The stamping industry has seen the emergence of a new generation of presses that address the limitations of traditional mechanical presses.
The solution is to use servo motors as direct power sources for presses, resulting in a highly precise and easily controlled sliding movement.
The servo press offers several advantages, such as controlled slider speed, versatility, energy efficiency and environmental friendliness. It is considered the third generation punch and the current trend in the development of the stamping industry.
The servo motor's programmable control capabilities allow for advanced precision control, including control of the press slider position.
Servo punches are used in production lines such as drawing, stamping, bending, cold forging, stamping and die testing.
AC servo motor drive technology is a focus of research in advanced forging equipment and a new development direction for international printers.
AC servo press offers multiple benefits, including high productivity, flexibility, precision, energy efficiency and environmental sustainability, reflecting the future development trend of forging machine tools.
As industries such as iron and steel, non-ferrous metallurgy, aerospace, high-speed rail, shipping, nuclear power, wind power and military demand higher performance parts, the need for advanced stamping equipment grows.
Mechanical presses have limitations such as fixed stroke, difficulty in controlling pressure and poor adaptability to processes due to the fixed movement characteristics of the slider.
The servo press addresses these challenges by providing a flexible press that meets the demanding requirements of modern industries.
What is a servo press ?
Servo refers to a feedback control system for mechanical displacement and acceleration, whose main function is to accurately track the input displacement or angular displacement with the output mechanical displacement. Servo stamping technology refers to a feedback control system/tracking system used to accurately follow the stamping process.
A servo press is a type of press powered and controlled by a servo motor. The servo motor drives the eccentric gear, allowing the slider to move.
With the use of advanced electrification control, the servo press can be programmed to control slider stroke, speed and pressure precisely. This allows the nominal tonnage of the press to be achieved at low speeds.
AC servo press structure
The structure of an AC servo press consists of a main drive system, an actuator and an auxiliary mechanism. The main drive system transfers power from the servo motor to the actuator and can be achieved through various transmission modes such as gear transmission, belt transmission, screw transmission or hydraulic transmission.
The actuator drives the reciprocating movement of the slider to complete the forging process and may take the form of a crank slider mechanism or a crank wedge mechanism.
The auxiliary mechanism increases the reliability of the AC servo press and expands its process applications, with common components including balance cylinders, brakes, lifting devices and position sensing devices.
The main drive system of the servo press can be divided into two types based on the servo motor drive mode: direct drive and reducer drive. Direct drive uses a low-speed, high-torque servo motor directly connected to the actuator, resulting in a simple structure, high transmission efficiency and low noise.
However, its limited torque restricts its use to small tonnage servo presses.
The main drive system widely used in commercial servo presses employs a deceleration mechanism and a force-increasing mechanism, which can assume three different transmission structures: engine deceleration crank connecting rod, engine deceleration crank connecting rod, and engine deceleration crank connecting rod. engine deceleration screw.
This approach allows a high-speed, low-torque servo motor to drive large-tonnage presses, making it the current trend in servo press development.
Table 1 Comparison of project parameters
| Project | Automatic Robot Line | Automatic Single Arm Manipulator Line | Crossbar Double Arm Transmission High Speed Line | Single Slider Multi Station Production Line | |
|---|---|---|---|---|---|
| Single Line Automation Cost | About 12 million yuan | About 20 million yuan | About 30 million yuan | About 15 million yuan | |
| Line Speed / SPM | 5~10 | 6~12 | 10~15 | 12~25 | |
| Production applicability | Multi variety and small batch | Multi variety, medium batch | Multiple varieties and large quantities | Variety, mass | |
| Production flexibility | high | commonly | commonly | low | |
| Production stability | low | commonly | high | ||
| Mold change time/min | 15 | 15 | 5 | ５ | |
| Press requirements | Operation mode | Once | Once | Single, continuous | continuity |
| Press spacing / M | 6.5~8 | 6~9 | 4.5~7 | ／ | |
| Sliding stroke | Small | more | big | big | |
| Mold height | Small | more | big | big | |
Advantages of the servo press
Beat improvement
As shown in Table 1, the stroke of the crossbar double arm transmission high-speed line is between 10 to 15 strokes per minute (SPM). Using a servo press, the high speed line beat can be increased to a maximum of 18 SPM.
