Welding in the World最新文献

The weld toe is known to be a critical point of fatigue failure in many welded constructions. Especially for research purposes but also for improving fatigue life predictions, the weld toes geometry is often described by a set of parameters, including the weld toe radius and the flank angle. There is no universal agreement on the definition of the geometry parameters as well as on measuring routines. To get an overview over used techniques and comparability between research labs, a comprehensive round robin study was conducted over the past years. Two measuring tasks were given to the participants. Part A: A machined specimen with well known geometry inspired by a cruciform joint was analyzed and the results were compared with the actual dimensions of the specimen. Part B: Welded specimens with unknown geometry were measured by the participants and the results were bench-marked against each other. The present study summarizes the findings of Part A. The study gives an overview over used measuring techniques, the influence of measuring equipment and the comparability of the results in the scientific community. Most of the participants achieved good results with their respective measuring methods for radii larger than 1 mm. Smaller radii tend to be overestimated.

This study uses a finite element method based simulation methodology for in-situ railhead repair welding to investigate how welding process parameters impact the repaired rail quality. The methodology includes material modeling with cyclic plasticity, phase transformations, transformation-induced plasticity, and multi-phase homogenization. The weld process modeling includes a 3D heat transfer analysis and a 2D Generalized Plane Strain (GPS) mechanical analysis. The Heat source model used in the thermal simulation is calibrated using measurements from a repair welding experiment. To assess the performance of the repaired rail, mechanical rolling contact simulations are performed to estimate the risk of fatigue crack initiation. The process parameter study is based on the Swedish stick-welding railhead repair procedure and focuses on factors affecting the repair quality, such as preheating and operation temperature conditions as well as variations in repair geometry. Significant findings highlight both the inherent robustness of the process and regions susceptible to parameter variations. Specifically, the powerful final zig-zag weld passes provide effective resilience against variations in additional heating, and the start and end stretches of the repair welding are the most susceptible to parameter variations. Chamfered and deeper cutout repair geometries are found to be effective in mitigating adverse effects. In agreement with field observations, the simulations identify the fusion zone of the base and weld filler material as the critical region of the repaired rail in operation. This is attributed to the integrated effects of unfavorable microstructures, longitudinal tensile residual stresses from repair welding, and tensile stresses during operational traffic loads.

The study aimed to assess the performance of several unsupervised machine learning (ML) techniques in online anomaly (The term “anomaly” is used here to indicate a departure from expected process behavior which may indicate a quality issue which requires further investigation. The term “defect detection” has often been used previously but the specific imperfection is often indirectly inferred.) detection during surface tension transfer (STT)-based wire arc additive manufacturing. Recent advancements in quality monitoring for wire arc manufacturing were reviewed, followed by a comparison of unsupervised ML techniques using welding current and welding voltage data collected during a defect-free deposition process. Both time domain and frequency domain feature extraction techniques were applied and compared. Three analysis methodologies were adopted: ML algorithms such as isolation forest, local outlier factor, and one-class support vector machine. The results highlight that incorporating frequency analysis, such as fast Fourier transform (FFT) and discrete wavelet transform (DWT), for feature extraction based on general frequency response and defined bandwidth frequency response, significantly improves performance, reflected in a 14% increase in F2 score, compared with time-domain features extraction. Additionally, a deep learning approach employing a convolutional autoencoder (CAE) demonstrated superior performance by processing time-frequency domain data stored as spectrograms obtained through short-time Fourier transform (STFT) analysis. The CAE method outperformed frequency domain analysis and traditional ML approaches, achieving an additional 5% improvement in F2-score. Notably, the F2-score (The F2 score is the weighted harmonic mean of the precision and recall (given a threshold value). Unlike the F1 score, which gives equal weight to precision and recall, the F2 score gives more weight to recall than to precision.) increased significantly from 0.78 in time domain analysis to 0.895 in time-frequency analysis. The study emphasizes the potential of utilizing low-cost sensors to develop anomaly detection modules with enhanced accuracy. These findings underscore the importance of incorporating advanced data processing techniques in wire arc additive manufacturing for improved quality control and process optimization.

