Welding in the World最新文献

In V groove butt welding with a ceramic backing material, the molten pool should penetrate well. Regardless of the gap fluctuations, the molten pool must maintain a good penetration shape. For this purpose, the molten pool state is detected using ResNet50 as one of the deep learning. The molten pool using a CMOS camera is taken. Fundamental experiments are performed, and images are collected for learning of ResNet50. Good estimation results are obtained for untraining data. The gap and its center are detected processing the molten pool images. The seam tracking is carried out using PI controller, with inputs being the difference between the wire tip and the gap center, and the output is Y axis position. The weaving width is adjusted to fit the gap. The molten pool state is controlled adjusting the travel speed of the welding torch, to keep constant the arc position, because the state of the molten pool depends on the arc position. If there is gap fluctuation as the disturbance and the reference of the arc position is same, it is difficult to get the same penetration of the molten pool. Therefore, the reference according to the output of ResNet50 is adjusted. Molten pool control is based on PI controller with the input is the difference between the arc position and its reference, and the output is the travel speed. The control performance is verified in a case where the gap varies from 7 to 3 mm, and good results are obtained.

Welding of dissimilar alloys is challenging due to differences in their physical and chemical properties. The main problem while joining dissimilar alloys is intermetallic compound (IMC) formation, which affects the weld quality. Controlling the heat input is necessary to minimize the formation of IMC. This work uses cold metal transfer (CMT) welding with low heat input. However, the application of CMT welding is limited to thin sheets due to low depth of penetration (DOP). Activated flux can improve the performance of CMT welding, thus improving the DOP and minimizing the weld width (WW) by arc constrict mechanism. In this investigation, the SiO₂ was used as an activated flux. The process parameters used in this study are welding current and welding speed, which were used to optimize tensile strength, hardness, DOP/WW ratio, and heat input. Numerous experiments were conducted as per the design of experiment using response surface methodology. The optimal input parameters from various experiments are a welding current of 150 A and a welding speed of 8.295 mm/s. The scanning electron microscope was used to analyze the microstructure of weld specimens. Energy dispersive spectroscopy and X-ray diffraction were used for elements and phase analysis.

The local geometry of the weld toe or the weld seam has a high influence on the fatigue strength of welded joints. Two main parameters for the geometrical description of the weld toe are the weld toe radius and the weld toe angle. Currently, there is no uniform definition or standardized measurement approach for the assessment of these parameters. For this reason, the presented extensive round-robin (RR) study focusses on the influence of different evaluation techniques and measurement systems regarding the mentioned parameters based on 3D surface scans. In total, 20 participants take part in this two stage RR (19 participants in the second part). In this work, the results of the second part (part B) of the RR, namely the evaluation of weld toe radius and weld toe angle on real welded joints, are presented, where the actual weld toe geometry is not known a priori. For this, 22 data sets were evaluated. The data sets consist of measured values for the radius and angle of the weld toe in relation to the position along the weld seam. In general, significant variations are determined for the evaluated weld geometry parameters, especially for the weld toe radius. It is also shown that the condition of the weld toe transition has a high influence on the parameter. Particularly for weld seams with a low weld toe angle, the measurement results for the radius of the individual participants show high variations. For small weld toe radii, the results are quite comparable between the participants. The results for the weld toe angle are comparable for flat welds, but a wide range of results is observed for sharp weld toes. The degree of automation of the measurement method also has a high influence on the results. The most accurate results are expected from manual measurements, while the fully automatic and semi-automatic methods show larger deviations.

The paper presents the results of research on artwork joints of considerable thickness (10 mm). Butt welds in artworks are always difficult to perform because access to the joint is often one-sided. Traditional arc welding technologies are of limited use for such one-off production tasks, as full access to the joint is required and after welding the bulge must be cleaned from all sides of the bar, which is often unacceptable. Existing brazing technologies require a controlled gap between the joining surfaces, which is impossible to achieve for a wide variety of joints in art designs. Increasing the gap results in a decrease in the mechanical properties of the structure. A synergistic combination of welding and brazing using TIG technology can ensure a high-quality joint for thick bars of art structures. For such joints and conditions, the technology of high-temperature arc (TIG) brazing with partial melting of the parts to be joined and subsequent introduction of brazing alloy (CuSi3) into the metal pools of the parts to mix the liquid metal of the parts and the brazing alloy was developed. The developed technology makes it possible to fill the gap between the surfaces of bar-type parts with one-way access in the flat position, with minimal need to clean up solder that has protruded beyond the part.

