Application and problems of welding robots in Changan Automobile Co., Ltd.

1 Introduction

With the development of society and the advancement of science and technology, robots have been widely used in various fields of society, and industrial robots are the most widely used. Since its inception in the early 1960s, industrial robots have been widely used in the industrial field after more than 40 years of development, becoming the main mechatronics equipment in the production automation of the automotive industry.

The main purpose of the application of robots in the manufacturing industry is to reduce production staffing, increase labor productivity, reduce labor intensity and improve product quality. Robots have two main advantages over traditional machines:

1) Easily automate the production process.

2) High adaptability to production equipment.

2, welding robot

Welding robots are currently the largest industrial robot application field. As the automobile manufacturing industry puts higher and higher requirements on the welding precision and speed of many components, the average worker has been unable to do the job; in addition, the sparks and smoke during welding cause harm to the human body, therefore, the welding process Full automation has become an important research topic, the most important of which is the application of welding robots.

3. The application of the robot in Changan Automobile Co., Ltd.

3.1. Application of KUKA robot in the welding line of 100,000 vans

In 1996, Changan Automobile Co., Ltd. built a new 100,000 SC6331 series minivan welding production line. This line first introduced the KRC32 6-axis pneumatic spot welding robot from KUKA of Germany, which was applied to the frame with the highest process requirements and the welding line. In the original manual welding line, the frame welding station and the welding station are due to the large number of welding points and the complicated structure of the welding parts, which is the bottleneck station that restricts the production of the whole line. The workers have long working hours, high labor intensity and equipment failure rate. High, solder joint quality is unstable and easy to cause crushing injury, which seriously restricts the production speed of the whole line, and the product quality is not guaranteed.

After the introduction of KUKA spot welding robots, first of all, the production cycle of 100,000 welding lines has been greatly improved, and the number of single-shift production of mini-vans has increased significantly, reaching five times the output of manual welding lines. Secondly, the labor intensity of workers has been greatly reduced. The time is greatly shortened and the working conditions are greatly improved. Thirdly, the quality of the mini van is significantly improved, and the body crushing injury is greatly reduced. Fourth, the KUKA welding robot has a very low failure rate, sufficient spare parts supply, high system stability, and operation. Maintenance is easy, a large number of equipment maintenance personnel are saved, and human resources are saved.

3.2. Application of COMAU, KUKA and OTC robots on 80,000 Changan Star welding lines

After the successful introduction of the KUKA welding robot, Changan Automobile Co., Ltd. re-introduced welding robots on the SC6350-"Changan Star" 80,000 welding production line, including the Italian COMAU H4 servo spot welding robot, and the Italian COMAU H1 stud. Welding robot, Japanese OTC arc welding robot, KUKA KRC type detecting robot.

The application level of SC6350 80,000 welding line robots is advanced. Servo welding tongs robots, arc welding robots and testing robots are the most advanced representatives of the domestic automotive industry.

Among them, the detection robot adopts the internationally advanced online detection method, and the detection equipment of the world-leading German Perceptron company is integrated with the German KUKA robot with the highest system stability, and the last work of the main line (car-forming) welding line. Bit-on-line real-time detection of each "Changan Star" body-in-white to control body size accuracy. The detection system design has a normal size deviation of ±2mm for the body-in-white. When the body-in-white size is out of tolerance, the production line will have an alarm prompt, and the measurement data of each body-in-white will be stored in the detection system for offline analysis.

The arc welding robot adopts the DR series seven-axis welding robot of Japan OTC Company. The design of the OTC robot body is compact, the structure is simple and clear, and the arc welding function is complete, which is especially suitable for gas shield welding of components with complicated structure. For example, the arc welding of the connecting beam on the SC6350 series micro-car frame assembly, because the beam is circular, requires circumferential welding, and the position of the component is low, the manual welding labor intensity is great, and the gas shielded welding is a toxic operation. The use of OTC arc welding robots overcomes these shortcomings that severely restrict production, fail to guarantee product quality, and impair the health of operators.

