Brief introduction of press brake machine
Press brake is used to complete the whole bending of sheet metal.
Generally, after one stroke of the ram, the sheet can be bent into a certain geometry of cross-section profile.
For example, by changing the press brake dies and bending several times, we can get more complex cross-section shapes.
In forging equipment, the press brake machine has become one of the most popular metal forming equipment.
It is widely used in aviation, shipbuilding, railway, electrical engineering, mining, engineering machinery, metallurgy, automobile, agricultural machinery, light industry, instrument, textile, electronics and other industries.
With the development of human beings and the continuous improvement of productivity and production level, people have higher requirements for material quality.
Industry and people’s livelihood industry have an urgent demand for the high-precision bending machine, such as high-speed rail, electric power, elevator, decoration, machinery manufacturing, kitchenware, anti-theft, etc.
Main technical parameters of press brake machine
- D——Throat depth
- E——Daylight(from top to top of the table)
- Ram stroke——The maximum distance the cylinder can extend
- Upright distance——Distance between the inside of the left and right column
- M——Worktable height
- b——Total height of the lower die
- d——Effective height of the top punch
- k——Clamping device height of the top punch
- Ram speed——Fast down, work feeding, return speed
General calculation method for type selection of press brake machine
- P – Bending force（KN）
- S – Sheet thickness（mm）
- S – Sheet width（m）
- V – Lower die opening width（mm）
- 650 – Calculation coefficient
Note: the results calculated by the above formula are based on Q235 ordinary steel plate with the tensile strength of 450-500n/mm2. When bending other different materials, the bending force is the product of the above results and the following factors
|Bronze (soft)||0.5||Stainless steel||1.5|
|Aluminum (soft)||0.5||Chromium molybdenum steel||2.0|
V opening of lower die corresponding to different plate thickness
Note: the larger the die opening “V” selected during bending, the smaller the bending force required during bending, and the larger the inner radius of the bending workpiece.
Classification of press brake machine
Upward-acting hydraulic press brake machine is the mainstream model in the current market, most of the press brake machine manufacturers adopt this structure.
The key technology of this kind of press brake machine is the synchronous control accuracy of the ram, which directly affects the operation of the ram and the quality of the parts.
Therefore, according to the different control methods of the ram, it can be divided into:
- Torsion shaft synchronous press brake machine
- Electro hydraulic synchronous press brake machine
Development of electro hydraulic proportional technology
In the later period of the Second World War, the speed of the jet fighter is constantly improving, so the control system has higher requirements on the rapidity, dynamic accuracy and dynamic rate.
At the end of 1940, the electro-hydraulic servo system first appeared on the plane.
In the 1960s, all kinds of electro-hydraulic servo valves came out, and the electro-hydraulic servo technology became more and more mature.
In the late 1960s, the demand for electro-hydraulic servo technology in civil engineering became more urgent and extensive. However, the traditional electro-hydraulic servo valve has very strict requirements for fluid medium, and the system energy consumption is also relatively large, so the manufacturing and maintenance costs are very high, which is difficult to be accepted by industrial users.
In the 1970s, in order to develop a reliable electro-hydraulic servo control technology with control accuracy and response characteristics that can meet the actual needs of engineering technology, electro-hydraulic proportional control technology developed rapidly. At the same time, industrial servo control technology was also developed.
Electro hydraulic proportional technology is a comprehensive technology, which not only realizes the hydraulic power transmission, but also has the flexibility and accuracy of electronic control.
With the development of numerical control technology and the birth of reliable proportional hydraulic components, electro-hydraulic proportional control technology has been widely used in recent years, among which the typical one is used for synchronous control of press brake machine.
Basic structure of hydraulic transmission circuit
The basic theory of hydraulic transmission is Pascal principle.
The pressure of each point in the closed cavity formed by oil pump, hydraulic valve, pipeline and oil cylinder is equal.
The oil pressure of the hydraulic system is produced by the load of the oil cylinder and changes with it.
The hydraulic transmission circuit is usually composed of oil tank, oil pump, hydraulic valve group, oil cylinder and connecting pipe.
