Welding in the World最新文献

The creep rupture life of weld joints decreases to values from half to one-tenth of that of the base metal in Cr–Mo heat-resistant steels. It is industrially very important to understand the creep performance of weld joints and to minimize the reduction in the creep performance of weld joints relative to the base metal. In this study, a consistent prediction computational workflow was developed for practical three-layer cladding welds that connect two modules. These are the weld heat transfer analysis module, which predicts the heat-affected zone (HAZ) shape from welding conditions, and the creep damage analysis module, which calculates the creep rupture life from the predicted shape of the HAZ. Using this workflow, we examined the effects of welding conditions on creep rupture life of 2.25Cr-1Mo steel. Welding conditions were selected on the basis of the design of experiment method, and the correlation between each factor and creep rupture life was evaluated by factorial effect analysis. The results clarify that the creep rupture life changed significantly depending on the control of welding heat input under conditions that simulate practical welding. This suggests that there is an appropriate welding heat input to bring the creep rupture life of weld joints close to that of the base metal. Although previous studies of creep rupture life with relatively simple HAZ geometries have indicated the correlation with the width and angle of HAZ, it was newly discovered that these indices cannot simply explain the creep rupture life of the weld joints with complex HAZ geometries that appear in practical welding. The effect of HAZ shape on creep rupture life is more complicated than previously reported, suggesting that more appropriate HAZ shape factors should be considered.

Given the tremendous growth of the microelectronics industry in recent years, soldering efficiency is more crucial than ever. Despite the great importance of the solder joints, these interconnections happen to be the weakest link in electronic packaging. Many surveys have been carried out in order to investigate their thermomechanical reliability but still incomplete since the electro-thermomechanical reliability is the one encountered in real operational services. A thorough insight into the multiphysics behavior of Pb-free solder joints is fundamental to enhancing the operational efficiency since the extent of their deterioration is a significant function of their compositions. This article investigates the response of various solder alloys (Sn63Pb37, SAC105, SAC305, SAC405, and InnoLot) to electrothermal loadings. The study explores their performance under different temperature conditions and examines factors such as melting temperature variations, residual stresses, and the impact of the IMC layer. The results highlight the superior reliability of SAC405, particularly regarding inelastic strain and premature damage. The study underscores the significance of mitigating these factors during electronics design and manufacturing to enhance solder joint lifetime. The findings contribute to advancing solder alloy reliability and improving electronic system performance.

This paper analyses the applicability of a modified strain approach to predict the fatigue life of HFMI-treated transverse stiffeners under variable amplitude loading (VAL) with random load sequences of a p(1/3) and linear shaped spectrum. Local stresses are determined using linear-elastic finite element analyses. The measured weld geometry and component imperfections are considered. From the hardness of the HFMI-treated zone and the base material, the elastic–plastic material behaviour and Coffin-Manson parameters to describe the damage parameter Woehler curve are estimated. Based on a hysteresis counting method (HCM), the damage for each closed hysteresis is calculated. The applied notch strain approach includes the impact of residual stresses and the influence of surface roughness. Thus far, the application of similar approaches has only been validated for welded components with comparatively low residual stresses and HFMI-treated welds subjected to constant amplitude loading. To validate the accuracy of the approach for HFMI-treated welds under variable amplitude loading, the approximated fatigue life is compared to the number of cycles derived from experimental investigations. In this study, it is shown in conjunction with experimental results that it is essential to consider the strength of the base material near the weld when assessing the service life. This area can be more critical than the HFMI-treated weld toe.

The local yielding behavior in base metal, heat-affected zone, fusion boundary region, and weld metal of low-alloy steel/Alloy 625 filler metal welds was quantified using digital image correlation instrumented cross-weld tensile test. The tested welds exhibited undermatching, matching, or overmatching weld metal yield strength with significant gradients in the local yielding behavior. An undermatching weld yielded at 69 MPa below the base metal yield stress, accumulating to 0.72% total strain. The base metal in an overmatching weld had 110 MPa lower yield strength than the weld metal. The strong strain hardening response in the Alloy 625 weld metal, within the uniform elongation range, and its constraining effect on the fusion boundary region and heat affected zone, led to extensive strain accumulation, necking, and final failure in the base metal of all tested welds. The yielding behavior of the tested welds was compared to stress-based criteria, utilizing minimum specified and as-delivered yield and ultimate tensile strength, and to strain-based criteria. The capability of digital image correlation instrumented cross-weld tensile testing to quantify local yielding and strain accumulation demonstrates potential application in proving conformity to stress-based and strain-based design criteria of dissimilar and matching filler metal welds.

