Introduction: The connection plate is a common component of engineering cranes. Its structure is shown in Figure 1. It is mainly composed of a base plate and four pins. The pin and the bottom plate are fixed by a circular fillet welding method. The previous welding method used a manual CO2 gas shielded flux-cored wire welding process. Since the welding seam is a circular fillet weld, it is easy to cause the appearance of the weld during manual work. low quality
The connecting plate is a common component of engineering cranes. Its structure is shown in Figure 1. It is mainly composed of a base plate and four pins. The pin and the bottom plate are fixed by a circular fillet welding method. The previous welding method used a manual CO2 gas shielded flux-cored wire welding process. Since the welding seam is a circular fillet weld, it is easy to cause the appearance of the weld during manual work. Disadvantages such as poor quality, low welding operation efficiency, and poor bonding between the welding line and the welding line are easy to cause "desoldering". At the same time, in order to ensure the appearance quality of the welding line, a grinding machine is required to grind the welding line after welding. It is easy to cause an increase in welding costs. 进行焊接作业，关键是需要设计合理的焊接机器人操作系统和制定合理的焊接工艺，确保成本质量的有效统一。 Through analysis, it is decided that the welding robot is used for welding the workpiece. The key is to design a reasonable welding robot operating system and formulate a reasonable welding process to ensure effective uniformity of cost quality.
Figure 1 Connection board structure
1. The overall plan of the welding robot
According to the size, structural characteristics of the connection plate and the form of the weld, considering that the bottom plate and the four pins are in the form of single-sided welds, the welds are regularly and uniformly distributed on the workpiece, and the welding process can be satisfied without displacement. Welding of all welds. In order to reduce costs and improve efficiency, when designing the overall plan of the welding robot, it was decided not to use robot peripheral equipment such as flip tools, but to use a fixed platform to achieve welding positioning of the workpiece. At the same time, in order to improve welding efficiency, the welding robot system solution adopted a machine Double-station mode, H-type arrangement, as shown in Figure 2, that the robot body is fixed between two self-made welding work positioning platforms. When working, one station welding robot automatically welds the workpiece on the human side, and the other The position can load and unload workpieces and perform operations alternately to ensure that the robot works continuously.
Figure 2 Overall plan of the welding robot
In order to ensure the accuracy of workpiece installation and positioning, reduce the number of robot welding pursuits, and ensure that the robot welding running trajectory is consistent with the welding trajectory required by the workpiece, positioning pin holes are designed on the workpiece and the welding positioning platform, and the connection plate is welded by one side and two pins. Precise positioning on the work platform.
2. Robot body selection
The robot body adopts a Dacheng welding robot with a six-degree-of-freedom articulated welding robot. It is equipped with a full-digital pulse welder power supply from Megmeet, and is equipped with an automatic gun-cutting wire-cutting fuel injection device and an arc safety protection device to meet the robot's use process. Medium safety protection and gun cleaning are needed.
3． Determination of welding process
The welding process uses argon-enriched mixed gas + solid cored wire instead of the original CO2 gas + flux-cored wire. Argon-rich protective welding has good weld pool visibility, easy operation, and suitable for all-position welding. At the same time, the arc is heated under the compression of the protective gas. Concentrated, fast welding speed, small molten pool, narrow heat affected zone, small welding deformation, good crack resistance, under the protection of inert gas during welding, it has the characteristics of good welding quality, which is very conducive to mechanization and automation in the welding process . However, due to the strong light radiation of the arc, in the overall scheme design of the welding robot, an arc safety protection device needs to be designed for safety protection. In order to improve the welding efficiency, a one-time welding process is adopted to avoid the reduction of production efficiency caused by repeated positioning of the welding robot.
