Mastering the Press Brake: What You Need to Know

Are you curious about how sheet metal is bent into complex shapes? Do you want to know more about the versatile and widely used press brake machine? Look no further!

In this blog post, we will take you on a journey through the technical parameters, classification, and development of the press brake machine. From the basic structure of hydraulic transmission circuits to the synchronous control accuracy of the ram, we will cover everything you need to know about this essential metal forming tool.

So, buckle up and get ready to learn!

Brief introduction of press brake machine

A press brake is utilized to carry out the complete bending of sheet metal.

Typically, after a single movement of the ram, the sheet metal can be bent into a specific cross-sectional geometry.

By adjusting the press brake dies and repeating the bending process, more complex cross-sectional shapes can be achieved.

In the realm of forging equipment, the press brake machine has emerged as one of the most widely used metal forming tools. It is utilized in a diverse range of industries including aviation, shipbuilding, railway, electrical engineering, mining, engineering machinery, metallurgy, automobile, agricultural machinery, light industry, instrumentation, textile, electronics, and others.

As human civilization develops and productivity and production levels continue to improve, there is a growing demand for high-quality materials. Both the industrial sector and industries that support people’s daily lives have an pressing need for high-precision bending machines, such as those used in the production of high-speed rail, electric power, elevators, decoration, machinery manufacturing, kitchenware, and security products.

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

Calculation formula:

• 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

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.

You can use the online calculator to make the bending force calculation much easier.

Classification of press brake machine

The Upward-Acting Hydraulic Press Brake Machine is the most commonly used model in the current market, with most press brake manufacturers adopting this design.

The key feature of this press brake machine is the synchronous control accuracy of the ram, which plays a crucial role in determining the operation of the ram and the quality of the resulting parts.

Based on the different control methods of the ram, this press brake machine can be divided into two types:

• Torsion Shaft Synchronous Press Brake Machine
• Electro-Hydraulic Synchronous Press Brake Machine

Development of electro hydraulic proportional technology

During the latter part of World War II, the speed of jet fighters was constantly improving, requiring more advanced control systems with higher requirements for rapidity, dynamic accuracy, and dynamic rate.

In 1940, the first electro-hydraulic servo system appeared on aircrafts. In the 1960s, various types of electro-hydraulic servo valves were developed, leading to a more mature electro-hydraulic servo technology.

However, by the late 1960s, the demand for electro-hydraulic servo technology in civil engineering was growing, but the traditional electro-hydraulic servo valve had strict requirements for fluid medium and consumed a lot of energy, making it expensive to manufacture and maintain.

In the 1970s, in order to develop a reliable electro-hydraulic servo control technology that met the actual needs of engineering, electro-hydraulic proportional control technology rapidly advanced. At the same time, industrial servo control technology also evolved.

Electro-hydraulic proportional technology is a comprehensive approach that combines hydraulic power transmission with the flexibility and accuracy of electronic control. With the advancement of numerical control technology and the availability of reliable proportional hydraulic components, electro-hydraulic proportional control technology has been widely adopted in recent years, with a typical application being the synchronous control of press brake machines.

Basic structure of hydraulic transmission circuit

The basic theory of hydraulic transmission is Pascal principle.

In a closed cavity formed by an oil pump, hydraulic valve, pipeline, and oil cylinder, the pressure at each point is equal.

The hydraulic system’s oil pressure is generated by the load of the oil cylinder and changes accordingly.

The hydraulic transmission circuit typically consists of an oil tank, oil pump, hydraulic valve group, oil cylinder, and connecting pipes.

The oil pump draws oil from the oil tank, generating flow which drives the movement of the oil cylinder through the hydraulic valve group.

The hydraulic valve group controls the flow direction and pressure of the oil, allowing it 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:

• Fast-moving
• Working
• Return

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

In a press brake machine cycle, from the top dead center to the speed change point, the ram moves downward rapidly at no-load speed.

From the speed change point to the bottom dead center, the ram moves downward at the working speed, and the bending of the workpiece is completed during this phase.

From the bottom dead center to the top dead center, the ram moves upward at the return speed, completing one cycle of the machine.

The three speeds and the positions of the three specific points can be adjusted through the numerical control system.

