The latest development of resistance welding techn

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The latest progress of foreign resistance welding technology

in recent years, with the rapid development of automobile, aerospace, construction, transportation, light industry, household appliances and other industries, the corresponding industrial products are constantly updated and developed in their materials, structures and application fields, and the requirements for the processing quality of products are constantly improving, As a widely used material processing technology in the manufacturing of these industrial products, resistance welding has also been greatly challenged

because the resistance welding process is quite complex, it includes a variety of influencing factors, such as: material to be welded, current, electrode pressure, power on time, electrode end face shape and size, shunt, distance from the welding point to the edge, plate thickness, workpiece surface state, etc., and these factors are interrelated and interact to a certain extent. At the same time, the invisibility of the nugget and the instantaneity of the welding process bring great difficulties to the welding quality control. In order to meet the needs of the development and application of new materials, new processes and new products in industry, so that the resistance welding process and equipment can meet the requirements of modern production, the welding industry in various countries has done a lot of work in the control of resistance welding process and equipment in the past decade, It mainly focuses on the following aspects:

1) computer simulation research of resistance welding process

2) weldability research of new materials

3) research on monitoring methods of resistance welding quality

Computer Simulation Research of resistance welding process

resistance welding is a complex process involving electricity, heat transfer, metallurgy and mechanics, including electromagnetism during welding, heat transfer process, metal melting and solidification, phase transformation during cooling Welding stress and deformation, etc. These factors must be controlled to obtain a high-quality welded joint. The traditional resistance welding process and parameter formulation method are obtained through a series of process tests and empirical data. However, in terms of development, with the development of computer technology, numerical simulation methods will play an increasingly important role. For example, using new high-strength steel and other materials to manufacture new engineering structures, especially for some important aerospace structures, there is little experience to rely on. If we only rely on experimental methods to accumulate data, it will take a long time and money, and any attempt and failure will cause significant economic losses. At this point, the numerical method will play its unique capabilities and advantages. As long as the applicability of the numerical method in dealing with a certain problem is proved by a small number of validation tests, a large number of screening work can be carried out by computers, rather than a large number of tests in workshops and laboratories. This greatly saves manpower, material resources and time, and has great economic benefits. Once various welding phenomena can be simulated by computer, we can determine the best design, best process method and welding parameters when welding various structures and materials through computer system. In addition, numerical simulation is also widely used to analyze the strength and properties of spot welded joints

due to the invisibility of nugget formation in resistance spot welding, it is quite difficult to observe its experiment, and the establishment of theoretical model is of great value to its analysis and research. Since the initial finite element analysis model of spot welding established by nied in 1984, many finite element models of spot welding have appeared, which provide a theoretical basis for actual production

with the in-depth application of finite element numerical simulation method in the field of resistance welding research, the international research in this field in recent years mainly focuses on the following three aspects:

1 using the electrical thermal mechanical coupling finite element simulation method

resistance spot welding process is a complex process with the interaction of electrical, thermal, mechanical and metallurgical phenomena, which includes electric field problems, heat conduction problems and thermal elastoplastic deformation problems, Therefore, the interaction and coupling effects of all these problems, the change of contact state between workpiece electrode and workpiece workpiece interface caused by pressure, and the thermal deformation play an important role in these interactions. Strictly speaking, to solve such coupling problems, we should solve the electric field, thermal field and force field at the same time. Therefore, in recent years, the finite element analysis of resistance spot welding has gradually developed from the analysis of isolated electric field, thermal field and force field to the analysis of electric thermal mechanical coupling. For example, the American scholar sun, X. used the electric thermal mechanical coupling finite element to simulate the nugget growth and thermal distribution in the process of spot welding, and studied the resistance spot welding of aluminum alloy and steel plate with intermediate transition materials. The simulation results are verified by experiments: this model can be used in the electrode selection stage, To reduce welding deformation and improve welding quality; Korean scholar Cha, b.w. obtained the residual stress after welding and the spot welding parameters that affect the residual stress through the electrical thermal stress analysis of the resistance spot welding process of 304 stainless steel; Feng, Z. and other scholars have developed an integrated model to simulate the process and performance of resistance spot welding, which combines the basic physical phenomena and load conditions in spot welding. This method is composed of three parts: process model, microscopic model and structural model. It can comprehensively evaluate the performance of spot welding joints under the action of electricity, heat and force; In the research of resistance spot welding of aluminum alloy, Japanese scholar De, a used the finite element model of electric thermal mechanical coupling to predict the nugget diameter, penetration, contact diameter between electrode and plate under different welding current, welding time and electric force. It was verified that this model is very useful for offline detection of the influence of welding parameters on the size of solder joint

