Vibration has a great impact and harm on industrial equipment and precision instruments, which can make the equipment and instruments unable to be used normally, and will be damaged frequently in serious cases.
At the same time, the vibration will spread through the soil, affect the foundation structure of the plant and reduce the service life of the plant.
People’s long-term vibration environment will affect their health, such as causing dysfunction of central nervous system and cardiovascular system, peripheral vasoconstriction, elevated blood pressure, accelerated heartbeat, affecting the function of digestive organs, etc.
It can also lead to endocrine changes, joint pain, loss of sleep, numbness of fingers and other symptoms.
The hazards caused by vibration are collectively referred to as vibration diseases.
For forging equipment, vibration is mainly generated during blank forging.
This post will discuss the generation, propagation and simple prevention of vibration of forging equipment.
Vibration caused by the motion mechanism of forging machinery
The forging machine has an unbalanced structure in its structure, so when the forging machine runs, it will produce vibration.
(1) The unbalanced structure of forging machinery (Fig. 1) includes sliding block, connecting rod, crankshaft, gear, etc.
Fig. 1 Unbalanced structure of forging equipment
The slider moves up and down, and the crankshaft, gear and connecting rod head rotate. These non-equilibrium moving parts will produce vibration force and make the forging machinery vibrate.
(2) Starting force of unbalanced parts.
Due to the quality factor of the movable parts and the characteristics of fast movement speed, especially the fast rotation speed of the slider parts, the action end of the rotating unbalanced parts and the round-trip moving part will produce a large starting force, resulting in the increase of the vibration of the forging machinery.
(3) When high-speed forging machinery and precision forging machinery are used for high-speed forging production, in order to reduce the operating vibration and improve the accuracy and stability of forging machinery, it will be considered to add a round-trip dynamic balance device (Fig. 2) or design a rotary balance device to reduce the operating vibration of forging machinery itself.
Fig. 2 Dynamic balancing device
However, these balancing devices often consume energy, which runs counter to the concept of economy and power saving of forging machinery.
Whether to adopt these operating balancing devices needs to fully consider their necessity, manufacturing cost, energy consumption, operating environment and other factors.
(4) Compared with the general industrial machinery, the start and stop of forging machinery need the operation power of instantaneous start and stop.
Therefore, it is necessary to select and match the clutch and brake with large capacity to make the movable parts start and stop instantaneously, but the vibration also occurs.
Hot forging and stamping machinery has large capacity and will produce large vibrations during instantaneous start and stop.
Therefore, it is necessary to balance the start and stop performance and vibration, and adjust the action speed of clutch and brake within the range that does not affect the operation of machinery, which is usually called soft clutch and soft brake.
Vibration produced by forging machinery during operation
The vibration produced by forging machinery will vary greatly due to processing types, application capacity, forging materials, production speed and mechanical design.
Period of vibration in forging process
(1) Vibration at the beginning of processing
The sliding block of forging machinery starts to move downward from the top dead center and makes the die impact the workpiece at a fixed speed.
At this time, the impact phenomenon will lead to vibration.
(2) Vibration near the processing terminal
When the sliding block of forging machinery is close to the lower dead center, the upper and lower dies will be subjected to strong pressure.
At this time, the stressed parts of each part will deform and vibrate with the impact of this load.
(3) Vibration after processing
When the processing is completed and the pressurized load is lost, the stress parts will also vibrate due to skew recovery.
This kind of vibration will vary according to the type of processing, and the vibration work such as cutting processing accounts for most of the whole vibration.
Influence of processing technology on vibration level
For forging machinery, the above processing methods and the composite processing methods combined with these methods will produce different vibration due to different processing methods.
(1) Blanking processing
After the upper die contacts the workpiece, when the maximum load is generated, the workpiece will break and lose the load.
The skew (bending) of the pressure parts such as the table body, sliding block, connecting rod, crankshaft and drive gear will be instantly liberated with the processing load.
At this time, strong vibration in the opposite direction of the load will occur. This phenomenon is generally called overshoot (Fig. 3).
Fig. 3 Schematic diagram of overshoot
(2) Bending processing
It will vary with the processing methods such as bending shape. Generally, the processing is started with a small load at the initial stage of processing.
In the final stage of processing, embossing processing is sometimes implemented in order to achieve the bending accuracy of products and obtain beautiful bending degree.
Embossing processing requires strong pressure, which will cause the vibration of forging machinery.
(3) Drawing processing
The forming load of the drawing process will gradually increase. The deep drawing process generally produces the maximum load at about 40% ~ 70% of the drawing height.
As it approaches the bottom dead center, the load will gradually decrease, so the forming vibration will be relatively small.
During deep drawing processing, in order not to produce indentation on materials or products, a device die pad to prevent wrinkles is generally used.