For an Electro-Hydraulic Synchronous CNC Press Brake Machine, there is a particular point known as the clamping point, which corresponds to the upper surface of the sheet on the lower die. The workpiece will be bent from this point, which is calculated automatically by the numerical control system.

The hydraulic transmission medium used is hydraulic oil, and its quality directly affects the performance and lifespan of the machine. In particular, the Electro-Hydraulic Synchronous CNC Press Brake Machine is equipped with a proportional servo valve, making the requirements for the hydraulic oil more stringent compared to other bending machines.

Users are advised to filter the hydraulic oil at least once a year.

Synchronous principle of torsion shaft synchronous press brake machine

The Torsion Shaft Forced Synchronization Control Technology is used in the operation of the ram of a bending machine.

The synchronous shaft is located on the left and right panels of the frame body and is connected to the ram through a connecting rod.

During operation, if one end of the ram moves faster, the ram drives the swing arm of the synchronous shaft to twist it through the connecting rod. The rigidity of the synchronous shaft generates a reverse force that reduces the speed of the ram, ensuring that the rams (Y1, Y2) run synchronously and maintain a parallel state to the worktable.

The precise positioning of the ram is achieved through the Rigid Positioning Control Technology of the built-in mechanical block. There are mechanical stops in the left and right oil cylinders, which stop the downward movement of the piston rod after it contacts the locating surface of the mechanical stop, controlling the final stroke position of the oil cylinder.

The mechanical stops of the left and right oil cylinders are adjusted synchronously through the connecting rod to control the relative parallel state of the rams (Y1, Y2) to the worktable.

Synchronous principle of electro hydraulic synchronous CNC press brake machine

The Press Brake Machine uses two oil cylinders to drive the ram up and down, completing the bending process. The synchronization of the two cylinders and the accurate positioning of the bottom dead center are critical.

The Electro-Hydraulic Servo CNC Press Brake Machine precisely controls the synchronization of the two oil cylinders and the accurate positioning of the bottom dead center through the CNC system. This results in a smooth movement of the ram and accurate positioning at the bottom dead center.

The position of the ram is detected in real-time by grating rulers installed on both sides of the machine and fed back to the CNC system. The numerical control system compares the feedback data from the two grating rulers and adjusts the proportional servo valve in the synchronous valve groups, controlling the opening size of the valve and the oil intake of the oil cylinder to keep the operation of the ram within an acceptable error range. This ensures that the rams (Y1, Y2) run synchronously and maintain a parallel state to the worktable.

The numerical control system also compares the feedback data from the grating ruler with the bottom dead center set by the system to confirm that the bottom dead center has been reached.

The Press Brake Machine uses a full closed-loop electro-hydraulic servo control technology for its synchronous control, with the position signal of the ram fed back to the numerical control system by the grating rulers on both sides. The numerical control system then controls the opening size of the synchronous valve and adjusts the oil intake of the oil cylinder, ensuring that the rams (Y1, Y2) run synchronously and maintain a parallel state to the worktable.

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 send correction instructions to the two synchronous valves to maintain the parallel state of the ram to the worktable.

The diagram depicts the components of the synchronous system of the Press Brake Machine, which mainly consists of hydraulic oil control and electrical signal transmission.

The pressure oil is controlled by the two synchronous valve groups and enters the two oil cylinders to drive the synchronized movement of the ram. The position of the ram movement is detected in real-time by grating rulers on both sides and fed back to the CNC system.

The CNC system analyzes and calculates the data, controlling the two synchronous valve groups through the servo amplifier. The feedback signal of the proportional servo valve’s spool position is also received and analyzed, forming a dynamic closed-loop control.

Throughout the ram’s movement, the numerical control system sets the parameters according to the program, utilizing the grating ruler and the feedback signal from the proportional servo valve’s spool position to dynamically control the synchronous valve group and achieve synchronized operation and accurate positioning of the bottom dead center.

Therefore, the synchronous control system of the Electro-Hydraulic Synchronous CNC Press Brake Machine mainly consists of the CNC system, grating ruler, and proportional valve.

