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Hydraulic CNC Bending Machine Operation Manual

A hydraulic CNC bending machine is a sheet metal processing device that uses a hydraulic drive system to move a slide up and down, applying pressure to metal sheets through upper and lower dies to bend the sheets to a predetermined angle and size.

This manual applies to common hydraulic CNC bending machines, including ordinary CNC hydraulic bending machines, servo hydraulic bending machines, hybrid hydraulic-electric bending machines, and machines equipped with CNC systems such as ESA, DELEM, Cybelec, and SC EL.

The specific operating interface may vary between manufacturers, tonnage, number of axes, and CNC systems. Therefore, in actual operation, the electrical diagrams, hydraulic schematics, CNC system manuals, and accompanying technical documents provided by the equipment manufacturer should be consulted.

1. Essential Knowledge Operators Must Master

Before commencing operation, operators should familiarize themselves with the following:

Equipment structure and names of major components
Basic operating procedures of the CNC system
Installation, adjustment, and use of bending dies
Sheet material, thickness, and dimensions
Relationship between bending force and equipment tonnage
Relationship between V-groove width, sheet thickness, and bending radius
Relationship between bending angle and springback
Operating mode of the back gauge system
Basic requirements of the hydraulic and lubrication systems
Location of emergency stop button and safety protection devices
Common alarm messages and basic handling methods

Untrained personnel are prohibited from operating the equipment independently.

2. Hydraulic CNC Bending Machine Equipment Overview

A hydraulic CNC bending machine is a sheet metal processing machine that uses a hydraulic system to drive a slide to move up and down, applying pressure to the metal sheet through upper and lower dies, causing plastic deformation and thus obtaining a specified bending angle and size.

A typical machine mainly consists of the following systems:

Frame system
Slide system
Hydraulic system
CNC system
Back gauge system
Die system
Worktable and compensation system
Electrical control system
Safety protection system
Lubrication system
Foot switch and operating device

Modern CNC bending machines typically achieve functions such as Y1/Y2 axis synchronous control, X-axis back gauge control, R-axis height control, Z1/Z2 axis lateral stop control, and worktable deflection compensation.

3. Main Components Of CNC Hydraulic Press Brake

A typical hydraulic CNC bending machine mainly consists of the following parts:

1) Frame

The frame typically consists of left and right side plates, a worktable, connecting structures, and an upper crossbeam, forming the load-bearing foundation of the entire bending machine.

Frame rigidity directly affects:

Bending accuracy
Bending angle consistency
Long-term stability
Equipment reliability under off-center loads

2) Slider

The slider holds the upper die and moves up and down under the drive of the hydraulic system.

During bending, the slider moves downwards, pressing the upper die between the sheet metal and the lower die, thus completing the bend.

3) Worktable

The worktable holds the lower die and bears the main reaction force generated during bending.

Some high-end hydraulic CNC bending machines are equipped with mechanical or hydraulic compensation systems to improve the consistency of the angle between the middle and ends during the bending of long plates.

4) Hydraulic System

A hydraulic system typically includes:

Hydraulic pump
Motor
Hydraulic valve assembly
Oil tank
Oil pipes
Hydraulic cylinder
Pressure detection and control components

The hydraulic system is responsible for generating and controlling the power required for the slide movement.

5) CNC System

The CNC system is the core control unit of the equipment.

Depending on the configuration, it can achieve:

Bending program editing
Angle control
Back gauge positioning
Multi-process automatic operation
Die parameter management
Bending sequence calculation
Axis position control
Production counting
Alarm diagnosis
Parameter backup, etc.

6) Back gauge System

The back gauge is used to determine the bending position of the sheet metal.

Common axis configurations include:

X-axis: Controls the back gauge’s forward and backward movement
R-axis: Controls the up and down movement of the stop finger
Z1/Z2 axes: Control the left and right stop finger positions

The actual axis configuration is subject to the equipment nameplate and CNC system configuration.

7) Dies

Bending dies typically include:

Upper die
Lower die
V-shaped lower die
Multi-V lower die
Special forming dies.

The choice of mold directly affects the bending angle, inner radius, bending force, and forming quality.

4. Pre-Start Safety Inspection

A comprehensive inspection must be conducted before starting the machine. production must not be started directly.

1) Mechanical System Inspection

Inspect:

Check for obvious deformation of the frame.
Check for secure installation of the upper and lower dies.
Check for cracks, chipped corners, or severe wear on the dies.
Check for cleanliness of the worktable.
Check for obstructions in the slide block movement area.
Check for foreign objects in the back gauge area.
Check for loose mechanical connection bolts.
Check for integrity of protective devices.

