The development of modern manufacturing technology requires presses to not only operate at high speed, high precision and large loads, but also to have greater flexibility. They must be able to design the movement curve of the slider according to different materials and process requirements.
Based on the abandonment of energy-consuming components such as flywheel and clutch in traditional mechanical presses, servo presses adopt AC servo motor as the power source of the press. The rotary motion of the motor is converted to the linear motion of the slider by means of an actuator such as a screw, crank, or connecting rod. This allows the servo press to achieve controllable movement of the slider, meeting the needs of flexible and intelligent stamping processing.
The servo press can improve the technical level and manufacturing capacity of complex-shaped stamping parts, high-strength plates and aluminum alloy plates. This fully reflects the future development trend of forging press machine tools.
Traditional press production status
The mechanical press is the most widely used stamping equipment in the metal and plastic processing industry. It is powered by a DC motor, AC motor or a variable frequency speed regulating motor, while the actuator is composed of a crank and a multiple connecting rod. The press operates by rotating the flywheel at high speed without load and releasing energy during the loading stage to complete the stamping process.
Disadvantages of the traditional mechanical press
Traditional mechanical presses have the following disadvantages.
Low production efficiency and large potential safety risks
Figure 1 shows the common production mode of the assembly line.
Traditional mechanical press assembly line operation
The operator is responsible for loading and unloading materials.
During operation, personnel face high work intensity, which can cause fatigue and potential safety risks. In addition, manual operation in the production process may cause deformation during transportation and production, which can greatly impact the compliance rate and assembly performance of parts.
Furthermore, assembly line operation means that if there is a problem in one process, the entire line can be brought to a halt, which can negatively affect production efficiency.
High energy consumption
The conventional crank operates by continuously turning the engine, which in turn turns the flywheel. The movement of the slider is controlled through the clutch, which uses the inertia of the flywheel.
However, this process results in a low energy utilization rate of only 65% for the high power motor. A significant amount of energy is wasted during the movement process, which increases production costs.
Large noise, large vibration and reduced die life
There are several types of noise generated by crank connecting rod machine tools:
Firstly, the noise generated by the mechanical press during sheet metal processing and forming can exceed 90dB, reaching 93dB.
Secondly, there is noise caused by engine idling.
Thirdly, noise is generated due to the change in impact motion when the press clutch and brake work.
Therefore, it is essential for operators to wear anti-noise earplugs to prevent hearing loss.
Simultaneously, the movement of the sliding block produces significant vibrations, which can adversely affect the functional parts of the die.
If the array operates in an environment with frequent vibration for an extended period of time, this may significantly impact its service life.
Product quality and performance cannot be guaranteed
The cold stamping process carried out at room temperature can result in various quality defects, such as cracks, wrinkles, bottlenecks and slip lines.
Various factors can influence process quality, including the forming process, sheet properties, die parameters, process parameters, equipment accuracy and working conditions.
When subjected to the same conditions as the forming process, the adequacy of the drawing speed is also a critical factor that cannot be neglected.
Traditional printers may not be able to control drafting speed effectively, leading to unstable production and inconsistent quality issues.
Advantages of servo press in stamping production
Improve production efficiency
The servo press maintains the advantages of the hand crank press, mainly in terms of production efficiency, which is much higher than that of a hydraulic press. This reflects the combination of the processing quality of the hydraulic press and the production efficiency of the mechanical press.
Furthermore, a servo motor-driven hand crank press can adjust the slider stroke according to different workpieces. During one cycle, it does not need to complete a full 360° rotation, but only swings at a certain angle to complete stamping production. This further reduces cycle time, minimizes invalid stroke and significantly improves production efficiency.
Thanks to the high precision and stability of the servo press, the quality of the parts is greatly guaranteed and the time required for die maintenance is reduced. Furthermore, the emergence of the servo press also reduces operational risk for personnel.
Energy saving and environmental protection
The conventional crank uses a motor to turn the flywheel, which in turn controls the movement of the slider via the clutch, depending on the inertia of the flywheel.