As shown above, the bending principle of the Electro-Hydraulic Synchronous Press Brake Machine is similar to that of a regular Press Brake Machine, which controls the bending angle by adjusting the pressing depth of the sheet in the lower die mouth through the top punch, or by pressing the workpiece into the same angle as the die.

The only difference is the control mode of the ram, which is controlled by the numerical control system through the electro-hydraulic proportional valve and the feedback from the grating ruler. This forms a full closed-loop, digital control mode for the bending depth.

The difference between two kinds of synchronous mode of press brake machine

The standard press brake machine relies on the torque tube to ensure that the ram moves in synchrony, while the synchronization of the electro-hydraulic press brake machine is achieved through the balance in the hydraulic oil circuit.

It is worth noting that the torsion shaft press brake operates using open-loop control, whereas the electro-hydraulic press brake uses closed-loop control.

Electro hydraulic synchronous press brake machine has the following obvious advantages

The fully closed-loop control system in the electro-hydraulic press brake machine enables continuous monitoring and control of the cylinder’s stroke. Once the cylinder begins to tilt, the system promptly issues commands based on the readings from the scales located on either side of the cylinder, which then prompt the proportional valves to make adjustments to keep the cylinders in sync.

In the electro-hydraulic press brake machine, it is possible to have one cylinder working at full load while the other operates at zero pressure in an off-load pressurized state.

Additionally, the electro-hydraulic synchronization system allows the ram to be tilted at varying angles, making it possible to bend workpieces at different angles, which is not possible with traditional press brake machines.

The pressure in the electro-hydraulic synchronous system is automatically regulated in each operating condition by the proportional pressure valve based on the system parameters.

This system can also smoothly transition from fast to slow speed, reduce hydraulic impact, and improve system stability.

The precise control of the cylinder position in the electro-hydraulic press brake machine makes it possible to bend the same die at different angles, making it a highly flexible machine tool.

Moreover, the automatic control of the entire process reduces errors caused by human factors and each working condition can be adjusted and corrected through CNC parameters.

In conclusion, the electro-hydraulic press brake machine improves production efficiency, increases the accuracy of parts, and transforms the machine into a tool that works for the operator.

Main components of electro hydraulic synchronous CNC press brake machine

The electro-hydraulic synchronous CNC press brake machine is comprised of an electric control system, the main machine, and auxiliary equipment.

Electric Control System:

The electric control system consists of an electrical control cabinet, a numerical control system console, and an operator station.

Main machine

The main machine is made up of an oil cylinder, a hydraulic system, a grating ruler position feedback system, a ram, a frame, and various tools.

The main machine is the central component of the hydraulic system and includes internal gear pumps from Voith in Germany, as well as various valves such as the filling valve, cartridge valve, lifting valve, proportional relief valve, electromagnetic directional valve, proportional pressure valve, and proportional servo valve.

Auxiliary mechanism

The auxiliary mechanism is equipped with various functional components that can be selected according to the needs of the user, including a worktable compensation mechanism, a backgauge, a quick-release die clamping device, a material carrier, an oil temperature control system that can cool or heat the oil, a photoelectric protection device, a centralized lubrication system, and more.

Press brake backgauge

The axes installed on the press brake machine are typically configured based on the processing requirements of the workpieces to be produced.

X Axis: This is a semi-closed-loop mechanical movement axis for the rear stop. If equipped with the X1 axis, it is the control axis for the left finger.

R Axis: This is the control axis for the vertical lift of the rear stop.

Z1 Axis: This is the mechanical axis for the left stop fingers that move left and right on the backgauge beam.

Z2 Axis: This is the mechanical axis for the right stop fingers that move left and right on the backgauge beam.

X Axis: Controls the back and forth movement of the rear stopper.

R Axis: Controls the up and down movement of the rear stopper.

Z1 and Z2 Axes: Control the movement of the two backstop fingers to the left and right, respectively.

Auxiliary–backgauge X1 axis

Auxiliary–6 axis backgauge

Bending accuracy

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 sheet metal bending, the edge of the bent workpiece will exhibit natural deflection, which is typically measured by its maximum deflection (δ).

According to stress analysis, the stress (σZ) in the deformation zone is tensile on the outside and compressive on the inside. These opposing tensile and compressive stresses create a bending moment, which is required to keep the workpiece straight during bending. However, at the end of the bending process, this moment disappears, causing the workpiece to deflect upward.

