Fully automatic welding technology and process control of steel pipe

All-position automatic welding of steel pipe means that when the steel pipe is relatively fixed, the welding trolley drives the welding torch to move around the pipe wall along the track, to realize automatic welding. Generally speaking, the all-position automatic welding device is composed of a welding trolley, a walking track, an automatic control system, and other parts. The purpose of developing an all-position automatic welding device is to improve welding quality and labor productivity and reduce the labor intensity of workers.

Welding trolley
The welding trolley is the driving mechanism to realize the automatic welding process. It is installed on the welding track and moves circularly along the pipe wall with the welding torch. It is one of the important links to realize the automatic welding of the nozzle. The welding trolley should have the characteristics of a beautiful appearance, small size, lightweight and convenient operation. Its core parts are a walking mechanism, wire feeding mechanism, and welding torch swing adjustment mechanism. The traveling mechanism is composed of a motor and a gear transmission mechanism. To make the traveling motor execute the position and speed commands issued by the computer control unit, the motor should be equipped with a speed measurement feedback mechanism to ensure that the motor is accurately aligned at each position of the steel pipe ring seam, and has a relatively Nice speed tracking feature. The wire feeding mechanism must ensure that the wire feeding speed is accurate and stable, has a small moment of inertia, has good dynamic performance, and should have sufficient driving torque. The welding torch swing adjustment mechanism should have the functions of the welding torch swinging left and right relative to the weld seam, staying at the left and right ends, controllable up and down, left and right posture, and adjustable welding torch angle. The above-mentioned parts of the welding trolley are all programmed and automatically controlled by the computer. After the program is started, the various parts of the welding trolley coordinate and act according to the logical order of the program. The welding process can also be manually intervened when necessary, and at this time the program can automatically adjust the welding parameters and execute according to the amount of intervention.

welding track
The track is a special mechanism installed on the pipe for the welding trolley to travel and position. Its structure directly affects the stability and position of the welding trolley, which also affects the welding quality. The track should meet the following conditions: convenient assembly and disassembly, easy positioning; reasonable structure, light weight; certain strength and hardness, wear resistance, and corrosion resistance. There are two types of rails: flexible rails and rigid rails. The so-called rigid track means that the body of the track is relatively rigid and not easily deformed, while the flexible track is relatively rigid. Both types of tracks have their characteristics. Accurate positioning of the rigid track, and small deformation after clamping, can ensure that the welding trolley runs smoothly, and the radial adjustment of the welding torch is small during welding, but it is heavy and inconvenient to assemble and disassemble. The flexible track is easy to assemble and disassemble, lighter in weight, and less precise than the rigid track.

Wire feeding method
The smoothness of wire feeding directly affects the welding quality. The wire feeding method can be simply divided into two methods: drawing and pushing. The installation position of the welding torch and the wire feeder is relatively close during wire drawing, and the resistance encountered by the welding wire after leaving the wire feeder during welding is small, so the wire feeding process can be guaranteed to be stable, but both the wire feeder and the wire reel must be installed on the welding trolley In addition, the weight of the welding trolley is increased, which increases the difficulty of manual assembly and disassembly, and the increased weight can easily cause the welding trolley to walk unsteadily. The use of small coils of welding wire with a diameter of 0.8mm or .0mm (the weight is about 5kg) reduces the weight and load of the welding trolley and makes the welding process easy to control, but it has a certain impact on the welding efficiency. When the wire pushing method is used, the wire feeding mechanism is installed outside the welding trolley, which reduces the volume and weight of the welding trolley and can use a high-power wire feeder and a large plate of welding wire with a diameter of .2mm (the weight is about 20kg). Thereby improving welding efficiency. However, since the wire feeder is far away from the welding torch when pushing the wire, there must be a wire feeding hose to connect the two. When the welding wire is continuously pushed to the nozzle of the welding torch, the frictional resistance on the welding wire is relatively large. The bending degree of the wire feeding hose has a certain influence on the stability of the wire feeding, and in severe cases, it will cause poor wire feeding. Therefore, the above factors must be fully considered when using the wire pusher.

