Vibration caused by the movement mechanism of forging machines
The forging machine has an unbalanced structure, which results in vibrations during operation.
(1) The components of the unbalanced structure in forging machines (Figure 1) include the sliding block, connecting rod, crankshaft, gear, etc.
Fig. 1 Unbalanced structure of forging equipment
The slider moves up and down while the crankshaft, gear, and connecting rod head rotate. These non-uniform moving parts generate a vibrational force, causing the forging machine to vibrate.
(2) Initial strength of unbalanced components:
Due to the quality factors of the moving parts and the high speed of movement, particularly the fast rotational speed of the sliding components, the end points of the unbalanced rotating components and reciprocating moving parts generate a significant initial force, leading to an increase in the vibrations of the moving parts. forging machines.
(3) To reduce operating vibrations and increase the accuracy and stability of forging machines during high-speed forging production, an alternative dynamic balancing device (Figure 2) can be added or a rotary balancing device can be designed to reduce operational vibrations of the forging machine itself.
Fig. 2 Dynamic balancing device
However, these balancing devices often consume energy, which conflicts with the economic and energy-saving principles of forging machines.
Implementation of these operational balancing devices requires comprehensive consideration of their need, manufacturing cost, power consumption, operating environment, and other relevant factors.
(4) Compared with general industrial machines, forging machines require high-power instantaneous start and stop operations during starting and stopping.
As a result, it is essential to select and match the clutch and brake with a large capacity to allow moving parts to start and stop instantly, but this can also result in vibrations.
Hot forging and stamping machines have high capacities and generate significant vibrations during instantaneous starts and stops.
To balance starting and stopping performance and vibrations, it is necessary to adjust the speed of clutch and brake action within a range that does not affect the operation of the machinery. This is commonly referred to as “soft clutch” and “soft braking”.
Vibration produced by forging machines during operation
The vibrations produced by forging machines can vary significantly depending on the type of processing, application capacity, forging materials, production speed and mechanical design.
Vibration period in the forging process
(1) Vibration at the beginning of processing:
The forging machine's sliding block starts moving downward from top dead center and causes the die to impact the workpiece at a fixed speed. This impact results in vibration.
(2) Vibration Near the End of Processing:
When the sliding block of the forging machine is close to bottom dead center, the upper and lower dies experience significant pressure. At this point, the stressed parts of each component will deform and vibrate under the impact of this load.
(3) Vibration after processing:
Once processing is complete and the pressurized load is removed, the stressed parts will also vibrate due to deformation recovery. This type of vibration varies depending on the type of processing, with cutting processing accounting for most of the overall vibration.
Influence of processing technology on vibration level
Mechanical forging processing can be broadly categorized into cutting processing, bending processing, drawing processing and forging processing.
For forging machines, the above processing methods and combinations of these methods result in different vibrations due to different processing methods.
(1) Suppression processing:
As soon as the upper die comes into contact with the part, the maximum load is generated and the part breaks, releasing the load. The deformation (bending) of pressed components such as table body, sliding block, connecting rod, crankshaft and drive gear is instantly relieved with the processing load. At this time, strong vibrations will occur in the opposite direction of the load. This phenomenon is commonly referred to as “overshoot” (Figure 3).
Fig.3 Schematic diagram of overtaking
(2) Bending processing:
The vibration produced during bending processing will vary depending on the processing method, such as the shape of the bend. Typically, processing starts with a small load at the initial stage.
In the final stage of processing, embossing can be used to achieve precise folding of the product and to produce a visually pleasing fold. Embossing requires significant pressure, which can result in vibrations in forging machines.
(3) Drawing processing:
The forming load in the drawing process gradually increases. During deep drawing, the maximum load is normally generated at around 40% to 70% of the drawing height. As the process approaches bottom dead center, the load decreases, resulting in relatively low forming vibrations.
To prevent indentations in materials or products during deep drawing, a device called a die is commonly used to prevent wrinkling. The contact position between the die base and the die is where the slider is closest to bottom dead center. When the workpiece impacts the upper die, a loud noise and significant vibration are generated.
(4) Forging processing includes the following methods:
Hot forging, cold forging, extrusion processing, embossing, compound processing, etc.
