Robot body welding process
With the increasingly high requirements for welding accuracy and speed and other indicators put forward by the automobile manufacturing industry, as well as the increasing personalized needs of users, in order to meet the market demand of multi-models and multi-batches, and improve the flexibility and elasticity of the production capacity of the body shop, industrial robots have been widely used in the body welding. This paper introduces the application of spot welding robot and arc welding robot system in body welding.
The structure and technology of car body largely determine the safety factor of riding. The body is composed of more than a dozen large assemblies and hundreds of sheet stamping parts, which are connected by spot welding, arc welding, laser welding, brazing, riveting, mechanical connection and bonding. Because the body in white involves many parts, complex processes and various types of equipment, the body planning has high requirements for welding process, welding fixture, quality control and maintenance. This paper introduces the application of spot welding robot system and arc welding robot system in body welding.
【 Spot welding robot system 】
The quality of spot welding directly affects the strength and safety of automobile body. Spot welding equipment is widely used in the production of automobile body because of its easy mechanization, low cost, mature technology and perfect supporting facilities. Now, the complete automation of the spot welding process has become a trend, and the robot spot welding system has been widely used, which is gradually replacing the manual spot welding.
one Pneumatic spot welding robot system
The pneumatic spot welding robot system includes the robot body, the robot controller, the spot welding controller, the automatic electrode grinding machine, the pneumatic spot welding pliers and the water gas control unit of the water gas supply
As the actuator of the spot welding robot, the pneumatic welding clamp is generally used, that is, the welding transformer is installed behind the welding clamp, which reduces the loss of the secondary cable and improves the welding quality. Due to the use of integrated welding pliers, the transformer must be as small as possible to improve the robot payload. For transformers with large capacity, the medium frequency inverter technology has been adopted: the 50Hz power frequency AC is changed into 600-1000Hz AC recirculation, so that the transformer volume is reduced and lightened.
The electrode assembly of the pneumatic welding pliers is basically similar to the manual welding pliers in form, which completes the contact with the workpiece and the electric welding function. In order to reduce the maintenance and renovation cost, the welding pliers assembly has the trend of modularization. Spot welding robot action is stable and reliable, high repetition accuracy, can replace heavy manual labor, and improve the welding quality, improve the flexibility of the production line.
In 2009, SAIC Passenger Car Corporation's Nanjing base built a new welding production line for 100,000 Roewe 350 series cars AP11. The line imported 49 six-axis pneumatic spot welding robots from Japan FANUC Company, which were applied to the assembly and welding of the total body welding station, side wall assembly and body body with high technological requirements.
After the successful construction of the new AP11 main line, SAIC Passenger Car Company Nanjing Base in 2011 to build MG5 model production line on the basis of AP11, once again introduced 10 spot welding robots of Japan FANUC company for 60,000 units of production capacity of AP12 main line. It is applied to the assembly and welding of the total assembly of the car body, the side parts, the side assembly and the body body, which require high process quality.
Different from the original AP11 main line, the construction and production of AP12 main welding line and AP11 line realize all equipment sharing, fully meet the needs of flexible mixed line production, and realize the full flexible production mode of short-time switching or no switching. In order to save construction costs and space, we have converted one robot on most stations of the production line to carry more than two welding tongs or gripper tools, and can quickly switch between welding tongs by using automatic tool exchange devices.
2. Servo spot welding robot system
In order to achieve higher welding quality and meet the performance requirements, AP12 line also introduced a new medium frequency spot welding servo torch control technology. This system can meet the requirements of high strength/ultra-high strength steel plate and multi-layer plate welding to meet the increasing requirements of automotive lightweight and anti-collision safety.
The servo spot welding robot system includes robot body, robot controller, medium frequency spot welding controller, automatic electrode grinding machine and servo spot welding pliers. The advantages of the servo welding gun are unmatched by the traditional pneumatic welding machine, which is characterized by replacing the pneumatic device with a servo device. According to the pre-prepared program, the servo controller issues instructions to control the servo motor according to the established speed and displacement feed, forming an accurate control of the electrode displacement and speed. The number and frequency of pulses determine the electrode displacement and speed. The motor torque determines the electrode pressure.
