Welding in the World最新文献

Large portions of infrastructure buildings, for example, highway and railway bridges, are steel constructions and reach the end of their service life due to an increase of traffic volume. Repair welding can restore the current welded constructional detail with a similar fatigue strength. However, due to the increase of fatigue loading (traffic), an increase of fatigue strength is needed in such bridge structures. For this reason, the combination of repair welding and high-frequency mechanical impact (HFMI) treatment was investigated in this study in order to quantify the increase of fatigue life by combining both methods. For this, transverse stiffeners made of steel grade S355J2 + N were subjected to fatigue loading until a pre-determined crack depth was reached. The cracks were detected by non-destructive testing methods. Weld repair was realized by removing the material containing the crack and re-welded by a gas metal arc welding (GMAW) process, following that post weld treated was applied by HFMI-treatment and the specimens were subjected to fatigue loading again. Hardness profiles, weld geometries, and residual stress states were investigated for both the original and the repaired condition. In the repaired condition without additional HFMI treatment, a similar fatigue life than in the original condition is observed for the specimens. The repair-welded and HFMI-treated specimens reach a significant higher fatigue life compared to the repaired ones in the as-welded condition.

The geometry of objects by means of wire arc additive manufacturing technology (WAAM) is a function of the quality of the deposited layers. The process parameters variation and heat flow affect the geometric precision of the parts, when compared to the actual dimensions. Therefore, in situ geometry monitoring which is integrated in such a way to enable a backward control model is essential in the WAAM process. In this article, an attempt is made to study the effect of four input variables, namely voltage (U), welding current (I), travel speed and wire feed rate on the output function in the form of two geometrical characteristics of a single weld bead. These output functions which are determinant of the weld quality are width of weld bead (BW) and height of weld bead (BH). A machine learning approach is utilised to predict the bead dimensions based on the input parameters and to predict the parameters by assigning suitable scores. For predicting the bead dimensions, two models, namely linear regression and random forest, shall be utilised, whereas for the purpose of classification based on weld parameters, k-nearest neighbours model shall be employed. Through this work, a wide dataset of parameters in the form of input variable and output in the form bead dimensions are generated for 316LSi filler material which shall be used as a training data for a machine learning algorithm. Subsequently, the predicted parameters shall be cross-checked with actual parameters.

In this study, an image-based method was developed for hot-wire laser narrow gap welding. The welding process was monitored based on image information processed using semantic segmentation, a method of classifying images by pixel. To control the welding position, an experimental system was configured that automatically follows the welding position by recognizing the position of the welding groove from the image during welding. In monitoring weld defects, a method was developed to predict the lack of fusion occurring on the wall surface using brightness information near the wall surface. For the lack of fusion occurring at the bottom of the groove, a defect detection method was developed by monitoring the molten pool shape using semantic segmentation. Defects were generated by intentionally reducing the laser power, and the defects were monitored from images taken during processing. In the unstable state where the laser power was reduced, the shape in front of the molten pool became unstable, and the occurrence of defects was monitored by capturing the shape change. In conclusion, this research made it possible to control and monitor the welding process with a single camera.

Maraging steel (M250) is extensively used in aerospace industries for the fabrication of solid propellant tanks in the welded and repair welded condition. The purpose of the investigation is to study the effect of multiple weld repairs on the microstructure and mechanical behavior of the alloy. The microstructure of the alloy in the as-welded condition contains two distinct heat-affected zones (HAZ) with different contents of reverted austenite. The results indicate that increased weld repair reduced the weld strength from 1722 to 1405 MPa whereas elongation increased from 5.8 to 6.1%. Fracture toughness was found to increase from 79 to 87.2 MPa√m. This is due to the increased content of reverted austenite of HAZ, which is a result of heat experienced by the zone during welding. The location of failure was predominantly along the HAZ 2 which is the mechanically weaker zone of the weld joint as revealed by microhardness measurements. Further, minor improvement in corrosion resistance is found due to increased content of austenite in HAZ in repair weld conditions.

