Search Results (38)

Direct copper-plated ceramic (DPC) substrates have emerged as a favored solution for power device packaging due to their unique technical advantages. AuSn, characterized by its high hermeticity and environmental adaptability, represents the optimal sealing technology for DPC substrates. Through the application of vacuum sintering techniques and adjustment of peak temperatures (325 °C, 340 °C, and 355 °C), the morphology and composition of interfacial compounds were systematically investigated, along with an analysis of their formation mechanisms. A gradient aging experiment was designed (125 °C/150 °C/175 °C × oxygen/argon dual atmosphere × 600 h) to elucidate the synergistic effects of environmental temperature and atmosphere on the growth of intermetallic compounds (IMCs). The results indicate that the primary reaction in the sealing weld seam involves Ni interacting with Au-Sn to form (Ni, Au)₃Sn₂ and Au₅Sn. However, upon completion of the sealing process, this reaction remains incomplete, leading to a coexistence state of (Ni, Au)₃Sn₂, Au₅Sn, and AuSn. Additionally, Ni diffuses into the weld seam center via dendritic fracture and locally forms secondary phases such as δ(Ni) and ζ’(Ni). These findings suggest that the weld seam interface exhibits a complex, irregular, and asymmetric microstructure comprising multiple coexisting compounds. It was determined that Tpeak = 325 °C to 340 °C represents the ideal welding temperature range, where the weld seam morphology, width, and Ni diffusion degree achieve optimal states, ensuring excellent device hermeticity. Aging studies further demonstrate that IMC growth remains within controllable limits. These findings address critical gaps in the understanding of the microstructural evolution and interface characteristics of asymmetric welded joints formed by multi-material systems. Full article

The seaming of geomembranes (GMBs) is a critical aspect of their successful functioning as barriers to liquid, with bonding and welding being the commonly employed methods. Due to the limitations of conventional welding methods at the connection points between the geomembrane and the structure, extrusion welding often results in damage at the seams. The bonding method, which has lower requirements for construction conditions, has emerged as a currently viable alternative seaming technique. Bonding techniques are widely applied in small reservoirs and embankments. This study investigates the performance of high-density polyethylene (HDPE) GMB seams bonded using asphalt-based adhesive (ABA) and non-asphalt-based adhesive (NABA). Seam tensile tests were conducted under wetting and freeze-thaw cycles (FTCs) conditions to evaluate the mechanical properties of the seamed GMBs. The results indicated that the seam strength of specimens bonded with ABA increased as wetting time and FTCs increased (with a maximum increase of 113.8%). In contrast, specimens bonded with NABA exhibited decreased seam strength under similar conditions (with a maximum decrease of 93.4%). Both types of specimens exhibited enhanced seam strength with increasing seam width. Due to wetting and FTCs, the seam efficiency of NABA-bonded specimens decreased, while that of ABA-bonded specimens showed slight improvement. However, the improved seam efficiency remained below 1.2%, an extremely small value. The axial tensile strength of bonded specimens was significantly lower than that of seamless specimens, failing to fulfill long-term safety operation requirements. Therefore, bonding method should be used cautiously at non-critical structural components where the welding is impractical but repair and replacement are relatively simple. The findings provide insight for GMB installers and design engineers in order to improve the performance of HDPE GMB seams. Full article

In pipeline all-position welding processes, laser scanning provides critical geometric data of width-changing bevel morphology for welding torch swing control, yet conventional second-order derivative zero methods often yield pseudo-inflection points in practical applications. To address this, a third-order derivative weighted average threshold algorithm was developed, integrating image denoising, enhancement, and segmentation pre-processing with cubic spline fitting for precise bevel contour reconstruction. Bevel pixel points were captured by the laser sensor as inputs through the extracted second-order derivative eigenvalues to derive third-order derivative features, applying weighted threshold discrimination to accurately identify inflection points. Dual-angle sensors were implemented to synchronize laser-detected bevel geometry with real-time torch swing adjustments. Experimental results demonstrate that the system achieves a steady-state error of only 1.645% at the maximum swing width, a dynamic response time below 50 ms, and torch center trajectory tracking errors strictly constrained within ±0.1 mm. Compared to conventional methods, the proposed algorithm improves dynamic performance by 20.6% and exhibits unique adaptability to narrow-gap V-grooves. The results of these studies confirmed the ability of the method to provide real-time, accurate control for variable-width weld tracking, forming a swing-width adaptive control system. Full article