In contrast, the press in Fig. 2 is driven by a servo motor, which provides the necessary torque to operate. Using mechanisms such as threaded rods and multiple connecting rods, the small engine can generate a large force without the need for a clutch. The motor drive unit also controls the starting and stopping of the engine.
Fig. 2 Servo press
The motor in a crank press rotates only during stamping since the flywheel is not present, resulting in savings in idling power consumption of both the engine and the flywheel.
Furthermore, the absence of a clutch reduces clutch-related energy consumption.
When compared with traditional presses of the same tonnage and servo presses, the servo press can save more than 35% energy.
Low noise and long die life
Using imported servo motor and CNC control system, a unique working characteristic curve can be created to regulate the punch speed during cutting. This helps reduce vibration and noise produced during cutting and also improves die life.
According to research carried out by the Komatsu company in Japan, the suppression noise generated by the servo motor-driven NC press is more than 20 dB lower compared to that of the conventional crank press.
Furthermore, as there is no idling of the engine and flywheel, no noise is produced during the blanking process.
Production and application of servo press
Relationship between press and blank
The working speed of the press is determined by both the sheet metal drawing speed on a macro level and the sheet metal deformation rate on a micro level.
Based on plastic formation theory, an increase in strain rate results in hardening of the material. However, when the deformation rate increases further, the heat generated in the plastic deformation process reduces the hardening effect (see Fig. 3).
Fig. 3 Relationship between sheet plasticity and strain rate
Based on the general trend of changes in sheet plasticity with strain rate, it can be seen that when the strain rate is relatively low (section ab), the increase in strain rate leads to a greater decrease in plasticity than the increase in temperature. In other words, the plasticity of the sheet decreases with increasing strain rate.
However, when the strain rate is high (section cd), the temperature effect becomes significant, causing an increase in plasticity equivalent to the decrease caused by the strain rate. As a result, the decrease in leaf plasticity is not significant.
When the strain rate reaches a certain limit (section), the plasticity of the sheet drastically reduces, causing the sheet to approach the edge of the crack.
From the above analysis, it can be concluded that increasing the working speed of the press leads to a decrease in plasticity due to an increase in deformation and tensile strength in the deformation area of the sheet. This, in turn, increases the stress in the force transfer area of the drawing part, increasing the risk of cracking.
Therefore, it is essential to check the press speed during the drawing process to ensure that it is within the maximum allowable sheet drawing speed, given the maximum allowable drawing speed of different sheets.
Practical application of servo press
Many companies are intrigued by how to ensure the formability and stability of parts while maintaining high production efficiency.
The automobile B-pillar reinforcement plate is a crucial load-bearing structural component of a vehicle body.
The B-pillar parts have several structural characteristics, including large forming depth, complex section changes, use of raw materials with high yield strength and significant differences in height between the parts.
However, during mold manufacturing and production, these parts are subject to problems such as cracking, wrinkling, and eccentric loading. Unfortunately, these problems cannot be completely avoided during the mold process and design.
As a result, requirements for press use increased significantly after production began.
The reinforcement plate of the automobile B pillar goes through five processing procedures, from the raw part to the finished product (see Fig. 4).
Fig. 4 Production sequence of automobile B pillar reinforcement plate using servo press
The emergence of servo press has solved the problem of producing B pillar reinforcement plates with high efficiency, precision, stability and quality. Furthermore, the servo press's intelligent monitoring system can collect real-time voltage changes during the production process.
If unqualified products or abnormal mold failures occur, the monitoring system will issue an alarm (Fig. 5), allowing on-site personnel to solve the problem promptly and avoid batch production of defective products or safety accidents.
Fig. 5 Intelligent monitoring of servo press tension change during B-pillar reinforcement plate production
Conclusion
An AC servo motor driven press can significantly increase the flexibility and intelligence of equipment while improving the monopolistic characteristics of a servo press. This makes it the direction for the development of new generation training equipment.
Considering its vast potential for diverse applications, manufacturing companies specializing in pressing equipment must accelerate research into this new technology and develop large servo presses with completely independent intellectual property rights.
