Welding in the World最新文献

To satisfy recent demands for reducing NVH (noise, vibration, harshness), vehicle weight, and improving collision safety, the development of reliable processes for dissimilar joining of lightweight vibration-damping aluminum to ultra-high strength steels is required. The resistance element welding (REW) process to join the dissimilar material involves a two-step process of pre-drilling a hole in the aluminum to insert the element and then welding to join the element to steel. Consequently, this increases cycle time and makes it challenging to ensure joint quality due to potential robot teaching errors. To overcome these limitations, an innovative one-step REW process was proposed to shorten the two-step REW process into a single process. However, the thermoplastic resin layer at the interface of the vibration-damping aluminum limits current conduction, posing challenges for REW. The current study introduces stainless-steel clips to bypass the thermoplastic resin layer between the vibration-damping aluminum, which limits the current conduction during the one-step REW process. The adjacent REW joint ensures further bypass of the current and acts as an initial weld point (shunt weld) for continuous one-step REW. Optimization of the welding variables was carried out to achieve excellent joint performance in terms of joint formation. Subsequently, the quality evaluation of the joint was done based on the evaluation of microstructure and mechanical properties. This process significantly enhances productivity with one-step REW instead of the traditional two-step welding. It surpasses the difficulty of welding the vibration-damping aluminum to HPF (hot press forming) steel.

Hybrid ultrasonic welding experiments on Inconel 625 alloy were carried out to address the challenges of refining microstructure. The welding process phenomena and resulting microstructures were systematically analyzed. Four distinct welding methods—conventional tungsten inert gas (C-TIG), ultrasonic-frequency pulsed TIG (UFP-TIG), ultrasonic vibration-assisted TIG (UV-TIG), and hybrid ultrasonic TIG (HU-TIG)—were compared in terms of grain morphology, grain size distribution, and overall refinement. In the weld zone adjacent to the fusion line, hybrid ultrasonic treatment demonstrated a superior effect on grain morphology adjustment. The results show that HU-TIG effectively suppresses columnar growth and increases the proportion of equiaxed grains, yielding a finer microstructure than the other methods. The synergy of ultrasonic-frequency pulsing and mechanical ultrasonic vibration enhances cavitation activity in the molten pool, promoting dendrite fragmentation and homogenizing elemental distribution. Moreover, ultrasonic-frequency pulsed arcs alter the physical properties of the molten pool, enabling the melt to respond more effectively to ultrasonic cavitation.

In this study, thin-walled parts of ER 4043 Al-5Si alloys were deposited using the cold metal transfer (CMT)-wire arc additive manufacturing (WAAM) process. The effects of variation of process parameters of wire feed speed (WFS), interlayer time interval (ITI), and travel speed (TS) on the microstructure and mechanical properties of thin-walled parts were investigated. The results showed that the microstructures of the thin-walled parts were composed of the α-Al phase and Al-Si eutectic phase. The samples deposited by WAAM consisted mainly of a large number of columnar grains and a few equiaxial grains. As WFS increased, heat input increased and reduced the temperature gradient; the average grain size of thin-walled parts increased significantly from 90 μm to 135 μm. The maximum texture intensity of the thin-walled parts is also increased. The ultimate tensile strength (UTS) of the samples decreased from 134 to 101 MPa. As ITI increased, the average grain size of thin-walled parts decreased from 122 to 85 μm due to higher subcooling and temperature gradient. This resulted in an increase in UTS from 104 to 130 MPa. Although the increased TS enhances the solidification rate, the average grain size of the thin-walled parts only decreases from 145 to 129 μm. The UTS of thin-walled parts was increased from 123 to 146 MPa. The tensile fractures of the samples were plastic fractures; therefore, the samples maintained high elongation (EL). In addition, the anisotropy in the mechanical properties results from differences in grain size, directional growth and inhomogeneous grain structure, eutectic microstructure, and texture.