4． Selection of welding power
Through the trial of multiple power sources, and according to the problems encountered during the trial, combining the material, shape characteristics, dimensional accuracy requirements, weld length and position characteristics of the workpiece, welding workload and robot efficiency, the welding robot system uses Full digital pulse gas shielded welding power source, namely pulse MIG welding process power source. As we all know, the accuracy of arc control in the welding process determines the quality of the welding. The all-digital pulse gas shielded welding power source uses digital technology, so the feedback time of the control system is reduced by several orders of magnitude compared with the traditional welding machine. This increases the accuracy and sensitivity of the feedback. When pulse welding is used, suitable pulse waveforms can be provided, and each pulse can be effectively controlled to transition only one droplet. This keeps the arc length constant throughout the welding process, almost no spatter during welding, and can achieve ultra-low heat. At the same time, the input welding can also overcome the defect of the end of the welding wire that affects the re-arcing and ball formation after the welding of the traditional GMA welding machine is completed, so as to achieve the best matching of welding quality and welding efficiency.
5． Wire diameter selection
Combining the requirements of welding quality and welding efficiency, the f1.6mm solid cored welding wire is used for the welding wire, which can meet the actual welding needs of the connection plate, and also facilitate the improvement of welding efficiency.
6. Determination of welding parameters
(1) Arc voltage and welding current Arc voltage is a key parameter during short-circuit transition. The arc voltage matches the welding current, which can achieve a small spatter, a good weld formation and a stable welding process. Through multiple tests, the arc voltage was determined to be 20 to 25V, and the welding current was determined to be 200 to 260A.
(2) Welding speed? The welding speed is increased, and the weld width, depth and remaining height of the weld are reduced, which are prone to defects such as undercuts, pores and under-penetration; too low welding speed is prone to problems such as burn-through, coarse structure, and large welding deformation.
空走时间平均点／1．5s。 After several tests, the welding speed was set at 400-800mm / min, the welding arc starting time was point / 0.5s, arc closing time point / 0.5s, and the robot idling time average point / 1.5s.
(3) Gas mixing ratio and flow rate are determined by using 80% Ar and 20% CO2 mixed gas, and the purity of CO2 gas is ≥99.5%. The determination of the gas flow must fully consider the differences between indoor and outdoor operating locations. The gas flow is too low, the protective gas is not stiff enough, and the weld seams are prone to generate pores. The large flow rate is easy to waste gas, and it may be caused by turbulence. The protection is deteriorated, and a gray oxide layer is formed on the surface of the weld, which reduces the quality of the weld. The general gas flow rate should be 15 to 25 L / min.
(4) Welding wire extension length When the welding wire extension length increases, the resistance heat on the welding wire increases, the welding wire melts faster, and the production efficiency is high, but when the extension length is too large, the welding wire is prone to overheating, resulting in severe melting and splashing. As a result, the welding process is unstable, and the proper extension length should be 10 to 12 times the diameter of the welding wire. Therefore, the extension length of the welding wire in this welding process is determined to be 16mm.
7. Robot actual welding application for connecting plates
实际焊接作业，连接板按照每组四个的固定位置安装在定位平台上。 In the actual welding operation of the welding robot designed by the above scheme, the connecting plates are installed on the positioning platform according to each group of four fixed positions. In the positioning process, in order to avoid the increase of costs and procedures caused by the additional positioning reference, the positioning method is fully utilized as the positioning reference in the selection of the positioning method (see Figure 3). The positioning method uses the inner hole of the pin According to the positioning holes that have been processed on the positioning platform according to the workpiece size in advance, inserting two positioning pins can realize the precise positioning of the "one side, two pins" on the positioning platform on the positioning platform. The welding robot is programmed according to the fixed trajectory and coordinate data, which can effectively realize the accurate automatic welding of the connection plate.
Figure 3 actual operation of robot welding
The welding robot adopts the above process and scheme to perform the welding of the connection plate. The workpiece positioning accuracy is high, the robot's movement accuracy is accurate, and the welding trajectory and the welding seam overlap are high. The welding seam formation using the traditional welding process and robot welding process is shown in Figures 4 and 5. As shown. It can be clearly seen from the figure that the welding seam formed by the robot is beautiful and full, so the welding efficiency and welding quality are significantly improved; and after the solid welding wire is used, the welding slag does not need to be cleaned, which brings about an improvement in the working environment and a reduction in labor intensity. The obvious effect is also a good application foundation for the full use of enterprise automation, intelligent and efficient welding robots.
Fig. 4 Weld seam of traditional welding process
Fig. 5 Weld seam of robot welding process