High-frequency mechanical impact (HFMI) like ultrasonic peening (UP) exhibits a significant fatigue life enhancement of welded joints. Previous studies with regard to effects of HFMI mainly focus on welded components or structures of plate thickness greater than 5 mm. The study aims to develop a new numerical approach for predicting the surface state induced by UP process, and investigate the residual stress distribution of 3-mm 7075 aluminum alloy thin-walled welded joint. A novel model was developed to introduce the excitation amplitude of the ultrasonic horn as an input parameter and investigate the pin kinematics. A parametric study of the UP process parameters on aluminum alloy thin sheet welded joint was performed. The results of pin kinematics indicate that the pin is accelerated at the initial stage of peening and presents stochastic and high-frequency oscillations after the initial phase. For thin sheet welded joint, tensile transverse residual stresses are induced in the surface layer of the weld toe groove, which have negative effect on fatigue performance. The sensitivity of process parameters shows that relatively low intensity of peening, including moderate excitation amplitude and high treatment speed, is recommended to obtain desired residual stress and weld toe geometry, as well as high work efficiency in industrial application. The numerical results of pin kinematics and the surface state of welded joint after UP agree well with the experimental results.

Online penetration monitoring of complex grooves remains challenging due to steel plates’ groove instability and welding heat distortion. Penetration is an accumulation process of material deposition. Temporal signals, such as video, can provide a more comprehensive characterization of the melt pool state. A deep learning method based on continuous video is designed to monitor groove welding penetration in-process. The proposed Fast Video-feature Extraction Net (FVENet) consists of a video extraction module and a multi-feature screening module. The efficient network can quickly extract high-dimensional data features in complex arc environments and achieve accurate results for backside melt width prediction. The feature extraction process of the network is explored by visualizing the results of different network layers. Experimental results indicate that the mean squared error (MSE) of FVENet reaches 0.0634 mm, outperforming other mainstream deep learning frameworks. The inference time under video input reaches 100 FPS. The network structure designed in this paper has the potential to become a universal template for processing melt pool images.

In laser welding, the achievement of high productivity and precision is a relatively easy task; however, it is not always obvious how to achieve sound welds without defects. The localised laser energy promotes narrow meltpools with steep thermal gradients, additionally agitated by the vapour plume, which can potentially lead to many instabilities and defects. In the past years, there have been many techniques demonstrated on how to improve the quality and tolerance of laser welding, such as wobble welding or hybrid processes, but to utilise the full potential of lasers, we need to understand how to tailor the laser energy to meet the process and material requirements. Understanding and controlling the melt flow is one of the most important aspects in laser welding. In this work, the outcome of an extensive research programme focused on the understanding of meltpool dynamics and control of bead shape in laser welding is discussed. The results of instrumented experimentation, supported by computational fluid dynamic modelling, give insight into the fundamental aspects of meltpool formation, flow direction, feedstock melting and the likelihood of defect formation in the material upon laser interaction. The work contributes to a better understanding of the existing processes, as well as the development of a new range of process regimes with higher process stability, improved efficiency and higher productivity than standard laser welding. Several examples including ultra-stable keyhole welding and wobble welding and a highly efficient laser wire melting are demonstrated. In addition, the authors present a new welding process, derived from a new concept of the meltpool flow and shape control by dynamic beam shaping. The new process has proven to have many potential advantages in welding, cladding and repair applications.

Wire arc additive manufacturing (WAAM) stands out in manufacturing metallic structures due to its great potential for application in industry for automated production of parts with large dimensions and considerable geometric complexity. Due to the wide presence of ribs and wall crossovers in several mechanical components, this work studied the thermal behavior of the low alloy steel wire AWS ER80S-G in a 10-mm-wide and 90-degree intersection, discovering its influence on the microstructure and hardness of the material compared to a flat wall. Thermal analysis showed that the cooling rate at the intersection is lower than that of a flat wall. However, the evaluation of the cooling curves in a CCT diagram of the steel, later confirmed by a metallographic analysis, indicated that the difference between these two regions was insignificant, as the microstructure was quite similar between them (76% ferrite, 20% pearlite, and 4% retained austenite). On the other hand, there was a significant difference among the layers in the same region, ranging from the morphology of acicular grains at the base and top to equiaxed grains in the intermediate region (ASTM grain size 9). This difference in microstructure was significant for the hardness of the material according to the deposited layer; however, there were few differences between the intersection and the flat wall. Therefore, there are no significant differences between these regions concerning the microstructure or cooling rate, with the variances observed in the hardness being more significant only among the layers deposited.

In infrared welding, the heating phase is the phase offering the highest flexibility of choice regarding the process parameters. In this phase, the process parameters such as the heating time, emitter power, and emitter-component distance can be individually selected and combined with each other. The defined heating phases have a different influence on the joining components. In this work, the effects of four heating strategies and their influence on the resulting temperature distribution over the joining surface, the possible thermal material degradation, the morphology of the joining zone, and the short-term tensile strength of the welded samples are investigated. In order to investigate the morphology, microsections are prepared which enable transmitted light microscopy of the black PA6 GF50 used. In summary, it can be concluded that different heating strategies have a different influence on the material even if the generated melt layer thickness is kept the same. Three of the four strategies result in material degradation on the joining surface. However, this has almost no effect on the resulting short-term strength of the weld. The results allow the interpretation that a high joining pressure compensates for the influence of the material damage by pressing the damaged material into the bead.