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Development of welding robot to promote welding automation

Part of the article: Popularity:Time:2018-07-02 16:58

n recent years, Chinese industry has been carrying on a "robotics" revolution, especially in the field of arc welding. After 2005, the robot has increased by an average of 130% per year. In this paper, the advantages of welding robot in automatic production, the development of welding robot system, the problem and solution of automatic application of welding robot and the application of welding robot in industry are briefly introduced in four aspects.
1. Advantages of welding robot in automatic production
From birth to the present, robots are most widely used in welding. According to statistics, by the end of 2007, the total installed capacity of welding robots in the world was close to 4O million units. As an advanced welding equipment, the application of welding robot has been popularized greatly. It is an important symbol to make the welding industry in the era of automation in China.
With the progress of science and technology, people's requirements for welding quality are higher and higher. Automatic production requires reducing manpower, improving product consistency, improving product quality, making it more suitable for mass production, reducing production costs and improving production efficiency. In artificial welding, it is difficult to maintain the stability and consistency of the welding work for a long time due to the influence of the objective and subjective factors, such as the technical level, the degree of fatigue, the sense of responsibility, the physiological limit and so on. Moreover, due to poor welding conditions, people who are willing to engage in manual welding are decreasing, and skilled skilled workers are in short supply. It can be said that welding robots meet the requirements of welding automation to a large extent, and the advantages of automatic production can be summarized as follows:
(1) to stabilize and improve welding quality and ensure its uniformity. Welding parameters such as welding current, voltage, welding speed and dry elongation have a decisive effect on welding results. When the robot is welded, the welding parameters of each weld are constant, and the quality of the weld is less influenced by human factors, which reduces the requirements for the operation of the workers, so the welding quality is stable. In manual welding, welding speed, dry elongation and so on are all changing. It is difficult to achieve uniformity of quality.
(2) improve the conditions of labor. Robot welding, workers only need to load and unload the workpiece, away from the welding arc, fog and splash. For spot welding, workers do not need to carry heavy hand welding clamps, so that workers can extricate themselves from high strength manual labor.
(3) improve labor productivity. The robot can be produced continuously by 24h.  With the application of high speed and high efficiency welding technology, the efficiency of robot welding is more obvious.
(4) product cycle is clear and easy to control product output. The production rhythm of robots is identical, so the production plan is very clear.
(5) shorten the cycle of product modification and replacement, and reduce the corresponding equipment investment. The welding automation of small batch products can be realized. The biggest difference between a robot and a special machine is that it can be adapted to the production of different parts by modifying the program.
2. Development of welding robot system
The development of electronic technology, computer technology, numerical control and robot technology provides favorable conditions for the automation of welding process, and has penetrated into various fields of welding. In the strict sense, the welding robot is a welding robot system or workstation, including robot body, robot control cabinet, welding machine system and wire feeding unit, displacement machine, fixture and so on. The typical welding robot system has three forms: welding robot workstation, welding robot production line and welding machine. Welding robot workstation is generally suitable for medium and small batch production, the welds of welded parts can be short and more complex, and the welding robot production line is especially suitable for many products and few quantities, and the welding machine is suitable for large and slow products with low number of welds. The weld is longer and the workpiece with regular shape is also more suitable. Which type of automatic welding production should be chosen depends on the actual situation of the enterprise.
In recent years, the technology of arc welding inverter has become mature. Most of the inverter power supply for robot arc welding is IGBT arc welding inverter controlled by single chip microcomputer. It is equipped with fine waveform control and fuzzy control technology, and the working frequency is 20-50kHz, up to 220kHz. The welding system has excellent dynamic characteristics and is suitable for robot automation and intelligent welding. The development of arc welding power is moving towards digitalization. The development direction of welding power source of welding robot is to adopt full digital welding machine. The most characteristic of the welding power is that the welding parameters are stable, the influence of the voltage fluctuation of the network, the Wen Sheng, the aging of the components and other factors is very small. It has high repeatability, the welding quality is stable, the forming is good, and the response speed of DSP is fast. It can control the inverter accurately according to the instructions of the main control system (given value). The output has the functions of output multiple current waveforms and high speed and stable regulation of arc voltage, and can meet the requirements of various welding methods for power supply.
Cao Lezhong mentioned the transformation of the displacement machine in the technical transformation of ROMAT76AW welding robot. The welding range of a single robot in length direction is only 6800mm, and it can not complete the welding work of SS9 type electric locomotive bogie side beam. The variable position machine is used for the rotation of the welding parts. The model of the position changing machine is WPR25000N, the head frame is fixed, the tail frame can move along the guide rail, bearing 2.5t, and can be rotated to any angle. The guide rail of the positioning machine is lengthened 1.6m, and the guide rail is required to be well connected. After the lengthening of the guide, the maximum distance between the head frame and the tail frame of the variable position machine is the driving motor (the original DC servo motor), 3M, which is the eighth axis of the updating machine (the rotating shaft of the variable position machine). The driving mode is AC servo drive to ensure that the workpiece moves smoothly and without moving during the displacement process, thereby improving the welding performance of the weld in the ship position.
