Search Results (111)

Real-time quality monitoring using molten pool images is a critical focus in researching high-quality, intelligent automated welding. To address interference problems in molten pool images under complex welding scenarios (e.g., reflected laser spots from spatter misclassified as porosity defects) and the limited interpretability of deep learning models, this paper proposes a multi-granularity spatiotemporal representation learning algorithm based on the hybrid enhancement of handcrafted and deep learning features. A MobileNetV2 backbone network integrated with a Temporal Shift Module (TSM) is designed to progressively capture the short-term dynamic features of the molten pool and integrate temporal information across both low-level and high-level features. A multi-granularity attention-based feature aggregation module is developed to select key interference-free frames using cross-frame attention, generate multi-granularity features via grouped pooling, and apply the Convolutional Block Attention Module (CBAM) at each granularity level. Finally, these multi-granularity spatiotemporal features are adaptively fused. Meanwhile, an independent branch utilizes the Histogram of Oriented Gradient (HOG) and Scale-Invariant Feature Transform (SIFT) features to extract long-term spatial structural information from historical edge images, enhancing the model’s interpretability. The proposed method achieves an accuracy of 99.187% on a self-constructed dataset. Additionally, it attains a real-time inference speed of 20.983 ms per sample on a hardware platform equipped with an Intel i9-12900H CPU and an RTX 3060 GPU, thus effectively balancing accuracy, speed, and interpretability. Full article

This paper investigates self-shielded flux-cored wires with an exothermic MnO₂-Al addition and the effect of hardfacing modes on the deposited alloy of the Fe-C-Mn system for the first time. Additionally, the paper proposes a new experimental research methodology using an orthogonal experimental design with nine experiments and three levels. At the first stage, it is proposed to use the Taguchi plan (L9) method to find the most significant variables. At the second stage, for the development of a mathematical model and optimization, a factorial design is recommended. The studied parameters of the hardfacing mode were travel speed (TS), set voltage on the power source (U_set), contact tip to work distance (CTWD), and wire feed speed (WFS). The following parameters were studied: welding thermal cycle parameters, microstructure, grain size, non-metallic inclusions, and mechanical properties. The results of the analysis showed that the listed parameters of the hardfacing modes have a different effect on the characteristics of the hardfacing process with self-shielded flux-cored wires with an exothermic addition in the filler. It was determined that for flux-cored wires with an exothermic addition, the size of the deposited metal grain size is most affected by the contact tip to work distance (CTWD). The research results showed that the travel speed (TS) had the main influence on the thermal cycle parameters (heat input, cooling time) and hardness. The analysis of the deposited metal samples showed that an increase in the travel speed had a negative impact on the number of non-metallic inclusions (NMIs) in the deposited metal. While the size of NMIs was influenced by the wire feed speed and the set voltage on the power source. Full article

Although structural aluminium alloys have many advantages (low self-weight, corrosion resistance, 100% recyclable), they are associated with some conservative design methods in Eurocode 9. Conservative reductions in aluminium’s mechanical properties in the welded connection zone and the limitations of extruded aluminium members (the relatively small dimensions and uniform shape of the profile over the length) significantly limit the use of aluminium in load-bearing structures. This paper summarises the background, planned activities, and preliminary results of the ongoing REAL-fit project. The aim of the project is to conduct comprehensive interdisciplinary research on the feasibility of applying innovative automated (robotic) welding technologies and reliable design methods for aluminium welded members, joints, and entire structural systems. In this paper, the shortcomings of the current design approach are identified, and experimental, numerical, and reliability-based methodology for possible improvements is proposed. Furthermore, the project considers the integration of the advanced direct design method (DDM) with the methods of life cycle assessment (LCA) and life cycle cost analysis (LCCA) as a possible direction for establishing a more holistic evaluation framework. This is precisely one of the project’s ultimate goals, which will assess the reliability and sustainability of economical aluminium structures throughout their life cycle. Full article

A zero-voltage switching (ZVS) push–pull self-oscillating arc ignition circuit was proposed, marking the first application of ZVS technology in welding arc ignition systems. The circuit’s working principle was analyzed, and time-domain waveforms of the switching transistors verified the realization of soft switching. A conducted interference test platform was established in order to assess the circuit’s electromagnetic compatibility under no-load and arc ignition transient conditions. In comparison with conventional domestic arc ignition circuits, the proposed ZVS circuit demonstrated substantially diminished quasi-peak interference levels, with a reduction exceeding 9.5 dB in both instances. Additionally, under no-load conditions, the ZVS circuit demonstrated interference levels comparable to those of a commercial Fronius system, while during arc ignition transients, it exhibited an over 5 dB reduction. The findings of this study demonstrate that the incorporation of soft-switching techniques into arc ignition circuits can effectively mitigate conducted interference, thus providing a promising and practical approach for industrial welding equipment. Full article

