Application of medium frequency servo robot welding tongs
At present, the frequency used for intermediate frequency welding is divided into power frequency and intermediate frequency. The power frequency is a common power frequency of 50 Hz. The intermediate frequency refers to 800 to 1000 Hz after the power frequency is pulse-width modulated PWM. The control principle is shown in Figure 1. (4) It is suitable for welding dissimilar metal MF spot welding welding current waveform can be set. The DC polarity effect and good thermal efficiency make the current welding thermal efficiency higher than the AC spot welding, and can be welded with low current. The soldering core temperature comparison of the spot welding is shown in Figure 2. Therefore, the intermediate frequency spot welding has welded steel, coated steel plate, stainless steel, aluminum and the characteristics of combined welding of different heat conductive materials, such as spot welding of aluminum and steel. In the body structure, the floor stringers are the core of the overall body strength. Therefore, in the design, the longitudinal beam is generally hot-rolled with a high-strength 2.5mm thick steel plate lap joint structure (see Figure 3). In the process of processing, these steel plates mainly have difficulty in forming, forming in place, large gap between plates, and welding strength. Good guarantee, welding spatter and other shortcomings. In order to solve these problems, equipment is used to compensate for the contradiction between design and process. Usually, medium frequency servo welding tongs are used. The intermediate frequency technology can overcome the problems of plate thickness, material problems, and servo technology to compensate for gaps between plates and incomplete formation.
Stainless steel Metal Hose used for conveying all kind of medium is a kind of flexible element made up of stainless steel ripple hose consisting of outer braided layer, one or multi-layer wire or steel belt net, with joints or flanges at both ends. Its characteristic is: corrosion-resistance, high temperature resistance, low temperature resistance(-196℃~+420℃), light weight, small volume, and good flexibility. It is widely used in aviation, spaceflight, oil, chemical industry, metallurgy, power, paper-making, wood, textile, building, medicine, food, tobacco, traffic and ect.
Specifications: Flexible Metal Hose Series Flexible Metal Hose Series,Flexible Metal Hose,Stainless Steel Flex Hose,Stainless Steel Flexible Hose HEBEI BAOSHI SPECIAL FLEXIBLE RUBBER CHEMICAL INDUSTRY CO., LTD. , https://www.hbbaoshihose.com
Welding Robot
With the development of industrial automation, robots have been widely used. According to different processing tools and operating objects of robots, they are mainly divided into welding robots, cutting robots, painting robots and transfer robots. According to their different structures, there are six-axis robots and seven. Axis robot, eight-axis robot.
The working tool of the welding robot is the welding tongs. According to the requirements of the process trajectory, the coordinate transformation and the movement of each axis drive the welding tongs to complete the target movement to achieve welding (see Figure 1). It has high flexibility, precision and high efficiency, providing a motion basis for the realization of IF servo welding tongs.
Introduction of intermediate frequency welding technology 
Figure 1 Principle of IF welding control
The IF welding output is DC, and its primary and secondary currents have little impact on the grid. Through the intermediate frequency and power frequency welding test, the current of each phase of the alternating current and intermediate frequency welding is compared under the same welding capacity. It can be seen from the output of the oscilloscope that the impact of the intermediate frequency welding on the power grid is small.
The advantages of medium frequency welding in body production are as follows:
(1) Good economic efficiency The intermediate frequency welding adopts three-phase input, the power factor is up to 0.9 and energy saving. 95% of the resistance welding machines of automobile manufacturers are AC. The AC spot welding machine and the power grid are connected by the thyristors. Therefore, there is a blank area, the heat is not concentrated and the welding quality is unstable. The medium frequency spot welder has three-phase load balance, low input, no grid transition process, high power factor and energy saving. In the car body-in-white welding, 160kVA AC suspension spot welder is often used, and only 70kVA is needed if the intermediate frequency spot welding tongs are used.