The recent technological advancements in today’s manufacturing industry have extended the quality control operations for welding processes. However, the realm of pre-welding inspection, which significantly influences the quality of the final products, remains relatively uncharted. To this end, this study proposes an innovative vision system designed to extract the seam gap width and centre between two components before welding and make informed decisions regarding the initiation of the welding process. The system incorporates a deep learning semantic segmentation network for identifying and isolating the desired gap area within an acquired image from the vision sensor. Then, additional processing is performed, with conventional computer vision techniques and fundamental Euclidean geometry operations for acquiring the desired width and the centre of that area with a precision of 0.1 mm. Additionally, a control graphical interface has been implemented that allows the operator to initiate and monitor the entire inspection procedure. The overall framework is applied and tested on a manufacturing case study involving the laser welding operations of sheet metal parts, and although it is designed to handle gaps of different shapes and sizes, it is mainly focused on obtaining the characteristics of butt weld gaps. Full article

In this paper, the butt joint of unequal thickness 410 ferritic stainless steel and RCL540 low-carbon alloy steel sheets are realized by laser welding. The effects of different laser powers on weld formability, mechanical properties, and residual stress in the welding process are investigated. It is observed that with increasing laser power, the heat accumulates at the bottom of the molten pool and weld metal, causing the ratios of upper and lower melt widths to decrease. The tensile test results show that all specimens fractured in the weak zone of the base metal on the stainless steel side at 10 mm from the weld seam. The residual stress distributions of the specimens are calculated using ABAQUS 2022 software and compared with the measurements of the blind-hole method. It is found that the stainless steel side produces tensile stresses, with the power increase offset by compressive stresses in the base metal. When the laser power is 1200 W, the welded joint has the best weld formability and mechanical properties and the least residual stress. The upper and lower melt width ratio is 1.17, the maximum microhardness of the weld metal is 374.7 HV, the maximum test force and tensile strength are 5617.5 N and 468.12 MPa, respectively, and the minimum values of the transverse and longitudinal stresses are −45.8 MPa and −106.4 MPa, respectively. Full article

In the field of welding detection, weld bead cross-section morphology serves as a crucial indicator for analyzing welding quality. However, the extraction of weld bead cross-section morphology often relies on manual extraction based on human expertise, which can be limited in consistency and operational efficiency. To address this issue, this paper proposes a multi-layer multi-pass weld bead cross-section morphology extraction method based on row–column grayscale segmentation. The weld bead cross-section morphology image is pre-processed and then segmented into rows and columns based on the average gray value of the image. In order to extract the feature of multi-layer multi-pass weld feature images, an outline showing the binarization threshold is selected for each segmented image (ESI). Then, the weld contour of ESI is extracted before image fusion and morphological processing. Finally, the weld feature parameters (circumference, area, etc.) are extracted from the obtained weld feature image. The results indicate that the relative errors in circumference and area are within 10%, while the discrepancies in maximum weld seam width and maximum weld seam height can be close to the true value. The quality assessment falls within a reasonable range, the average value of SSIM is above 0.9 and the average value of PSNR is above 60 on average. The results demonstrate that this method is feasible for extracting the general contour features of multi-layer multi-pass weld bead cross-section morphology images, providing a basis for further detailed analysis and improvement in welding quality assessment. Full article

Weak magnetic detection technology can detect stress concentration areas in ferromagnetic materials. However, the stress non-uniform characteristics of pipeline welds lead to significant differences in stress distribution range and values between inner wall welds and outer wall welds. This discrepancy makes it crucial to further evaluate the impact of stress non-uniformity on magnetic signals. To study the magnetic signal characteristics under the influence of residual stress in weld seams, a magneto-mechanical analytical model was established based on the magnetic charge theory and the distribution characteristics of residual stress in the weld seam. The magneto-mechanical relationship and magnetic signal distribution characteristics at the inner and outer wall welds of the pipeline are calculated. Furthermore, the effects of different excitation intensities on the amplitude growth characteristics of magnetic signals are analyzed and compared. To verify the analysis model, weld detection experiments with different excitation intensities were designed. The results show that both the peak-to-valley values of the normal component and the peak values of the tangential component of the outer wall weld are lower than those of the inner wall weld. Conversely, the peak-to-valley width of the normal component and the peak width of the tangential component are greater than those of the inner wall weld. Additionally, the rate of increase in weak magnetic signal amplitude decreases in a first-order exponential relationship with increasing excitation intensity. The average decay rates of the normal and tangential component amplitude growth rates for the inner wall weld are 34.03% and 27.9%, respectively, while for the outer wall weld, they are 31.75% and 28.01%, respectively. This study contributes to the identification and quantitative assessment of weak magnetic signals in inner and outer wall welds. Full article

