The hottest welding robot and its application

2022-08-22
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Welding robot and its application

1. welding robot

welding robot is an industrial robot engaged in welding (including cutting and spraying). According to the definition of the international organization for Standardization (ISO) industrial robot terminology standard, industrial robot is a multi-purpose, reprogrammable automatic control manipulator with three or more programmable axes, which is used in the field of industrial automation. In order to adapt to different uses, the mechanical interface of the last axis of the robot is usually a connecting flange, which can be connected with different tools or end effectors. Welding robot is to install welding tongs or welding (cutting) guns on the end shaft flange of industrial robot, so that it can weld, cut or heat spray

1. Composition of welding robot

welding robot mainly includes robot and welding equipment. The robot is composed of the robot body and the control cabinet (hardware and software). Welding equipment, such as arc welding and spot welding, is composed of welding power supply (including its control system), wire feeder (arc welding), welding gun (pliers), etc. For intelligent robots, it should also be cleared) there should be sensing systems, such as laser or camera sensors and their control devices. Figures 1a and b show the basic composition of arc welding robot and spot welding robot

2. Main structural forms and performance of welding robots

welding robots produced all over the world are basically joint robots, most of which have six axes. Among them, axis 1, 2 and 3 can send the end tool to different spatial positions, while axis 4, 5 and 6 solve the different requirements of tool posture. The mechanical structure of the welding robot body mainly has two forms: one is the parallelogram structure, and the other is the side (pendulum) structure, as shown in Fig. 2a and B. The main advantage of the side mounted (tilting) structure is that the upper and lower arms have a wide range of activities, so that the working space of the robot can almost reach a sphere. Therefore, this kind of robot can work upside down on the rack to save floor space and facilitate the flow of objects on the ground. However, this side mounted robot, whose 2 and 3 axes are cantilever structures, reduces the stiffness of the robot and is generally suitable for robots with small loads, such as arc welding, cutting or spraying. The upper arm of the parallelogram robot is driven by a pull rod. The pull rod and the lower arm form two sides of a parallelogram. Hence the name. The early developed parallelogram robot has a relatively small workspace (limited to the front of the robot), which is difficult to work upside down. However, the new parallelogram robot developed since the late 1980s has been able to expand the workspace to the top, back and bottom of the robot, without the stiffness problem of the measuring robot, so it has received widespread attention. This structure is suitable for both light and heavy robots. In recent years, robots for spot welding (with a load of 100 ~ 150kg) mostly use robots with parallelogram structure

each axis of the above two robots is rotating, so the servo motor is driven by cycloidal pinwheel (RV) reducer (1 ~ 3 axes) and harmonic reducer (1 ~ 6 axes). Before the mid-1980s, DC servo motors were used for electrically driven robots. Since the late 1980s, countries have successively changed to AC servo motors. Because the AC motor has no carbon brush and good dynamic characteristics, the new robot not only has a low accident rate, but also has a large increase in maintenance free time and a fast acceleration (deceleration). For some new light robots with a load of less than 16KG, the maximum speed of the tool center point (TCP) can reach more than 3m/s, with accurate positioning and low vibration. At the same time, the control cabinet of the robot also uses a 32-bit microcomputer and a new algorithm, so that it has the function of self optimizing the path, and the running track is closer to the teaching track, as shown in Figure 3

3. Characteristics of spot welding robot

(1) basic functions of spot welding robot spot welding does not have high requirements for the robots used. Because spot welding only needs point position control, there is no strict requirement for the moving track of the welding tongs between points. This is also the reason why robots can only be used for spot welding at first. The robot for spot welding should not only have sufficient load capacity, but also have fast speed, stable action and accurate positioning when shifting between points, so as to reduce the shift time and improve work efficiency. The load capacity of the spot welding robot depends on the type of welding tongs used. For the welding tongs separated from the transformer, a robot with a load of 30 ~ 45kg is sufficient. However, on the one hand, due to the long secondary cable and large power loss, this welding tongs is not conducive to the robot extending the welding tongs into the workpiece for welding; On the other hand, the cable keeps swinging with the movement of the robot, and the cable is damaged faster. Therefore, at present, the use of integrated welding tongs is gradually increasing. The weight of this welding tongs together with the transformer is about 70kg. Considering that the robot should have enough load capacity and be able to send the welding tongs to the space position for welding with a large acceleration, the heavy robot with a load of 100 ~ 150kg is generally selected. In order to meet the requirements of short distance and rapid displacement of welding tongs during continuous spot welding. The new heavy-duty robot has the function of completing 50mm displacement in 0.3s. This puts forward higher requirements for the performance of the motor, the computing speed and algorithm of the microcomputer

