Welding in the World最新文献

Through the analysis of the magnetic field around the arc, the feasibility of controlling the arc shape and performance by the external axial magnetic field is clarified. Combined with the derived mathematical expression of the alternating axial magnetic field generated by the energized solenoid, the magnetic field and its distribution were simulated with COMSOL Multiphysics and MATLAB software, and the effects of the magnetic head structure and parameters on the magnetic field and its distribution were determined. A magnetic head was designed and manufactured according to the simulation results, and the welding process experiments were carried out. The experimental results show that the high-frequency axial magnetic field can significantly compress the arc and improve the welding penetration.

CrS/NbC reinforced Co-based self-lubricating composite coatings were successfully prepared on the surface of Cr12MoV steel by high-frequency micro-vibration (HFMV) assisted laser cladding technology. The microstructure, phase composition, microhardness, and wear resistance of the composite coatings were studied by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), microhardness tester, and friction-wear tester. The results show that there were excellent metallurgical bonding and free of pores and cracks in the CrS/NbC Co-based self-lubricating composite coating with 10% WS₂ prepared by laser cladding at 552 Hz vibration frequency. The appropriate vibration frequency could cause strong convection in the molten pool and refine the microstructure, which made NbC hard particulates and CrS lubricants to be evenly distributed in the composite coating. In particular, the refined CrS and NbC in the upper area of the coating were combined with each other to form a dense network microstructure. Moreover, the hardness of the coating prepared at the vibration frequency of 552 Hz was significantly improved due to its excellent microstructure compared with the without vibration and 985 Hz vibration frequencies and the maximum hardness reached 652.8 HV_0.5. Its wear resistance was also significantly improved, and the friction coefficient of the coating was reduced to 0.451. Only abrasive wear and slight adhesive wear were observed on the coatings surface, and the tearing layer and wear loss of grinding defects were significantly reduced.

Climate change exacerbates the need for resource-efficient and cost-effective production processes across manifold industries, including the field of electrical connections. This specific field is characterized by a conflict of objectives, i.e., weight reductions while maintaining joint strength and electrical conductivity. From a material point of view, the use of aluminum as a conductor material is suitable for this application, as it is lighter than copper, a classical conductor material. Electrical conductors are often used in the form of flexible cables, so-called stranded wires. This type of conductor as well as the fact that the sole use of aluminum in electrical systems is not feasible, e.g., because the predetermined connection terminals of power electronic components are made of copper, creates a substantial demand for dissimilar aluminum-copper cable arrester joints. However, traditional fusion-based welding processes have proved incapable of reliably producing these dissimilar aluminum-copper joints because of thermophysical effects and chemical incompatibilities, the latter eventually leading to the formation of intermetallic phases. These phases adversely affect the quality of the joint in terms of both mechanical and electrical performance. Yet, magnetic pulse welding, a pressure welding process, is ideally suited for producing dissimilar metal joints on the basis of a low energy input during the welding process. Consequently, the formation of intermetallic phases is restrained. However, magnetic pulse welding has not been sufficiently investigated for the reliable contacting of stranded cables to tubular arresters. As a result, this paper focuses on the fabrication of tubular stranded cable arrester joints using magnetic pulse welding. To shed light on possible material combinations, aluminum-to-aluminum and copper-to-copper joints as well as their dissimilar counterparts are welded. Subsequently, the joints are characterized with regard to their microstructure and quasi-static material strength. Electrical characterization comprises the four-wire Kelvin measurement method to evaluate the resistance of the electrical joints. The results demonstrate that magnetic pulse welding is ideally suited to join the aforementioned material combination and joint configuration due to its process characteristics eventually leading to material continuity. As a result, the stranded wires are welded to the tubular arresters rather than crimped. Consequently, a comparative analysis of the joint properties with those of the joining partners shows that the measured electrical resistances and mechanical tensile forces may be considered very good.

Welding of AlSi10Mg alloys fabricated by additive manufacturing (AM) has been recently conducted to meet the demands for joining or repairing them. However, high susceptibility to porosity occurring in weld metal (WM) poses a significant challenge for fusion welding of AM AlSi10Mg alloys. The laser metal deposition (LMD) process has emerged as a promising welding solution due to its low dilution rate for reducing the porosity. In this study, LMD welding of AM AlSi10Mg alloys was carried out employing different heat inputs with five and eight tracks. The study systematically assessed the impact of heat input on porosity, microstructure, and mechanical properties of the welded joints. The results show that the decrease of heat input from 180 to 75 J/mm results in a substantial reduction in porosity from 7.0 to 2.1%. This reduction leads to a 29.4% increase in ultimate tensile strength (UTS) and an 11.7% increase in elongation index (EI). Furthermore, the upper region of joints with eight tracks possessing low heat input displays lower porosity and superior mechanical properties than the bottom region with relatively high heat input. The WM with eight tracks exhibits refined α-Al cells and Si-rich eutectic phases, improved connectivity of Si-rich networks, and increased solid solution strengthening, compared to the five-track joints with higher heat input. As a result, low heat input of the upper region in the LMD welded joints has been effective in minimizing hydrogen pores, enhancing WM microstructure, and improving the mechanical properties of welded joints in AM AlSi10Mg alloys.

