The rapid development of science and technology has greatly improved production efficiency, which is reflected in the continuous improvement of equipment automation in the stamping production line, which promotes stamping production with high production efficiency to a new level, and can improve product quality and reduce single-piece production cost under the condition of mass production.
At present, most stamping shops in automobile factories use high-speed automatic stamping lines.
There are big differences in the degree of automation of these production lines, so the pace is different and there is still a lot of room for improvement.
The maximum production beat of the stamping line using direct servo drive technology officially adopted by a high-end German automobile manufacturer reached 23 times/min.
Equipment overview
The stamping production line can carry out the stamping production of automobile panels and other large-sized formed parts.
As shown in Figure 1, the stamping line of the entire vehicle factory is composed of line head system (A), large press (B), handling equipment (C) and line tail system (D).
Compared with the traditional manual production line with very low efficiency, the application of automatic equipment can reduce the cost and increase efficiency.
line head system
The front loading unit unpacks and transports the plate to the gripper position of the first handling equipment, which is entirely composed of:
2 metal plate loading carriages (with adjustable magnetic separator), material height detector (which can be placed on the plate carriage or on the beam of the unstacking hand), end material detector, unstacking hand (manipulator or robot) , servo feeding device (generally magnetic conveyor belt), dual material detection device, scanner, plate washer, plate lubricator, centering table and its servo control system.
Now we will discuss the scanner and its related technologies.
The stamping production line can operate normally and quickly to produce high-quality parts. Quick and accurate sheet metal alignment is essential.
The use of scanner and image digitization technology on the optical centering platform can improve the gripping accuracy of the equipment and reduce the failure rate.
When using different handling equipment, the application of the scanner is different.
Figure 2 shows an arrangement mode, in which A is the scanner and B is the centering platform.
In the stamping line where the mechanical arm is used to grasp the parts, as the stamped parts are always in the fixed height plane of the upper surface of the conveyor belt, the application of this technology is actually a quantitative analysis of the position of the part displaced in a two-dimensional plane.
By installing the scanner vertically in the beam, the image passing through the sheet can be recorded, and then the image can be transmitted to the scanner controller.
Through comparison between the standard position and the actual position, the corresponding signal can be output to the center console driving device, which controls the servo motor to perform the corresponding action to ensure the accuracy of the sheet position captured by the handling device subsequent.
If the process requires cleaning the surface of the sheet metal, it can also directly assess whether there are excessive oil stains by analyzing the image of the sheet metal.
When the crossbar robot is used as moving equipment between presses, the six axes provided by the robot itself, supplemented by the longitudinal feed axis of the beam and the conveyor shaft of the final collector, can make the moving equipment have a very high degree of freedom, so that its gripping attitude can be adjusted according to the displacement of the plate.
The deviation vector between the teaching position of the board and the actual position calculated by the scanner controller is transmitted to the robot control system through fieldbus to realize accurate grasping of the robot.
Press
In the stamping production line, the press is the equipment that has the greatest impact on the quality of formed parts.
By setting reasonable parameters for each part, various automotive panels that meet design requirements can be stamped.
The press can be divided into mechanical press and hydraulic press according to the working principle. The hydraulic press is a machine that uses the Pascal principle and liquid pressure to transmit energy, while the mechanical press converts the rotary movement of the motor into the vertical movement of the slider through the mechanical structure (such as the crank connecting rod).
H hydraulic press
Compared with the mechanical press, the hydraulic press has the advantages of large working pressure, large adjustable range of working stroke, maximum pressure output at any stroke position, stepless speed adjustment and so on, but it has major shortcomings in work frequency.
In the stamping production line produced by the vehicle factory, the hydraulic press is not applicable due to the demands of the production rate.
Servo Press
Mechanical press can be subdivided into servo press (also known as CNC press) and general mechanical press.
Traditional mechanical press controls the speed of AC motor through frequency converter, uses flywheel to store energy and clutch to control energy transmission.
Its pressure curve is generally sinusoidal, that is, the nominal tonnage is always reached before bottom dead center and the stroke is fixed and adjustable.
The servo press uses servo technology and traditional mechanical technology to control the movement of the slider through a complex electrical control system.
The servo press can arbitrarily program the speed and pressure of a certain position in the slider stroke, and can also reach the rated ton of the press at low speed.
Some printer manufacturers at home and abroad have made achievements in this field and launched commercialized products, which are called “third generation press”.
The servo press is undoubtedly an important direction in the development of forming equipment. Its advantages are shown in Table 1.