The results of experimental studies in the manufacture of components of the supporting structure of the first wall panel, carried out as part of the manufacture of a model of the International Thermonuclear Experimental Reactor (ITER) using laser welding technology, are presented. The influence of laser welding modes on the quality of formation, microstructure characteristics, and mechanical properties of a welded joint made of 10 mm thick 316L steel was studied. A coaxial nozzle was designed and manufactured to protect the weld pool with a curved trajectory. The mechanical properties of the welded joint are 98–100% that of the base metal, and the microhardness of the welded joint and base metal is in the range of 180–230 HV. It was established that the lower part of the weld metal on the fusion line has transcrystalline grains and differs in δ-ferrite content; due to a high welding speed, the ratio of the depth to the width of the welding seam is 14 times. The width of the rectilinear part of the seam is 15–20% larger than its curved part. Full article

This study advances the vibration-assisted welding (VAW) technique for joining medium-carbon, low-alloy steels, which are typically challenging to weld. Traditional welding methods suggest low linear energy and mandatory pre- and post-heating due to these steels’ poor weldability. However, VAW employs a vibrating table to maintain part vibration throughout the automatic MIG/MAG welding process. This study tested the VAW technique on 42CrMo4 steel samples, achieving satisfactory weld quality without the need for pre- and post-heating treatments. This research revealed that while vibration frequencies between 550 Hz and 9.5 kHz minimally affect the appearance of the weld joint, the oscillation acceleration has a significant impact. The acceleration along the weld axis (a_x), combined with the welding speed and vibration frequency, affects the weld surface’s appearance, particularly its scaly texture and size. Lateral acceleration (a_y) alters the seam width, whereas vertical acceleration (a_z) affects penetration depth at the root. Notably, if the effective acceleration (a_ef) surpasses 40 m/s², there is a risk of molten metal expulsion from the weld pool or piercing at the joint’s base. The quality of the joints was assessed through macroscopic and microscopic structural analyses, micro-hardness tests in the weld zone, and bending trials. The mechanical properties of the VAW samples were found to be acceptable, with hardness slightly exceeding that of the samples subjected to pre- and post-heating. Moreover, the VAW process significantly reduced energy consumption and operational time. The employed vibration system, with a power rating of 100 W, operates for just a few minutes, resulting in substantially lower energy usage compared to the traditional pre- and post-heating method, which typically requires a 5 kW electric furnace. Full article

In the welding process of thick plate narrow gap pulse gas metal arc welding (P-GMAW) overhead welding station, the arc characteristics and droplet transfer behavior that become more complex due to the combined effects of narrow gap groove, gravity, and welding torch oscillation. The welding stability is more difficult to control. High-speed imaging and electrical signal acquisition systems were established to observe and record the arc behavior and droplet transfer during the welding process at different oscillation widths, further revealing the formation mechanism of welding seam in narrow gap P-GMAW overhead welding station. Research has found that with an increased oscillation width, the arc deflects towards the sidewall from a trumpet-shaped symmetrically distributed around the center of the groove at an increasing deflection angle, and the droplet transfer changes from one droplet per pulse to multiple droplets per pulse, resulting in defects such as lack of sidewall fusion and undercutting of the weld seam. Based on the welding process discussed in this study, it is recommended to use an oscillation width of 2.6 mm. Full article

Brittle intermetallic compounds, formed during the welding process of titanium/aluminum (Ti/Al), lead to a significant reduction in joint mechanical properties. The purpose of this study is to mitigate the formation of brittle phases during the laser welding of dissimilar Ti/Al metals, thereby enhancing the mechanical properties of the joints. In this investigation, an innovative approach is adopted, utilizing Nb foil as an interlayer to effectively minimize the formation of brittle intermetallic phases during dissimilar welding. A comprehensive analysis of the microstructure of the transition layer was conducted using material characterization methods, including scanning electron microscope equipped with an energy dispersive X-ray spectrometer. The mechanical performance of the welded joints was assessed using tensile testing. The results indicate that the effective welding width and joint penetration depth at the joint interface were reduced in Ti/Al dissimilar metals when Nb was added as an intermediate layer, under the same welding process parameters, when compared to unalloyed weld seams. Furthermore, the utilization of a 0.05 mm Nb foil as the intermediate layer results in a significant 25% increase in the average shear strength compared to the other condition, with the average shear strength of the joint reaching its peak value at 192 N/mm. The unalloyed Ti/Al weld joint usually fractured along the melting zone, displaying complete brittle fracture characteristics. After Nb microalloying, the joint typically fractures along the transition zone and interface, exhibiting both cleavage and ductile fracture characteristics, indicating the combination of a brittle and toughness fracture. This study provides experimental evidence and new insights for welding Ti/Al composite structures, with significant theoretical and practical applications. Full article

