Foreword
The rapid development of technologies such as computers, information, and networks has brought profound changes to the living environment and cultural atmosphere of human beings. This profound change must be reflected in the original manufacturing and even welding projects. Virtual engineering is a new field that emerges as the times require and moves forward at an alarming rate. Advanced manufacturing technologies proposed in recent years include, for example, computer integrated manufacturing systems (CIMS), concurrent engineering, and agile manufacturing. CIMS integrates relevant information in CAD, CAE, CAPP, CAM, CAT and other computer-aided technologies through the network. Virtual engineering further refines and implements the entire manufacturing process on a computer. To achieve welding virtual engineering is very complicated, it is a huge project in itself. It includes heat source, process control, welding metallurgy, stress deformation and other aspects. This article only introduces some developments at home and abroad in recent years from the perspective of welding mechanics simulation and the work we have done in this field for many years.
Welding mechanics studies include weld heat transfer, weld deformation and residual stress, weld cracks, and mechanical behavior of welded joints. Especially in recent years, with the development of high technology, as well as the application of automatic control and robots, the precision requirements for welding products are getting higher and higher. However, the law of variation of welding deformation and residual stress is still insufficiently understood and difficult to grasp. For example, in the CIMS system for controlling manufacturing precision in the automotive industry, welding deformation becomes the only factor that is difficult to predict and control. Over the years, scholars and experts at home and abroad have conducted a lot of research in the field of welding mechanics. In recent years, the author has also done a lot of research work in this field, and has published more than 100 academic papers at home and abroad. Some research results have been successfully applied in engineering. The introduction of this paper hopes to play a facilitating role in research and practical engineering applications in this field.
1. Development trends at home and abroad
In 2000, the Institute of Joint Science of Osaka University in Japan proposed a national project worth two billion yen ($20 million) in five years: “development of efficient and safe welding technologyâ€, in fact it contains a welding virtual project. Research. Its purpose is to develop a computer interface that is user friendly and efficient and securely soldered. It also gives three precision simulation programs, namely the welding process simulation program, the welded area organization prediction program and the deformation prediction program (Fig. 1). The objectives of each simulation program are: (1) The welding process simulation program includes an arc plasma model that requires no assumption of local thermodynamic equilibrium, and the prediction accuracy of the weld pool size is ±10%. (2) The microstructure prediction program of the welded area includes a formation model of acicular ferrite, which requires prediction of ferrite, acicular ferrite composition and room temperature strength within ±5%, ±10%, and ±50Mpa, respectively. (3) The welding deformation program includes the out-of-plane deformation prediction accuracy within ±15%. In order to develop the above simulation program, a series of precise experimental verifications, including physical properties, such as the surface tension of the molten pool in the plasma environment, the thermal conductivity of the solid state and the molten pool, are required.
Figure 1 Welding numerical simulation
With regard to the development of numerical methods for welding mechanics, in the early 1970s, Ueda Ueda of Japan first proposed the theory of welding thermal elastoplastic analysis considering the mechanical properties of materials and temperature, based on the finite element method, so as to make complex dynamic welding stresses. Analysis of the strain process is possible. Since then, HD Hibbert, EF Ryblicki, Y. Iwamuk, and K. Masubuchi of MIT in the United States have done a lot of research work on the prediction and control of welding residual stress and deformation. Canada's J. Goldak et al. analyzed the welding thermal stress from melting point to room temperature and proposed the constitutive equation for each temperature range. Swedish L. Karlsson et al. analyzed the welding deformation and stress of the slab splicing, especially the change of the gap at the front end of the weld and the influence of the spot welding. JB Leblond of France conducted theoretical and numerical studies on the plastic behavior of steel during phase transition. Based on the above research, etc., the SYSWELD special software was developed. The software can be used for the analysis of processes such as quenching, surface treatment, welding, heat treatment and casting, including material phase transformation, volume change and latent heat effects, surface hardness calculation, residual stress and strain calculation, and pre- and post-interaction treatment. T. Inoue et al. studied the coupling effects of temperature, phase transition and thermal stress in the temperature change process with phase transition, and proposed the general form of the constitutive equation under the condition of considering the coupling effect. Recently, the British Welding Institute has developed a "Structural Deformation Prediction System" (SDPS) that can be used to predict weld deformation of complex structures.
In the early 1980s, Xi'an Jiaotong University and Shanghai Jiaotong University began research on the theory of thermal elastoplasticity of welding and numerical analysis. Xi'an Jiaotong University cooperated with Hudong Shipyard to carry out experimental and numerical studies on the mechanism and prevention of cracks in single-sided welding terminals, and achieved remarkable results. Shanghai Jiaotong University published a monograph on the application of numerical analysis in welding in 1985, and introduced the research results at home and abroad. They developed a two-dimensional plane deformation and axisymmetric welding elastoplastic finite element analysis program, and successfully applied in welding stress analysis such as thin plates, slabs and tubes. In the 1990s, Shanghai Jiaotong University and Osaka University of Japan were three-dimensional. The welding stress and deformation problems have been studied together, and several ways to improve the calculation accuracy and convergence have been proposed. The relevant 3D welding analysis program has been developed and there are many successful application examples. In recent years, Tsinghua University and Tianjin University have also carried out numerical simulations of welding mechanics processes. Tianjin University directly applied the results of numerical analysis of local residual stress distribution in the study of fatigue strength of welded joints by local method.
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