Research on resistance welding of galvanized steel sheets
Research on resistance welding of galvanized steel sheets Text / Ming Anjun ã€Abstract】 Compared with other ordinary steel plates, galvanized steel sheets have excellent corrosion resistance. Electric resistance welding is an important production process and has been widely used in many fields, such as automobiles, home appliances, metal containers, Buildings, etc. However, the life of electrodes for resistance welding of galvanized steel sheets is very short. Nowadays, new types of resistance welding electrode materials have been under development, and people are eager to improve the service life of resistance welding. In recent years, various countries have conducted extensive research on resistance welding of galvanized steel sheets, and strive to find solutions to overcome various performance problems existing in electric resistance welding, thereby reducing the cost associated with manufacturing electrode materials. In this paper, the research on resistance welding of galvanized steel sheets is carried out, and some problems encountered in galvanized steel sheets are analyzed, and corresponding solutions are proposed for these problems. [Keywords] galvanized steel; resistance welding 0 Preface At present, the fuel tanks of Chinese automobiles are generally manufactured by using lead plates, which are not only costly, but also easily lead to environmental pollution. After the galvanized steel sheet is used to manufacture the fuel tank, not only the cost can be greatly reduced, but also the environmental pollution and the employee's physical harm can be reduced, but the service life must be greater than the original fuel tank. However, in the manufacturing process, we encountered a very big challenge, that is, the problem of difficult welding of electric resistance welding, especially the seam welding problem with air tightness requirements. In the manufacturing process, most of the foreign countries use electro-galvanized steel sheets with less zinc adhesion instead of seam welding, but this will greatly reduce the fuel tank life. In order to find the reasons for the difficulty in resistance welding of galvanized steel sheets, we have put forward a set of theories related to the determination of process parameters after repeated research. After tracking and investigation, the results are good. The experimental situation is now analyzed as follows. 1 Experimental materials and equipment 1) Material situation Fuel tanks are typically manufactured using lead-plated steel sheets, and the physical properties of the coating elements determine the difference between the lead-welded and galvanized sheet resistance welds. The materials selected for the experiment were lead-plated steel sheets. The physical properties of the lead and zinc coatings of the two materials are shown in Table 1. Table 1 Physical properties of plating elements Melting point (°C) Boiling point (°C) Hardness (diamond = 10) Character proportion Lead (Pb) 327.502 1740 1.5 Face-centered cube 11.3 Zinc (Zn) 419.58 907 2.5 Intensive hexagonal 7.13 2) Equipment situation Spot welding, projection welding and seam welding equipment were selected in this test. Their details are shown in Table 2. Table 2 Overview of spot welding, projection welding and seam welding equipment model Fixed capacity (KVA) Electrode material used Electrode width and diameter (mm) Place of origin Seam welder FN-150-5 150 Zirconium copper 6 (extreme) Shanghai Spot welding DN2-100 100 Zirconium copper 5 Shanghai Suspension spot welder DN2-75 75 Zirconium copper 5 Shanghai Note: The cone plane is the geometry of the spot welding electrode, the thickness of 7.5mm is the geometry of the seam welding electrical grade, and the roller electrode is extremely thick 6mm. 2 resistance welding 2.1 spot welding Spot welding on the fuel tank of the car is mainly used for the connection between the body and the partition plate and the fuel filler pipe bracket. Since the alloying reaction occurs between the plating layer and the electrodes under the condition of high-temperature welding, when the number of welding reaches a certain amount, a layer of zinc-copper alloy is formed on the surface of the electrode, which not only causes serious wear of the electrode, but also expands. The diameter of the welding surface causes the current density to become small, the welding quality is seriously degraded, and even pit corrosion occurs. After detailed analysis, we believe that it is very important to perform reasonable electrode cooling for spot welding. It is necessary to ensure that the cooling water flow is sufficient to ensure that the electrode can work in the greenhouse. The test tells us. The water flow should be controlled at 0.5 L/min, which is the best result. In addition, the number of hits should be increased by about 2,000 points, not to exceed, which is similar to spot-plated plate spot welding. The main reason for the spattering problem during spot welding is that the boiling point of zinc is too low, as long as the welding time and the flow rate of the cooling water are grasped during operation. The pilot also determined the process parameters of the spot weld joint, as detailed in Table 3. Table 3 Process parameters of spot welded joint Electrode pressure Welding power supply (A) Welding time (week) Plate thickness (mm) device Fuel pipe support plate 1500 1200-1500 10 1.2 DN2-75 Partition and body 5000 1300-1500 8 1.2 DN2-100 Fuel tank tube 6500 12500-13500 8 1.2 DN2-75 2.2 projection welding The oil drain hole in the fuel tank is actually formed by welding a 16 mm diameter hex nut inner hole and its own punching hole. The nut also has an ultra-thin coating, but when welding, compared with spot welding or seam welding, the thickness of the coating between the galvanized sheet and the galvanized sheet is reduced by half, and the welding is easier than the former two. See Table 4. Table 4 Process parameters of the convex welded joint Electrode pressure (N) Welding power supply (A) Welding time (week) Plate thickness (mm) device Oil drain 6500 13000-16000 8 1.2+ nut thickness DN2-400A 2.3 Seam welding Seam welding requires high airtightness when using galvanized sheet. Through analysis, we know that the difference between galvanized sheet and lead-plated sheet resistance welding is actually determined by the difference in physical properties of zinc and lead. Including the hardness, melting point, etc. of the elements, these have a great influence on the welding performance. Of course, the most influential factor is the boiling point temperature of the element. Table 5 shows the optimum process parameters for seam welding. It uses a welded fuel tank with a length of 950 mm, effectively avoiding leakage. Table 5 Optimal process parameters Current (A) Pressure (N) Time (on, off) Speed ​​(m/min) result Ab(MPa) Lead plate 20000 1960 3,2 2.90 Not leaking 317 Galvanized sheet No. 1 20000 2500 3,2 2.90 leak 337 Galvanized sheet 2 25000 6370 5,3 1.42 Not leaking 355 3 Conclusion Through experiments, we know that the resistance welding of galvanized steel fuel tanks does have many problems in the manufacturing process. When the external conditions are certain, we should consider whether the welding is standardized, so that we can not only clear our thoughts, but then ask questions. Ask, a strong solution. When welding galvanized sheets, it is extremely easy to cause electrode wear. Here we recommend selecting relatively inexpensive Cu-Cr and Cu-Zr electrodes. In the test, we have determined the specific measures of the process parameters. The use of galvanized steel sheets to make fuel tanks not only achieves better economic benefits, but also achieves better social benefits. 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