The automotive industry is currently in a paradigm shift transferring the fleet over from internal combustion vehicles to battery electric vehicles (BEV). This introduces new challenges when designing the body-in-white (BIW) due to the sensitive and energy-dense battery that needs to be protected in a crash scenario. Press-hardening steels (PHS) have emerged as an excellent choice when designing crash safety parts due to their ability to be manufactured to complex parts with ultra-high strength. It is, however, crucial to evaluate the crash performance of the selected materials before producing parts. Component testing is cumbersome and expensive, often geometry dependent, and it is difficult to separate the bulk material behaviour from other influences such as spot welds. Fracture toughness measured using the essential work of fracture method is a material property which has shown to be able to rationalise crash resistance of advanced high-strength steel (AHSS) grades and is thereby an interesting parameter in classifying steel grades for automotive applications. However, most of the published studies have been performed at quasi-static loading rates, which are vastly different from the strain rates involved in a crash. These higher strain rates may also lead to adiabatic self-heating which might influence the fracture toughness of the material. In this work, two PHS grades, high strength and very high strength, intended for automotive applications were investigated at lower and higher strain rates to determine the rate-dependence on the conventional tensile properties as well as the fracture toughness. Both PHS grades showed a small increase in conventional mechanical properties with increasing strain rate, while only the high-strength PHS grade showed a significant increase in fracture toughness with increasing loading rate. The adiabatic heating in the fracture process zone was estimated with a high-speed thermal camera showing a significant temperature increase up to 300 °C. Full article

Despite their excellent mechanical properties, martensitic stainless steels present significant welding challenges due to their susceptibility to cracking and forming brittle microstructures during thermal cycles. While electron beam welding offers advantages through its high energy density and precise control over conventional welding methods, the induced residual stresses remain a critical concern. This study aims to determine surface residual stresses in electron beam welded AISI 410 martensitic stainless steel using a self-developed C-scan mode Magnetic Barkhausen Noise (MBN) measurement system. A novel calibration and measurement methodology was developed to establish a quantitative relationship between MBN signals and residual stress state. The residual stresses in the welded specimens were analyzed systematically using MBN and X-ray diffraction (XRD) measurements and microstructural characterization. The results revealed a strong correlation between MBN parameters and residual stress states, showing notable variations across the weld zones, i.e., approximately +350 MPa in the heat-affected zone and −50 MPa in the base metal. The experimental findings were also validated through finite element simulations. The correlation between experimental and numerical results confirms the reliability of the proposed MBN-based methodology and system. These findings provide valuable insights for industrial applications, offering a rapid and reliable non-destructive method for residual stress assessment in critical welded components. Full article

To address the challenges of strong arc light noise, metal spatter, and smoke interference in weld seam recognition, we propose DRST-Net, a dual-branch cross-attention feature fusion network. The encoder of DRST-Net consists of two branches: ResNet50 for detailed feature extraction and Swin Transformer for global semantic modeling. The network also incorporates a cross-attention feature fusion (CaFF) module, which utilizes the self-attention mechanism to dynamically integrate local features from ResNet50 with global semantic information from Swin Transformer. This design allows DRST-Net to effectively merge both detailed and global features, enhancing the accuracy and robustness of weld seam recognition. The experimental results show that DRST-Net outperforms the current leading models, achieving a mIou of 86.17%, mPre of 92.32%, and F1_score of 91.68%. The model performs especially well in complex environments with noisy backgrounds and intricate details. Ablation experiments confirm the effectiveness of the dual-branch structure and the cross-attention fusion module. This approach provides a practical and reliable solution for automated welding tasks, offering significant improvements in both accuracy and robustness. Full article