Table 1 advantages of the servo press
| High precision | The position of the slider is controllable (servo control and position feedback device control), and the overall position accuracy can reach 0.01mm. |
| Flexibility and intelligence | By using servo motor instead of ordinary induction motor, arbitrary characteristics of the slider can be obtained and the corresponding process curve can be optimized. |
| Streaming optimization | Fax reception does not use intermediate transmission devices such as clutch and flywheel, which reduces vibration, noise (about 159% can be reduced by 250) and energy loss, and is easy to maintain. |
| Improve equipment life and work efficiency | The structure is simple, the service life of the die can be increased by up to three times, and the service life of the equipment can also be improved: the adjustable stroke feature greatly improves its working efficiency. |
Hot stamping technology
The light weight of the automobile is one of the development directions of the automobile.
The light weight of the automobile aims to reduce the weight of the vehicle, reduce fuel consumption, reduce pollution emissions and improve the power of the automobile, but ensure that the strength and safety performance of the automobile are not reduced.
In stamping forming, the selection of ultra-high-strength steel is an important way to make the automobile light.
At room temperature, ultra-high-strength steel has low plasticity and is difficult to form.
Due to the limitations of cold stamping, it is difficult to solve problems such as stamping cracks, geometric accuracy, wrinkling and springback.
The cold stamping production process is difficult to meet the requirements of forming accuracy.
Therefore, hot stamping technology emerged.
This technology consists of heating the sheet above the austenitizing temperature, then pressing and forming, at the same time, quenching in the press at a cooling rate exceeding 27℃/s to obtain martensite, so that the stamped parts can meet the requirements in mechanical properties and dimensional accuracy.
The advantages and disadvantages of different heating methods are as follows:
(1) Radiant heating has the advantages of low heat utilization rate, large land cover and high cost.
(2) Conduction heating (resistance effect), low heating uniformity and high requirements for metal sheets.
(3) Induction heating (electromagnetic induction), high heat utilization, fast speed and small space.
For technical reasons, at present, the heating equipment of the stamping production line basically adopts radiation heating furnace.
Nearly 100 domestic companies have hot stamping production lines, which can produce TS1500 automotive panels.
In the context of the broader application prospect of ultra-high-strength steel, hot stamping equipment and technology is also an important development direction.
Handling equipment
Generally, handling equipment has at least four moving axes.
By pre-teaching the position of the sheet metal and using the special final pickup for each part, sheet metal handling is carried out in the stamping production line, which is mainly divided into manipulator and robot.
M manipulator
Fig. 3 shows a four-axis press handling manipulator.
The automatic control software identifies the position of the upper press slider and confirms that there is no interference with the manipulator's material grasp in this position.
Then, the output signal controls the manipulator to move to the part grip teaching position.
The vacuum generator in the final pickup grips and lowers the sheet through air suction and blowing action, in order to automatically handle the parts between the presses.
Manipulator production line can also be divided into single-arm line and double-arm line.
Compared with the single-arm line, the double-arm line has higher efficiency and fewer errors.
At present, many main engine factories have been put into use and are expected to be more widely used in the future.
Robot
When the robot is used as equipment for moving stamped parts, compared to the manipulator, the robot has more degrees of freedom, a more complex structure and a large difference in cost.
The crossbar robot is a typical product. The robot combines crossbar technology and robot technology to achieve 8 moving axes and higher production efficiency.
In some special occasions, such as in manual production transforming line or limited by other problems on site, the layout robot has its unique advantages.
The cutting press of an automobile factory production line uses the FANUC robot as loading and unloading handling equipment.
Tail system
The line tail system (also known as line tail stacking system) transports the sheet metal transported by the last manipulator to the specified position, and then carries out framing and storage.
The traditional tail system mainly uses a conveyor belt to transport parts (similar to the main conveyor belt) and then structure manually, and then the material structure is stored by a forklift.
Because the beat of the automatic stamping line can basically reach 10 pieces/min, and a single stacking station generally does not meet the requirements, most production lines will divert the finished products and then load the sheet into the material frame after checking the part quality manually or by equipment.
At present, the rear station is one of the main human stations in the stamping production line, and the labor intensity is high, which is not conducive to ergonomics, and the frequent transfer of material structure by forklift also presents a certain risk of collision .
This post introduces mature automatic traction equipment – AGV cart, which has a high degree of automation, small volume and easy control.
The cart is equipped with electromagnetic or optical automatic guidance devices, which can travel along the specified guidance path, and the travel path can be controlled by the computer or electromagnetic track.
The reasonable arrangement of the AGV cart in the line tail system can improve the automation rate and reduce the risk of man-machine interference.
Conclusion
The automation of the stamping production line has been greatly improved, but with the improvement of market demand and the continuous application of new technologies, stamping equipment is constantly updated.
Understanding various stamping automation equipment on the market and their working principle can effectively improve the technical ability of equipment engineers and continuously optimize the performance of stamping equipment in terms of quality improvement, capacity improvement, safety, energy saving and cost reduction.
