The realization of robot production automation in the metal stamping industry

The automobile body sheet metal stamping line is an important equipment in the automobile production process, and its production quality and efficiency directly affect the quality and production efficiency of the automobile. Stamping production automation is an effective measure and main method to increase labor productivity and improve working conditions. With the continuous improvement of the quality of my country's automobile and electrical products and the continuous expansion of production scale, it is imperative for my country's metal stamping industry to realize production automation.

The production methods in the stamping process include traditional manual production methods (as shown in Figure 1) and automated production methods (as shown in Figures 2 and 3). From the aspects of product quality stability, labor intensity, safe production, and production efficiency, automated production methods have greater advantages and are also the development trend of stamping production methods. The stamping automation production line is divided into manipulator automation production line, robot automation production line and multi-station press production line.

The difference between manipulator automated production line and robot automated production line is mainly manifested in the following aspects.

Installation method: The robot line is installed on the ground, and there is no mechanical connection with the press; the manipulator line is installed with steel beams between the press columns and attached to the press.

Use characteristics: The robot line is more flexible through the switching of the end picker and the adjustment of the robot's motion trajectory.

Production cycle: The production cycle of the robot line is 7 pieces/min～10 pieces/min, and the production cycle of the manipulator line is 8 pieces/min～12 pieces/min.

Investment cost: low investment in robot lines, high investment in manipulator lines. Because the production cycle is a comprehensive index, it not only depends on a certain equipment, but also depends on the coordination and matching relationship of automation equipment, presses, and Molds. If it reaches 10 pieces/min or more, the requirements for presses and molds are corresponding. Increase means increase in investment. Comprehensive consideration, the use of robot automation line is more economical and applicable.

The manipulator automation line is suitable for large-spacing press production lines, as well as for the automation transformation of existing production lines. By replacing the end picker, the robot automated production line can be suitable for the production of multiple models, with higher flexibility.

The operation cycle mode of the robot automatic stamping production line is: stacking and destacking (robot destacking)-sheet material transfer-sheet material oiling-sheet material centering-feeding robot feeding-(first press stamping)-unloading robot taking Material and feeding-(press stamping)-(cycle according to the number of processes)-unloading robot reclaiming and feeding-(end press stamping)-end-of-line robot reclaiming and discharging-belt conveyor conveying-manual palletizing. This article takes the robot stamping automation production line of Great Wall Motor as an example to design its overall layout and electrical control.

2.1 System composition

This system includes destacking system, oiling machine, centering station, press and loading and unloading system, and line end conveying system.

The destacking system adopts a cyclic double stacking table, the guide rail is arranged parallel to the press, and the stamping sheet is placed on the non-working stacking table with a crane or a forklift, and then a valid signal is used to confirm that the loading is completed, and the system will be removed in one After the stacking is completed, the stacking table is automatically changed to ensure continuous production; the stacking car is equipped with a magnetic splitter, and the stacks are automatically destacked into single sheets by magnetic force. There are dual-material detection and dual-material handling devices on the depalletizing robot to ensure that a single sheet is fed every time. The depalletizing robot places the sheets on the adjustable length magnetic conveyor belt, and the sheets are sent to the oiling machine. Whether the sheets are oiled and the oiling position can be set by programming. After the sheets are oiled, they are transferred to the centering station. The centering stage adopts a mechanical centering stage, which can be easily moved and fixed. At the same time, it uses a gravity centering or visual centering system to ensure that the repeated positioning of the sheet is fast, accurate and firm; the feeding robot is aligned according to each part Position, change the running trajectory, and accurately transport the sheet metal to the press; Carry out robot simulation teaching and offline programming for different stamping parts to adapt to the co-line production of multiple parts; The end of the line conveyor adopts a belt conveyor , Place a belt conveyor at the end of the production line to ensure that the robot of the last press directly places the parts on the belt conveyor to achieve the effect of output. The software enables the robot to track the movement of the press, and realizes the synchronization function of the press and the robot, which can maximize the overlap between the loading and unloading and the press movement, and achieve the purpose of smoothly switching its speed to shorten the production cycle and reduce the mechanical load. By adding an external axis as the seventh axis of the robot for servo control, the spacing between the presses is arranged more freely; at the same time, the robot's transmission range and handling speed are improved, and the production cycle is faster.