Stiffened panels are common structural units in marine vessels, civil and aerospace structures. Production via welding can lead to excessive distortion of their plates, which negatively affects structural integrity and dimensional accuracy. Conventional practical approaches for distortion control are costly, making simulation models attractive tools to mitigate distortions. Prediction of welding distortions using finite element (FE) simulations is computationally intensive, especially when used repeatedly in design and optimization. Effective surrogate models in the form of deep learning could alleviate this issue, but the selection and construction of deep neural networks for this purpose are presently unclear. This study focuses on predicting welding-induced distortions in a T-joint. Two neural networks—a multilayer perceptron (MLP) and a convolutional neural network (CNN)—are employed to predict distortions. Two case studies are conducted for each model, exploring variations in geometry and welding sequences. The database is generated from FE simulations of the gas metal arc welding (GMAW) process. The effects of welding order and direction on distortions are studied, concluding that an appropriate selection of welding sequence and direction can reduce distortion by up to 40%. This data is then used to train the neural networks. The MLP and CNN models are designed and trained to predict distortion fields by tuning their architecture and other hyperparameters. Results demonstrate that both models are effective; however, the CNN achieves higher accuracy for complex distortion patterns, highlighting its suitability for more intricate scenarios. 

Controlling prior-β grain morphology is crucial for achieving specific isotropic properties in Wire Arc Additive Manufacturing (WAAM). Arc oscillation has been proven effective in refining grain size during aluminum welding, primarily due to the dendrite fragmentation mechanism. However, its impact on the grain structure of Ti-6Al-4 V remains underexplored. In this study, various arc oscillation amplitudes were applied to assess grain morphology evolution. In the stringer method (without oscillation), 100% equiaxed grains were observed in both the transverse and longitudinal directions due to lower heat input. As oscillation amplitude increased, the grain structure gradually transformed from equiaxed to columnar. At an amplitude of 6 mm, 80% columnar grains were obtained. To understand these findings, numerical simulations were conducted to quantitatively analyze the thermal history. SYSWELD calculations showed that a larger oscillation amplitude (6 mm) significantly influenced the weld pool shape (height and width), amplifying the temperature gradient (G) to nearly twice that of the specimen without oscillation during solidification. Furthermore, the dendrite fragmentation mechanism suggests that although thermal fluctuations caused by oscillation were observed in the molten region, they gradually dissipated after one or two remelting cycles. Controlling the frequency of these thermal fluctuations and the weld geometry presents a potential approach to modifying prior-β in Ti-6Al-4 V using arc oscillation.

Challenges in terms of reliability still surround thermal measurement methods in welding processes. However, the temperature distribution within the weld pool can provide important resources for understanding behaviors and explaining phenomena. This work aims to study the effect of gravity on the temperature distribution within the weld pool under different welding positions using an in-house developed equipment. First, a combination of optical settings and a calibration procedure were established. Experiments were carried out with the same welding parameters under flat, horizontal, vertical upward, and vertical downward positions. The thermal field from the backside of fully penetrated thin plates was accessed using the TIG process. The device allowed a well-delimited and detailed weld pool thermal field assessment. Dimensionless numbers were quantified, and Marangoni shear stress was plotted on the weld pool surface. Along the transversal weld pool direction, a symmetrical heat distribution was stated in the flat position, while an asymmetrical one was observed in the others. The Marangoni effect played a crucial role in all the experiments, emerging as the dominant driving force in 1G and 2G positions. It governed the fluid flow within the weld pool by influencing temperature gradients over time, which, in turn, altered the direction and magnitude of shear stress on the free surface. Notably, in the 2G position, the observed asymmetry in the weld pool features may be attributed to the combined effects of buoyancy and Marangoni forces acting together. Finally, through the developed equipment, it was possible to evaluate the impacts of gravity on the heat distribution within the weld pool and demonstrate its contribution to dynamics studies.