(2) welding equipment of spot welding robot the welding equipment of spot welding robot adopts integrated welding tongs, and the welding transformer is installed behind the welding tongs, so the transformer must be as small as possible. For transformers with small capacity, 50Hz power frequency AC can be used, while for transformers with large capacity, inverter technology has been adopted, which has an important impact on the world plastic machine market; 2. Due to the continuous increase in the number of exports of China's plastic machinery, the 0Hz power frequency AC has changed to 600 ~ 700Hz AC, reducing the volume of the transformer. After voltage transformation, 600 ~ 700Hz alternating current can be directly used for welding, and secondary rectification can also be carried out for DC welding. The welding parameters are adjusted by the timer, see Figure 1b. The new timer has been computerized, so the robot control cabinet can directly control the timer without additional interface. The welding tongs of spot welding robots usually use pneumatic welding tongs. The opening between the two electrodes of the pneumatic welding tongs generally has only two strokes. And once the electrode pressure is set, it cannot be changed at will. In recent years, a new electric servo spot welding tongs has appeared, as shown in Figure 4. The opening and closing of the welding tongs are driven by the servo motor and fed back by the code disk, so that the opening of this welding tongs can be arbitrarily selected and preset according to the actual needs. Moreover, the pressing force between electrodes can also be adjusted steplessly. This new electric servo spot welding tongs has the following advantages:

1) the welding cycle of each welding spot can be greatly reduced, because the opening degree of the welding tongs is accurately controlled by the robot, and the welding tongs can start to close when the robot moves between points; After a little bit of welding, the welding tongs are opened, and the robot can move at the same time. It is not necessary to wait until the robot is in place before the welding tongs are closed or the robot moves after the welding tongs are fully opened

2) the opening of the welding tongs can be adjusted arbitrarily according to the condition of the workpiece. As long as there is no collision or interference, the opening can be reduced as much as possible to save the opening of the welding tongs and the time occupied by the opening and closing of the welding tongs

3) when the welding tongs are closed and pressurized, not only the pressure can be adjusted, but also the two electrodes are gently closed when closed, reducing impact deformation and noise

4. Characteristics of arc welding robot

(1) the basic function of arc welding robot. The arc welding process is much more complex than the spot welding process. The tool center point (TCP), that is, the motion trajectory of the welding wire end, the posture of the welding gun, and the welding parameters all require accurate control. Therefore, in addition to the general functions mentioned above, the arc welding robot must also have some functions suitable for the requirements of arc welding

although in theory, a robot with five axes can be used for arc welding, it will be difficult to use a robot with five axes for welds with complex shapes. Therefore, unless the weld is relatively simple, 6-axis robot should be selected as far as possible

in addition to the track of zigzag corner welding or small-diameter round weld welding mentioned in Figure 2 above, the arc welding robot should also have software functions of different swing styles for programming, so as to make swing welding. Moreover, at the pause point in each cycle, the robot should automatically stop moving forward to meet the process requirements. In addition, it should also have the functions of contact locating, automatically finding the starting position of the weld, arc tracking and automatic re arc striking

(2) welding equipment for arc welding robots arc welding robots mostly use gas shielded welding methods (MAG, MIG, TIG), and the usual welding power sources such as thyristor type, inverter type, waveform control type, pulse or non pulse type can be installed on the robot for arc welding. Since the robot control cabinet adopts digital control, and the welding power supply is mostly analog control, it is necessary to add an interface between the welding power supply and the control cabinet. In recent years, foreign robot manufacturers have their own specific supporting welding equipment, and the corresponding interface board has been broadcast in these welding equipment, so there is no additional interface box in the arc welding robot system in Figure 1a. It should be pointed out that the arc time accounts for a large proportion in the working cycle of the arc welding robot, so when selecting the welding power supply, the capacity of the power supply should generally be determined according to the duration of 100%

the wire feeding mechanism can be installed on the upper arm of the robot, or it can be placed outside the robot. The hose between the welding gun and the wire feeder is short, which is conducive to maintaining the stability of wire feeding. When the robot sends the welding gun to some positions, the hose is in a multi bending state, which will seriously affect the quality of wire feeding. Therefore, the installation method of wire feeder must consider the problem of ensuring the stability of wire feeding

2. Application of welding robots

the 1980s was the decade when welding robots were applied and developed fastest in production internationally. Since the 1990s, the pace of applying welding robots has also accelerated significantly in Chinese factories. It should be clear that the welding robot must be equipped with corresponding peripheral equipment to form a welding robot system. Welding robot systems that are widely used at home and abroad have the following forms:

1 Welding robot workstation (unit)

if the workpiece "research results cannot lie in the laboratory" does not need to be displaced during the whole welding process, the workpiece can be positioned on the workbench with a fixture. This system is the simplest. However, in actual production, more workpieces need to be shifted during welding, so that the weld is welded in a better position (posture). In this case, the positioner and robot can move separately, that is, the robot rewelds after the positioner is shifted; It can also move at the same time, that is, the positioner changes position while the robot is welding, which is often referred to as the coordinated movement of the positioner and the robot. At this time, the motion of the positioner and the motion of the robot are combined, so that the motion of the welding gun relative to the workpiece can not only meet the requirements of the weld trajectory, but also meet the requirements of the welding speed and the posture of the welding gun. In fact, at this time, the axis of the positioner has become a part of the robot. This welding robot system can have as many as axes, or more. The latest robot control cabinet can be a combination of two robots to coordinate the movement of 12 axes. One of them is

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