After the hydraulic oil is sucked from the oil tank by the oil pump, it generates flow and drives the oil cylinder to move through the hydraulic valve group; By changing the flow direction and flow of pressure oil, the hydraulic valve group controls the oil cylinder to meet the movement requirements of the machine tool.
Basic principle of hydraulic transmission of press brake machine
Each stroke of the press brake machine is divided into three working conditions, namely:
There are three specific points that determine the starting and ending positions of each working condition, namely:
- Top dead center
- Speed change point
- Bottom dead center
Correspondingly, the ram moves at three speeds, namely:
- No load speed
- Working speed
- Return speed
From the top dead center to the speed change point, the ram goes down rapidly at no-load speed;
From the speed change point to the bottom dead center, the ram goes down at the working speed, and the bending of the workpiece is completed in this working condition;
From the bottom dead center to the top dead center, the ram moves upward at the return speed.
So far, the machine has completed one stroke.
The three speeds and the positions of the three specific points can be changed in the numerical control system.
For the electro-hydraulic synchronous CNC press brake machine, there is a specific point —- clamping point: the position corresponding to the upper surface of the sheet on the lower die.
From this point, the workpiece will be bent.
This point is calculated automatically by the numerical control system.
The medium of hydraulic transmission is hydraulic oil.
The quality of the hydraulic oil used in the machine tool will directly affect the performance and service life of the machine tool.
In particular, the electro-hydraulic synchronous CNC press brake machine is equipped with a proportional servo valve, so the requirement of hydraulic oil is more strict than other ordinary bending machines. Users are advised to filter at least once a year.
Synchronous principle of torsion shaft synchronous press brake machine
The rigid torsion shaft forced synchronization control technology is used in the operation of the ram of the bending machine.
The synchronous shaft is installed on the left and right wall panels of the frame body, and the swing arm of the synchronous shaft is connected with the ram through a connecting rod. During the operation of the ram, when one end runs faster, the ram drives the swing arm of the synchronous shaft through the connecting rod to twist the synchronous shaft.
Due to the rigidity of the synchronous shaft itself, the reverse force is generated to force the ram to reduce its speed, so that the ram (Y1, Y2) are controlled to run synchronously and always keep the relative parallel state to the worktable.
The precise positioning of the ram adopts the rigid positioning control technology of the built-in mechanical block.
There are mechanical stops in the left and right oil cylinders. During the downward movement of the oil cylinder, after the locating surface of the piston rod contacts with the locating surface of the mechanical stop, the piston rod is forced to stop downward movement, so as to control the final stroke position of the oil cylinder. Between the left and right oil cylinders, the mechanical stop of the left and right oil cylinders is adjusted synchronously through the connecting rod, so as to control the ram (Y1, Y2), always keep the relative parallel state to the worktable.
Synchronous principle of electro hydraulic synchronous CNC press brake machine
The press brake machine drives the ram up and down by two oil cylinders to complete the bending process.
The synchronization of the two cylinders in the whole movement process and the accurate positioning of the bottom dead center are particularly important.
The synchronization of the two oil cylinders and the accurate positioning of the bottom dead center of the electro-hydraulic servo CNC press brake machine are precisely controlled by the CNC system: on the one hand, the ram runs smoothly; on the other hand, the ram can be accurately positioned at the bottom dead center.
The position signal of the ram is detected in real-time by the grating installed on both sides of the machine and fed back to the CNC system.
On the one hand, the numerical control system compares the feedback data of two grating rulers, and adjusts the proportional servo valve in the two synchronous valve groups, controls the opening size of the valve, and adjusts the oil intake of the oil cylinder, so as to control the operation of the ram within the allowable error range. Thus, the ram (Y1, Y2) are controlled to be synchronized and always keep parallel to the worktable; on the other hand, the feedback data of the grating ruler is compared with the bottom dead center set by the system to see if it reaches the bottom dead center.
The full closed-loop electro-hydraulic servo control technology is adopted for the synchronous control of the press brake machine: the position signal of the ram is fed back to the numerical control system by the grating ruler on both sides, and then the numerical control system controls the opening size of the synchronous valve, adjusts the oil intake of the oil cylinder. Thus, the ram (Y1, Y2) are controlled to run synchronously, and the parallel state of the worktable is always maintained
Synchronous schematic diagram of electro hydraulic synchronous CNC hydraulic press brake machine
If there is any positioning error on both sides of the ram, the numerical control system will make correction instructions to the two synchronous valves to ensure the parallel state of the ram to the worktable.
