Application of robot welding technology in aerospace
Multi-axis linkage space curve welding seam variable polarity plasma arc automatic welding equipment and omnidirectional intelligent mobile welding robot system, this product is developed for large spacecraft with large size, weak rigidity, complex structure and other manufacturing needs. In an era of increasing intelligence, it shows us a new possibility of upgrading the manufacturing model.
With the advancement and advancement of key national science and technology projects, the development of large space vehicles will be carried out in the future under the framework of major national special programs such as manned spaceflight and lunar exploration projects, deep space exploration, and spacecraft orbit service and maintenance. Large aerospace vehicles generally have the characteristics of large size, weak rigidity, and increasingly complex structural forms. In the structure of large aluminum alloy spacecraft, there are a large number of complex forms of welds, such as the intersecting lines formed by spherical, cylindrical, round table shells and circular and shaped flanges. Spacecraft manufacturing has high-quality, high-reliability, high-flexibility, high-efficiency, and low-cost requirements, so the upgrade of the manufacturing model is imminent.
The demographic dividend era has passed, and the mechanical processing and manufacturing process with mechanization and automation as the mainstream has become an effective means to improve social production efficiency and promote the development of enterprises and social productivity. Welding technology, as one of the important processing processes in machinery manufacturing, is widely used in aerospace, rail transportation, petrochemical industry and other industrial fields. Robot automated welding technology can significantly improve the production efficiency of large-volume product processing, and product quality reliability and consistency are greatly enhanced. In this paper, the exploration and practice of robotic automatic welding are carried out in response to the welding needs of several typical products in large spacecraft structures.
Multi-axis linkage variable polarity plasma arc welding robot equipment and process
1.1 Requirements and scheme design of complex space curve welds
In the structure of large aluminum alloy spacecraft, there are a large number of complex forms of welds, such as the intersecting lines formed by spherical, cylindrical, round table shells and circular and special-shaped flanges. At present, most of the welding of such curve welds is done by manual tungsten arc welding. The main problems in the production process of manual tungsten arc welding are:
① Repeated repair welding affects product development progress.
②The amount of heat input is large, and the welding residual stress level is high, which easily causes the product size to be out of tolerance.
In response to this demand, a 11-axis linkage space curve weld VPPA perforated vertical welding robot welding system scheme based on articulated robot was proposed
1.2 Development of special welding head
At present, there are still problems such as burning of tungsten electrodes and insufficient dynamic response capability for real-time adjustment when welding aluminum alloy space curve welds with a general plasma torch. In order to further ensure and improve the welding quality of VPPA space curve welds, a special plasma welding head with suitable volume and quality (<15kg), high precision and high degree of automation is designed. The plasma welding head can adjust the attitude of the welding gun and adjust the angle and speed of the wire feed under video monitoring. The welding gun attitude adjustment includes a welding gun telescopic mechanism, a welding gun axial rotation mechanism, and a welding gun translation mechanism.
Through the control of the special welding head, the molten pool state and arc shape can be finely adjusted during the welding process. The mechanical positioning accuracy of the head can reach the level of ± 0.1mm. This process can be automatically controlled by statistical analysis of welding parameters, image processing of welding process and artificial intelligence technology. Since the fine adjustment of the welding process does not require high control speed, it is also possible to manually adjust the operation of the welding head through the operator ’s observation of video monitoring and welding parameter monitoring.
1.3 Multi-axis linkage VPPA welding equipment system integration and application
Adopting standing robot welding workstation system. The 6-axis robot is installed on a three-dimensional mobile device, and the workpiece is installed on a 2-axis positioner. The three-dimensional mobile device can realize the independent adjustment of high direction (z-axis), horizontal direction (x-axis), and vertical direction (y-axis), increase the moving range of the robot, and make its effective welding range meet the requirements of product welding. Through the integration of the 6-axis robot + 3D mobile device + dual-axis positioner system, real-time control of the relative position of the welding torch and the welding seam is realized, so that the relative position of the VPPA welding torch and the welding seam is always In a vertical relationship. Completed multi-axis linkage variable polarity plasma arc large-scale automatic welding equipment
2.1 Welding demand for large thin-walled weak rigid products
The radiators of large spacecrafts such as spaceships and space stations are used as active heat dissipation equipment for spacecrafts. Their processing quality and lifespan will directly determine the success or failure of space missions. The radiator is assembled by welding the liquid pipe circuit, the heat pipe circuit and the metal skin. It is a complex skin structure with large size, weak rigidity and strong constraint. The structure of a typical spacecraft radiator is shown in Figure 4. Due to the very complicated spatial orientation of a large number of liquid / heat pipelines, the actual position of the pipeline wing welding edge pre-positioned on the tooling is difficult to accurately guarantee, and a large number of welds are produced in turn The welding deformation will further reduce the position accuracy of the wing-shaped welding edge of the pipeline. In response to this demand, an omnidirectional intelligent mobile welding robot composed of an omnidirectional intelligent mobile platform and a robot welding system installed on the platform is proposed. Compared with the traditional coordinate robot special machine system, the system has strong operational flexibility and work Space adaptability, broad application prospects.