Servo welding gun has the characteristics of enhancing diagnosis and monitoring, simplifying welding clamp design, improving flexibility, reducing maintenance rate, improving running time and reducing production costs (gas consumption/spare parts/power saving), and will be the main equipment used in the future automotive assembly line. Among them, the quality and efficiency of frequency spot welding are much higher than that of power frequency welding, mainly in the following aspects:
(1) Reduce the synchronous and coordinated movement of the robot and the welding pliers, which greatly improves the production rhythm and minimizes the jump path between welding spots and obstacles; The electrode opening can be shortened at will to reduce the closing time of the welding clamp; After the welding start signal is sent out, the pressure can be controlled faster and better; Faster change of welding pressure, the pressure adjustment speed of up to 200kgf/cycle (98N/ms); Can avoid and inhibit spatter well, effectively ensure and improve welding quality; After the welding completion signal is sent, the welding pliers can be opened faster; Reduce electrode replacement and grinding time; Quick calibration after gun change, electrode grinding and replacement.
(2) Improve welding quality Soft contact can achieve very little product impact, but also reduce noise; Repeatable compression with high accuracy; Precise constant pressure control in welding; The pressure can be adjusted during welding. More stable electrode management and control.
Compared with the pneumatic welding torch, the progressive and precompression process of the servo welding torch is the two key stages that affect the welding efficiency. Programmable electrode travel and speed can reduce the progressive time of multiple solder joints on the same station, and can also improve welding productivity. Taking prepressure as an example, Figure 2 shows the change of electrical force of pneumatic welding torch and servo welding torch in the welding process. Assuming that the set prepressure is reached, the electrical force will remain constant. As shown in the table, a welding spot of the servo welding gun can save 0.44s, taking a car about 3500 ~ 5000 welding points as an example, will save 26 ~ 37min welding time, productivity has been greatly improved, and the production capacity of the body welding line has been greatly improved.
Arc welding robot system
The characteristics of automobile body structure determine that the manufacture of automobile body is inseparable from arc welding technology. The spark and smoke caused by traditional manual arc welding do great harm to human body, the working environment is bad, and the requirements for workers' skills are higher, the quality consistency of welding seam is poor, and the fluctuation is also large. Especially for the important structural safety parts of automobiles, the welding quality plays a decisive role in the safety of automobiles, so there is a trend of gradually adopting automatic arc welding robots to replace manual methods.
The design planning of the robot workstations should first consider whether it can meet the production program, the flexibility and welding quality of the workstations, as well as the selection and electric control design of the robots and welding guns. Specific contents include:
The design parameters of robot system include payload, number of axes, freedom range of each axis and control system.
The working range and posture of the robot fully consider the form of the body, the position of the arc welding point and the form of the fixture. The welding of interference danger points was simulated by 3D design model, the shape of welding gun and fixture and the robot operation position were repeatedly modified, and the feasibility demonstration and design amendment were carried out after the scheme was determined.
Determine the height of the robot and the distance from the front and back to the left and right to ensure that all arc welding points are reachable by the robot torch. The reliable way to optimize the design is to simulate the actual welding work through the robot simulation software. The specific method is to add the 3D model of the station fixture, workpiece and welding gun, assemble and debug the workstation in the virtual environment, simulate the path, and find out whether there is interference, so as to adjust the relative size of each part to achieve a reasonable.
Process timing design, control flow chart design. The equipment composition of arc welding robot workstation includes arc welding robot, robot controller, welding machine, gun cleaning system, conveying system, welding fixture, smoke exhaust and dust removal equipment, safety screen, arc shielding curtain and water and electrical unit.
The Roewe 350/MG5 production line in Nanjing Base of SAIC Passenger Car Corporation uses four arc welding robots from FANUC of Japan and advanced CMT welding machine system (with "cold" metal transition welding technology) from Fronius of Austria. CMT welding technology system is characterized by: as a complete "cold" technology, almost no current state of droplet transition, low heat input; Able to perform sheet/ultra-sheet welding; Ensure no splash transition, reduce the cleaning work after welding; Reliable arc starting and good bridging ability make the welding process easy to operate; Welding process wire feeding stability, welding process expert database, simplify and shorten the process debugging process.