The diagram shows the components of the synchronous system of the press brake machine, which is mainly composed of hydraulic oil control and electrical signal transmission.
The pressure oil, controlled by the two synchronous valve groups, respectively enters the two oil cylinders to drive the ram to move synchronously; the position of the ram movement is detected by the grating ruler on both sides in real time and fed back to the CNC system. After the analysis and calculation of the CNC system, the two synchronous valve groups are controlled by the servo amplifier, and the feedback signal of the spool position of the proportional servo valve is received at the same time for analysis, calculation and control the synchronous valve group again to forms a dynamic closed-loop control.
In the whole running process of the ram, the numerical control system sets the parameters according to the program, combined with the grating ruler and the feedback signal of the proportional servo valve spool position,
The synchronous valve group is dynamically controlled to realize synchronous operation and accurate positioning of the bottom dead center.
From this, we can see that the synchronous control system of electro-hydraulic synchronous CNC press brake machine is mainly composed of CNC system, grating ruler and proportional valve.
From the above content, we can see that the bending principle of electro-hydraulic synchronous press brake machine is basically the same as that of ordinary press brake machine, which is to control the bending angle forming (free bending) by the sheet pressing depth in the lower die mouth (bending depth) by the top punch, or to press the workpiece into the same angle (shape) as the die (bottom pressing bending).
The only difference is the control mode of the ram.
The simple overview is: The numerical control system controls the electro-hydraulic proportional valve, and the feedback of the grating ruler forms the digital control mode of full closed-loop bending depth.
The difference between two kinds of synchronous mode of press brake machine
The common press brake machine relies on the torque tube to force the ram to synchronize, and the synchronization of the electro-hydraulic press brake machine is completely realized by the balance of the hydraulic oil circuit.
The torsion shaft press brake machine is open-loop control while electro-hydraulic press brake machine is closed-loop control.
Electro hydraulic synchronous press brake machine has the following obvious advantages
- The fully closed-loop control system allows the stroke of the hydraulic cylinder to be monitored and controlled at all times. Once the cylinder is tilted, the system will quickly issue commands based on the values of the scales located on both sides of the cylinder, so that the proportional valves can make adjustments to keep the cylinders in sync.
- The electro-hydraulic press brake machine can be fully off-load pressurized, with one cylinder working at full load and the other cylinder at zero pressure.
- The electro-hydraulic synchronization system also allows the ram to be tilted down to bend workpieces with variable angles, a function that is not possible with ordinary press brake
- The pressure of the electro-hydraulic synchronous system in each operating condition is also regulated automatically by the proportional pressure valve according to the parameters of the system.
- The electro-hydraulic synchronous system can achieve smooth transition from fast to slow speed, reduce hydraulic impact and improve system stability.
- Because of the precise control of the position of the cylinder, the same die can be bent at different angles, which makes the press brake machine a flexible machine tool.
- In the whole working state of the press brake machine, the whole process automatic control can reduce the error caused by human factors. Of course, each working condition can be adjusted and corrected through CNC parameters.
- Improve the production efficiency, improve the accuracy of the parts, to achieve machine for person.
Main components of electro hydraulic synchronous CNC press brake machine
The electro-hydraulic synchronous CNC press brake machine is composed of the electric control system, main machine and related auxiliary machines.
Electronic control system
The electric control system consists of electric control cabinet, numerical control system hanging box and operation station;
The main machine is composed of oil cylinder, hydraulic system, grating ruler position feedback system, ram, frame and toolings;
The main machine is the main component of the hydraulic system.
- Internal gear pump – Voith, Germany.
- Filling valve, cartridge valve, lifting valve, proportional relief valve, electromagnetic directional valve, proportional pressure valve and proportional servo valve.
The auxiliary mechanism has many functional parts to choose from, such as worktable compensation, backgauge, die fast clamping device, material carrier, oil temperature cooling or heating device, photoelectric protection device, centralized lubrication and so on.