Weld defect detection is an important task in the welding process. Although there are many excellent weld defect detection models, there is still much room for improvement in stability and accuracy. In this study, a lightweight deep learning model called WeldNet is proposed to improve the existing weld defect recognition network for its poor generalization performance, overfitting, and large memory occupation, using a design with a small number of parameters but with better performance. We also proposed an ensemble-distillation strategy in the training process, which effectively improved the accuracy rate and proposed an improved model ensemble scheme. The experimental results show that the final designed WeldNet model performs well in detecting weld defects and achieves state-of-the-art performance. Its number of parameters is only 26.8% of that of ResNet18, but the accuracy is 8.9% higher, while achieving a 24.2 ms inference time on CPU to meet the demand of real-time operation. The study is of guiding significance for solving practical problems in weld defect detection, and provides new ideas for the application of deep learning in industry. The code used in this article is available at https://github.com/Wanglaoban3/WeldNet.git.

Keyhole Tungsten inert gas (K-TIG) welding can realize single-sided welding and double-sided forming. However, due to the influence of gravity, undercuts always occur in K-TIG horizontal welding. In order to expand the application scenarios of K-TIG and achieve automatic welding, a magnetic controlled K-TIG horizontal automatic welding system is proposed in this paper. A longitudinal magnetic field is used to weaken the influence of gravity and improve welding quality. The OCR (Object-Contextual Representations)-SVM (support vector machines) model is proposed to identify the welding penetration states during K-TIG horizontal welding, whose accuracy rate is 93%. In order to solve the problem of slow convergence and poor learning of difficult-to-learn classes, a loss function called Unified Focal loss was used, which achieves a mIoU (the mean of Intersection over Union) score of 91.48%.

Using different rotational speeds in friction stir welding is a new way to improve the microstructure and the impact toughness of the weld. However, the specific speed most suitable for Q1100 ultra-high strength steel has yet to be discovered. Here, friction stir welding of 8 mm thick Q1100 ultra-high strength steel was carried out at constant welding speeds of 375 rpm, 475 rpm, and 600 rpm. With the aid of an optical microscope, a microhardness tester, an impact tester, a tensile tester, and a field emission scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) system, the microstructure characteristics such as the carbide precipitation phase in the original austenite grains, the dislocation pattern within the martensitic lath, and the fracture morphology of the impact specimens were analyzed. The results show that the overall hardness and impact toughness of the advancing side and retreating side of the stirring zone show a trend of first increasing and then decreasing with the increase of the rotational speed, in which the hardness value of the advancing side of the same speed is higher than that of the retreating side. In contrast, the impact toughness is higher on the retreating than on the advancing side. At 375 rpm, the carbide is needle-like, the martensite bundle is narrow, and there are more high-angle grain boundaries, the hindrance to crack expansion is significant, and the toughness is higher relative to the base material. At 475 rpm, the martensite bundle widens, the number of high-angle grain boundaries increases, both the advancing and retreating sides are ductile fractures with small tearing dimples of varying sizes distributed around the large tearing dimples, and the toughness increases relative to 375 rpm. When the speed at 600 rpm, the carbide is coarser, the martensite bundle is more expansive than at 475 rpm, the number of high-angle grain boundaries is reduced, the tearing toughness dimples are unevenly distributed, and the toughness is reduced. Compared to 375 rpm and 600 rpm, the joint cooling rate is either faster or slower, and the 475 rpm cooling rate is just right in between. Meanwhile, when the rotational speed at 475 rpm, the average hardness of the joint is 375 HV, the impact work at − 40℃ is 51 J, and its tensile strength and elongation are 998 MPa and 3.09%, respectively, with the best comprehensive mechanical properties.

In this work, the technical feasibility of micro-friction stir lap welding to join 0.5-mm ultra-thin aluminium and copper sheets was studied. After identifying the processability windows of important parameters such as plunge depth, welding speed and material positioning, the effect of welding speed to join the ultra-thin AA5052 and C11000 sheets was assessed. Welding speeds were varied from 50 to 400 mm/min. The relationship of the welding speed to the joint quality, such as microstructure, tensile lap shear strength, weld surface roughness and joint electrical resistance was elucidated. It was found that the dissimilar sheets only joined when the copper sheet was placed on top of the aluminium sheet. Feasible welding was found at welding speeds of 50 mm/min and 70 mm/min, a constant rotational speed of 1500 rpm and a plunge depth of 0.55 mm. The welds possessed similar average tensile lap shear strength of 16 to 18 MPa but differed in microstructure and joint electrical resistance. More visible stir zones with lamella bands were found in the microstructure of welds produced at 50 mm/min, indicating a higher degree of mixing, albeit with excessive flashes and tunnel defects near the joint interface. On the other hand, the welds produced at 70 mm/min exhibited limited mixing and lamellar intermetallic compounds. Tunnel defects were mostly at the advancing side within the copper layer, and hook defects were absent. With selected processing parameters, micro-friction stir welding ultra-thin copper sheets to aluminium sheets is demonstrably feasible for less critical applications.

A transient 3D numerical model was established to investigate the multi-coupling transport phenomena in the Al-alloy GMAW bead-on-plate welding process. An integrated self-adaptive distribution mode of “arc current density-arc pressure-electromagnetic force-arc heat” was proposed to adapt to the evolution of the surface morphology of the molten pool. The heat and force state of the molten pool was analyzed to investigate its influence on the bead formation. The results showed that the arc pressure and droplet impingement promoted the backward flow of the liquid metal, thus forming the gouging region. It decreased the concentration of the arc current density, thereby reducing the superheat of the liquid metal and facilitating the filling of the weld toe. Based on the characteristics of the temperature and velocity fields, the characteristics of weld formation in the three stages of arc preheating, melting, and solidification were analyzed. This study revealed the relationship between molten pool behavior and bead formation, promoting the implementation of Al-alloy GMAW in welding and additive manufacturing.