Application Progress of Robot Welding Technology in Steel Bridge Manufacturing

Driven by the construction of major bridge projects such as the Hong Kong-Zhuhai-Macao Bridge and the Deep-Medium Corridor, the application of robotic welding technology for steel bridge manufacturing in my country has made considerable progress in the past decade. The application of robotic welding technology has greatly improved the welding quality and effectively improved the fatigue resistance of key welds. The welding application and development of the plate unit robot, the bridge panel three-dimensional unit robot, the portable all-position robot and the steel guardrail column robot are introduced in detail, and the development trend of the welding technology of the steel bridge manufacturing robot is given a certain outlook.

1 Preface

Welding is the most important process and processing technology for steel bridge manufacturing. In the manufacturing stage of the factory, almost all parts and components need to be welded; in the site installation stage, welding is also one of the main connection methods. The quality of the weld is directly related to the structural safety and service life of the steel bridge. The welding efficiency largely determines the manufacturing cycle of the steel bridge product. Traditional steel bridge manufacturing is a labor-intensive industry. The production operations are mainly manual operations, with low production efficiency, high labor costs, and poor welding quality stability due to human factors. Welding robots have begun to be used in many industries in China. The passenger car industry, construction machinery industry, and railway vehicle industry have been widely used. Most other industries have just begun to apply or have just started. At present, in the field of engineering construction, bridge steel structure Some leading companies in the industry have also been used. The intelligent upgrade of welding not only enables workers to avoid close contact with welding fumes, arcs and other harmful sources, but also achieves the goal of improving production efficiency and quality.

In 2011, China Railway Mountain Bridge Group Co., Ltd. (hereinafter referred to as China Railway Mountain Bridge), Wuchuan Heavy Engineering Co., Ltd. (hereinafter referred to as Wuchuan Heavy Industry), etc. took the opportunity of winning the bid for the steel box girder manufacturing project of the Hong Kong-Zhuhai-Macao Bridge to construct steel box The beam and plate unit automated manufacturing production line is equipped with various special welding machines, which basically realizes mechanization and automatic welding, and changes the production method based on manual welding and semi-automatic welding of welders. At the same time, the U-shaped rib unit robot welding system is researched and applied. The robot welding system for the transverse partition unit has created a precedent for the application of domestic steel bridge robot welding technology.

In 2019, Wuhan Shipbuilding Industry Corporation, China Railway Baoqiao Group Co., Ltd. (hereinafter referred to as China Railway Baoqiao), and China Tieshan Bridge won the bid for the steel box girder manufacturing project of the deep and medium channel. The deep and medium channel is a world-class integrated bridge-island-tunnel-water The super-large cross-sea transportation cluster project that integrates the "under-hub interoperability" has complex construction conditions, large-scale projects, and very high comprehensive technical difficulties. The project proposes to use intelligent manufacturing to promote the transformation and upgrading of the steel structure manufacturing industry, to ensure high-quality construction and long-life service of bridge engineering, and to carry out research on key technologies for intelligent steel box girder manufacturing, in order to further improve the application of robotic welding technology in steel bridge manufacturing The level provides important engineering practice opportunities.

Since the beginning of the 21st century, with the rapid development of the national economy, my country’s bridge construction has made remarkable achievements. With the support of the "transportation power" strategy, with the advantages of large span, short construction period, and good environmental protection benefits, steel structure bridges It has a broad space for development. At present, the application of robot welding in the steel bridge manufacturing industry is still in its infancy and development stage, and is only used in some bridge types and structures. Among them, the application range of steel box girder plate unit welding is relatively large. This article gives a detailed introduction to the application and development of robot welding technology in the steel bridge industry in China in the past ten years, and makes some prospects for technology development trends.

2 Robotic welding technology of plate unit

Steel box girder manufacturing is generally divided into three stages: plate unit manufacturing, segment assembly, and site installation. The types of plate units include U-rib unit, plate-rib unit, cross-rib unit and cross-rib unit, etc., and the width is general It is 3~4m, and the length is generally 10~20m. The manufacturing of the plate unit mainly involves the welding of the fillet welds of the stiffeners. The number of welds is large and the quality requirements are high.

