Application of the hottest medium frequency spot w

2022-08-22
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Application of medium frequency spot welding machine in automobile industry

with the rapid development of automobile industry, the safety of automobile body structure and the application of new materials pose new challenges to the welding process of body in white. For the welding of coated steel plates, glued steel plates, multilayer plates and plates of different materials, the traditional power frequency welding machine is difficult to meet the welding requirements, and various advanced welding processes and welding equipment, such as medium frequency welding machine, laser welding machine, etc., came into being

in recent years, some foreign enterprises that produce large quantities of cars have applied medium frequency spot welding robots and servo technology spot welding robots to the car body in white welding line. Especially in Europe, the use of medium frequency spot welding robots has accounted for 40%, and has been extended to the spot welding of aluminum alloy car bodies. In China, the medium frequency welding machine has also been more and more widely used in major automobile factories, such as FAW Volkswagen, Chery, Beijing Hyundai, Dongfeng Nissan and other manufacturers have applied the medium frequency welding machine to automatic line welding or manual spot welding

compared with the traditional power frequency welding machine, the biggest advantage of the medium frequency welding machine lies in the good DC polarity and good welding quality. Taking the application of rexrothpsq6000 medium frequency welder in Chery car A5 body in white production line as an example, this paper illustrates the good welding quality and performance of the medium frequency welder

at the skeleton assembly station of A5 BIW production line, robots use power frequency welding machines to weld. At the threshold of the left and right side walls of this station, there are 10 welding spots welded by four layers of plates with a total thickness of 5.5mm. The welding quality of the welding spots here is very unstable. When the welding current is too large, it will cause the solder joint to burn or burn through; When the welding current is adjusted small, it will cause weak welding or faulty welding. No matter how you adjust the welding parameters, you can't get a stable and good welding spot quality, because there are not only a large number of plate thickness and steel plate layers, but also a certain assembly gap during assembly, and the power frequency welding machine can't automatically adjust the welding parameters according to the actual assembly state to ensure the welding quality. In this regard, rexrothpsq6000 medium frequency welding machine can just overcome the defects of power frequency welding machine

before using the medium frequency welding machine, the technician uses the four layer plate test plate to carry out the welding test with the power frequency welding machine and the medium frequency welding machine respectively to observe the welding quality. The test materials of the four ply plates are four cold-rolled low-carbon steel plates combined with

(1.8+1.5+1.5+0.8) mm. The electrode diameter of the welding tongs is 16mm. The welding parameters have been optimized through many tests. The final test results are shown in Table 1

it can be seen from table 1 that the welding performance of medium frequency welding machine is significantly better than that of power frequency welding machine for the welding of multi-layer plates, whether from the operating environment, or from the quality and stability of welding joints. Since the current of the medium frequency welder is very close to the DC current, there is no current peak during welding, and the heat increase during welding is relatively stable without fluctuation, so there is little or even no welding spatter. Therefore, the operating environment of the medium frequency welding machine is much better than that of the power frequency welding machine, and the current thermal efficiency of the medium frequency welding machine is higher than that of the AC current, so the nugget diameter of the welding spot of the medium frequency welding machine is 1 ~ 2mm larger than that of the power frequency welding machine. Table 1 Comparison of the welding results of power frequency welding machine and medium frequency welding machine on the four-layer plate

then use power frequency welding machine and medium frequency welding machine to weld the welding points of the four-layer plate at the threshold of the side wall of the A5 car body. The test results are basically consistent with the test results made with the test plate. See Figure 1 for the specific body welding points. The nuggets of the five welding spots welded by the medium frequency welder are between 5 ~ 6mm, and the nuggets of the three welding spots welded by the power frequency welder are between 3 ~ 4mm