- Hot forging:
Due to the high temperature of the material, the contact time between the die and the part must be minimized. The speed of the sliding block must be fast, and the contact time between the high-temperature material, the product and the die must also be reduced. As a result, when large components such as crankshaft, gear and sliding block are started and stopped quickly, the starting and stopping vibrations of the forging machine will increase. At the same time, as the product forming time is short and the processing impact is high, significant vibrations are produced.
- Cold forging:
Due to the slow deformation speed of the metal structure of the processed material, it is not possible to form at a fast processing speed. As a result, forging machines typically employ a low-speed drive mechanism (elbow joint and connecting rod) in the stamping area. The impact speed between the workpiece and the upper die is slow and the forming time is long, so the load change speed of the forging machine is slow, resulting in relatively low load vibrations.
- Forging Processing:
Regardless of whether it is hot or cold forging, a strong load is normally generated at the end of the process, leading to vibrations caused by the recovery of the stressed parts after processing.
- Composite Processing:
Composite processing typically involves a combination of lower pressure processing such as cutting (blanking), bending and stretching. In this case, the load generated by cutting processing at bottom dead center completes the cut before bottom dead center, causing instantaneous overshoot.
In the case of residual vibrations caused by overshoot, the bottom pressing process starts at bottom dead center, causing a significant increase in impact and more powerful vibrations.
Composite Vibration Analysis
During operation, the forging machine may produce operating vibration due to its own rigidity and operating conditions. Load vibration is produced by the type of processing and load, and deformation vibration is generated from the natural vibration of the workpiece, die and machine.
Vibration characteristics such as type, amount, cycle number and time may change slightly during the forging process, sometimes increasing and sometimes canceling each other out.
To improve product accuracy and increase die life, some customers require the rigidity of the table body to be 5 to 6 times that of typical forging machines, which also increases its relative capacity.
These machines are designed to not only provide high precision but also offer a low noise and low vibration working environment.
Vibration Propagation
(1) The vibration produced by forging machines is transmitted to the machine foundation and the surrounding area through the ground and foundation soil.
(2) For general vertical universal drawing forging machines, the vibration generated on the mounting surface is a significant factor. This initial vibration force is estimated at 10% to 40% of the weight of the machinery, which can cause vibration waves to spread throughout the foundation.
Vibration prevention measures in forging machines
(1) Mechanical Structure Prevention
In the design of forging machines, dynamic balancing devices are added to the structure to eliminate the unbalanced moment of inertia caused by asymmetrical parts such as crankshafts and connecting rods. Additionally, rotating parts with circumferential symmetry undergo dynamic balance testing to prevent vibrations resulting from unbalanced moments of inertia caused by manufacturing errors.
(2) Brake release setting prevention
Vibration can occur during starting and stopping of forging machines. By reducing the combined speed of the clutch and brake or selecting a soft clutch and brake without affecting the capacity of the press, mechanical vibration can be effectively reduced.
(3) Forging and die prevention machines
Vibration can be reduced through the stamping process and die structure design. These include reducing the demand for stamping pressure and avoiding excessive stamping load, selecting forging machines with reduced stamping speed near bottom dead center to avoid large impacts, and reducing the demand for stamping pressure through early heat treatment of the blank. stamping for hot forging stamping. to reduce impact and vibration.
(4) Prevention of vibration transmission of forging machines
Vibration can be reduced from being transmitted to the surrounding environment through the foundation by using a vibration isolator on the forging machine. In addition, a vibration isolation trench can be designed around the forging machine foundation to reduce vibration transmission and ensure the accuracy of the surrounding equipment.
Conclusion
With the growth of the economy and advances in living standards, environmental protection and the well-being of workers have become increasingly important to both the state and the public.
Ensuring the safety of operators against environmental risks is becoming an inevitable trend.
Effective prevention and control measures can only be taken through a complete understanding of the factors and transmission path of vibration caused by forging operations. Although vibration is an inevitable aspect of forging operations, its impact on the environment can be reduced by modifying the mechanical design and implementing a vibration isolation system. However, there is a trade-off between investment cost and environmental protection that must be carefully considered.