2.1 Robot welding system of U-rib cell

Figure 1 shows the U-rib automatic assembly and robot positioning welding system, which was jointly developed by China Tieshan Bridge and Tangshan Kaiyuan Robot System Co., Ltd. The system is composed of two mechanical arms, hydraulic system, gantry structure, electrical control system, machine tool traveling system, track system, working platform, clamping and positioning device, lateral adjustment mechanism and roller guide device. The system has been installed in Successfully applied in projects such as the steel box girder manufacturing of the Hong Kong-Zhuhai-Macao Bridge, the positioning welding adopts the solid-core welding wire rich argon gas shielded welding process.

Under the condition of U-rib single-sided welding, weld penetration and root fusion quality have an important impact on the fatigue performance of U-rib fillet welds. Tack welds are often weak parts. The robot tack welding system effectively avoids manual work. The situation that the quality of tack welding is not easy to control improves the stability of weld quality. Of course, with the popularization and application of U-rib double-sided welding technology, tack welding is remelted by subsequent welds as internal welds or temporary welds of joints, and its quality prominence is no longer obvious.

Figure 1 U-rib automatic assembly and robot positioning welding system

(1) Robot welding system based on gas shielded welding

Figure 2 shows the U-rib unit robot welding system, which was jointly developed by China Tieshan Bridge and Tangshan Kaiyuan Robot System Co., Ltd. The system consists of two cantilevered semi-gantry frames, mobile devices, four mechanical arms, welding power supply and transformer, control system, water cooling box, gun cleaning and wire cutting device and other facilities. With hydraulic anti-deformation tire frame, it can match 4 All welds are simultaneously welded by robot ship position. The robot has the functions of contact sensing and arc tracking. Before welding, the sensor voltage is applied to the front end of the welding wire to detect the position of the workpiece, so as to avoid misoperation due to the size or position error of the workpiece. During the welding process, the manipulator swings to detect changes in welding current and arc voltage, and adjust the position of the welding torch at any time according to the changes to realize the tracking of the weld. For U-ribs with a thickness of 8mm, the CO2 gas shielded welding process with metal powder cored flux-cored wire is generally used, and the welding is formed in two passes, the bottom and the cover. The appearance of the weld is well formed, and the weld penetration is stable, which can meet 80% melting. Transmission rate requirements.

Compared with portal multi-head (6 heads) gas shielded welding machine welding, U-rib plate unit robot welding has advantages in welding seam tracking accuracy and appearance shaping, but there are only 4 welding guns in a welding system, which cannot realize the board All U ribs on the unit are welded simultaneously, which is obviously behind in terms of welding efficiency. In addition, due to the application of U-rib internal welding technology, the U-rib internal fillet weld has the "bottom-sealing" effect. At present, more and more U-rib external welding is carried out by submerged arc welding. The submerged arc welding process has greater welding Seam penetration and higher welding efficiency.

Figure 2 U-rib robot welding system

(2) U-rib robot welding system based on submerged arc welding process

Chen Jin et al. introduced a new type of U-rib outer fillet welding equipment-U-rib submerged arc external welding robot welding system, using 4 sets of M-20iA six-axis manipulators produced by FANUC and R-30iB (Plus) control system , At the same time, the cantilever walking trolley, the horizontal sliding slide module and the lifting slide module adopt the servo motors of the FANUC servo system, and are connected to the R-30iB (Plus) control system. Each robot is equipped with an OSL-50 laser weld tracking system produced by Oxford Sensors in the United Kingdom. The system can locate and track the weld in real time, establish communication with the robot, and provide real-time feedback on the weld. The position data also guides the robot to correct the position, so that the welding gun can accurately weld the welding seam. The welding system is matched with φ1.6mm and φ3.2mm welding wires to cope with various welding applications. At the same time, a flux recovery and delivery system is installed on each welding gun to complete the flux delivery and recovery during welding. The part of U-rib submerged arc robot welding system is shown in Figure 3. After the U-rib internal welding process is completed, the submerged arc external welding robot welding system can weld the groove of the U-rib plate unit with a thickness of 12mm for full penetration at one time, without the need for welding bottoming. Affected by the mechanical structure, this equipment has only 4 sets of welding systems installed. Compared with at least 6 sets of welding systems of special welding machines, its welding efficiency is lower.

Figure 3 Part of U-rib submerged arc robot welding system

2.2 Robot Welding System of Diaphragm Unit

Diaphragm unit is the main component of steel box girder. It is mainly composed of panels, horizontal stiffeners, vertical stiffeners and manhole rings. Compared with U-rib/slab-rib unit, the weld form is more diverse, including Straight line section, curve section, flat fillet welding, vertical fillet welding and wrap fillet welding, etc. The use of robot welding technology is an effective way to realize its automatic welding

path.