In view of the application status and technical challenges of steel–wood composite joints in architecture, this paper proposes an innovative connection technology to solve issues such as susceptibility to pry-out at beam–column joints and low load-bearing capacity and to provide various reinforcement methods in order to meet the different structural requirements and economic benefits. By designing and manufacturing four groups of beam–column joint specimens with different reinforcement methods, including no reinforcement, structural adhesive and angle steel reinforcement, 4 mm thick steel sleeve reinforcement, and 6 mm thick steel sleeve reinforcement, monotonic loading tests and finite element simulations were carried out, respectively. This research found that unreinforced specimens and structural adhesive angle steel-reinforced joints exhibited obvious mortise and tenon compression deformation and, moreover, tenon pulling phenomena at load values of approximately 2 kN and 2.6 kN, respectively. However, the joint reinforced by a steel sleeve showed a significant improvement in the tenon pulling phenomenon and demonstrated excellent initial stiffness characteristics. The failure mode of the steel sleeve-reinforced joints is primarily characterized by the propagation of cracks at the edges of the steel plate and the tearing of the wood, but the overall structure remains intact. The initial rotational stiffness of the joints reinforced with angle steel and self-tapping screws, the joints reinforced with 4 mm thick steel sleeves, and the joints reinforced with 6 mm thick steel sleeves are 3.96, 6.99, and 13.62 times that of the pure wooden joints, while the ultimate bending moments are 1.97, 7.11, and 7.39 times, respectively. Using finite element software to simulate four groups of joints to observe their stress changes, the areas with high stress in the joints without sleeve reinforcement are mainly located at the upper and lower ends of the tenon, where the compressive stress at the upper edge of the tenon and the tensile stress at the lower flange are both distributed along the grain direction of the beam. The stress on the column sleeve of the joints reinforced with steel sleeves and bolts is relatively low, while the areas with high strain in the beam sleeve are mainly concentrated on the side with the welded stiffeners and its surroundings; the strain around the bolt holes is also quite noticeable. Full article

According to the mechanical characteristics of joints in steel–concrete composite bridge decks under the combined bending and shear, improved joint details with simple structure and convenient construction were studied, including lapped U-bars, lapped headed bars, and lapped hook bars. In order to test the mechanical properties of the three joint details and compare them with the existing lapped/welded linear bars, the tests of five specimens were carried out. The cracking load, ultimate load, failure mode, crack pattern, and reinforcement strain were analyzed. The test results showed that the joint with lapped U-bars and hook bars exhibited ductile failure, while the joint with lapped headed and lapped/welded linear bars exhibited brittle failure. The cracking load of the five specimens was basically the same. The crack first occurred at the interface of pre-cast concrete and wet joints. When the ultimate bearing capacity was reached, the vertical main cracks were generated near the interface of the lapped U-bars, lapped hook bars, and welded linear bars specimens. The diagonal cracks were generated at the wet joint of the lapped headed bars specimen and lapped linear bars specimen. The lapped U-bars specimen had the highest bearing capacity, which was 22.8%, 14.2%, 50.4%, and 32.1% higher than the capacities of the lapped headed bars, lapped hook bars, lapped linear bars, and welded linear bars specimens, respectively. The load–deflection curves and crack mode obtained from the FEM of the lapped U-bars joint specimen were consistent with the test results. The bearing capacity of the FEM (351.3 KN) was 1.8% less than the test result (357.6 KN), which indicates that the bearing capacity calculated by the finite element model is reliable. There are 80 models with varying lap lengths and concrete strengths. The self-organizing migrating algorithm was used to fit the coupling effect of lap length and concrete strength. Based on doubly reinforced beam flexural capacity formulas, a bearing capacity calculation for lapped U-bars joint was proposed. The mean value of the formula calculation result and the finite element result ratio is 1.03, and the variance is 0.0004. Full article

A large number of MIG welding tests were carried out on a 3 mm thick 7075 aluminum alloy plate prepared by the self-developed jet forming–extrusion–drawing process of 7075 high-strength aluminum alloy welding wire, and the welding process of the welding wire and the change in the performance of the welded joint after T6 heat treatment were studied. The results show that the self-developed wire has a good forming joint and a wide welding process window: the welding speed is 5–7 mm/s, and the welding current is 100–150 A. The main precipitated phases in the joint were η(MgZn₂), S(CuMgAl₂), Mg₂Si, and Al₁₃Fe₄, which were continuously distributed at the grain boundaries in the form of coarse networks or long strips, which was an important reason for the weak performance of the joints. After the heat treatment of T6, the precipitated phase in the joint was greatly reduced, the element segregation phenomenon was improved, and the residual precipitated phase was mainly Al₁₃Fe₄ and a small amount of insoluble phase Fe and Si, and the recrystallization size of the heat-affected zone was refined. Through heat treatment, the average microhardness of the joint was increased from 110 HV to 150.24 HV, and the tensile strength was increased from 326 MPa to 536 MPa, reaching 97.5% of the strength of the base metal, indicating that the softening phenomenon was significantly improved after heat treatment, and the joint had excellent performance. Full article