Another concern is the introduction of high-precision, high-reliability servo spot welding robots. This type of robot uses COMAU's H4 spot welding robot and integrates the SIAKY servo welding tongs system. The welding spot welding quality is stable and accurate. The most outstanding feature of servo welding tongs compared with pneumatic welding tongs is that during the welding process, the welding tongs have high welding quality and good solder joints, which greatly improves the welding quality of the body-in-white and makes the “Changan Star” well deserved. Become a micro-car boutique in China.

4. Application experience of welding robot

The welding robot has been used in Changan's automobile production line for seven years. According to the actual application, the following experiences are for everyone to study together:

4.1, the use of welding robots must meet safety requirements

Welding robots can replace humans in dangerous and harmful environments, and at the same time bring another potential danger, that is, robotic injuries. For this reason, when the welding robot is running online, no one can enter the area where its motion safety is located, and there should be no interference in the motion area. This is the most important principle for the safety management of welding robots. In addition, in addition to the general industrial safety regulations, it is also necessary to pay attention to the particularity of the welding robot and take corresponding and reliable countermeasures. For example, the security measures we are using now:

(1) Install a safety fence for the welding robot and its peripheral equipment to prevent accidental injury from entering a dangerous area.

(2) A plug-in electric contact switch is arranged on the safety door at the entrance of the safety guardrail, and the switch is connected with the safety return circuit of the welding robot. Once the safety door is opened, the robot controller will cut off the driving power of the robot, and the robot immediately stops moving.

(3) Install multiple emergency stop switches at the nearest location to the welding robot. Once an emergency or dangerous situation occurs, the worker can press the emergency stop to stop the robot.

(4) Reduce the movement speed of the welding robot during teaching operation, and teach by personnel trained in professional technical operation.

(5) The welding robot safety circuit is integrated with the production line safety circuit. When the production line encounters an emergency, the production worker can press the emergency stop switch of any station on the line to stop the robot.

4.2. Control device for welding robot

Although the welding robot itself has a very complete control system, each welding robot as a separate automation equipment system is always a subordinate workstation in a production line or a production system, and must have corresponding external control devices. Remote control to meet the simultaneous and orderly production requirements of various automation equipment on the automated production line.

Related control devices commonly used in welding robots include programmable controllers and online monitoring devices.

The programmable controller coordinates and cooperates with various automation equipments including welding robots on the production line to automate the production process in an orderly manner.

The online monitoring device is a human-machine interface between the operator and the production system. It collects real-time data from the production system and can conditionally modify the production data in real time, thus real-time monitoring of the production line scene and remote real-time control of the production line operation. the goal of. The use of an online monitoring device makes it easy to issue work orders, start or stop all automation equipment including welding robots, and know the status of the production system in real time.

Changan's 80,000 Changan Star welding line uses Siemens WIN CC online monitoring system and Siemens programmable controller. All welding robots must be controlled by their own control system, and must accept PLC and WIN. Remote control of CC online monitoring system to ensure synchronous operation with other automatic equipment on the production line.

4.3. Extension of the welding robot system

In order to meet the actual needs of Changan's 80,000 “Changan Star” welding line, COMAU Company took into account the stability of the production line system and the stability of the body-in-white product quality when designing the control system. Has the following extensions:

(1) Increase the external sliding shaft

The external sliding shaft of the welding robot, like the other six basic shafts, contains servo drives and servo motors. Together with the corresponding mechanical transmissions, it can effectively expand the range of motion of the robot and achieve maximum in complex or narrow spaces. Good working posture, can also be arbitrarily positioned by teaching to maintain the highest positioning accuracy. In the actual application of spot welding, the welding robot including the external shaft drive can accurately reach the required solder joint position and achieve the best welding posture, so the spot welding effect is better without noise and solder droplet splash, and the solder joint shape after soldering Beautiful and high quality welding.

For example, 80,000 welding line main line 730 total work station, using fully automatic parts assembly and welding process, the station has a total of 6 COMAU welding robots, to complete the left / right side of the frame and the frame assembly and the entire white The welding of the body, plus the work station includes the assembly of the top cover, the assembly of the frame and other parts, the fixtures, the conveying device, the automatic welding tongs and many other devices, the space is extremely limited, in order to ensure the welding of the group, a total of 4 robots are used. The sliding outer shaft is used to complete all work in a narrow space with high quality, high speed and safest.