In hybrid additive manufacturing, components or semi-finished products manufactured by conventional primary forming are enhanced or modified by additive manufactured structures. However, systematic investigations focusing on the critical transition area between the specific properties of the substrate (like high-strength) and the additively manufactured component, made of specific filler material, are still lacking. The focus of the present study was to determine the influence of heat control on the ∆t_8/5 cooling time, the distortion, the mechanical properties, and the residual stresses in the transition area of hybrid-additive components. This contributed to the knowledge regarding the safe avoidance of cold cracking, excessive distortion, a reduction in yield stress, and the implementation of hybrid DED-arc manufacturing. The heat control was varied by means of heat input and working temperature such that the ∆t_8/5 cooling times corresponded to the recommended processing range. The heat input has a greater influence on the cooling time in the transition area than the working temperature. Working temperature and the total energy applied per layer have a significant effect on component distortion. The lowest working temperature of 100 °C in combination with the highest total energy per layer leads to significantly greater distortion compared to manufacturing with a high working temperature of 300 °C and low total energy per layer. In addition, the longitudinal residual compressive stresses in the sensitive transition area are reduced from − 500 MPa to approx. − 200 MPa by adjusting the working temperature from 100 to 300 °C. Such complex interactions must be clarified comprehensively to provide users with easily applicable processing recommendations and standard specifications for an economical hybrid additive manufacturing of components made, for example, of high-strength steels in the transition area.

Joining of dissimilar AZ31 Mg alloy and Cu- 8Zn alloy by using zinc interlayer through Friction Stir Welding (FSW) has been studied for the first time. The process parameters include 1200 rpm rotational speed and 20 mm/min traverse speed. Microstructural characterizations were performed to study material flow behavior, grain refinement and IMCs formation whereas, mechanical characterization includes hardness and tensile tests. SEM EDS and XRD were used for identification of phases and fracture behavior. The study revealed that for direct joining of Mg/Cu, the stir zone (SZ) mainly consisted of two-phase region containing δ-Mg and Mg₂Cu along with fragments of Cu particles. Small amount of MgCu₂ was also observed in the form of intercalated layer along with Cu. Voids and tunnelling defects were also observed. On the other hand, the application of Zn interlayer has completely modified the structure of SZ which contains well distributed mixture of δ-Mg and MgZn. A very thin layer of MgZn₂ and MgO was observed in the SZ. Average tensile strength of Mg/Cu with Zn interlayer has improved to 93 MPa which is the highest joint strength as compared to the previously reported joint strength of Mg/Cu weld.

A 42SiCr experimental steel was heat-treated by the quenching and partitioning (Q&P) heat treatment to achieve a combination of high strength and ductility. The associated microstructure is characterized in literature by finely distributed martensite laths with a small volume fraction of retained austenite embedded. The goal of this work is to provide a comprehensive characterization of the mechanical properties of all subzones in the heat-affected zone (HAZ) of welded 42SiCr-Q&P steel. Dedicated microspecimens were subjected to a specifically selected thermal cycle in a dilatometer and characterized by mechanical testing and microstructural assessment. One specimen series is dedicated to the assessment of the mechanical properties of the material after welding; another four specimen series represent some carefully selected strategies to mitigate adverse effects of welding. Tensile testing revealed a decrease in yield strength in the HAZ by up to 35%. The ductility of the material showed inverse behavior. Material in the supercritical zone shows > 2000 MPa of ultimate strength, but at the same time is very brittle. The most remarkable result showed that the embrittlement in the supercritical zone can be successfully mitigated by holding the material at temperatures in the range of 200–250 °C for 5 min upon cooling, resulting in a yield strength of around 1400 MPa along with a ductility of > 10%, restoring the desired property combination. This very promising observation suggests fusion welding of 42SiCr-Q&P might be possible by means of preheating, maintaining the superior mechanical properties of Q&P in the weld.