Arc quenching has many advantages, including generating large amounts of heat in a short time, a self-quenching ability, and simple equipment. The electric arc energy from a TIG welding machine was used to modify the surface properties of S45C Carbon Steel Cylinders. The study focuses on the impact of arc length, current intensity, travel speed, gas flow rate, heating angle, and pulse on surface hardness after arc quenching an S45C steel tube with a cylinder surface. The study found that the hardness reduces from 45.1 HRC to 41.2 HRC as the current intensity increases from 125 A to 140 A. According to Taguchi’s results, the ranking of factors which have the greatest impact on surface hardness are pulse time, travel speed, intensity, gas flow rate, arc length, and heating angle. The pulse time has the highest impact because it directly influences the heating input, followed by the travel speed. Arc length and heating angle, on the other hand, have the least effect. The base metal, heat-affected area, and hardened area are the three distinct areas that make up the microstructure structure. After the arc quenching process, the case hardening depth is represented by the heat-affected zone at 1536 μm. A highly colored residual austenite and a needle-shaped martensite phase make up the hardened region. The hardened region is 1200 μm thick and has a hardness of more than 300 HV0.3. The study’s findings may improve the application and understanding of the arc quenching treatment procedure in the industrial sector. Full article

Single-layer spatial grid joints are crucial to structural safety, with commonly used welded hollow spherical joints and cast steel joints. However, these traditional joints face limitations, including a rigid design, excessive weight, and susceptibility to stress concentration. As engineering practices advance, these joints struggle to meet modern requirements. This paper introduces a generative method for designing rigid joints in single-layer spatial grid structures, based on Audze space-filling criteria. The method’s mathematical formulation is presented, followed by developing novel joint configurations by exploring various cross-sectional forms, retention mass, and geometric elements, while considering bending moments. A comparative analysis of static properties between the new and traditional joints shows promising results. The generative approach demonstrates significant innovation, producing lightweight, aesthetically pleasing, and structurally efficient joints. Compared to conventional welded hollow spherical joints, the new joints exhibit a 57% reduction in self-weight, a 51% decrease in maximum equivalent stress, and a 24% reduction in maximum displacement. This method enables versatile and optimized joint design for single-layer spatial grid structures, offering enhanced strength, safety, and aesthetic appeal. Full article

The article presents a method of developing a mathematical model of the arc surfacing process performed using the self-shielded flux-cored filler metal wire with the chromium cast iron (Fe15) weld deposit. A three-level design (static, determined, and complete) was used to determine the function of the test object, thus enabling the simulation of deposition rate in relation to wire feed speed and electrode extension. The deposition rate for the specified set of surfacing parameters amounted to between 4.31 kg/h and 11.25 kg/h. The study was also concerned with identifying the effect of the significance level of test factors and interactions between them on the resultant factor, as well as an assessment of the adequacy of the test object function. In relation to significance level α = 0.01, regression coefficients b₀, b₁, b₂, and b₁₁ significantly affected the deposition rate of the surfacing process. Coefficient b₂₂ was significant at a level of 0.40, whereas coefficient b₁₂ was significant at a level of 0.15. The mathematical model presenting the effect of wire feed speed and electrode extension, as well as interactions between them on the deposition rate of the surfacing process, was adequate for the adopted level of significance α = 0.05. Full article

External magnetic field (EMF)-assisted high-current CO₂ welding is beneficial for improving the large spatter and poor performance of the welding heat-affected zone for mild steels under high-current welding specifications. In this paper, the droplet transfer behaviors were determined using a high-speed camera on a self-developed magnetically controlled CO₂ welding system. Based on these welding specifications, a three-dimensional, transient, multi-energy field coupling welding system model to investigate the mechanism of the droplet and molten pool in EMF-assisted welding was developed. The microstructure and mechanical properties of the welded joint were systematically studied. The results show that the Lorentz force applied by the EMF to twist the droplet decreases the accumulated energy in the short-circuited liquid bridge and changes the liquid metal flow condition, both of which reduce the spatter by 7% but increase the welded joint hardness by 10% and tensile strength by 8%. Full article

The development of more recyclable materials is a key requirement for a transition towards a more circular economy. Thanks to exchange reactions, vitrimer, an attractive alternative for recyclable materials, is an innovative class of polymers that is able to change its topology without decreasing its connectivity. In this work, a bisphenol compound (VP) was prepared from saturated cardanol, i.e., 3−pentadecylphenol and vanillyl alcohol. Then, VP was epoxidized to obtain epoxide (VPGE). Finally, VPGE and citric acid (CA) were polymerized in the presence of catalyst TBD to prepare a fully bio−based vitrimer based on transesterification. The results from differential scanning calorimetry (DSC) showed that the VPGE/CA system could be crosslinked at around 163 °C. The cardanol−derived vitrimers had good network rearrangement properties. Meanwhile, because of the dynamic structural elements in the network, the material was endowed with excellent self−healing, welding, and recyclability. Full article