(2) Swing welding in arc welding

Through the correct setting of the software, the arc welding robot can realize the lateral swing of the wire tip while advancing along the weld seam. The mode, frequency and amplitude of the swing can be set according to the process requirements, thereby achieving the purpose of improving the quality of arc welding.

(3) Automatic switching of robot tools

In the same place, there are 80,000 welding line 730 stations. In order to save the working space and shorten the working time, the welding robot No. 15 (No. 16) must complete the welding work of the white body of the total work station, and it is also responsible for the production line from the side wall. The side wrapping components are grabbed and placed on the main line to assemble with the frame and the top cover. Therefore, the two welding robots adopt the world's leading “gun/hand” automatic switching technology, and the programmable controller controls the robot to perform servo when the production line needs it. Automatic switching of welding tongs and gripper tools. In this way, a robot can complete the work that two robots need to complete, saving both cost and space.

4.4, robot programming

The KUKA robot of Changan's 100,000 welding line is programmed with APS software under the WINDOWS operating system. The motion program must be uploaded and downloaded in the WINDOWS environment. The COMAU robot on 80,000 welding lines is programmed with arbitrary text. The editor, after compiling, downloads the program to the robot controller using PCINT computer simulation software. The common feature of these two kinds of robot programming is that they can realize off-line programming and online teaching, which provides powerful help for the design and simulation of the production line. The difference is that COMAU robots adopt a language structure similar to PASCAL's high-level programming language. For those who have studied computer programming languages, they can understand very quickly and easily. After receiving some basic training, they can be quite perfect. Robot control program. KUKA robots use their dedicated robot programming language, and technicians must receive professional programming training from KUKA to be competent in programming. OTC robot's control program programming is relatively easy, basically using simple, easy-to-understand motion instructions, the meaning is clear at a glance.

4.5, the successful introduction of servo welding tongs

The five KUKA spot welding robots used in 100,000 welding lines are all welded with pneumatic spot welding tongs. Due to the wear of the electrode caps of the welding tongs, the control system uses the number of calculated welding points to incrementally compensate the welding current. Methods. In principle, this is an open-loop compensation method, which does not actually reflect the true loss of the electrode cap of the welding tongs. Therefore, there is a certain instability in the welding quality of the vehicle body.

On 80,000 welding lines, all COMAU spot welding robots use SIAKY servo welding tongs and control systems. The servo welding tongs exist as an external axis of the robot. A set of driving software is added to the robot control system. The external shaft is completely controlled by the robot controller like the other six basic axes. In this way, the external axis is integrated with the other six axes, and the robot control system can calculate the real position of the axis in real time through the external axis drive software. In practical applications, after completing the welding work of each car body, the robot control system will perform an automatic correction function on the external shaft-servo welding tongs by checking whether the actual zero position of the shaft (servo welding tongs) changes. It is confirmed whether the electrode cap is worn, which ensures the automatic closed-loop control of the welding pressure, and the stability of the welding quality of the vehicle body is greatly improved.

4.6. Applying welding robots to achieve flexible production

Changan Company has many types of miniature cars and complex varieties. In the past manual production lines, if it is necessary to mix and produce different types of models of the same model, the manual welding speed is greatly reduced due to the difference of workpieces and tools, and the quality of the produced automobile products is also presented. Out of instability.

After the introduction of the welding robot, it is only necessary to pre-program several sets of different motion and welding procedures that are suitable for the production of different models. The robot will automatically call the corresponding working procedures and the tools required for welding different body bodies according to the working instructions of the production line. That is, it can automatically adapt to the complex changes of the models on the production line. Even 80,000 welding lines with high frequency and mixed production of various types of vehicles can cope with it. It will never be caused by the mis-welding, mis-welding, misalignment or unadjusted welding specifications of the manual welding line, which is easy to occur due to the mixed production of multiple vehicles in a single shift. The production line runs at the same speed. reduce. The wide application of welding robots has brought unprecedented vitality to the realization of flexible and automated production of Changan's automobile manufacturing.