(2) Welding quality High medium frequency welding Because the welding current is small, the heat generated by the electrode is small, the electrode usage time is prolonged, and the welding condition range is expanded. Since the frequency is up to 1000 Hz, the secondary current output capability is strong, the waveform is straight, and the size range of the nugget is expanded. There is almost no splash, and the current in the primary stage of the welding increases naturally, and the surface quality of the solder joint is good. After testing, in the single-phase AC welder spot welding 100 solder joints, the single-phase rectifying welder is 130 solder joints, the intermediate frequency spot welder is 240 solder joints; the same for the coated steel sheet, the single-phase AC welder is 110 solder joints. The medium frequency spot welder has 355 solder joints, and the medium frequency spot welder has a stable welding range. In the body welding process, when the diameter of the weld nugget is 5 mm, the welding current is 1.5 times the calculated current. The welding current of 0.7mm coated steel plate single-phase AC welding machine is 8.7kA×1.5=13kA, which produces spatter under the condition of standard welding current; while the welding current of medium frequency spot welding machine is 5.6kA×1.5=8.4kA, the welding current is set without splash. .
(3) Welding circuit Small and lightweight IF spot welding robot system welding tongs and rectifying welding transformer integration, the quality of IF rectifying welding transformer is about 1/5 to 1/3 of single-phase AC type, and the quality of welding tongs is reduced. 1/3 to 1/2. 
Figure 2 Comparison of nugget temperature between AC and MF spot welding
(5) Wide welding specifications? The response speed is 1ms, the current can reach the set value faster, and the parameters can be analyzed more and more accurately.
Servo welding pliers
At present, the welding tongs used in body welding are mainly classified into two types: pneumatic welding tongs and servo welding tongs according to the power source.
Pneumatic welding tongs
Because the pneumatic welding tongs have the advantages of easy control, relatively simple structure, easy maintenance, etc., they are widely used at present, but there are problems such as poor welding quality and high cost. The main disadvantages are:
1) Pneumatic welding tongs can only use one welding pressure when welding, which is not conducive to controlling welding quality.
2) The pneumatic welding tongs cannot control the moving speed of the electrode during welding and pressurization, and the impact on the workpiece is large, and the workpiece is easily deformed.
3) The noise generated by the pneumatic welding tongs during welding is large, and the welding pressure cannot be accurately controlled, and welding spatter is generated, which deteriorates the working environment.
4) Although the compensation of the amount of wear on the electrode is considered on the pneumatic welding tongs, since the specific value of the wear amount cannot be calculated, there are still problems affecting the welding quality.
2. Servo welding pliers
In order to overcome these shortcomings and improve the controllability of the welding process, servo welding tongs have been more and more widely applied to spot welding of automobile bodies in recent years with the increasing maturity of servo control technology.
The structure of the servo welding tongs mainly includes a servo motor, a transformer, a ball screw mechanism and a welding tong body. The power source of the servo welding tongs is a servo welding machine, and the servo motor is equivalent to the cylinder of the pneumatic welding tongs. The servo welding tongs realize the welding motion process by linear motion of the servo motor rotating motion through the ball screw to the electrode of the welding tongs.
In the welding robot system, the servo motor of the servo welding tong is directly controlled by the servo controller of the robot, which is equivalent to an additional tooling axis of the robot. The feedback data of the servo motor encoder accurately controls the amount of movement of the electrode, thus making the welding tongs The stroke motion of the moving side electrode is in the robot control, so that the position and speed process of the electrode movement process of the welding tongs are controlled at any time.
Servo welding tongs also have the following advantages:
(1) Improving the welding quality The amount of pressure applied during the spot welding process has a great influence on the welding quality. How to realize the dynamic controllable pressure in the welding process is an important means to ensure the welding quality.
For servo welding tongs, firstly, the servo motor output torque in the servo welding tongs can be controlled by the robot servo controller. Therefore, the electrode pressure can be easily controlled, so that it can be set according to different plate thicknesses and solder joint positions. Determine the electrode pressure at each solder joint to avoid solder quality problems caused by excessive or insufficient pressure. At the same time, in the welding process, the pressurization process can be divided into several sections according to the energization current curve, and the different pressures are set to achieve the highest quality pressurization curve. High-quality solder joints are easily obtained by precise control of the pressure, especially in controlling the spattering of the welding process, and the dynamic control of the pressure can achieve good control effects.
Secondly, when the welding tongs are closed and pressurized, not only the pressure can be adjusted, but also the two electrodes are lightly closed when closed, which realizes soft contact control, that is, the electrode can be gradually pressurized when the electrode contacts the workpiece, reducing the workpiece to the workpiece. The impact reduces the amount of work required to repair the surface of the body in subsequent processes.
