Yes, it is possible to estimate fluid flow behavior in the weld pool by analyzing the temperature distribution in the fusion zone. The temperature distribution in the weld pool provides valuable information about the thermal dynamics and fluid flow within the molten metal during welding processes.

The temperature of the weld pool is influenced by various factors, including the heat input, welding speed, material properties, and the geometry of the weld joint. Analyzing the temperature distribution can help in understanding the heat transfer mechanisms, fluid flow patterns, and the solidification process in the weld pool.

Computational models, such as finite element analysis (FEA) or computational fluid dynamics (CFD), can be employed to simulate the thermal behavior and fluid flow in the weld pool. These models take into account the governing equations of heat transfer, fluid dynamics, and phase change to predict the temperature distribution and flow patterns during welding.

Experimental techniques, such as infrared thermography or thermocouple measurements, can be used to capture the temperature distribution in real-time during the welding process. By combining experimental data with numerical simulations, researchers and engineers can gain insights into the fluid flow behavior within the weld pool.

Understanding the fluid flow in the weld pool is crucial for optimizing welding parameters, minimizing defects, and ensuring the desired mechanical properties of the welded joint. It can also contribute to improving welding processes, enhancing the quality of welds, and advancing the overall understanding of metallurgical phenomena during welding.

Numerical simulation for dynamic behavior of molten pool in tungsten inert gas welding with reserved gap

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Abstract

A 3-dimensional transient numerical analysis model of tungsten inert gas (TIG) welding with a reserved gap was established in this study. The loss of the total heat input and change in arc pressure due to the reserved gap were considered in this model. The dynamic variations of the flow field and deformation in weld pool were analyzed. Simulated results indicate that the maximum sag of weld pool is larger, and the top surface area of weld pool is smaller as the reserved gap increases. The flow tendency of the molten metal is mainly backward, and the top surface of the weld pool is higher in the front part and lower in the rear part. The liquid metal flows from both sides to the middle, bringing heat into the gap. The liquid metal in front of the weld pool flows to the back of weld pool through the gap, which facilitates weld penetration.