The longer the bend plate is, the greater the deflection (δ) will be. Similarly, the wider the bend plate is, the smaller the plate width, the greater the deflection (δ) will be.

However, reducing the bending angle from 150° to 90° will reduce the deflection (δ).

In addition, as the plate thickness increases, the deflection (δ) will increase proportionally.

Applying pressure to the edge of the bending sheet, such as through correction bending or three-point bending, can improve the straightness of the workpiece.

Factors affecting bending accuracy

The main factors that influence bending accuracy in a press brake machine are the stiffness of the press brake, the bending mode, and the bending force.

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

1）Air bending

2）Three point bending

3）Coining

3. Bending force

How does bending force change during bending?

1）Free bending of acute punch

As illustrated in the accompanying figure, in the free bending mode, the sheet material is made of Q235 steel, which is considered to have ideal elastic-plastic behavior with linear hardening. The yield strength of this material is σS = 250 MPa, and its hardening modulus (also known as the tangent modulus) is 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 depicted in the accompanying figure, the upper die is designed with a wide R180 arc, and the sheet material is set as X80. This material has ideal elastic-plastic behavior with linear hardening, and its yield strength is σs = 552 MPa. The hardening modulus (also known as the tangent modulus) of this material is 840 MPa.

The results of ANSYS analysis are as follows

Bending force curve:

Design principle and implementation of convex worktable

When the press brake machine is in operation, it will cause deformation, which is mainly due to the application of force at both ends of the machine. This force, generated during the bending process, causes deformation in the ram and the worktable, resulting in inconsistencies between the two ends of the workpiece and its central angle.

To analyze the press brake machine, the finite element method is widely used due to its speed and accuracy.

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 has a three-layer splint design, with compensating oil cylinders located throughout the structure.

When the system applies pressure to the compensating cylinders, it pushes up the middle splint of the three-layer splint, resulting in compensation for the deformation.

Mechanical compensation of worktable

To control the position, compensation is provided at the corresponding point during bending to counteract the elastic deflection deformation of the machine.

Mechanical compensation is achieved through a group of wedges with inclined planes, which can provide 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

Driving mode

Electric control system

The electric control system is the driving force behind the machine tool, controlling each action and function of the machine.

During the operation of the CNC press brake machine, the movement of the ram and changes in working conditions are controlled by the solenoid valve. The task of the electric control system is to alter the power status of the solenoid valve under different working conditions.

The solenoid valve is the executing component of the electric system and also the control component of the hydraulic system. The connection between the electro-hydraulic system and the electrical control of the hydraulic system is established through the electromagnetic valve.

For traditional torsion shaft machine tools, the electric control system is relatively simple and only requires controlling the gain and loss of power for several solenoid valves. Synchronization is not a concern in the operation process.

However, in the case of the electro-hydraulic press brake machine, the servo valve is used to control the synchronization of the two cylinders due to changes in the synchronization mode. The problem of synchronous control is solved by the electric control system.

As a result, the electro-hydraulic servo bending machine must have a numerical control device to constantly detect the position of both ends of the ram, calculate the opening of the servo valve at each moment, and control the servo valve amplifier to ensure synchronization during operation. To achieve this, any electro-hydraulic servo press brake machine must have two proportional servo valves and two grating rulers to detect and control the position on both sides.

The electric control system of the electro-hydraulic servo press brake machine is illustrated in the following schematic diagram.

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:

• MD320
• E21
• E200
• E210
• DA41
• S525

MD320 system：

• 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.

E200 system：

• 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

E210 system：

• 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.

DA41S system：

• 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)

S525 system：

• 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 is well-known for electro-hydraulic numerical control system, which is also the most widely used brands.

DA–52S

• Digital programming
• Up to four axis control

DA–56S

• Digital programming
• 2D graphics programming
• Up to four axis control

DA–66T

• Touch screen control
• Digital programming
• 2D graphics programming
• 3D display
• Support more than four axis control

DA52S

• 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

DA56S

• It has all the functions of da52s
• 10”TFT800×600
• 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

DA66T

• 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.