2.2 Integration of omnidirectional mobile welding robot system
The omnidirectional mobile automatic welding robot is an intelligent flexible manufacturing equipment with a set of "intelligent mobile platform + flexible welding robot + laser tracking and video monitoring system" as the core. The equipment is based on the KR-30 robot of Germany KUKA company and the CMT welding machine of Funis. It is equipped with an omnidirectional intelligent mobile platform car. It has developed a mobile automatic welding robot system, and is equipped with a laser tracking system. The deviation angle of the returned laser signal and the optical axis of the measurement system can correct the deviation of the welding gun trajectory caused by welding deformation in real time. The operator can obtain real-time weld pool information through the welding video monitoring system to realize the automatic welding of people in the loop.
(1) Intelligent mobile platform system The intelligent mobile platform system is a high-end omnidirectional mobile equipment product based on intelligent control, which provides an efficient solution for the flexible transfer and precise positioning of large and heavy-duty products. Product features: all-round flexible movement, precise control, large security load, and intelligence. The omnidirectional intelligent mobile platform car uses a 2t carrying platform car, and realizes all-round movement of the platform car through independent control of the four sets of wheel systems; at the same time, it is provided with vacuum suction foot support, which can be used for stable support during the work process; Obstacle avoidance device and emergency stop device are used for emergency braking.
2.3 Application of omnidirectional mobile welding robot products
For the first time, the intelligent mobile welding robot system was applied to the welding of complex space curve welds of large thin-walled structures, which solved the problem that the assembly accuracy of the complex space curve welds of large-size radiator tube sheets is low and automatic welding cannot be implemented. The welding production site is shown in Figure 7.
The weld structure of the product structure in Figure 7 is mainly divided into two forms: one is tube-to-pipe welding, a double V-shaped weld structure with 6mm on one side, and one is tube-to-plate welding, 0.8mm and 1mm heterogeneous Aluminum alloy welding structure. For tube-to-tube "deep V-shaped" welds, high-frequency pulses are added on the basis of ordinary CMT welding parameters, which increases the stiffness of the arc, reduces the heat input of the weld, and the weld is full and effective Welding defects are suppressed, and product quality reliability and pass rate are greatly increased. In addition, the welding parameters of the space curve weld of the unequal thickness aluminum plate at all positions were optimized; the plate deformation problem in the butt weld of the thin plate was solved by changing the tooling pressure plate method; the weld seam was solved by adding the automatic swing welding function of the welding gun at the end of the robot Uneven gaps.
Conclusion
1) In response to the welding needs of complex space curve welds of large spacecraft, 11-axis linkage variable-polarity plasma arc large-scale automatic welding equipment was developed, and a special welding head for variable-polarity plasma arc was designed and developed to realize the whole process of closed curve weld VPPA perforated welding can be successfully applied to the welding of spacecraft metal seal large bottom space curve welds.
2) Through hardware integration and software communication, an intelligent mobile welding robot system based on intelligent mobile platform vehicles, flexible welding robots and laser tracking and video monitoring was developed. By optimizing the welding process, the problem of high-efficiency welding of unequal thickness aluminum alloy plates and double V-shaped thick plates is solved, and the welding application of typical products of spacecraft radiators is realized.
3) Intelligent welding based on full-process data driving is the future development trend. Research on data-driven intelligent inference technology, use data mining to establish association rules, provide basis for intelligent pre-welding planning and online intelligent control, and realize the upgrade of manufacturing mode.