The axis equipped on the press brake machine are generally configured reasonably according to the technological requirements of the workpiece processed by users.
- X axis–It is a semi-closed-loop mechanical movement axis of the rear stop. If equipped with X1 axis, this is the left finger control axis.
- R axis–Control axis for vertical lifting of the rear stop
- Z1 axis–The mechanical axis of the left stop fingers that move left and right on the backgauge beam.
- Z2 axis–The mechanical axis of the right stop fingers that move left and right on the backgauge beam.
- X axis–Control the back and forth movement of the rear stopper
- R axis–Control the up and down movement of the rear stopper
- Z1、Z2 axis–Respectively control the movement of the two back stop fingers to the left and right
Auxiliary–backgauge X1 axis
Auxiliary–6 axis backgauge
Angle error and straightness error
Question: is there angle error and straightness error in the “ideal bending state”?
Stress and strain analysis of sheet metal bending process
Straightness error analysis
- After the springback of sheet metal bending, the edge line of the bending workpiece will appear natural deflection, which is usually expressed by its maximum deflection δ.
- According to the stress analysis, the stress σZ in the deformation zone is tensile stress on the outside and compressive stress on the inside. The two opposite tensile and compressive stresses form a moment in bending direction, which is the moment required to keep the workpiece straight during bending. But at the end of the bending, the moment disappears, causing upward deflection.
- The longer the bending plate, the larger the deflection δ.
- The wider the bending plate, the smaller the plate width, the larger the deflection δ.
- During the bending angle change from 150 ° to 90 °, the deflection δ is reduced.
- With the increase of plate thickness, the deflection δ increases in proportion.
- Pressure is applied on the edge line of the bending sheet, such as correction bending and three-point bending, which can improve the straightness.
Factors affecting bending accuracy
Press brake stiffness, bending mode and bending force are the main factors affecting bending accuracy.
1. Press brake stiffness
How to determine the stiffness index of press brake machine in design?
Deflection deformation of press brake machine
2. Bending mode
2）Three point bending
3. Bending force
How does bending force change during bending?
1）Free bending of acute punch
As shown in the figure below, in the free bending mode, the sheet material is Q235, the material is ideal elastic-plastic + linear hardening, and the yield strength is σS = 250Mpa, hardening modulus (Tang mod value: 1050 MPa).
The results of ANSYS analysis are as follows
Bending force curve:
The results of the analytical method are as follows
2）Wide knife bending
As shown in the figure below, the upper die is wide arc R180, the sheet material is set as X80, the material is ideal elastic-plastic + linear hardening, the yield strength σs = 552mpa, and the hardening modulus (Tang mod value: 840mpa).
The results of ANSYS analysis are as follows
Bending force curve:
Design principle and implementation of convex worktable
When the press brake machine is working, the machine will produce deformation, and the main reason for the deformation is that the force application point of the machine is at both ends of the machine, and the ram and worktable will produce deformation due to the force during the bending process, which leads to the inconsistency between the two ends of the workpiece and the middle angle.
The finite element method, which is fast and accurate, has been widely used to analyze the press brake machine.
Convex curve of 100 ton 3-meter press brake machine obtained by finite element method:
There are several methods to compensate for deflection deformation:
- Saddle shaped worktable with fixed deflection compensation;
- Top punch wedge compensation;
- Worktable cylinder compensation; pressure control mode
- Mechanical compensation of worktable; position control mode
Worktable cylinder compensation
The worktable is a three-layer splint structure, in which the compensating oil cylinders are distributed.
When the system supplies pressure to the compensating cylinder, the compensating cylinder pushes up the middle splint of the three-layer splint to produce the compensating effect.
Mechanical compensation of worktable
In order to control the position, that is to say, according to the deflection curve during bending, the same amount of anti-deformation is given at the corresponding point, which just makes up for the elastic deflection deformation of the machine during bending.
Mechanical compensation is composed of a group of wedges with inclined plane, which can form reverse compensation
Before bending loading, pre convex state
After the bending is loaded, the actual compensation state is changed
Loading simulation animation of the convex worktable
Electric control system
The electric control system is the power part of the machine tool, and each action and function of the machine are controlled by the electric control system.