In this paper, the welding of T2 copper and Al1060 was realized by vacuum diffusion welding process. The microstructure evolution, mechanical properties, and corrosion resistance of Cu/Al diffusion bonding layer were explored. The results show that intermetallic compounds Al₂Cu, AlCu, and Al₄Cu₉ generate at the joint under the welding condition of holding for 60 min at 530 °C. When the holding time reaches 90 min, a new phase of Al₂Cu₃ generates, and the diffusion bonding layer evolves into a four-layer structure. The thickness of diffusion layer increases with the extension of holding time and is affected by the body diffusion. The shear strength of the joint increases first and then decreases with the extension of holding time. The maximum shear strength of 20.91 MPa can be obtained under the holding time condition of 60 min, and fracture mainly occurs between Al₂Cu and AlCu phases. Nanoindentation hardness and elastic modulus of intermetallic compound phase are much higher than those of copper and aluminum matrix. Specifically, Al₄Cu₉ phase exhibits the largest nanoindentation hardness and elastic modulus of 11.062 GPa and 132.8 GPa. The corrosion resistance of diffusion bonding layers is significantly different from that of the base material. Compared with copper, the corrosion potential of each diffusion layer and aluminum matrix is relatively lower. The corrosion rates of diffusion layers and base materials are in descending order of Al > Al₂Cu > AlCu > Al₄Cu₉ > Cu.

In the present research, the possibility of using friction stir deposition (FSD) for the additive manufacturing (AM) of aluminum parts has been evaluated and checked. For this purpose, consumable tool technique was used for depositing bulk samples in the shape of linear and cylindrical parts. The current friction stir additive manufacturing (FSAM) process was carried out through the deposition of AA6061-T6 consumable rods on a substrate of the same material. For each of the linear and cylindrical types, six samples were deposited in three layers using different production parameters. FSD tool speeds including rotational, linear, and vertical were the production parameters. To evaluate the additive manufactured parts, appearance, microstructure, hardness, wear properties, and corrosion resistance were inquired. The apparent appearance characteristics for both linear and cylindrical samples were continuous layers with sufficient thickness without cracks and cavities. In terms of microstructure characteristics, the hot plastic deformation during FSAM caused enormous grain refinement (~ 560%) through the dynamic recrystallization and decreasing the precipitate size (~ 31%) by the dissolution of precipitates in the matrix, compared with the AA6061-T6 consumable rods. These microstructural changes and production parameters were correlated with the amount of frictional heat generated during the process. In order to find this correlation, the change in amount of heat input by changing the production parameters and its effect on the microstructural characteristics were discussed. For both linear/cylindrical samples, by increasing the consumable tool rotational speed and decreasing its linear/vertical speed (increase in deposition time), the heat input increased, which led to more dissolution of precipitates (decreasing their size) and grain growth (reduction of grain boundaries as the preferred precipitation sites). Decreasing the precipitate size and precipitate content reduced the three-body wear mechanism and lowered the corrosion prone areas, which improved the wear and corrosion properties, respectively. Although the dissolution of precipitates reduced the hardness of samples compared to the hardness of consumable rods (AA6061-T6), the enormous grain refinement caused by FSAM compensated this deficiency. Finally, the properties of additive manufactured parts are as follows: relatively good hardness (~ 60 HV), excellent wear rate (about 3 µgr/N.m), low friction coefficient (0.6–0.8), and excellent corrosion rate (less than 5 mpy).