3. Problems and solutions in the automation application of welding robots
The welding robot in the current application is still a "teaching and reproducing type", its welding path and process parameters are set in advance, the requirements for the consistency of operation conditions are very strict, and the function of sensing feedback and real-time adjustment of external information is lack in the process of welding. However, the changes in the environment and conditions in the actual welding process are unavoidable, such as the joint position, the dispersion of the weld gap and the size of the weld, the difference between the teaching track and the actual weld, the thermal deformation, the penetration and the formation of the weld in the welding process, which will cause the welding quality. The fluctuation of quantity and cause the production of welding defects. In order to overcome the influence of various uncertain factors in welding process on the quality of precision welding, it is urgent to adopt the technology of information feedback and intelligent control to improve the adaptability or intelligent level of the current welding robot so that it can realize the initial welding position identification and autonomous guidance, the real-time weld deviation and tracking, and the welding pool dynamics. The acquisition of feature information, the adaptive adjustment of process parameters and the real-time control of the weld forming, that is, the autonomous intelligent control of the robot welding process, which makes up for the defects of the welding robot in automatic welding.
Chen Shanben and others use artificial intelligence technology to simulate the welder's observation, judgment and operation behavior, and study the key technology of welding robot based on visual information sensing, such as initial welding position identification and autonomous guidance, weld tracking, dynamic process of weld pool and intelligent control of weld formation, and develop local environment autonomous intelligence. The welding robot LAIWR (local autonomous intelligent welding robot, Local Autonomous Intelligent Welding Robot) integrated system, is applied to the welding of the important structure parts of the space equipment. In order to realize the optimal management and coordination control of many hardware components and functional software of LAIWR system, the intelligent function of autonomous control of robot system is realized.
With the continuous development of robot research and the continuous development of the robot field, the robot simulation system plays an important role in this field as a safe, reliable and flexible tool for robot design and research. "The application of OPENGL in the dynamic simulation of industrial robot" (1) is a discussion on the development of the 6R robot simulation system combined with the 6R (rotary joint) welding robot. The process of simulation interface and system graphic interaction is also given. The dynamic simulation of multi degree of freedom and multi joint robots is carried out to achieve the purpose of studying multi degree of freedom and multi joint robots.
"Visual sensing aluminum alloy pulse MIG welding width control system" describes the problem that the heat accumulation of aluminum alloy in the welding process is strong and the constant parameter welding is easy to produce various defects. The fuzzy expert control system is designed. The image of the molten pool and the corresponding image processing software are obtained by CCD to calculate the size of the weld width. Then the fuzzy controller controls the welding heat input. The expert system is responsible for the matching of the pulse parameters, thus maintaining the width of the weld, which is to ensure the stability of the welding quality and adapt to the production requirements of the automation.
Other measures include the transformation of the peripheral structure of welding robot, the transformation of welding process. In the field construction of steel structure, the shape of the structure is complicated. Apart from the conventional round and square workpiece, there are discontinuous, elliptical, shape changing workpiece, thick wall and large work piece. It is necessary to solve the automatic welding of the site to the maximum limit and give full play to the site construction utilization rate of the welding robot. It is difficult to improve the welding efficiency. By summarizing the field welding practice of "bird's nest" and following a large number of welding engineering practice, the RHC-2 and RHC-3 series flexible track welding robot is developed, which can use direct guide, circular guide and flexible guide to realize all position welding of various complex surfaces, and design the online weld track teaching and on-line full position welding parameter control. The function control program of system and off-line welding parameter setting, and the development of independent learning and open expert system, can be adapted to track tracking of irregular weld, and the automatic welding of multi-channel and multi position welding and full position welding can be realized.
4. Application examples of welding robot in industry
The main applications of arc welding robot are in the manufacturing of ships, auto parts, motorcycles, bicycles, sheet metal and other industries. In addition, the application of arc welding robots is also being expanded in the industry of medium and thick plates with engineering machinery.
Welding automation is the key to the progress and upgrading of shipbuilding industry. After more than 10 years' hard and unremitting efforts, China's shipbuilding automatic welding technology has made considerable progress and fruitful results. As we all know, shipbuilding welding technology is the key technology of modern shipbuilding. In the hull construction, the welding time occupies about 30%~40% of the total construction time of the hull, and the cost of welding accounts for about 30%-50% of the total cost of the hull construction. Ship welding quality is an important index for evaluating ship quality. Welding efficiency directly affects shipbuilding cycle and shipbuilding cost. Therefore, welding automation will be the key to the progress and upgrading of the shipbuilding industry. It is also a major trend in the shipbuilding industry. With the development of welding technology, the trend will be more and more obvious.

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