2. 2 Control system

2. 2. 1 Overall control plan

This system includes destacker, oiling machine, centering station, loading and unloading system, and end-of-line conveying system. The electrical control between each sub-system is based on the principle of centralized monitoring and decentralized control. In the control system of each control part, the typical control mode of the equipment layer and the control layer is adopted, and different network structures and software and hardware configurations are used in each layer to realize different functions.

2. 2. 2 Control layer

Each part of the control system adopts the PLC control mode with the form of fieldbus, which has the functions of independent control and connected automatic control. In order to ensure the stable and reliable operation of the system, Siemens S7-416-2DP PLC can be used, and the field bus adopts Siemens Profibus and industrial Ethernet control system. The data exchange between the PLCs of each control part and between each PLC and the upper computer adopts the industrial Ethernet method for the monitoring system to be used for networking. The control system of the press needs to be equipped with an Ethernet card to interface with the robot control system, and the control system and the robot system can realize information exchange and interlocking connection through Profibus-DP field bus.

2. 2. 3 Device layer

The equipment layer is at the bottom of the entire control system and is the key link of the entire control system. It mainly includes on-site operating stations, on-site equipment detection units (such as proximity switches, photoelectric switches), other on-site input devices, and on-site actuators (such as motors, Solenoid valve), etc., directly or through the field bus to connect with the PLC in the control layer, send the input signal to the PLC, and send the PLC output instructions to the field device. The junction boxes of various sensors and valves communicate with the corresponding control unit through the field bus (Profibus-DP).

2. 2. 4 Human Machine Interface HMI

The HMI of this system adopts SIEMENS touch screen, each control unit is equipped with a touch screen, and uses Profibus bus communication. The unit's touch screen has indicator lights and operation buttons (or knobs), which can display information such as error alarms and self-diagnosis. The relevant I/O signals of this unit are displayed on the HMI and are distinguished by different colors. Once there is a faulty node, the system will continue to alarm, and the HMI will display the fault point on the current screen for the staff to find.

2. 3 Security System

Safety is the biggest feature of the automated production line. This system adopts the SafetyBus protection system based on the German PILZ safety PLC, and is equipped with complete safety devices, real-time control and display of the safety zone status, timely sound and light alarm signals or shutdown, and communication with the main PLC system Adopt Profibus-DP bus. The acousto-optic alarm unit, as an auxiliary tool for the entire line of safety systems, can promptly notify the operator for handling when abnormal conditions such as equipment startup and shutdown, equipment failures, loading and unloading failures, and alarms at various safety monitoring points in the safety system occur. There is a lifting door in front of the destacking system, which is a rolling door. The opening and closing of the lifting door is interlocked with the conversion of the two stacking platforms. When one stacking platform is empty, before the other stacking platform enters, the lifting door opens, and the stacking platform opens; the current stacking platform opens out. After that, the lift door fell. The lift door is electric lift, and is controlled by the operator from the corresponding console. They detect 2 travel switches when they are closed, and use a sensor when they are open. In the case of ensuring the safety of the work unit, a light curtain unit (transmitter/receiver) allows the related stacking trolley to enter and exit, that is to say, the press line runs automatically. If the related stacking trolley is not in the transitional stage, but people or foreign objects block the light curtain, the disconnection of this light curtain unit will cause the power of the entire press line robot to be cut off (except for the robot in the programming mode), and the stacking unit will be disassembled The control circuit power supply is disconnected. All the emergency stop signals of the entire control system and the safety interlock signal between the press and the robot are connected to the safety PLC system, and the interlocking control is carried out through the PLC program.

2. 4 Simulation

Simulate the operation of the stamping line in the virtual environment to avoid errors such as interference and unreasonable tempo that are discovered at the production site; through offline programming of the robot, the robot's motion trajectory and route are simulated to shorten the on-site debugging cycle. The trajectory of the robot is shown in Figure 4.

The application of robotic stamping automation not only improves labor conditions, reduces labor intensity, but also ensures production safety, improves labor productivity and product quality, reduces energy and raw material consumption, saves auxiliary processing time, and reduces product costs. With the gradual shortening of the production and debugging cycle of production lines, robotic automated production lines have become more and more accepted by automobile OEMs and have become the mainstream of stamping automated production lines.