5. Problems in the application of welding robots

Although the welding robot has been widely used in Changan's automobile manufacturing production, the quality of automobile welding has been greatly improved, and the labor productivity of the enterprise has been effectively improved. However, there are still many problems worthy of further research and improvement.

5.1. Re-teaching after positional offset

The teaching reproduction type welding robot must perform on-line teaching and then reproduce the operation if a welding position shift occurs, and this work now requires a large amount of production time. If it can be taught and simulated offline using advanced computer dynamic simulation technology, it will be a revolutionary improvement in welding robot applications.

5.2. The problem of seam tracking of arc welding robots.

When the teaching regenerative arc welding robot performs arc welding, the dynamic tracking feedback of the weld can not be performed. Therefore, when the weld has slight changes, the weld quality cannot be guaranteed. If the intelligent technology can be applied, the condition of the weld can be dynamically tracked. Guarantee the reliability and stability of arc welding quality.

5.3. Spare parts for welding robots.

At present, due to the fact that the application of domestic robots is not very extensive, domestic robot technology has yet to make great progress. The special parts of robots cannot be designed and manufactured in China. After Changan has applied a large number of welding robots, the problem of accessories has become the most headache in robot applications. The problem. Because the components of the robot are mostly special components (especially the electrical control part), the technical level is quite high, so it must be imported from abroad, and the imported robot spare parts are expensive. Most domestic agent companies are unwilling to cause a backlog of funds due to a large number of pre-purchases. The time period for importing spare parts is long, which has caused considerable difficulties for the automobile production line.

5.4. The robot's axising process takes up too much time.

The calibration process of the KUKA, COMAU, and OTC robots used by Changan Company takes a relatively long time. For the automatic production line of the pipeline, the economic loss caused by the shutdown is very huge. If high-intelligence detection means can be applied, the robot can automatically and quickly recover to the state before the failure after the basic parameters of the shaft are lost or changed, which will bring huge production benefits to the automated production line.

5.5. Problems with the robotic electrical control system.

The three welding robots used by Changan Company have a very high mechanical reliability and manufacturing level of the body, and the probability of failure of the body (referring to mechanical failure) is extremely small. However, in contrast, the failure rate of the electrical control system is very high, the most prone part is the circuit and components of the drive part, and the fault frequency of the connector is also quite high.

The degree of integration of robot control circuits in the world today has become higher and higher, and the continuous advancement of control technology has greatly reduced the failure rate of the control part. However, for welding operations in automobile manufacturing, such as harsh environments, high operating intensity, and large voltage fluctuations, if the specific conditions of automobile production can be made, the degree of system integration can be further improved, and the system can further enhance the anti-interference ability. The ideal of Changan's application of a large number of robots to realize a completely unmanned production line in the future will become a reality.

5.6. Collision between robots and other equipment or obstacles on the workstation.

In Changan's two welding lines, there have been many accidents in which robots collide with robots and robots collide with other equipment or obstacles due to mistakes in signal exchange. After the post-analysis of the robot working program, it is found that the current robot control system uses external I/O signals to exchange the working states of each other when processing the signal exchange. The signal detection is only measured in a "point" manner, that is, in a certain motion. In the program line, confirm whether a certain exchange signal exists to determine whether the robot continues the following work, instead of continuously detecting other obstacles or robot states in a moving area, so that once the detection process ends, the movement track of the robot is wrong or When the handshake is not normal, a collision occurs.

Nowadays, the application scale of robots is getting bigger and bigger, and more and more robots work together in a narrow space. The exchange of signals between them has become very common. If it can be used in the robot control system, it is similar to Microsoft WINDOWS. The background processing of the operating system to monitor the working status of other obstacles or robots in real time to determine whether the robot should continue to work in areas where interference is possible. The collision problem should be effectively controlled or even completely solved.

In summary, the welding robot provides a favorable guarantee for the mass production, high efficiency and high quality of the automobile manufacturing industry. At the same time, the problems exposed by the welding robot in practical applications also prompt us to continuously study advanced technology. Constantly seeking more effective means to make welding robots make greater contributions to China's automobile manufacturing industry.

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