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This study investigates the effect of welding parameters on the microstructural evolution and mechanical properties, such as tensile strength and hardness, in mild steel plates welded using gas metal arc welding (GMAW). The welding parameters examined include welding current, arc voltage, and gas flow rate, with ER K-71 T filler wire as the consumable material. Results indicate that a higher welding current and reduced gas flow rate result in a maximum tensile strength of approximately 533 MPa. However, discrepancies were noted in the microhardness data across different zones, with the heat-affected zone (HAZ) exhibiting a hardness of 115.8 HV, while the weld zone and base metal showed values of 76.7 HV and 112.9 HV, respectively. Microstructural analysis revealed the presence of bainite and ferrite with a tempered martensitic structure in the welded area, demonstrating that the combination of welding parameters plays a critical role in controlling phase transformations and mechanical behavior. It is essential to reconcile the observed hardness values with the conclusions drawn to ensure accurate interpretation of the data. Highlights: The study investigates how different welding process parameters, including current, voltage, and gas flow, affect the internal structure and mechanical characteristics of weld metal. It was found that the highest tensile strength is achieved with a combination of high welding current and low gas flow rate. The welded joint shows greater hardness in the heat-affected zone compared to the original metal, with the fusion zone being less hard. Analysis of the weld area reveals the presence of bainite, ferrite, and tempered martensite, which are responsible for the mechanical properties observed. [ABSTRACT FROM AUTHOR]

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In weld-based manufacturing processes such as welding and metal deposition additive manufacturing (AM), the weld bead is a direct indicator of manufacturing quality. For example, the geometry of the weld bead was optimized to a net shape which outperformed conventional geometries. Automatic monitoring of weld bead is thus of prime importance for welding process control and quality assurance. This paper develops a general-purpose convolutional neural network (CNN) for pixel-level detection and monitoring of beads, regardless of welding materials, machine, manufacturing conditions, etc. To achieve the generality, we collected a great variety of welding images containing 2677 single-line beads from 231 research articles, followed by pixel-wise hand-annotation. Consequently, the trained CNN can recognize different beads from various backgrounds at a pixel level. Case studies show that compared to the image-level classification in prior research, its pixel-level labeling permits real-time, complete characterization of weld beads (e.g., detailed morphology, discontinuity, spatter, and uniformity) for more informed process control. This research represents a significant step towards developing a truly human-like monitoring system with low-level scene understanding ability and general applicability. [ABSTRACT FROM AUTHOR]

Weld bead segmentation is important for the automation of quality control and inspection of welded joints. Due to the irregularity and the lack of topological information of the point cloud, it is hard to effectively segment the bead from the weld in 3D point cloud. This research investigates a novel method by using the 3D texture features and global features of point cloud subregions to achieve submillimeter precision segmentation of 3D weld point clouds captured by a RealSense depth camera. First, a preprocessing algorithm that combines a 2D image processing method with a segmentation method based on the global bead profile is proposed to improve the segmentation performance of the algorithm. Then, based on different feature selection algorithms and machine learning (ML) classifiers, the classification performance of the algorithm is effectively optimized. The experimental results show that choosing appropriate subregion sizes and features can significantly improve the segmentation performance of the algorithm. The average error in the bead width is less than 1 mm. Compared to other methods based on laser profile and ML, it has much better accuracy. [ABSTRACT FROM AUTHOR]

This paper presents an automated Non-Destructive Testing (NDT) system for the in-service inspection of orbital welds on tubular components operating at temperatures as high as 200 °C. The combination of two different NDT methods and respective inspection systems is here proposed to cover the detection of all potential defective weld conditions. The proposed NDT system combines ultrasounds and Eddy current techniques with dedicated approaches for dealing with high temperature conditions. Phased array ultrasound was employed, searching for volumetric defects within the weld bead volume while Eddy currents were used to look for surface and sub-surface cracks. The results from the phased array ultrasound results showed the effectiveness of the cooling mechanisms and that temperature effects on sound attenuation can be easily compensated for up to 200 °C. The Eddy current results showed almost no influence when temperatures were raised up to 300 °C. [ABSTRACT FROM AUTHOR]