High carbon ferrochrome hardfacing alloys are widely used to protect machinery equipment exposed to a combination of abrasion and impact. Strengthening high-chromium iron-based alloys with alloying elements is an important strategy for developing its wear resistance and impact property. In this study, novel complex Fe-xCr-C-Nb-Mo-V-W hardfacing alloys with varying Cr contents of 14, 18 and 23 wt. % were prepared using open arc welding. The effects of the Cr content and the heat treatment on the microstructure, abrasive resistance and impact property of the hardfacing alloys were evaluated. With the rise in Cr content, the area fraction of M₇C₃ hard phase improves from 56 to 62%, while the grain size of M₇C₃ is refined from 26.5 μm to 22.0 μm. Results show that increasing Cr content increases the abrasive resistance but declines the impact property of the hardfacing alloys. Heat treatment at 900 °C decreases the area fraction of M₇C₃ phase and induces the grains coarse, resulting in the descent of the abrasive resistance and ascent of the impact property of the hardfacing alloys. Abrasive test results highlight that the importance of area fraction and grain size of M₇C₃ phase for abrasive resistance. However, the martensite/ austenite matrix with toughness plays the predominant role in the impact resistance by absorbing and dispersing the impact energy.

Creep-resistant steels such as 13CrMoV9-10 are utilized in the manufacture of thick-walled pressure vessels and are typically joined by submerged arc welding (SAW). However, these materials are susceptible to stress relief cracking (SRC) if the required post weld heat treatment (PWHT) is not applied correctly. Existing PWHT guidelines, encompassing heating rate and dwell (or holding) time at a given temperature, are derived from a synthesis of empirical knowledge and typically free-shrinkage weld experiments to assess the susceptibility to SRC. Therefore, this study discusses the combined effect of the PWHT heating rate under free-shrinkage compared to restrained shrinkage. Welding experiments were conducted (using plates with a thickness of 25 mm) for both shrinkage conditions for a variety of heating rates and maximum temperatures. In-situ acoustic emission analysis was used to locate propagating SRCs during PWHT. Hardness measurements, mechanical property characterization (Charpy impact strength), and microstructure correlation were used to evaluate the SRC susceptibility. The results suggested that the influence of heating rate could not be directly related to SRC formation and that the initial weld microstructure prior to PWHT was more relevant in terms of very high hardness in the coarse grain heat affected zone, especially that of the last beads in the top layer of the welding sequence. This was seen in the form of random, unexpected SRC occurrence in only one specimen at a heating rate commonly used in welding practice (approximately 100 K/h). In this context, the additional effect of an external shrinkage restraint on SRC must be considered in the form of increasing mechanical loads during welding, which are typically not within the scope of welding practice. To mitigate the probability of SRC during PWHT, it is imperative to reduce the welding heat input and to restrict the structural shrinkage restraint of the weld joint.

Weld reconstruction technology based on visual sensors is a crucial component of intelligent robotic welding systems. In thick-wall workpieces with big groove multi-layer automatic welding, precise measurement of the workpiece and weld seams directly affects subsequent weld path planning and posture planning of the welding torch. To address this issue, this study employs a three-line structured light measurement system for weld profile detection. A sub-plane fitting algorithm is proposed for 3D reconstruction of weld grooves, accompanied by a rapid workpiece coordinate system establishment method using three-line structured light to ensure accurate boundary segmentation. However, direct welding based on reconstructed feature points cannot guarantee high-quality results. Therefore, we investigated the effects of key process parameters, such as welding position, direction of welding, and torch inclination angle on weld bead geometry. A second-order general rotational composite design was implemented to develop regression models correlating welding parameters with weld bead characteristics. Finally, integrated process planning combining reconstruction data with optimized welding parameters was implemented for torch trajectory and orientation planning. Experimental results demonstrate that this methodology effectively satisfies quality control requirements for automated welding of thick-walled structural components.