Tungsten inert gas (TIG) welding is recognized as a high-quality, versatile, and cost-effective welding method. However, the occurrence of humping defects significantly restricts its progression toward higher efficiency. This study investigates the impact of surface tension variations on the formation of humping defects in stainless steel high-speed TIG welding. Through a combination of numerical simulations and experimental comparisons, the study reveals the formation mechanisms of several typical humping weld profiles. The results indicate that the interplay between surface tension and molten pool temperature is a critical factor influencing the occurrence of humping defects. In the thin layer of the weld pool, the backflow of molten metal is obstructed, forming a “stagnation zone.” Here, the liquid metal solidifies prematurely, dividing the weld pool and contributing to humping formation. Variations in weld pool flow dynamics, influenced by surface tension, are the primary reason for different humping morphologies. Adjusting the surface tension state of the molten pool can effectively suppress humping defects, alter the molten pool morphology, and enhance welding efficiency without additional heat input.

The role of chemical composition on the presence of δ-ferrite in P91 weld metal in the as-welded condition was studied by systematically varying five alloying elements (Cr, Ni, Mn, Si, and Mo) in 28 gas–metal arc welds. The effect of thermal treatment on the δ-ferrite content was also investigated. Metallography analysis of the as-welded beads showed that 18 of the 28 welds contained 0.3 to 6.2% δ-ferrite in martensite. Sixteen of the 28 welds fully complied with chemical composition specifications, including the limit of the sum of (Mn + Ni). Of the sixteen welds that complied with the AWS A5.28/A5.28 M:2022 (ER90S-B91) chemical composition specification, thirteen contained δ-ferrite. Based on these results, lower specification limits for Mo and Si are proposed to ensure a fully martensitic microstructure. Empirical formulae were applied to evaluate their accuracy in predicting the P91 as-welded microstructure: ten of the 28 welds (36%) were incorrectly predicted. Based on these results, the recommended Schaeffler Cr_eq and Kaltenhauser ferrite factor maximum limits should be lowered to 11.5 and 6, respectively, to limit the presence of δ-ferrite in the P91 as-welded microstructure. Phase-transformation temperatures were evaluated against the amount of δ-ferrite in beads in the as-welded condition. It was observed that a wider (Ae₄ − Ae₃) temperature range was beneficial in suppressing δ-ferrite in the final as-welded microstructure. Higher peak temperatures and slower cooling rates during welding also reduced the amount of δ-ferrite in P91 weld metal.

Welded structures are subjected to various repetitive loads during operation. Such repeated loads may initiate fatigue cracks and eventually cause fatigue failure in structures. Fatigue failure prevention is one of the most important issues to be carefully considered in the assessment of the structural integrity. Therefore, numerous studies have been conducted on fatigue performance evaluation of welded structures. During actual operation, various mean stresses act on welded structures, and these mean stresses have a significant influence on fatigue life assessment. However, there is not sufficient research explicitly explaining the mean stress effect in low cycle fatigue regime, especially when compressive mean stress is included. In this regard, the mean stress effect in low cycle fatigue regime was investigated. The target material is high strength steel with yield strength of 600 MPa or above that is commonly used due to excellent mechanical properties and weight reduction. A series of fatigue tests were performed on the high strength welded T-joint under various stress ratio conditions. Conventional mean stress correction models such as Goodman and Soderberg models are attempted for the interpretation of LCF results. However, the conventional methods are not successful to effectively correlate the mean stress effects. Therefore, relatively new methods, structural strain and effective mean stress methods, are applied. The results applying the structural strain method exhibited improved mean stress correction results by gathering the fatigue test data within a narrow band with test data in various mean stress conditions. From the results of this study, it is expected that the mean stress effect can be considered in more consistent manner for fatigue life assessment using structural strain and effective mean stress methods.