Additive manufacturing is becoming increasingly important for industrial production. In this context, directed energy deposition processes are in demand to achieve high deposition rates. In addition to the well-known laser-based processes, the electron beam has also reached industrial market maturity. The wire electron beam additive manufacturing offers advantages in the processing of copper materials, for example. In the literature, the higher energy efficiency and the resulting improvement in the carbon footprint of the electron beam are highlighted. However, there is a lack of practical studies with measurement data to quantify the potential of the technology. In this work, a comparative life cycle assessment between wire electron beam additive manufacturing (DED-EB) and laser powder additive manufacturing (DED-LB) is carried out. This involves determining the resources for manufacturing, producing a test component using both processes, and measuring the entire energy consumption. The environmental impact is then estimated using the factors global warming potential (GWP100), photochemical ozone creation potential (POCP), acidification potential (AP), and eutrophication potential (EP). It can be seen that wire electron beam additive manufacturing is characterized by a significantly lower energy requirement. In addition, the use of wire ensures greater resource efficiency, which leads to overall better life cycle assessment results.

The effects of Cr addition on the microstructure, mechanical properties, and corrosion behavior of two weld metals containing Ti or Mo within the Ni-Cu alloys used in high-speed train bogies were investigated. The results show that Cr can increase the acicular ferrite (AF) by about 15%, reduce the primary ferrite (PF) and the ferrite with second phase aligned (FSP), and slightly increase the M-A constituents in the weld containing Ti. Cr addition scarcely alters the AF, leads to a decline in PF and an increase in FSP, and causes a substantial increase in M-A constituents from 0.4 to 2.5% in the as-welded zone containing Mo. Meanwhile, it was found that Cr addition negatively affects weld toughness in the weld containing Mo due to the increase in the proportion and size of M-A constituents and the coarsening of inclusions. Regarding the corrosion resistance, Cr addition can promote the absorption of Cr on the surface of inclusions. This is the main reason for the reduction of the initial corrosion rate of the weld containing Mo, while this effect is attenuated in the welds containing Ti. In addition, Cr addition can densify the inner and outer rust layers, thereby reducing the corrosion rate of the welding rust layer.

This study investigates the impact of travel speed on the weld quality of AA7075-T651 aluminum alloy using the cold wire pulsed gas metal arc welding (CW-PGMAW) process. By maintaining a constant heat input of 0.4 kJ/mm while varying travel speed between 90 and 100 cm/min, the study examines the process’s influence on microstructure, porosity, and liquation cracking. Results demonstrate that CW-PGMAW effectively refines microstructure and reduces defect formation compared to conventional GMAW. While mechanical properties showed improvement, further optimization is necessary to achieve base metal equivalent properties. The findings contribute to the understanding of CW-PGMAW for challenging aluminum alloys and provide a foundation for future process enhancements.

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The hydrogen steel gas-shielded welding wire was utilized in the WAAM technique, and the microstructure, crystal structure, and properties of the parts generated by layer-wise deposition were analyzed and evaluated. The study revealed that the components exhibit good quality, devoid of significant defects, and demonstrate robust internal metallurgical bonding. The metallographic structure mainly consists of pearlite and ferrite. The distribution of microhardness in the parts is fairly consistent, with mean microhardness values of 196.6 HV_0.1 (transverse) and 196.7 HV_0.1 (longitudinal). The parts exhibit exceptional mechanical properties, with a transverse yield strength of 406 MPa, an elongation rate of 14.2%, and a longitudinal yield strength of 380 MPa, an elongation rate of 18.9%. At − 30 °C, the average transverse Charpy impact value is 95.7 J, and the average longitudinal is 117 J.

Laser welding offers distinct advantages over traditional methods: less heat impact, no filler metal needed, and strong weld penetration. It is efficient and cost-effective, perfect for joining materials like the stainless steel 301LN, and ideal for industries addressing climate change. This study delves into the impact of various operating parameters on weld quality, specifically focusing on microstructure and microhardness. Using the Taguchi method, it is designed an experimental setup to systematically analyze these factors. The microstructure analysis shows a unique grain structure in the weld bead and a small heat-affected zone (HAZ), indicating precise welding control. Weld penetration measurements correlated with specific operating parameters using microstructure imaging. The microhardness analysis further underlined the control over HAZ thickness, crucial for ensuring the integrity of the welded joint. Through analysis of variance (ANOVA), it is identified significant factors affecting physical properties, help to construct a mathematical model to quantify parameter influences accurately. Findings suggest that minimizing the focal spot diameter is key to optimizing weld penetration, albeit in a delicate balance with welding speed and laser power settings. Adjusting these parameters can also influence the chemical composition match between the weld bead and base material, crucial for structural integrity. For achieving the desired hardness close to the base material, specific parameter ranges are recommended: a beam oscillation amplitude of 1.45 mm, a beam oscillation amplitude between 2.82 and 2.97 kW, and a focal spot diameter above 0.34 mm. Findings offer practical insights for improving weld quality and efficiency in industrial applications.