Numerical simulation technology in the hottest Aer

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Numerical simulation technology in aerospace welding

welding process is a complex process including thermal coupling, heat flow coupling, thermal metallurgy coupling and other thermal effects. Welding heat effect runs through the manufacturing process of the whole welded structure, and the welding heat process directly determines the microstructure, stress, strain and deformation after welding. Therefore, accurate analysis of welding thermal process is of great significance for guiding the formulation of welding process, microstructure analysis of welded joints, welding residual stress analysis and welding deformation analysis

when using ordinary arc welding or laser or electron beam and other high-energy beam methods for welding, highly concentrated heat sources are used for heating, and small welding pool will be generated near the central action point of the heat source. The whole weld pool and heat affected zone are distributed with non-uniform large gradient temperature field, which will have a very important impact on the manufacturing process and usability of welded structures

with the development of computer software and numerical simulation technology, it is possible to predict the feasibility of welding process in the welding manufacturing process and integrate it with the design, development and manufacturing of welding products. The emergence of digital manufacturing also requires designers to complete welding modeling with the help of information technology, and quickly develop products and processes, so as to reduce the impact of uncoordinated factors in the actual production process. The characteristic parameters are: ring stiffness: place the degree of pipe sample

through numerical simulation, we can study the heat, stress and metallurgical changes caused by welding, and predict the ability of welding deformation and residual stress, which is helpful for product developers to choose the most appropriate welding method and predict the welding performance more accurately. Integrating the welding thermal simulation process into the product design system can reduce the time required from product design to production, reduce production costs, reduce rework, and improve production efficiency

welding thermal numerical simulation can verify the process behavior that has an important impact on product quality, which will help to improve the design of welding products, deepen the understanding of welding process, and select the optimized process

Research on numerical simulation

the temperature distribution, microstructure transformation, welding residual stress and deformation during welding are all related to the thermal process. Therefore, in order to obtain a high-quality welding structure, these factors must be controlled, and accurately control the dimensional tolerance and precipitated phase to achieve the best prediction and control of the change process of welding temperature, microstructure and residual stress, which is particularly important for the control of welding quality

at present, the main computer display of numerical simulation of welding process is not zero. There are the following aspects:

1 Numerical simulation of welding temperature field, including welding heat conduction, arc physical phenomena, heat and mass transfer behavior of welding pool, etc

2. Numerical simulation of welding stress and deformation, including transient thermal stress and strain and residual stress and strain during welding

3. Welding chemical metallurgy and physical metallurgy process simulation, including chemical element transition, solidification, grain growth, segregation, solid-state phase transformation, heat affected zone embrittlement and hydrogen diffusion

4. Numerical simulation of mechanical behavior and properties of welded joints, including fracture, fatigue, mechanical inhomogeneity, geometric inhomogeneity, microstructure, structure and mechanical properties

5. Numerical simulation of welding quality evaluation, such as evaluation and prediction of cracks, pores and other defects

6. Numerical analysis of special welding processes, such as resistance welding, laser welding, electron beam welding, diffusion welding, ceramic and metal connection, etc

the commonly used numerical simulation methods of welding thermal process include difference method, finite element method and boundary element method. At present, there are many mature calculation and analysis software available for welding process analysis. These software can carry out linear and nonlinear finite element analysis of two-dimensional and three-dimensional electrical, magnetic, thermal and mechanical problems, and have the pre and post-processing function of automatically dividing the finite element lattice and automatically sorting out the calculation results and forming visual graphics. Therefore, the users do not need to compile simulation software from scratch. They can use commercial software and add secondary development when necessary, that is, they can get the desired results. However, before numerical simulation, it is necessary to comprehensively understand the relevant basic theories, modeling methods, initial and boundary conditions, data preparation and solution principles, so as to get the correct simulation results

in the numerical simulation of welding process, the simulation of welding temperature field and stress-strain field has the largest number, started earlier, and accumulated rich experience, which has been applied in practical production