Fig. 1 broken inspection results of welding joints of four layers of plates by intermediate frequency welding machine and power frequency welding machine

after a period of on-site verification, the intermediate frequency welding machine can not achieve zero pollution in essence at the threshold of A5 side wall. The welding quality of four layers of plates is qualified and stable, which is significantly superior. We have adopted a multi cavity mold to the welding quality of power frequency welding machine. Such excellent welding quality is not only related to the DC polarity of the medium frequency welder, but also to its control system. Rexrothpsq6000 medium frequency welding machine has powerful monitoring software and a high degree of intelligence. It adopts constant power control technology and servo motion controller (pneumatic element), which can control the welding current, welding time, welding power and welding pressure in a full closed loop

constant power control technology is to monitor the secondary current and secondary voltage. By adjusting the welding time and welding current, it ensures that the input power of each welding nugget is equal. Therefore, it can effectively compensate for non machine disturbance factors such as welding shunt, poor welding assembly, and changes in the composition of welding base metal. First, it selects a standard test plate according to the welding conditions and establishes a current. But now ducere has changed the sample curve of claim and resistance, and then in the actual welding work, it compensates the actual welding current and welding time according to the actual welding resistance (see figures 2 and 3)

Figure 2 welding parameter curve with glue interference between welding plates

Figure 3 welding parameter curve with coating interference between welding plates

Figure 2 is a welding parameter curve with glue interference between welding plates, the red curve is the actual welding current time curve, the black curve partially coincident with it is the welding current time curve of the welding sample, and the green curve is the actual welding resistance time curve, The black curve partially coincident with it is the welding resistance time curve of the welding sample. The sample is the welding of the same steel plate without glue. When there is glue between the welded plates, the plate resistance is much higher than the sample resistance, so the welding current suddenly increases at the beginning, causing the glue layer to be broken down, At the same time, Zhejiang Liancheng Electronic Technology Co., Ltd. plans to invest in the construction of zahanaoer Industrial Park to process 300000 tons of aluminum alloy new material products (aluminum plate, aluminum strip, aluminum foil, aluminum forging hub and aluminum alloy new material) welding current every year, so as to prolong the welding time and ensure the quality of welding joints. Figure 3 is a curve of welding parameters with coating interference between welding plates. The meaning of the curve is the same as Figure 2. When there is coating interference between welding plates, the control system compensates by increasing the welding current

because rexrothpsq6000 medium frequency welder has the advantages of the above two aspects, its welding quality control is far better than that of power frequency spot welder. However, its disadvantage is that the price is 6 ~ 8 times higher than that of ordinary power frequency welding machine, and the one-time investment is large. However, its comprehensive performance will determine its application degree. Let's take a look at its comprehensive performance. Compared with ordinary power frequency welding machines, it has the following characteristics:

1 The welding current of the medium frequency welding machine is close to complete DC. Because there is no obvious peak current, the size of the nugget expands steadily, there is almost no splash, and the welding quality is stable and the thermal efficiency is high. Compared with power frequency welding machine, the welding current of medium frequency welding machine can be reduced by 40%, and the service life of electrode can be greatly extended

2. The transformer of medium frequency welding machine is small in weight and volume, and the input power is low, so it is convenient to use transformer connected welding tongs. When used in robot spot welding operation, the load of the robot can be reduced, while when the power frequency welding machine is used on the automatic line, a robot with stronger load capacity is required

3. The response speed of medium frequency welding machine is only 1/20 of that of power frequency welding machine. The current can reach the set value faster, analyze parameters more accurately, and control welding quality more accurately

4. The three-phase load of medium frequency welding machine is balanced, the power factor is high (about 0.9), and energy saving. While the two-phase power frequency welding machine is difficult to ensure the balance between phase voltages when working, and the power factor is low (about 0.6), while the three-phase power frequency welding machine is difficult to achieve constant current output

5. The medium frequency welding machine is suitable for welding a variety of materials and dissimilar metals, such as aluminum alloy, stainless steel, high-strength steel plate and other materials. In addition, the welding quality of galvanized sheet and ordinary multilayer sheet is also much higher than that of power frequency welding machine. The power frequency welding machine is only suitable for materials with good welding performance, such as low-carbon steel plate

from the perspective of comprehensive performance, the energy cost of medium frequency welding machine is nearly 1/3 less than that of power frequency welding machine. It is suitable for automatic line application, has a high degree of intelligent control, and is suitable for a wide range of materials. It meets the increasing requirements of automotive safety and the development direction of new material welding. It will be more and more widely used in the automotive industry. (end)

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