Selection of welding process
At present, in addition to manual welding, submerged arc automatic welding processes, and gas-shielded welding processes are mostly used for steel pipe welding.
Automatic submerged arc welding has the characteristics of good weld formation, high welding efficiency, and low welding cost. position, the tube turns. It is impossible to rotate the pipe when welding long-distance steel pipes, so "two to one" can only be used in the prefabrication of pipes. If the submerged arc welding process is adopted for all-position automatic welding of steel pipes, the welding device must be equipped with a flux feeding, supporting, and recovering mechanism, which makes the structure of the welding device more complicated, which brings inconvenience to the operation and assembly and disassembly, and increases The load of the trolley is reduced, which affects the stability of the trolley. Submerged arc welding generally adopts the welding method of thick welding wire and high current. It is used for all-position automatic welding, which may cause welding defects such as droplet drooping and flow due to the high deposition rate, which will affect the shape and quality of the weld seam. Therefore, submerged arc welding is more difficult to realize the automatic welding of steel pipes in all positions.

If the welding process of flux-cored welding wire and gas shielding is used, if it is formed multiple times, it will take a lot of work and time to clean the slag on the surface of the weld each time; Circulating cooling water can greatly improve the welding efficiency, so not only the structure of the welding device is complicated, but also the weight increases. Because the price of flux-cored wire is higher, and the gas source of shielding gas must be solved at the same time, the welding cost is higher. The single-use of self-shielded welding wire saves the shielding gas, but there is a problem of difficult slag removal. If the welding process of the solid core wire and gas protection is adopted, if it is formed in multiple passes, the welding process can be simply divided into three stages: priming, filling, and covering. The speed is slower than forced molding. The protective gas is generally a mixture of pure carbon dioxide gas, carbon dioxide, and argon or carbon dioxide and oxygen. The mixed gas of carbon dioxide and argon can make the arc combustion stable and less spatter during welding, but it is difficult to find the source of argon gas in field construction, and the price is high. From an economical point of view, it is best when welding oil pipelines. Try to use pure carbon dioxide as the shielding gas. For construction in areas where conditions permit, it is ideal to use carbon dioxide and argon as protective gases.

control method
In the welding process, the walking speed of the welding trolley, the wire feeding speed, and the left and right vibration frequency of the welding torch are the three main parameters, and the up and down adjustment of the welding torch can be ignored. Use a vertical line to divide the circumference of the pipe into left and right semicircles, and then divide the two semicircles clockwise and counterclockwise to determine the welding nodes. Ideal welding parameters can be obtained at each node of the weld through a large number of experiments. However, the actual welding and test data will not be the same. During the welding process, welding parameters can be adjusted according to the actual situation, such as wire feeding speed, vibration frequency, and other parameters. However, the adjustment of these parameters is interrelated. If the wire feeding speed is adjusted properly, the vibration frequency and welding speed may not be appropriate. Only after a certain period of exploration can several parameters be adjusted and matched. If another control method is adopted, the situation is quite different. The wire feeding speed, welding vehicle walking speed, and welding torch vibration frequency are taken as three dependent variables, placed in a space coordinate system, time is used as an independent variable, welding current and voltage are used as boundary conditions, and finally, the wire feeding speed, welding The relationship between the traveling speed of the trolley and the vibration frequency of the welding torch is the space coordinate equation. In the actual welding, each adjustment is the same time adjustment of the above three parameters, to ensure the accuracy of the adjustment process.

In the face of increasingly fierce competition in the international market, to occupy a place in the steel pipe welding market, the construction equipment and technical level must be improved. Therefore, the research on the steel pipe all-position automatic welding device has very important practical significance for improving the steel pipe construction level in our country.