Configurable curve
As illustrated in Figure 1, the servo press has the ability to set different curves depending on the specific situation.
Fig. 1 Servo press can set different curves
Energy conservation
Figure 2 shows the power flow during the acceleration and deceleration phases.
Fig. 2 Servo motor current flow direction during operation
Reduce drawing speed
As illustrated in Figure 3, low drawing speed reduces the impact on the die, leading to an improvement in die life and a reduction in die cost.
Fig.3 Schematic diagram of drawing speed
Reduced footprint
Downsizing equipment can reduce investment in facilities, infrastructure and other facilities. As shown in Figure 4, using the four-string press as an example, a traditional mechanical press production line consists of a multi-link press and three eccentric presses, requiring a foundation length of approximately 25 meters. In comparison, a production line consisting of four servo presses would only require a foundation length of approximately 16 meters.
Fig. 4 Comparison between traditional mechanical press and servo press
Improve production efficiency
The stroke length can be set to the minimum required for production and the forming speed appropriate for the processing content can be maintained.
1) Full stroke mode → bottom dead center accuracy can reach ±0.02mm.
2) Half stroke mode (pendulum mode) → Bottom dead center accuracy can reach ±0.02mm, improving SPM.
3) Reverse mode → lower dead center accuracy by up to ± 001 mm.
Product quality is high
Closed-loop feedback control ensures bottom dead center accuracy, reducing burr formation on the product and preventing the generation of defective products.
Unique automatic die height correction servo function:
The change in position of the slider can be measured and corrected to ±0.01 mm from the preset value through the use of a linear grid scale on each stroke, ensuring a high degree of accuracy at bottom dead center.
Linear grid ruler position ↓
The bottom dead center of the servo has an automatic correction function that guarantees the accuracy of the bottom dead center within ±0.01 mm even after prolonged production, thus ensuring a high yield of products.
Low noise and long service life
Low noise mode, which reduces the contact speed between the slider and the sheet metal, significantly reduces noise compared to a traditional mechanical press.
Additionally, the die experiences minimal vibration, leading to extended service life.
Controllability of slider movement
Users can use this feature to create a customized sliding motion mode that suits their processing technology, thereby improving the accuracy and stability of products.
This leads to increased die life and productivity, as well as quiet cutting and the ability to process a wide range of materials, including magnesium alloys.
The servo press can be used for processes such as cutting, stretching, stamping and bending, and can provide performance curves for different materials. The ability to pause the slider while maintaining pressure improves the quality of the formed part.
Energy saving and environmental protection
The energy-consuming components of the traditional mechanical press, such as the flywheel and clutch, have been eliminated, resulting in fewer drive parts and a simplified mechanical transmission structure.
The need for lubricating oil is reduced and the stroke is controllable. Reduced engine consumption leads to a significant decrease in operating costs.
Practical application
The servo punch is mainly used in production processes such as drawing, stamping, bending, cold forging, stamping and die testing.
Thanks to the use of PLC control, digital technology and feedback control methods, the servo punch offers advanced precision control. This includes the ability to control the position of the pressure slider.
The monitoring system and compensation control allow the slider position to be controlled with an accuracy of ±0.01 mm. The movement mode can be programmed, allowing control of the speed and trajectory of the slider.
This reduces stamping speed, noise and vibration, improving the stamping working environment and extending die life.
Furthermore, the output force of the slider can be controlled with an accuracy of ±1.6% of the maximum output force. This allows the formation of large panels using high-strength steel plates and aluminum alloys in the automobile industry.