(1) Based on offline programming technology

According to the needs of the steel box girder manufacturing project of the Hong Kong-Zhuhai-Macao Bridge, China Railway Mountain Bridge, Wuhan Shipbuilding Industry Corporation, China Railway Baoqiao, etc. are equipped with a diaphragm welding robot system. The robot welding system of the diaphragm unit adopts a gate structure, and each system is equipped with two manipulators, which are fixed on a rotating bracket. The bracket moves left and right on the crossbeam of the mast, and the mast is driven by a servo motor to walk on the longitudinal rail, so that the working range of the manipulator can cover the entire board unit, as shown in Figure 4.

The welding system is equipped with a dedicated offline programming software and a teaching programming operator. The operator can use the offline programming software to complete the programming work on the computer, and use the teaching programming method to proofread and correct, and complete the programming flexibly and efficiently. The robot has arc tracking and contact sensing functions. The position of the workpiece is detected before welding, and the welding path is corrected in real time during the welding process, which can effectively eliminate the influence of workpiece assembly deviation and clamping position deviation on welding. Robot welding can eliminate welding blind areas when welding with mechanical trolleys and reduce welding joints. In addition, through the program setting, automatic and continuous fillet welding of the ends of the plate ribs is realized, which ensures the welding quality, as shown in Figure 5. The diaphragm unit is generally welded by CO2 gas shielded welding with metal powder-cored flux-cored wire. For fillet welds with a foot size of 9mm or more, a multi-layer and multi-pass welding process is required.

Figure 4 Offline programming of the transverse partition robot welding system

Figure 5 Automatic continuous fillet welding seam forming

2) Based on visual recognition technology

In order to further improve the intelligent level of diaphragm unit welding, Wuchuan Heavy Industry will use a welding robot based on visual recognition technology for deep and medium channel steel box girder diaphragm unit welding in 2020. The welding robot system adopts a portal structure. Two manipulators are inverted under the moving portal beam. The portal frame walks on the longitudinal track. The robot moves horizontally on the beam. The working range of the manipulator can cover the entire board unit, as shown in Figure 6. Shown. The laser sensor installed on the gantry beam is used to scan and collect the contour of the workpiece to automatically identify the position to be welded; adaptive logic programming technology (ALPT) is used to intelligently plan the welding path based on the collected data, without the need for 3D model import and programming teaching, It can save the preparation time and reduce the skill level requirements of the operators. When intelligently planning the welding path, follow the principle of efficiency optimization to improve the overall arcing efficiency of robot welding as much as possible, while increasing the number of welding joints to a certain extent.

Figure 6 Robot welding system for visual recognition of diaphragm

Point laser sensing method is used for welding positioning, automatically find the appropriate arc point, welding torch swing welding, and arc sensing seam tracking technology to ensure welding accuracy. In order to avoid the influence of the positioning weld on the accuracy of laser positioning, the positioning weld must be kept at a certain distance from the arc starting point. The robot welding system can complete the welding of various types of welds such as cross-baffle hole ring stiffening, bevel stiffening, flat fillet welding, vertical fillet welding and wrap fillet welding. The shape of the orifice stiffened weld is shown in Figure 7.

Figure 7 Formation of the ring stiffening weld

2.3 Robot welding system for transverse rib unit

In 2020, Wuchuan Heavy Industries will use a welding robot for the welding of transverse ribs (see Figure 8). The robot system is equipped with two manipulators under the rail-type gantry, and a set of industrial cameras are equipped on the gantry beam. The gantry moves longitudinally, the depth camera panoramic recognition system scans the workpiece to generate a three-dimensional point cloud image, and the relevant data is provided to the workpiece recognition algorithm software to complete the intelligent recognition and positioning of the type of the workpiece and the contained components, and then automatically complete the programming of the workpiece welding to achieve fully automatic Programming function. Before this, it is necessary to establish the type library of the transverse ribs and the feature library of the components, and establish the corresponding welding process library. A laser sensor is installed at the end of the manipulator, using line laser scanning technology (see Figure 9), which can accurately locate the weld and realize the tracking function during the welding process. The welding gun adopts a non-swing method for welding. A welding fume absorption device is installed on the welding gun to achieve a good fume and dust removal effect.

