Galvanized sheet spot welding machine / galvanized sheet welding machine
Shanghai Hao Jing's galvanized sheet spot welding machine uses intermediate frequency inverter technology, which successfully completes the problems of spot welding machine in galvanized sheet welding technology, thus prompting Hao Jing's medium frequency inverter spot welding machine to weld on galvanized sheet and aluminum plate. Another masterpiece in the field.
1. Difficulties in welding galvanized sheet
The presence of the galvanized layer makes the galvanized sheet have unique advantages in terms of rust prevention of the car body, but it is also the surface zinc layer that makes it more difficult to weld: due to the low resistivity, low hardness, and low melting point zinc on the contact surface Layer, which reduces the contact resistance, uneven current field distribution, and affects the formation and size of nuggets. With satisfactory welding quality, the applicable welding parameter range is small. Because the zinc layer has a low melting point, the surface is easy to burn. After the electrode is stained, an alloy is formed on the electrode surface, which is prone to overheating and deformation, which reduces the electrode life and affects the welding quality. Galvanized sheet is prone to welding spatter when welding, which affects the stability of the quality of the solder joint. Cracks, pores, or softened structures appear; during spot welding of galvanized steel, due to unreasonable welding specifications, some zinc will remain in the joints. Zinc-iron alloys may form fine cracks or pores during the nucleation and crystallization process. Softened tissue can also form over time.
2. Ways to improve spot welding quality of galvanized steel
(1) Select and strictly control the welding process parameters. According to the actual experience of the factory, when spot welding galvanized sheet, the current should be increased by 20% to 30% compared with the non-plated steel sheet. At the same time, the electrode pressure should be increased by 20% and the preload time should be increased 10%. Strong specifications are recommended to meet high current requirements.
The evaluation of spot welding quality of galvanized steel refers to the strength and corrosion resistance of a single welding point, and more importantly, the qualification rate of the welding point under large production conditions. There are quite a few factors that affect welding quality in actual production, such as fluctuations in network voltage, shunting, electrode wear, and assembly quality. Due to the small range of welding parameters of galvanized steel, the welding parameters need to be strictly controlled during the spot welding process, and the process parameters need to be adjusted when the plate thickness changes.
(2) Use reasonable electrode materials, electrode shapes and sizes, and ensure good electrode cooling. The frustum-shaped electrode tip end face is considered the best. When the size is increased, the contact area is increased, the current density is reduced, and the heat dissipation effect is enhanced, which all weakens the heating degree of the welding zone, so the size of the nugget is reduced, and the bearing capacity of the solder joint is reduced. The diameter of the end face is generally 6-8mm. If it exceeds 8mm, it needs to be ground in time. The upper and lower electrodes of the welding tongs and the plate should be kept as vertical as possible during welding.
If the life of an electrode tip is regarded as a cycle, it can be divided into three stages: the initial stage, the stable stage, and the final stage. The initial stage of welding is the dozens of joints at the beginning of welding, often accompanied by spatter, copper color and a small amount of adhesion; The period is the period when the welding quality is stable and there is no spatter, copper color and adhesion; the last period is the last stage of the welding life, and spatter, copper color and adhesion reappear. Different welding parameters, the proportion of each stage is significantly different, we need to reasonably adjust the welding parameters and strive to expand the proportion of the stable period.
The electrode materials mainly include Cu-Cr (0.8% Cr), Cu-Zr (0.15% Zr), Cu-Cr-Zr, and dispersion-strengthened copper (Also referred to as DSC) containing Al3O2 particles. Factory experience shows that in some cases of actual production, when using DSC 20 grade alloy electrodes, electrode adhesion is reduced.
(3) The pulse method is used to weld the galvanized steel plate. One is to increase the preheating and post-heating currents, and the other is to increase the slow-rise and slow-down currents. The change of current can promote the formation of welding nuclei. The change of current before welding helps the uniform formation of welding nuclei. The change of current after welding helps to confine the nugget and prevent spatter. In addition, it can also be combined with secondary welding to make the galvanized layer melt and flow to the surrounding for a longer time to ensure the welding quality.
(4) Adding control functions, improving control accuracy, and real-time monitoring of welding parameters This measure has a lot to do with the overall mechanization and automation of the factory, and it is not easy to control them individually.
3. Advantages of intermediate frequency inverter DC spot welding machine when welding galvanized steel
The intermediate frequency inverter DC welding machine has many advantages over the industrial frequency welding machine, such as higher welding energy, more accurate parameter adjustment, and reduced electrode heat and mechanical pressure. A large part of these advantages are beneficial to galvanized sheet welding. This makes the intermediate frequency inverter DC welder show absolute advantages when welding galvanized steel. Among them, the "zero-transition-PWM" or "zero-switch-PWM" converter of the intermediate frequency inverter DC welding machine expands the welding specification adjustment range by 3 to 4 times by adjusting the duty cycle, which can fully balance the welding parameters.
The influence of various welding parameters on welding quality is as follows: Welding current: The effect of current on the heat generation is greater than both resistance and time. If the current is too large, it will spatter and the strength of the solder joint will decrease. Welding time: The length of time also has a great impact on the quality of spot welding. If the time is too long, excessive heat input will also cause splashing, which will reduce the strength of the welding spot. In order to ensure the nugget size and strength of the solder joint, the welding time and current can complement each other within a certain range. The choice of strength and weakness specifications depends on the properties of the metal, its thickness, and the power of the welder used. Electrode pressure: If the pressure is too small, it is easy to cause splashing. If the pressure is too large, the contact area of the welding zone will be increased, the current density will be reduced, and the size of the nugget will be reduced.
In addition, the intermediate frequency inverter DC welding machine also has the advantage of dynamic adjustment. Its time adjustment resolution can reach 1ms, the response speed of feedback control is fast, and the control accuracy is high. In addition, the intermediate frequency inverter DC welding machine has no current peak, no extra cooling time, and no interactive magnetic field, which reduces the heat and mechanical pressure of the electrode, thereby slowing the electrode tip wear. It meets the requirements of serious electrode loss when welding galvanized sheet, and makes the shape of the electrode tip easy to maintain and difficult to stick.
4. Energy-saving advantages of IF inverter DC spot welding machine
The IF inverter DC spot welding machine has a compact welding current pulse, no inductance component, and a power factor as high as 0.9. Compared to the AC welding machine's power factor of 0.6 to 0.7, the energy saving effect is very obvious. Figure 2 is a comparison of welding energy consumption between power frequency AC and intermediate frequency DC welding machines. With the same welding parameters at the welding end, the welding energy consumption of intermediate frequency DC welding machines is 20% lower than that of power frequency AC welding machines. Significant energy saving effect.
The significant advantages brought by IF inverter DC resistance welding due to its own IF characteristics and DC characteristics have been recognized by the entire welding industry. The IF inverter DC welding machine has significantly reduced volume and weight, as well as high efficiency and energy saving, low power loss, The advantages of fast dynamic response, excellent control performance and excellent electrical performance make it more suitable for emerging welding plates such as galvanized sheet and high-strength sheet, which have brought revolutionary changes to the development of welding equipment.