(2) Reducing the production cost The servo welding tongs can calculate the position of the two electrodes when they are contacted by the servo motor control and the feedback of the encoder. By comparing with the original standard position, the wear amount of the electrode can be calculated. On the one hand, the robot can compensate the running length of the electrode through this result, ensure the position of the contact gap between the electrode and the workpiece is normal, and improve the welding quality; on the other hand, the accuracy of the electrode is improved, the wear amount of the electrode is accurately calculated, and the frequency of replacement of the electrode is controlled. Reduce production costs.
(3) Increasing the efficiency The servo welding tongs can be clamped while moving to the solder joints under the control of the robot. The welding cycle of each solder joint can be greatly reduced because the opening degree of the welding tongs is precisely determined by the robot. Controlled, the welding tongs can begin to close during the movement of the robot between points. After welding, the welding tongs are separated from the workpiece, and the robot can drive the welding tongs to the next target. It is not necessary to wait until the robot is in place and the welding tongs are closed or the welding tongs are fully opened and the robot moves again. The speed of each solder joint welding cycle increases the overall working cycle. The opening degree of the welding tongs can also be arbitrarily adjusted according to the condition of the workpiece, as long as no collision or interference occurs to reduce the opening degree as much as possible, so as to save the time taken for the welding tongs to open and close.
(4) Improve the precise pressure control of the servo welding tongs in the working environment, effectively avoiding the welding spatter caused by insufficient pressure, and the soft contact control eliminates the noise when the electrode is in contact with the workpiece, and improves the working environment.
The advantages of servo welding tongs on the quality of welding make it gradually replace the traditional pneumatic welding tongs and are widely used in spot welding robot systems.
In order to achieve good control of the welding process, the servo welding tongs need to set the corresponding physical parameters when connecting with the robot. In addition to the basic parameters such as the size, center of gravity and quality of the welding tongs, the welding tongs and pressure for the servo welding tongs should be set. Special parameters such as servo motor current relationship curve and clamp arm bending amount compensation coefficient.
Application example of medium frequency servo robot welding tongs
In summary, robotic spot welding tongs can be divided into four categories: power frequency pneumatic welding tongs, power frequency servo welding tongs, medium frequency pneumatic welding tongs and medium frequency servo welding tongs. The medium frequency servo welding tongs have great advantages in controlling welding quality and cost saving, and it is also the reason why it is gradually popularized and used. 
Figure 3: Longitudinal beam lap joint structure
This kind of equipment and technology is used in the floor welding station of Chery Q235. The welding point strength of Q235 here has been zero since the commissioning of NQST, and there has never been any unqualified solder joint. This technology also optimizes the dual-process of spot welding and CO2 welding at the girders of the floor girders of other models. Now only spot welding can be used to ensure strength, improve labor efficiency, reduce costs and improve the operating environment of employees. And avoided security incidents.
Prospects for body welding and material development
With the increasing safety requirements for automobiles, coupled with the strict control of the weight and cost of automobiles, the materials used in the body will gradually reduce the number of commonly used cold-rolled steel sheets, and new materials will become more and more, for example: high-strength steel sheets. Hot-formed steel sheets, laser-welded steel sheets, plated steel sheets, plastic sheets, etc. These steel sheets have the advantages of high strength, light weight, low cost, and the like, but the disadvantages of welding difficulties are widespread. The intermediate frequency servo technology can overcome the shortcomings of soldering difficulties, so it will be widely used. China should increase its research on medium frequency servo welding technology to make it better serve the body welding process.
Conclusion
The IF servo robot welding tongs are a comprehensive product of automation technology and advanced welding technology. Its emergence not only solves many previous welding defects, saves production costs, improves energy utilization, improves the operating environment of employees, greatly improves the level of welding technology, and lays a good foundation for the improvement of automobile manufacturing. As a technician, we must increase the research on automatic and advanced welding technology to contribute to the Chinese automotive industry.
1. ISO 9001/ API Q1 / ISO14001 / OHSAS 18001 Certificate
2. Large stocks Timely delivery
3. Professional
4. Good after-sale service