2 accuracy analysis of computer simulation

with the increasingly extensive application of computer simulation method in the research of resistance welding process, in order to further develop it for industrial production, we must consider how big the error of this simulation method is? How to improve the accuracy of numerical simulation and make the results closer to the actual welding situation. Recently, some foreign scholars have made special research on this aspect. For example, American scholar Cavendish, James C. mentioned in the article: an important problem in the evaluation of computer simulation model is to judge whether it is accurate enough. Usually people use Bayesian theorem statistical strategy to analyze the error range of simulation calculation, but statistical analysis becomes quite difficult in the case of a large number of inputs and unknown parameters and a large amount of data. Hasselman, Timothy and other scholars used the electric thermal mechanical finite element model to analyze the resistance spot welding process of aluminum alloy, and calculated the nugget size and surface indentation, using the principal element method based on the uncertainty model method, through the linear mean square deviation of nugget size and indentation statistics, the prediction accuracy of the finite element method was obtained

3 industrial application of computer simulation

computer numerical simulation has the advantages of low cost, flexible and convenient parameter change, but most of them are used for off-line calculation and simulation. How to effectively apply this method to industrial production to evaluate and control welding quality has also become a focus of welding scientists in recent years. Based on long-term engineering research and industrial cooperation, Danish scholars Zhang and Wenqi have developed a new welding software based on finite element method: sorpas, which is used to simulate the process of resistance projection welding and spot welding. In order to enable the software to be directly applied by engineers and technicians in the factory, all parameters in resistance welding are considered and automatically implemented in the software. The software supports windows friendly interface, flexible operation, flexible geometric design of workpiece and electrode, and parameter setting is like a formal welding machine. It can be used in industry to support product development and process optimization. Now volkswangen, Volvo, Siemens, abb and other companies have begun to adopt this software. Li and Wei of the University of Washington in the United States put forward a spot welding quality evaluation model based on the spot welding meeting site, which will be divided into three sub fields. It uses a finite element analysis model to represent the change of the contact area, and applies it according to the simulation results. The test shows that this method is successful under different electrode sizes, electric forces, welding time and current, and it will provide important information for resistance welding monitoring and control

Research on weldability of new materials

with the rapid development of industry, higher requirements are put forward for the performance of industrial products (especially automotive) shell materials, and the upgrading of product materials is promoted. For example, in order to improve the corrosion resistance of automobile shell and improve the service life of automobile, galvanized steel plate is widely used in automobile body manufacturing instead of ordinary cold-rolled steel plate; In order to reduce the overall weight of the body and save energy consumption, major automobile companies around the world are developing vehicles with aluminum alloy or high-strength steel bodies. Because resistance spot welding is widely used in the assembly and manufacturing of sheet metal structures such as automobile bodies, in order to ensure the welding quality, it has become a very urgent task to study the resistance spot welding performance of new materials such as aluminum alloy, galvanized steel sheet and high-strength steel. In recent years, welding workers in various countries have done a lot of theoretical and practical research work in this regard, and have made some achievements

1 research on resistance spot welding of aluminum alloy

the characteristics of aluminum alloy, such as low melting point, low yield strength, good conductivity and heat conductivity, and the existence of surface oxide film, have brought great difficulties to resistance spot welding. In recent years, welding scientists in various countries have mainly done the following research:

in the research on the electrode life of aluminum alloy spot welding, lum, l of the University of Waterloo in the United States, used scanning electron microscopy Sem/edx, XRD and other methods, the research shows that: from electrode decay to final failure, it mainly experienced four stages: Aluminum stripping, aluminum and copper alloying, electrode end face corrosion spots and electrode end face pits. Because corrosion spots and pits originated from aluminum stripping and alloying, the author believes that regular cleaning of electrode surface can increase electrode life, which is conducive to the application of aluminum alloy in automobile production; Fresz, B of the University of California studied the influence of the alloy composition of the copper electrode on the electrode life. Different copper electrode materials such as Cu Cr, Cu Zr, Cu Cr Zr and Cu be were used in the test; Dorn, Lutz and other scholars proposed the use of composite electrodes in spot welding aluminum alloy to improve its service life. They studied the use of composite electrodes inlaid with tungsten at the end of chromium zirconium copper electrodes to weld aluminum alloy. They found that the electrode service life can be 1.5 to 2 times higher than that of the manufacturers of Alex Thomson sailing race, 60 foot carbon fiber reinforced Hugo Boss racing boat and BAC (Briggs automotive company) automobile company, which produces mono supercars

in the process research of aluminum alloy spot welding, sari, H. and other scholars studied the relationship between electrode contact radius and contact resistance during aluminum alloy spot welding, as well as the relationship between electrode contact radius and workpiece to workpiece contact area through aluminum alloy spot welding process test; CHO, y of the University of Michigan in the United States used experimental research methods to compare the resistance spot welding processes of aluminum alloy and steel. According to the leaf profile curve obtained from the test, the range of available welding current and the button diameter after the damage of the welding spot were determined, and these two parameters were used to evaluate the spot welding quality of aluminum alloy and steel. The test showed that electro rigid PVC foamed plastic was widely used in construction, decoration, furniture The pole size in advertising and other fields has a great impact on the button diameter after the steel solder joint is damaged, but there is no good corresponding relationship with the aluminum solder joint, and the button diameter after the aluminum solder joint is damaged fluctuates greatly

in addition, the finite element simulation of aluminum alloy spot welding process is also a research hotspot of scholars all over the world in recent years

Research on resistance spot welding of high strength steel

advanced high strength steel has strength

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