With the elimination of solidification defects, friction stir welding becomes the most effective process for joining flat and curved surfaces. Tool geometry (tool pin profile, shoulder diameter) and tool rotation speed mainly contribute to the overall weld quality. The study evaluates the simultaneous effect of tool geometry, rotational speed, base offset and double pass Friction Stir Welding (DP-FSW) on the defect formation and the mechanical properties. Micro-structure and macro-structure have been analysed for weld strength and hardness characterisation, and found, at high tool rotation speed maximum hardness is achieved in the Stir Zone (SZ). A small tunnel present near the middle proved to be more detrimental than the large one at the bottom. Grain refinement in the SZ was 87.2% while augmentation in hardness was 21.3 HV. Maximum tensile strength of approximately 103% with decent bead profile is obtained, using taper cylindrical tool at 710 rpm with 14 mm shoulder diameter. Fractography of the fractured surface revealed a pure ductile failure. It has been discovered that with base offset the strength of the weld is increased. However, reduction of 4.8% was obtained with DP-FSW. Better weld profile gives better strength. With DP-FSW, a significant improvement in bead surface is obtained. [ABSTRACT FROM AUTHOR]

In the present study, the laser melting deposition (LMD) technology was adopted to fabricate FeCoCrNiMn and FeCoCrNiMnAl0.75 high entropy alloys (HEAs). Then, laser welding method was used to join the HEAs in forms of similar (FeCoCrNiMnAl/FeCoCrNiMnAl and FeCoCrNiMnAl0.75/FeCoCrNiMnAl0.75) and dissimilar (FeCoCrNiMnAl0/FeCoCrNiMnAl0.75) combinations, respectively. Ultra-depth field microscope and electron backscatter diffraction detection were used to observe the macro-morphology and microstructure, respectively. It was found that the width of the weld bead and heat-affected zone with higher aluminium content was larger. In both base metals and welded joints, aluminium promoted the face-centered cubic (FCC) phase transfer into body-centered cubic (BCC), significantly refined the grain and the dislocation density of HEA is also increased, which increased strength and hardness, and decreased ductility. Highlights The FeCoCrNiMn/FeCoCrNiMn, FeCoCrNiMn/FeCoCrNiMnAl0.75, FeCoCrNiMnAl0.75/FeCoCrNiMnAl0.75 joints were produced by laser welding. The widths of the weld bead and heat-affected zone increased with higher Al content. The weld bead with higher content of Al exhibited higher strength and hardness, but lower ductility. [ABSTRACT FROM AUTHOR]

An investigation has been done to identify the heat source model suitable for numerical modeling of the Gas Metal arc Welding (GMAW) welding process. In the present investigation, a numerical model was constructed to simulate the GMAW welding process through transient thermal analysis for different thermal heat source models for weld deposition of Mild steel considering semi-cylindrical weld bead geometry. The Gaussian heat source with radial coordinate system and double ellipsoidal thermal heat source have been considered to develop a Finite Element Analysis (FEA) model. Validation of numerical analysis results has been confirmed through experimental investigation. Numerical modeling confirms the utilization of both heat sources, i.e. Gaussian and Double ellipsoidal for the prediction of the weld bead deposition profile. However, the numerical modeling developed using a double ellipsoidal heat source has more resembles experimental investigation due to the utilization of bead profile data. However, the Gaussian heat source is found to be suitable in the case of the unavailability of experimental data. The experimental studies show a variation in the weld bead geometry, along its welding direction due to multiple environmental factors. The microstructural investigation also shows the development of a fine columnar grain structure at the welding bead & weld penetration zone, and the grain structure became coarser at the Heat Affected Zone (HAZ). [ABSTRACT FROM AUTHOR]