Figure 8 Robot welding system for transverse ribs

Figure 9 Line laser scanning welding positioning

Because the transverse rib robot welding system has the function of intelligent recognition and positioning of the workpiece, the workpiece does not need to be strictly positioned before welding; the transverse rib unit is paired in two groups, and the two manipulators can weld at the same time, which improves the welding efficiency. After the welding of one side of the transverse rib is completed, the whole is turned over and the other side is welded. It should be noted that the polished area to be welded should not be too bright, so as not to affect the reliability of laser sensor welding positioning and tracking. The transverse rib unit is generally welded by CO2 gas shielded welding with flux-cored wire.

3 Robot welding technology for three-dimensional unit parts of bridge deck

The three-dimensional unit parts of the bridge deck are welded by the U-rib unit and the transverse rib unit. The connection welds between the tooth-shaped edges of the transverse ribs and the U-ribs and the panels form multiple sets of "groove welds", including flat fillet welding and vertical welding. Fillet welding, end welding. Due to the requirement of fatigue resistance, the quality of the weld details is very high. Continuous arc welding is required when the flat position welding is converted to the vertical position welding, and the end welding of the vertical fillet welding is full and smooth. In accordance with the construction requirements of the steel box girder manufacturing project of the deep and medium channel, Wuchuan Heavy Industry adopted the bridge deck three-dimensional unit robot system in 2020 to realize the automatic welding of the welding seam of this component. The robot welding system has two manipulators upside-down under the rail-type gantry, with functions such as offline programming, contact sensing, arc tracking, and multi-layer and multi-pass welding. The moving gantry spans two three-dimensional unit work stations. The three-dimensional unit robot welding workstation is shown in Figure 10.

Figure 10 Three-dimensional unit robot welding workstation

Before each group of "groove welds" are welded, three-direction contact sensing technology (see Figure 11) is used to detect five positions in the figure in turn. Contact sensing is a method used to detect the position deviation of the target workpiece. When the consistency of the workpiece cannot meet the welding requirements, the welding deviation is automatically judged before welding. According to the deviation, the robot system compensates for the established welding procedure. , Thus ensuring the accuracy of the actual welding path. Due to the short length of each weld, arc sensor tracking is not required during the welding process.

Figure 11 Three-direction sensing point setting of offline program

When robot welding is welding at the end of vertical welding, the welding torch posture and welding parameters need to be adjusted in time. The arc-extinguishing molten pool of each side welding torch needs to cross the center line of the toothed plate to ensure that the welding seam at the surrounding weld is full and smooth. When double welding torches are simultaneously carrying out encircling welding on both sides of a weld, the welding pool heat is too large and the cooling rate is slow, and it is easy to drip down and form weld bumps. Therefore, two manipulators are used to misalign the left and right sides of the "groove weld". Welding helps ensure good weld formation (see Figure 12 and Figure 13).

Figure 12 Dislocation welding of two manipulators

Figure 13 End wrap fillet welding forming

Before robot welding, manual welding is required for the large part of the assembly gap (above 2~3mm). Compared with solid wire gas shielded welding, the use of flux-cored wire gas shielded welding has requirements for assembly gap control and positioning welding. It is relatively low, the appearance and quality of the weld is better, and the welding efficiency is relatively high, as shown in Figure 14. Part of the flat fillet welding between the toothed plate and the panel requires a foot size of 10mm, and a total of two layers of three passes are required. The robot is used to weld two consecutive fillets at the flat fillet welding position in advance, and then the continuous welding of the "groove weld" is performed after the slag is removed. . The appearance of multi-layer multi-pass welding is shown in Figure 15.

Figure 14 "Groove weld"

Figure 15 Appearance of multi-layer multi-pass welding

4 Application of portable all-position welding robot

For steel bridge segment assembly or bridge site welding, due to the large space size of the structural parts and a large number of structural welds in the cabin, the working conditions are complicated, and the implementation of automatic welding is difficult. At present, manual welding is still the main method. . For some long straight welds, portable all-position automatic welding trolleys or robots are used for welding. In actual production, the proportion of portable automatic welding trolleys is relatively high, and the proportion of intelligent welding robots is relatively small. Among them, MICROBO portable all-position intelligent welding robots are used. Representative. MICROBO is mainly composed of robot body, swing mechanism, control box, teach pendant, guide rail, welding power source, wire feeder and welding gun. MICROBO can automatically obtain the workpiece thickness, groove angle, root gap and other data, and automatically generate welding parameters such as welding current, welding voltage, welding speed, etc. It can automatically generate the number of welding layers and Welding gun swing and other parameters have many advantages such as intelligence, high efficiency, and easy operation.