Difficult to mold materials such as magnesium alloy, aluminum alloy and titanium alloy can be facilitated through the combination of die design and peripheral system control.
Switch type servo structure
Crankshaft direct drive servo structure
Figure 5 shows the Schuler multistation press with dual servo and bottom drive.
Fig. 5 Schuler double servo bottom drive press
The dual servo bottom drive press is powered by two separate groups of servo motors, one on the left and one on the right. These motors drive the four guide columns on each side, allowing the sliding block to move.
Independent transmission mechanisms on the left and right sides allow the table to have large dimensions on both sides, making it suitable for large tables and high tonnage presses, as shown in Figure 6.
Fig. 6 Double servo multistation press
The double servo bottom drive press uses the precise control of two groups of servo motors to achieve synchronous movement of the slider on the left and right sides.
In case of eccentric load on the slider, the parallelism of the slider can be adjusted through electrical control, making it more flexible and adaptable to meet user needs.
Compared with common presses, the bottom drive press has better eccentric load resistance and precision curves. While still meeting accuracy requirements, it offers greater resistance to eccentric loads and a larger area for eccentric load application.
Development trend
As competition in the manufacturing industry becomes increasingly intense, there is a growing demand for servo presses to efficiently produce high-precision, high-quality products.
The servo press offers multiple benefits, including composition, high efficiency, precision, flexibility, low noise, energy efficiency and environmental sustainability, which aligns with the future development trend of forging machines.
The servo press has the ability to adjust the forming stroke and speed to meet different production requirements, ensuring bottom dead center accuracy and reducing the occurrence of burrs on the product. Furthermore, the small die vibration improves the die life.
The servo press design represents a departure from traditional mechanical presses as it eliminates the flywheel, clutch and brake, reducing the machine's operating costs.
Servo presses will play an increasingly important role in major manufacturing industries such as electronics and automotive, as well as other precision manufacturing fields.
How to choose a servo press
First, it depends on the required precision of the servo press.
Accuracy refers to the degree to which pressure and position reach the specified stopping point. It is related to the driver resolution, the pressure transmitter resolution, the precision of the servo motor and the response speed of the equipment.
With the mature and integrated control of servo motor and driver, the repetition accuracy of servo press is getting higher and higher and its application field is getting wider and wider.
If high precision is required for the servo press, the focus should be on the configuration when choosing.
Secondly, it depends on the structure of the servo press.
Generally, the structure of the servo press produced by manufacturers is not unique. The most common structures are four-column, single-column, arch-type, horizontal, and portico structures.
The four-column structure is economical and practical, while the single-column and arch structures are mainly designed for easy operation.
The horizontal structure is commonly used for longer products, and the gantry structure has the advantage of occupying a larger tonnage.
Therefore, structure selection should be based on the size and structure of the product.
Servo press functions include forging, stamping, assembly, assembly, pressing, forming, flanging and surface pulling.
Different functions have different structural differences, so it is necessary to choose the appropriate servo press according to the needs of the product process.
Conclusion
The stamping industry will undergo significant changes with the emergence of the servo punch, a product that promises to greatly increase the competitiveness of stamping companies and positively impact the development of several stamping industries.
However, despite its potential benefits, the technology remains expensive and unstable due to most manufacturers not having fully mastered the core servo punch technology.
As a result, it is difficult for low-value stamping companies to invest in expensive servo presses, especially during the current economic slowdown and reduced benefits from the automotive industry.
However, with the expected improvement of the economy in the future, the market demand for servo presses is predicted to be huge, and major manufacturers are expected to develop stable and cost-effective servo presses in the next 5 to 10 years to boost production. global. competitiveness of printing companies.
Using an AC servo motor to drive a press can significantly increase the flexibility, intelligence and operating characteristics of the equipment, which is the development direction of the next generation of forming equipment.
As related technologies advance and competition with imported products intensifies, the market price of servo technology is expected to decrease rapidly, leading to wider adoption in the field of forming equipment.