Introduction

TIG welding, a critical joining technique in modern manufacturing, has the advantages of high arc stability, low cost, and good weld formation; it is widely used in the welding process of important components, such as pressure vessels and pipes [1]. The technology of one-side welding with back formation is needed in producing important sheet welding structures or in environments with limited back working space. A gap is typically required in welding processes that use one-side welding with back formation technology, and such a gap is an important condition to achieve penetration and good back formation [2]. However, ensuring gap uniformity during welding is difficult due to assembly errors and thermal deformation. The dynamic behavior of fluid flow and the distribution of temperature field directly affect the penetration and shape of the weld. Therefore, the effect of gap on welding temperature field and flow field is very important for high-quality butt welding. It is difficult to completely and accurately obtain the temperature distribution and fluid flow of weld pool by experimental means. Numerical simulation contributes to reveal the influence mechanism of the gap on the dynamic behavior of the molten pool flow field and the penetration, which has a certain theoretical guiding significance for the process optimization and penetration control of reserved gap butt TIG welding.Meanwhile, heat source is an important factor in determining molten pool behavior in numerical simulation. Eager and Tsai [3] established a Gaussian heat source model to approximately characterize heat flux density of the spot heated by the arc on the workpiece. They theoretically predicted the molten pool, which was in good agreement with reality. Goldak et al. [4] established a double ellipsoidal heat source model, in which the source of the heat is improved. The Gaussian and double ellipsoidal heat source models are commonly used to study weld pool behavior in TIG welding. Given that the numerical simulation requirements for special welding processes are continuously improving, a combined-type welding heat source model is considered an ideal option and must thus be developed. Han et al. [5] used three types of combined heat sources to simulate the temperature field of the K-TIG welding process. They found that the temperature field obtained from the combined heat source of double ellipsoidal heat source and three-dimensional Gaussian heat source was in line with the actual situation. However, no reserved gap was considered in those heat models.Fluid flow has close relation to forces in the weld pool. Oreper et al. [6] analyzed the TIG welding pool of a fixed arc and established a corresponding two-dimensional axisymmetric mathematical model while considering electromagnetism, surface tension, and buoyancy. Kou et al. [7] built a three-dimensional quasi-steady-state model in the moving arc TIG welding and analyzed the convection in the molten pool. Fan et al. [8] settled the irregular molten pool boundary and liquid–solid interface through boundary matching coordinates and analyzed the fluid flow and temperature field of full-penetration weld pool in TIG welding via numerical calculations. Zhao et al. [9] established a 3D transient numerical analysis model of TIG welding to calculate the evolution of weld pool during welding, and analyzed the forces in the weld pool and proposed a criterion for full penetration. Based on this study, Zhao et al. [10] developed a simulation model of a weld pool in full-penetration state, calculated the dynamic changes in the forces acting on the molten pool, and analyzed the percentage of each component of the slump and support forces. Meanwhile, Xu et al. [11] calculated the flow field of the molten pool of TIG and A-TIG via numerical simulation. Their results showed that the active agent changed the surface tension gradient which, in turn, caused the molten metal flow pattern to change, resulting in a strong eddy current and an increased penetration depth. Han et al. [12] established a 3D model of TIG welding and discussed the effects of buoyancy, arc pressure, drag force, and Marangoni force on the formation and molten pool flow behavior. They concluded that the Marangoni force is the main driving force, whereas the effect of buoyancy is the smallest in TIG welding. Huang et al. [13] analyzed the molten pool flow behavior during GTAW welding by high current through particle tracking technology. They reported that the molten metal is affected by complex driving forces during the flow process. Furthermore, the liquid metal at the centerline diffuses to both sides of the weld pool, and the surface molten metal performs a more complex rotating motion inside the molten pool during the forward-to-back movement.The inevitable surface deformation of weld pool has been explored by some researchers. Kong et al. [14] simulated the temperature field and fluid flow in TIG welding pool and the change in free surface by using Cast3M software. They predicted the shape and dimension of the weld pool. Traidia and Roger [15] studied the arc and weld pool behavior of pulsed current GTA welding on the basis of a unified model and found changes in the free surface at the bottom and top of the molten pool through force balance equations. Li et al. [16] established a unified model of GTAW using static equilibrium and dynamic mesh technology and then analyzed the effect of interface deformation on the shape of the weld pool. Pan et al. [17] proposed a 3D model to explore the weld pool behavior as well as weld shape in high-speed VP-GTAW. They found that the outward flow mode of the molten metal under surface tension is the main flow, and the counterclockwise cycle at the middle area of the molten pool is driven by electromagnetic force. Meanwhile, the weld pool surface was deformed due to the driving of arc pressure. Huang Yong et al. [18] built a three-dimensional transient TIG welding pool numerical model and tracked the free surface deformation in the weld pool using the volume-of-fraction (VOF) method. They observed the deformation behavior of the weld pool surface and the distribution of its heat transfer and velocity field under the independent actions of buoyancy, Marangoni force, electromagnetic force, and arc pressure under high current. Meng et al. [19,20] established models of arc heat flow, arc shear stress, arc pressure, and electromagnetic force on the basis of the physical characteristics of the large surface deformation of the weld pool in high-current and high-speed TIG welding. The results indicated that the arc shear force mainly promoted the free surface deformation in weld pool, which was inhibited by surface tension. All the above-mentioned studies examined gap-free welding and did not consider a reserved gap.Cho et al. [21] carried out three-dimensional transient numerical simulations of multiple welding positions during GMAW with and without gaps in the V-shaped groove, after which they analyzed the weld pool flow patterns at different welding positions. The simulation results showed that forming a fully penetrated weld in a flat position proved to be very difficult when welding thick plates without reserved gaps. Cho et al. [22] used computational dynamics to study the weld pool dynamics in laser keyhole welding with gap-preserved butt welding, in which the diameter of the wire is larger than the gap. Their results showed that when keyholes are present, the momentum at the rear of weld pool area is considerably reduced compared with the momentum at the front. However, the above-mentioned studies ignored the effect of the butt gap on the heat source distribution and liquid metal flow.In this study, a 3-dimensional transient numerical model of the TIG welding pool with a reserved gap was developed considering the influence of this gap on the arc thermal-mechanical distribution. The simulation was carried out on FLUENT software to analyze the characteristics of temperature and flow fields in the molten pool. The established model was validated by comparing the experimental data with the calculated results. Our findings help provide a deep understanding of the process of TIG welding with a reserved gap.

Section snippets

Mathematical models A schematic of the geometric model for TIG welding with reserved gap is shown in Fig. 1. As the weld pool behavior during the welding process involves extremely complex heat and mass transfer phenomena, these are difficult to consider completely in the mathematical model. On the premise of ensuring the calculation accuracy, the following basic simplifying assumptions are followed in the mathematical modeling process to effectively reduce the calculation time and the cost: (1)The molten metal flow

Simulation and verification of the welding process Based on the mathematical model established above, a numerical simulation of the TIG welding process with a reserved gap was performed in this study. The Q235 low-carbon steel was applied as base metal, and the reserved gap was 0.6 mm. Table 1 shows the specific parameters of the TIG welding process.The size of the calculation domain was set at 20 mm × 8.3 mm × 4 mm. The geometric model was initialized using FLUENT software. The initialization conditions are as follows:

The average

Conclusion (1)A 3-dimensional transient numerical analysis model of TIG welding with a reserved gap was established in consideration of the effect of gap and the deformation of free surface on the arc heat-force distribution during welding. The simulated data show favorable agreement with the experimental results. Moreover, the proposed model can reasonably and accurately reflect the dynamic changes in the molten pool. (2)The gap has a great influence on the arc heat-flow distribution. Before fusion, the arc

Funding This work was supported by the National Natural Science Foundation of China (No.51675309)

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements This work was financially sponsored by the National Natural Science Foundation of China (No. 51675309).

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Yes, analyzing the temperature distribution in the fusion zone can provide insights into the fluid flow behavior in the weld pool. Temperature gradients influence fluid dynamics, affecting factors like convection and material flow during welding processes.