Aiming to diminish the defects caused by high-speed pulsed GMAW (Gas Metal Arc Welding), such as lack of penetration, lack of fusion, humping and undercut, this paper proposes an improved twin-wire GMAW welding process by introducing the impact of additional shielding gas on the molten pool, and the effects of different shielding gas flowrates on the mechanical properties and microstructure of the welded seams were investigated. The purpose of introducing additional shielding gas was to use the airflow hood formed by gas injection to isolate air. The impact force generated by the jet might change the original natural solidification mode of the molten pool, which had the effect of improving weld formation and stirring the pool. The airflow hood formed during the process of the additional shielding gas jet impact welding of the molten pool might extend the protection time for the surface of the welding molten pool. The 2205 duplex stainless steel plate was used as the base material for the butt welding test, and the welded seams were subjected to a tensile test, hardness analysis, and metallographic analysis. The results indicated that as the flowrate of additional shielding gas increased in the range of 8 L/min~16 L/min, the width of the welded seam increased and the height of reinforcement decreased gradually. However, a weld seam with a lower middle region and higher sides would appear when the gas flowrate became excessively large. Under the identical welding current and for welding speeds of 160 cm/min, 180 cm/min and 200 cm/min, respectively, the joint formed under the flowrate of 12 L/min had the highest tensile strength (824.3 MPa) among the test specimens under different flowrates of 8 L/min, 12 L/min and 16 L/min. The test results indicated that the jet impact force was relatively moderate when the flowrate of the additional shielding gas was 12 L/min, and thus was optimal for the welded seam. Full article

Hollow tubes are generally manufactured using porthole die extrusion. A finite element software QForm is used to analyze the material flow of aluminum alloy A6061 tubes inside a specially designed porthole die during tube extrusion. High welding pressure and shorter transverse seam length are required for a sound product. Various extrusion conditions and die geometries and dimensions affect the bonding strength of the products. In this paper, the effects of die geometries on the welding pressure are discussed using the Taguchi method. The simulation results show that a higher welding pressure is obtained with a larger porthole radius, a larger welding chamber height, and a larger bearing length, while a larger bridge width increases the welding pressure slightly. For transverse seam lengths, a shorter transverse seam length can be obtained with a smaller porthole radius and a smaller welding chamber height, and a shorter bridge width and bearing length decrease the transverse seam length slightly. The transverse seam region and flow patterns are observed. Tube expanding tests were also conducted. From the expanding test results, it is known that the fracture position did not occur at the welding line and the bonding strength could reach up to 160 MPa. Full article

Thick-walled X80 pipelines for oil and gas transportation are difficult to relocate due to their large size. In the process of narrow-gap overhead welding, welding defects, such as bulges and lack of sidewall fusion, can appear easily. To avoid these defects and to improve the welding quality of thick-walled pipelines, the GMAW welding method is adopted in this paper. The formation characteristics of the weld and the influence of arc oscillation parameters, such as the oscillation width and sidewall dwell time, on the formation process of narrow-gap overhead welding seams are studied. In this research, it was found that, in the NG-GMAW overhead welding position, there was a downward trend in the middle of the formed surface of the weld pool. Defects, such as finger-shaped penetrations and lack of sidewall fusion, were prone to occur due to gravity. The increased oscillation width was beneficial for reducing the protrusion in the middle of the weld seam, but an excessive oscillation width can easily cause undercut defects. The sidewall dwell time has little effect on the protrusion in the middle of the weld seam, but it can increase sidewall penetration, thereby avoiding the occurrence of incomplete sidewall penetration. Full article

The welding of steel–aluminum dissimilar metals plays a vital role in promoting automobile lightweight. However, it is tricky to obtain good mechanical properties of steel–aluminum laser weldments. Based on the principle of preheating welding, the laser double-pass reciprocating welding method of steel–aluminum dissimilar metals was proposed. In the experiment, different weld spacing such as 0, 0.5, 1.0, 1.5, and 2.0 mm were set, and numerical calculations of the temperature field of the molten pool were carried out. The results show that the tensile strength of weldment depends on the mechanical properties of the second weld seam in the optimal welding parameters. Compared with other weld spacing, when the weld spacing is 1.5 mm, the preheating temperature, peak temperature, and pool width on the steel side of the second weld are lower. In contrast, the weld penetration’s peak value and molten pool center’s temperature reach the maximum on the aluminum side. The thickness of the steel/aluminum transition layer changed from 14 to 11 to 8 μm with increased weld spacing. Moreover, the fracture mode of the second weld is a ductile fracture. Furthermore, the average tensile strength can reach 76.84 MPa. The results show that appropriate weld spacing and preheating temperature can effectively improve the tensile strength of the welding joint. Full article