Understanding the flow characteristics within the molten pool and the creation of the weld shape holds significant theoretical and engineering importance. Numerical simulation is the best method for understanding the flow behaviour in the molten pool due to its greater flexibility and cost competitiveness, which enable efficient exploration of such intricate phenomena. The dimensions of the geometry are generally crucial in determining the flow pattern in the molten pool. Marangoni convection may occur in thin plates due to changes in surface tension, while thicker plates may experience buoyancy forces from natural convection. It would be intriguing to understand the flow pattern when thin plates are treated with a smaller laser beam diameter. Three numerical models have been created in the present paper using COMSOL Multiphysics to analyse the flow characteristics within the molten pool. The first model assumes laminar flow in the molten pool, while the other two models assume turbulent flow (yPlus and k-ω model). The models incorporate a pulsed heat source that is simulated using COMSOL's events interface, which adjusts the time steps depending on the speed of the solution changes. The three models consider the temperature dependent thermo-physical properties, track the solid-liquid phase interface with keyhole, account for Marangoni convection and buoyancy forces. The melt pool shapes calculated by the models are compared with experimental results and found to be comparable. The intensity of the flow in the molten pool is determined by using dimensionless numbers like the Marangoni number and the ratio of the Marangoni number to the Grashof number. [ABSTRACT FROM AUTHOR]

Laser welding of A516 steel was performed using the filler metal to serve as the interlayer. The effects of laser welding parameters on the melt pool microstructure, weld bead shape, dimensions of the melt pool, and temperature field around the melt pool were investigated. The results indicated that the nozzle distance had the most significant influence on the temperature around the molten pool. As the maximum energy of the laser beam was irradiated on the center of the filler, the highest value of the temperature near the fusion zone was about 360°C. The welding speed, determining the overlap factor, had a considerable effect on the weld bead shape. The laser power, therefore, could determine laser beam line energy to melt the filler volume effectively. Enhancing the laser power up to 450 W increased the temperature to about 300 °C; also, the melting rate of the filler used was almost completed and the weld bead appearance was clearly improved; therefore, the width of the melt pool was increased by about 10%. Increasing the nozzle distance from 3 to 7 mm also reduced the width of the molten pool by about 75% and 40% with and without the filler, respectively. By using the filler metal, the geometry of the welding bead changed from a concave one to a convex one. The major fusion zone microstructure of the fusion zone was an acicular ferrite characterized by needle-shaped ferrite crystallites. [ABSTRACT FROM AUTHOR]

WAAM (wire-and-arc additive manufacturing) is recently gaining much interest for the fabrication of parts with wide size. A crucial issue associated to this technology is how to control the process variables to achieve expected qualities of parts. The aim of this investigation is to explore the relationship of the heat input (Q) with the forming quality of 308L stainless steel. The outcomes demonstrate that the heat input has significant effects on the shape, microstructures, and mechanical properties of the walls. Both the height and width of single weld beads increase with an increment in Q. The walls fabricated with the low heat inputs feature better mechanical properties and lower surface roughness. The tensile strengths (YS 0.2% and UTS) and the surface roughness (S a) of the walls built with the lower heat input (230 J/mm) are 292 ± 4.95 MPa, 523 ± 4.24 MPa, and 106 μm, respectively, whilst YS 0.2% = 273 ± 4.34, UTS = 482 ± 5.66 MPa, and S a = 179 μm for the wall fabricated with the higher heat input (576 J/mm). This investigation contributes to enriching the understanding on the WAAM process of steels and helping operators to select a proper heat input for specific applications. • The connection of the heat input to the forming quality of 308L steel by WAAM was explored. • The WBs' dimensions increase with the augmentation of the heat input. • The microstructure of WAAMed 308L steel comprises dominant austenite and residual ferrite. • The microstructure in the walls is the result of the thermal cycles and varies region-by-region. • The surface quality and material properties of parts can be enhanced by reducing the heat input. [ABSTRACT FROM AUTHOR]