In the working process of the CNC press brake machine, the movement of the ram and the change of working condition are realized by the control of the solenoid valve.
Therefore, the task of the electrical control system is to change the power status of the solenoid valve under different working conditions. In other words, the solenoid valve is the executive component of the electrical system, and it is also the control component of the hydraulic system. The connection between the electro-hydraulic system and the electrical control of the hydraulic system are realized by the electro-magnetic valve.
For the traditional twist axis machine tool, the electrical control system is very simple, only control several solenoid valve gain and loss of power is enough, the electrical system does not need to consider the synchronization problem in the process of operation.
But for the electro-hydraulic press brake machine, due to the change of synchronization mode, servo valve is used to control the process synchronization of two cylinders.
The problem of synchronous control is completed by the electrical control system, so the electro-hydraulic servo bending machine must adopt the numerical control device, constantly detect the position of both ends of the ram, and calculate the opening of the servo valve at each moment through the system, which is controlled by the servo valve amplifier to ensure the synchronization in the operation process.
Therefore, any electro-hydraulic servo press brake machine must have two proportional servo valves and two grating rulers to detect and control the position of both sides.
Schematic diagram of the electric control system of electro hydraulic servo press brake machine
The schematic diagram only shows the control of the ram of the electro-hydraulic press brake machine.
Torsion shaft numerical control system
The common CNC systems of torsion shaft synchronous press brake machine are as follows:
- 15 programs, 20 steps for each program, 20 cycles for each step.
- It has semi-automatic and manual functions.
- Automatic concession function.
- Function of eliminating lead screw clearance.
- The control accuracy is 0.03mm.
- 240 x 128LCDdisplay
- 40 programs, 25 steps for each program.
- Automatic back off function, elimination of lead screw clearance function.
- Multi-step programming.
- Power off memory.
- Parameter backup and recovery.
- The control accuracy reaches 0.01mm
- Including all E200 functions.
- 6-inch TFE LCD.
- 100 programs, 25 steps for each program.
- 15 upper and lower molds can be edited.
- Angle editing: automatically calculate the bending depth.
- Bright LCD display
- Beam stop control
- Backgauge control
- Angle programming
- Tool programming
- Retract function
- Up to 100 programs
- Up to 25 bends per program
DA-41T / 42T system:
- Panel-based housing
- Bright LCD screen
- Beam stop control (Y)
- Backgauge control (X)
- Retract functionality
- Manual movement of all axes
- Backgauge control (R) (DA-42T)
- Crowning function (DA-42T)
- Pressure control (DA-42T)
- Color 7-inch TFE LCD.
- 128MB fixed hard disk.
- 3 axis control, can control mechanical compensation.
- Angle programming, with mold library.
Electro hydraulic numerical control system
Cybelec brand from Switzerland and Delem brand of Holland are well-known for electro-hydraulic numerical control system, which are also the most widely used brands.
- Digital programming
- Up to four axis control
- Digital programming
- 2D graphics programming
- Up to four axis control
- Touch screen control
- Digital programming
- 2D graphics programming
- 3D display
- Support more than four axis control
- 4 + 1 axis
- 7 “TFT screen
- Storage capacity 64M
- Mold / material / product warehouse
- USB data storage function
- One page parameter programming and quick programming
- Built in PLC editing function
- Angle correction database
- It has all the functions of da52s
- Determination of bending process
- 60 die editing
- 2D graphics programming: unfold length calculation
- Fast detection and calculation of safety area of interference die
- Built in CF card structure: stable
- Storage capacity: 256M
- All functions of DA56s
- 3D product graphic simulation display
- Industrial grade 17 inch infrared touch screen
- It can be operated with gloves and is not affected by dust and scratches
- Complete windows application package
- Drawingat will
- User program application in multi task environment
Recently, Delem has made a lot of upgrades to the control system of the press brake machine. The mainstream systems all use touch control. For more information, please visit this page.
Wrap it up
Through the above study, I think you must have a deeper understanding of the bending machine. Of course, in the bending category, there is more knowledge about press brake machine and toolings. Hope those blog post can bring you some benefits.