Welding in the World最新文献

Friction surfacing (FS) is a solid-state deposition process in which layers are deposited on a substrate surface by frictional heat and severe plastic deformation of a consumable stud material below its melting temperature. Bonding occurs due to accelerated diffusion. The deposition of several layers on top of each other is referred to as multi-layer FS (MLFS), a promising candidate for additive manufacturing (AM) as it offers advantages over fusion-based AM. In this study, the MLFS process for the precipitation-hardenable alloy AA2024 is investigated regarding the influence of environmental process conditions, i.e., preheating of the substrate like other AM processes as well as underwater and room temperature experiments. The influence of ambient conditions on the process behavior, the layer geometries, the microstructure, and the mechanical properties is shown. Preheating the substrate leads to an overall higher process temperature (424.1 °C), resulting in thinner and wider layers, larger grains, an overaged microstructure, and a smooth hardness transition in the MLFS stacks from top (140 HV0.1) to bottom (95 HV0.1). The lower the process temperatures, e.g., for underwater FS (326.5 °C), the thicker and less wide the layers and the smaller the grains. The hardness shows a periodic pattern at the layer interface, which is more pronounced at lower process temperatures, i.e., the hardness values range from 100 HV0.1 to 150 HV0.1.

Friction stir welding (FSW) can be challenging for joining thick heat-treatable aluminum alloy plates due to limitations with the single-pass method and heat distribution. To address these challenges, the double-sided FSW (DS-FSW) method was developed. It allows for welding the unwelded side of the plate which cannot be reached by the pin’s height at the first pass. DS-FSW has been proven to overcome many challenges and has been found to be a great solution for FSW in welding thicker plates. During DS-FSW implementation, some drawbacks related to machine parameters were discovered but were addressed through tool development. However, the time efficiency issue was only solved when two identical tools were used. This approach, known as simultaneous DS-FSW (SDS-FSW), significantly reduced processing time. It also led to improved microstructures and mechanical properties based on survey results. The dual-tool simultaneity provided flexibility for dwelling into the workpiece in different ways, such as parallel side-by-side, tandem in-line, and staggered transverse, which were mostly used for lap welding in single-pass FSW and showed remarkable performance. Regardless of the dwelling method used, the impact of process parameters in FSW must always be taken into consideration, emphasizing the importance of the tool profile and machine-related parameters being in optimal working order.

Two carbon low alloy steels 42CrMo and 36Mn2V were successfully jointed using continuous drive friction welding. The effects of forging pressure and post-weld heat treatment on microstructure and mechanical properties of joints were investigated in detail. Results reveal that with increasing the forging pressure, the tensile and yield strength increase firstly and then decrease. The as-welded joint with the highest yield strength (708 MPa), largest elongation (14.2%), and high impact toughness (57.24 J) were obtained with the 35 MPa forging pressure. After post-weld heat treatment, the joint yield strength, elongation, and impact toughness were increased to 798 MPa, 18.1%, and 71.02 J, respectively. The microhardness measurement results indicate that the as-welded joints show higher Vicker hardness than the two base metals. After post-weld heat treatment, the microhardness was decreased owing to martensite elimination. The above findings provide a basis for the implementation of friction welding of dissimilar steels used for drills in the coal-mining industry.

An attempt has been made to join aluminium alloy (AA) 2219 and titanium alloy Ti-6Al-4V by solid-state diffusion bonding (SSDB), as this process ensures no macroscopic deformation during the joining. The quality of SSDB joints formed at the bonding temperature in the range of 500–540 °C is evaluated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The bonding strength of the joints is evaluated by shear test, and hardness is tested using the Vickers microhardness method. It is observed that the hardness and shear strength values are increased with an increase in bonding temperature owing to the formation of intermetallic compounds at the joint interface like Al₃Ti, Al₂Ti and AlTi. Maximum shear strength of 82 MPa and hardness of 286 HV_0.05 are observed for the specimen bonded at 540 °C.

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.