The contact position between the die pad and the die is at the position where the slider is earlier from the lower dead center.
Due to the impact between the workpiece and the upper die, huge sound and vibration will be generated.
(4) Forging processing includes the following processing methods
Hot forging, cold forging, extrusion processing, embossing, composite processing, etc.
1) Hot forging
Because the material is high-temperature, the contact time between the die and the workpiece should be shortened as far as possible, the sliding block speed should be fast, and the contact time between the high-temperature material and the product and the die should be shortened as far as possible.
Therefore, when the large crankshaft, gear, sliding block and other components are quickly started and stopped, the vibration of the start and stop of the forging machinery will become larger.
At the same time, because the product forming time is short, the processing impact is large, And produce great vibration.
2) Cold forging
Due to the deformation speed of the metal structure of the processed material, it is impossible to form at the rapid processing speed, so most forging machines using the driving mechanism (elbow joint and connecting rod) with slow speed in the processing area of stamping machinery are selected.
The speed of impact between the workpiece and the upper die is slow, and the forming time is also long, so the change speed of the load loaded by the forging machine is slow, Therefore, the load vibration will be relatively small.
3) Forging processing
In terms of forging processing, whether it is hot room or cold room, a strong load will generally be generated at the processing terminal, so after processing, the vibration caused by the skew recovery of the stressed parts will be generated.
4) Compound processing
Generally, the combination of bottom pressure processing such as cutting processing (blanking), bending and stretching is in the majority.
At this time, the load generated by cutting processing at the lower dead center will complete the cutting processing before the lower dead center, resulting in overshoot in an instant.
In the case of vibration caused by residual overshoot, the bottom pressing process is started at the bottom dead center, so the impact will increase greatly and produce more powerful vibration.
Compound analysis of vibration
When the forging machine is processed, the rigidity and operation condition of the forging machine itself will produce operation vibration, the processing type and load will produce load vibration, and the deformation vibration will be generated according to the natural vibration of the formed workpiece, die and forging machine itself.
The type, quantity, cycle number, occurrence time and other factors of vibration will produce slight changes during processing of forging machinery, sometimes increase and sometimes offset each other.
From the point of view of product accuracy and die life, some customers require that the table body rigidity be 5 ~ 6 times higher than that of general forging machinery, and it is natural that its relative capacity be greatly improved.
In addition to high precision, these machines can also achieve a certain degree of low noise and low vibration for their working environment.
(1) The vibration generated by the forging machinery will be transmitted to the foundation of the machinery and to the surrounding through the ground and foundation soil.
(2) The vibration generated by the mounting surface of forging machinery is a general vertical universal drawing forging machinery, which will produce a vibration starting force equivalent to 10% ~ 40% of the mechanical weight, which can propagate vibration waves through the foundation.
Vibration prevention measures of forging machinery
(1) Mechanical structure prevention.
In the design of forging machinery, the dynamic balance device is added to the structure, so as to eliminate the unbalanced moment of inertia caused by asymmetric parts such as crankshaft and connecting rod.
At the same time, the dynamic balance test shall also be conducted for the rotating parts with circumferential symmetry to avoid vibration caused by unbalanced moment of inertia caused by manufacturing error.
(2) Prevention of brake release configuration.
The forging machinery will vibrate when starting and stopping.
If the combination speed of clutch and brake is reduced or the brake equipped with soft clutch and soft brake is selected without affecting the capacity of the press, the mechanical vibration can be effectively reduced.
(3) Prevention of forging machinery and die.
Through the stamping process and die structure design, reduce the demand for stamping pressure and reduce the vibration caused by excessive stamping load;
Select the forging machinery with reduced stamping speed near the bottom dead center to avoid vibration due to large impact;
For the hot forging stamping process, because the stamping forming time needs to be very short, the demand for stamping pressure can be reduced through the early heat treatment process of stamping blank, so as to reduce the impact and reduce the vibration.
(4) Prevention of vibration transmission of forging machinery.
The vibration isolator can be selected by the forging machinery to reduce the transmission of vibration to the surrounding environment through the foundation, and the vibration isolation ditch is designed around the forging machinery foundation, so as to reduce the transmission of vibration of the forging machinery and ensure the machining accuracy of the surrounding equipment.
With the development of economy and the improvement of life, the state and people pay more and more attention to environmental protection and working environment.
The environmental protection of operators has become an inevitable trend.
Only by understanding and mastering the factors and transmission path of vibration caused by forging operation can effective prevention and control countermeasures be made. Vibration is inevitable during forging operation.
The impact of vibration on the environment can be effectively reduced by changing the mechanical design and vibration isolation system, but the cost investment and environmental protection are still a contradiction, which needs to be considered comprehensively.