Experiments were carried out with the same welding parameters under flat, horizontal, vertical upward, and vertical downward positions. The thermal field from the backside of fully penetrated thin plates was accessed using the TIG process. The device allowed a well-delimited and detailed weld pool thermal field assessment. Dimensionless numbers were quantified, and Marangoni shear stress was plotted on the weld pool surface. Along the transversal weld pool direction, a symmetrical heat distribution was stated in the flat position, while an asymmetrical one was observed in the others. The Marangoni effect played a crucial role in all the experiments, emerging as the dominant driving force in 1G and 2G positions. It governed the fluid flow within the weld pool by influencing temperature gradients over time, which, in turn, altered the direction and magnitude of shear stress on the free surface. Notably, in the 2G position, the observed asymmetry in the weld pool features may be attributed to the combined effects of buoyancy and Marangoni forces acting together. Finally, through the developed equipment, it was possible to evaluate the impacts of gravity on the heat distribution within the weld pool and demonstrate its contribution to dynamics studies.

High carbon ferrochrome hardfacing alloys are widely used to protect machinery equipment exposed to a combination of abrasion and impact. Strengthening high-chromium iron-based alloys with alloying elements is an important strategy for developing its wear resistance and impact property. In this study, novel complex Fe-xCr-C-Nb-Mo-V-W hardfacing alloys with varying Cr contents of 14, 18 and 23 wt. % were prepared using open arc welding. The effects of the Cr content and the heat treatment on the microstructure, abrasive resistance and impact property of the hardfacing alloys were evaluated. With the rise in Cr content, the area fraction of M₇C₃ hard phase improves from 56 to 62%, while the grain size of M₇C₃ is refined from 26.5 μm to 22.0 μm. Results show that increasing Cr content increases the abrasive resistance but declines the impact property of the hardfacing alloys. Heat treatment at 900 °C decreases the area fraction of M₇C₃ phase and induces the grains coarse, resulting in the descent of the abrasive resistance and ascent of the impact property of the hardfacing alloys. Abrasive test results highlight that the importance of area fraction and grain size of M₇C₃ phase for abrasive resistance. However, the martensite/ austenite matrix with toughness plays the predominant role in the impact resistance by absorbing and dispersing the impact energy.

Creep-resistant steels such as 13CrMoV9-10 are utilized in the manufacture of thick-walled pressure vessels and are typically joined by submerged arc welding (SAW). However, these materials are susceptible to stress relief cracking (SRC) if the required post weld heat treatment (PWHT) is not applied correctly. Existing PWHT guidelines, encompassing heating rate and dwell (or holding) time at a given temperature, are derived from a synthesis of empirical knowledge and typically free-shrinkage weld experiments to assess the susceptibility to SRC. Therefore, this study discusses the combined effect of the PWHT heating rate under free-shrinkage compared to restrained shrinkage. Welding experiments were conducted (using plates with a thickness of 25 mm) for both shrinkage conditions for a variety of heating rates and maximum temperatures. In-situ acoustic emission analysis was used to locate propagating SRCs during PWHT. Hardness measurements, mechanical property characterization (Charpy impact strength), and microstructure correlation were used to evaluate the SRC susceptibility. The results suggested that the influence of heating rate could not be directly related to SRC formation and that the initial weld microstructure prior to PWHT was more relevant in terms of very high hardness in the coarse grain heat affected zone, especially that of the last beads in the top layer of the welding sequence. This was seen in the form of random, unexpected SRC occurrence in only one specimen at a heating rate commonly used in welding practice (approximately 100 K/h). In this context, the additional effect of an external shrinkage restraint on SRC must be considered in the form of increasing mechanical loads during welding, which are typically not within the scope of welding practice. To mitigate the probability of SRC during PWHT, it is imperative to reduce the welding heat input and to restrict the structural shrinkage restraint of the weld joint.

Aiming at the problem that silicon carbide particle reinforced aluminum matrix composites (SiC_p/Al MMCs) are prone to interfacial reaction between the matrix Al alloy and reinforced SiC particles at high temperature, which forms Al₄C₃ brittle compounds that affects the joint performance, an oscillating laser wire-filling welding process with preseted gap was developed. The high-quality welding connection of SiC_p/2009Al MMCs with a thickness of 1.6 mm and 30% vol was achieved by optimizing the process parameters, and the microstructure and mechanical properties of the joint were analyzed. The results show that the preseted gap can effectively reduce the dilution rate of the base metal, reduce the number of holes, and reduce the generation of the brittle Al₄C₃ phase. With a 1.3-mm gap, a welded joint with good surface forming and no defects such as pores, undercuts, and inclusions could be obtained. The dilution rate of the base metal was about 12%, and the size of the Al₄C₃ brittle phase was reduced from tens of microns to submicron levels with its number significantly reduced. The microstructure of the weld zone (WM) was dominated by dendrites, while the vicinity of the fusion zone (FZ) presented a mixture of equiaxed, dendrite, and columnar crystal phases. The tensile strength of the welded joint was 233 ± 3 MPa. The elongation after fracture was about 3% with all fracture positions near the fusion line, showing the characteristics of brittle-ductile fracture. The lack of Cu element and the insufficient strengthening phase of θ′ (Al₂Cu) result in low microhardness in the WM region.

Weld reconstruction technology based on visual sensors is a crucial component of intelligent robotic welding systems. In thick-wall workpieces with big groove multi-layer automatic welding, precise measurement of the workpiece and weld seams directly affects subsequent weld path planning and posture planning of the welding torch. To address this issue, this study employs a three-line structured light measurement system for weld profile detection. A sub-plane fitting algorithm is proposed for 3D reconstruction of weld grooves, accompanied by a rapid workpiece coordinate system establishment method using three-line structured light to ensure accurate boundary segmentation. However, direct welding based on reconstructed feature points cannot guarantee high-quality results. Therefore, we investigated the effects of key process parameters, such as welding position, direction of welding, and torch inclination angle on weld bead geometry. A second-order general rotational composite design was implemented to develop regression models correlating welding parameters with weld bead characteristics. Finally, integrated process planning combining reconstruction data with optimized welding parameters was implemented for torch trajectory and orientation planning. Experimental results demonstrate that this methodology effectively satisfies quality control requirements for automated welding of thick-walled structural components.

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.