Figure 1 the simulation of welding pool

temperature field is the basis for the simulation of welding stress-strain field and other phenomena in the welding process, which requires the construction of heat source model according to the welding process and the requirements of numerical simulation. The main goal of establishing the heat source model is to find the heat flow distribution form under the condition of corresponding welding parameters, so that the boundary line of the simulated molten pool (see Figure 1) is consistent with the weld fusion line observed in the experiment. Welding stress and deformation are related to plastic deformation during welding. Generally, the area where plastic deformation occurs is much larger than the area where metal melts. Due to mechanical relaxation, the welding stress and deformation are not sensitive to the heat and mass transfer process in the weld pool during the welding process. Therefore, for the analysis of welding mechanics, many complex heat transfer phenomena in the weld pool during the welding thermal process are relatively secondary. In this way, the solid heat conduction theory based on Fourier law can be used to solve the welding temperature field, The model can be simplified by changing the high-temperature thermophysical properties of the material, regardless of the complex heat transfer processes such as convection in the molten pool. Under the corresponding heat input conditions, as long as the fusion zone boundary (fzb) simulated by the heat source model is consistent with the actual weld fusion line, it can be considered that this kind of welding heat source model is reasonable, and this criterion is defined as the weld pool boundary criterion. The simulation of welding temperature field based on the criterion of weld pool boundary can fully meet the requirements of welding mechanical analysis (see Figure 2)

Figure 2 numerical simulation results of electron beam welding temperature field

the plastic deformation and heat transfer inside the welding deformed workpiece occur in the same space domain and time domain, but because the deformation and heat transfer belong to different physical properties, which are described by the elastoplastic problem and the transient heat conduction problem respectively, it is difficult to analyze their corresponding field quantities by the method of simultaneous solution. Generally speaking, the elastic-plastic finite element method uses the incremental method to gradually solve the relevant fields of the workpiece (such as velocity field, stress field, strain field, etc.), while the temperature field is gradually integrated by the time difference scheme. In this way, the deformation and temperature can be calculated at a certain instant, and their interaction can be taken into account through the connection between them, so as to achieve the coupling analysis of the welding thermal process (see Figure 3)

Fig. 3 simulation results of welding deformation of beam and plate structure

although the numerical simulation results of welding temperature field and residual stress and strain have some practical applications, due to the complexity of the welding process, there is still a large gap between a large number of numerical simulation research results of the welding process and the practical application, and there are many problems to be solved in the simulation. For the problems that can be solved, there are problems of low accuracy or high cost. Therefore, Further research on simulation technology is needed, and at the same time, the test technology to verify the numerical simulation results should be continued to be developed

Application of numerical simulation

in aerospace structure lean production and improved matrix infiltration of filler concurrent engineering, weldability numerical analysis has great development potential. In the production of Airbus 340 aircraft in Europe, the longitudinal reinforcing ribs of the aluminum alloy skin panel of the aircraft fuselage can be reduced by 20% by laser beam welding. The main challenge of welding is to maintain low deformation (especially transverse deformation) and reduce residual stress (especially longitudinal tensile stress). To consider the change of joint type, welding sequence, cooling conditions, clamping mode, longitudinal preload and other measures to achieve low deformation and residual stress, and determine these measures and their possible combinations, welding thermal numerical simulation technology is needed

Figure 4 the design process supported by numerical analysis

the design process of Airbus 340 aircraft can be divided into a series of work (see Figure 4), and the numerical simulation of the process plays an important role in the design process (see Figure 5). Figure 6 shows the numerical simulation supporting the welding process research

Figure 5 definition of manufacturing process in the design process

Figure 6 development of welding process supported by numerical analysis

welding process based on engineering analysis, numerical simulation and computer-controlled automatic production will be widely used, which will transform welding from experience based process to physical model-based process, and the welding production process will be based on a more rigorous scientific basis. The core of this transformation is simulation based on a comprehensive knowledge system, and information technology will play an important role; This knowledge includes data on welding performance, process, material and application. The comprehensive physical basic model of welding process will cover the whole life cycle of welding products. Numerical simulation will also play an important role in the integrity assessment, life prediction and damage repair of aerospace welded structures. (end)

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