At present, the MICROBO welding robot has applied cases in the butt joint of the steel box girder segment assembly panel bottom plate and the main welding seam of the steel anchor box of the pylon. The application scenario of the MICROBO welding robot for assembling the steel box girder section of the deep and medium channel of Wuhan Shipbuilding Industry Corporation is shown in Figure 16, and the appearance of the welding seam is shown in Figure 17.

Figure 16 Application scenario of MICROBO welding robot

Figure 17 Appearance of weld formation

5 Robot welding application of steel guardrail column

The anti-collision guardrail is an important subsidiary structure of the bridge, and the guardrail pillars are generally welded by steel plates. For example, the total number of steel guardrail columns in the main passage bridge project of Ningbo Zhoushan Port is about 50,000 pieces, and the weight of a single piece is about 70kg. The maximum external dimension is 380mm×240mm×1270mm. The overall dimensions are uniform, which is convenient for mass automated welding and manufacturing. The weld form is fillet weld, and the size of the weld foot is 5~7mm.

Wuchuan Heavy Industry has developed and developed the first steel guardrail column automatic assembly welding robot workstation system in the industry. Parts assembly and welding are all completed by robots. For the first time, robot technology is introduced into the assembly process of bridge parts (see Figure 18). The system integrates functions such as intelligent parts recognition, 7-axis snatching, 360° full rotation without dead angle installation, adsorption and nondestructive clamping, infrared scanning comparison, arc tracking and power parameter intelligent matching. The positioner can turn the workpiece to adjust the welding seam to the flat welding position, which is conducive to the appearance of the welding seam. It adopts barreled flux-cored welding wire for welding, the diameter of the welding wire is 1.6mm, and the welding efficiency is high.

Figure 18 Robot welding workstation for steel guardrail column

6 Conclusion

1) In the past ten years, driven by the construction of major bridge projects such as the Hong Kong-Zhuhai-Macao Bridge and the Deep-Medium Corridor, robotic welding technology has begun to be applied in domestic steel bridge manufacturing, and the scope of application has been gradually expanded, greatly improving the processing of steel bridges. The automation and intelligent level of manufacturing have effectively improved the welding quality and the fatigue resistance of key welds.

2) The welding robot based on offline programming technology is used for the welding of U-rib unit, transverse partition unit, panel three-dimensional unit and other structures. The welding path and welding gun posture can be freely planned according to the structural characteristics; welding based on visual recognition and independent programming technology The robot has been used in the welding of the transverse partition unit and the transverse rib unit, which can save the preparation time and effectively reduce the skill requirements for the operators; the portable all-position welding robot has certain applications in the segmental assembly and welding, and its adaptability is also low. Needs to be further improved. Technologies such as contact sensing, arc sensing, and laser sensing are all applied in the welding of steel bridge manufacturing robots, and play a good role in positioning the welding starting position and tracking the weld seam.

3) The welding process plan is an important factor that affects the application effect of robot welding. For the welding joints of the plate unit and the main single-pass weld, the flux-cored wire CO2 gas shielded welding process is a relatively good choice. Among them, the flat fillet welding position For fillet welds, metal powder-cored flux-cored wire CO2 gas shielded welding has better process performance; for multi-pass welding of thick plates, solid wire is used for argon-enriched protection, which eliminates the slag removal process and is more adaptable.

4) Welding robots based on visual recognition and independent programming technology have a higher level of intelligence, which is the development direction of robot welding technology, but its reliability and adaptability need to be further improved.

5) High-efficiency welding is an important development direction of robot welding technology. Increase the number of robotic arms in the robot welding system, reduce the preparation time before welding, and improve arc efficiency. The use of high-efficiency welding technology can effectively increase the efficiency and productivity of robot welding.

6) Steel bridge segment assembly and thick plate structure welds are difficult points in the application of robotic welding technology. The control of component assembly precision, robotic welding intelligent technology, and the development of advanced welding processes will be important technical approaches to solve the above problems.