The development of suitable welding processes is required to meet the ever-increasing demands on joining processes, particularly for lightweight construction and increasing environmental awareness. Friction stir welding (FSW) represents a promising alternative to conventional fusion welding processes, particularly for the joining of low-melting-point materials such as aluminium and magnesium alloys, which present a number of challenges, including the formation of pores and the occurrence of hot cracks. The central element of the process is the friction stir welding tool, which consists of a shoulder and a probe. The rotation and the simultaneous application of pressure during the joining process create a friction-based heat input through the tool. The excellent mechanical properties resulting from dynamic recrystallisation during the welding process are a major advantage of the process. As a result, strengths comparable to those of the base material can be achieved. However, FSW is subject to process-specific challenges, including high process forces, which result in the fabrication of complex and robust devices. Additionally, high dynamic loads on the friction stir welding tools must be considered. In many cases, the design of friction stir welding tools is based on empirical data. However, these empirical values are machine-, component- and material-specific, which often results in under- or overmatching of friction stir welding tools. Sudden probe failure, component scrap, and low process reliability are the direct consequences of undermatching. Overmatching results in enlarged tools with limited accessibility, high heat input, and high process forces, leading to component deformation. The aim of this study is to determine the load on the probe by separating the forces and torque of the shoulder and the probe in order to be able to make statements about the load acting on the probe and the resulting stress state. The knowledge of the stress state can be employed to design friction stir welding tools, both statically and dynamically, for a specific welding task. A strategy was devised to distribute the load exerted on the shoulder and probe. To this end, the length of the probe was gradually reduced between the welding tests. The investigations were carried out with a force-controlled robotized welding setup in which AA 6060 T66 sheets with a thickness of 5 mm were welded. A Kistler multicomponent dynamometer type 9139AA allows to measure the Cartesian forces to be recorded in the x-, y-, and z-directions with a sampling rate of 80 kHz. The weld seam properties were determined by visual and metallographic inspections as well as tensile and bending tests in accordance with DIN EN ISO 25239–5.

An effect of distances between the flyer plate and the explosive (d = 30, 40, 50, and 60 mm) on the welded interfaces of tin (Sn)–aluminum (Al) plates is discussed. Sn (flyer) and Al (base) plates were welded by adopting an underwater explosive detonation system. The interfaces were characterized using a metallurgical microscope and scanning electron microscope (SEM). As the distance (d) was increased, a change in the wavy parameters (amplitude and wavelength) of the interfaces was observed. The experimental results for welded Sn/Al plates were investigated based on the welding window (WW) constructed using numerical software (AUTODYN-2D). Based on the data, window parameters (the collision point velocities, V_c, and the collision angles,β) for welded Sn and Al plates were found to be in agreement with numerical data, and plates welded at a water distance of 60 mm exhibited good quality of welding.

In compact box-shaped steel structures, partial penetration welds are frequently selected as the welding technique, and root fatigue failure might manifest in these joints. In order to ensure the structural integrity of steel structures, it is necessary to develop an assessment approach for evaluating the efficacy of post-weld heat treatment (stress relief) in enhancing the fatigue strength of root-failed welded joints. In this study, bending fatigue experiments employing stress ratios of R = 0 and − 1 have been carried out on as-welded and stress-relieved welded joint specimens. The test objects include root-failed plug weld specimens, as well as toe-failed out-of-plane gusset weld joint and T-joint specimens. The welding residual stresses near the root notch and weld toe are measured by X-ray diffraction technique. The assessment of the mean stress effect on fatigue strength has been examined through the utilization of the modified MIL-HandBook-5D equivalent stress range. The equivalent stress range is evaluated by using two fatigue assessment stresses: structural stress and elastic–plastic local stress. It has been confirmed that all fatigue test results, irrespective of the failure mode or the joint type, whether from the as-welded or stress-relieved specimens, can be closely approximated using a single S–N curve with either definition of the equivalent stress. This outcome indicates the accomplishment of assessing the mean stress effect on the fatigue strength of welded joints with various failure modes and joint types.

In this research, dissimilar friction stir welding of AZ31 magnesium alloy and St37 steel sheets was performed to investigate the effect of Zn, Cu, and brass interlayers on the microstructure and mechanical properties of the joint. After conducting microstructural and mechanical evaluations, welding with a Zn interlayer exhibited the best strength and bonding efficiency, achieving 161 MPa and 60%, respectively. Since mechanical and metallurgical bonding at the interface plays a complementary role in improving welding properties, the presence of the Zn interlayer, by deoxidizing and enhancing reactions at the interface, increases the thickness of the Fe-Al-based intermetallic compound layer from 110 nm in welding without an interlayer to 300 nm. This results in improved mechanical properties of the welds. Examination of the fracture surfaces from the tensile test samples shows that all samples exhibit brittle fracture, except for the sample with the Zn interlayer, which displays a combination of ductile and brittle fracture.