2) Hydraulic System Inspection

Inspect:

Check for normal hydraulic oil level.
Check for ruptured oil pipes.
Check for leaks at joints.
Check for obvious oil leaks in the hydraulic cylinders.
Check for abnormal noises from the hydraulic station.
Check for hydraulic oil temperature within the allowable range.
If serious oil leaks are found, the equipment must not be operated.

3) Electrical System Inspection

Inspect:

Whether the power supply voltage meets equipment requirements.
Whether the electrical cabinet is normal.
Whether the grounding is reliable.
Whether the cables are damaged.
Whether the control panel is normal.
Whether the emergency stop button is in the released state.
Whether safety light curtains and other protective devices are normal.

4) Working Environment Inspection

The following must not be piled up around the equipment:

Scrap sheet metal
Tools
Oil drums
Cables
Flammable materials
Miscellaneous items unrelated to production.

The operating area should maintain sufficient lighting and passage space.

5. Correct Start-up Procedure

A typical hydraulic CNC bending machine can be started up in the following sequence:

Step 1: Connect Main Power

Turn on the main power supply of the equipment.

Observe whether the electrical cabinet, control system, and related indicator lights are normal.

Step 2: Start CNC System

Start the CNC controller and wait for the system to complete initialization.

Do not operate other functions during system startup.

Step 3: Release Emergency Stop

After confirming that there are no people or obstacles around the equipment, release the emergency stop button.

Step 4: Start Hydraulic System

Press the hydraulic pump start button.

Observe whether the hydraulic system exhibits:

Abnormal noise
Severe vibration
Oil leakage
Abnormal pressure
Alarm messages

Step 5: Equipment Return to Reference Point

Some CNC press brake bending machines require a return-to-reference-point operation after startup.

Follow the prompts of the CNC system to establish the correct mechanical position reference for each control axis.

Step 6: No-load Run Inspection

Perform a low-risk no-load run without any sheet metal to check:

Slider up-and-down movement
Back gauge movement
Axis positioning
CNC system display
Safety protection devices

Production can only begin after confirming everything is normal.

6. Sheet Material Preparation Before Bending

Bending quality depends not only on the bending machine but also on the sheet material itself.

Before processing, the following should be confirmed:

1) Material

Common materials include:

Q235 carbon steel
Q355 high-strength steel
Stainless steel
Aluminum plate
Copper plate
Galvanized plate, etc.

Different materials have different yield strengths and springback characteristics.

1) Material

Common materials include:

Q235 carbon steel
Q355 high-strength steel
Stainless steel
Aluminum plate
Copper plate
Galvanized plate, etc.

Different materials have different yield strengths and springback characteristics.

2) Sheet Material Thickness

The actual sheet thickness must be confirmed; it cannot rely solely on the material label.

For example, a sheet material nominally 3 mm may have a certain tolerance in its actual thickness.

3) Sheet Material Length

Confirm that the sheet material length matches the effective working length of the bending machine and the process requirements.

4) Sheet Material Surface

Inspect for:

Scratches
Rust
Burnt burrs
Weld slag
Oil stains
Oxide scale

For workpieces with high decorative value, protective films, soft pads, etc., should be used to reduce die indentations.

7. Bending Die Selection

Die selection is a crucial step in bending operations.

1) Selecting the Lower Die V-groove Based on Plate Thickness

Generally, a wider V-groove results in a larger inner radius (R) during bending, which in turn changes the required bending force.

Actual V-groove selection must comprehensively consider:

Plate Thickness
Material
Bending Radius
Bending Angle
Bending Force
Die Allowable Load

It cannot be simply assumed that “the larger the V-groove, the better.”

2) Upper Die Selection

Select based on workpiece structure:

Standard Straight Die
Pointed Die
Eagle Beak Die
Gooseneck Die
Segmented Die
Special Forming Die

For workpieces such as boxes, deep grooves, and U-shaped parts, special attention should be paid to whether the upper die will interfere with the workpiece.

8. Die Installation Operation

1) Before Installation

Turn off unnecessary motion functions and ensure the equipment is in a safe state.

Clean:

Upper Die Clamping Area
Lower Die Installation Area
Die Contact Surface

2) Installing the Upper Die

Correctly install the upper die into the upper die fixture.

Inspection:

Die direction
Die length
Die locking status
Die height
Die segment position

3) Install the lower die

Install the lower die on the worktable.

Check if the lower die is:

Stable placement
Reliable locking
V-groove direction consistent
Correct connection of each segment

4) Die alignment

After installation, check if the center lines of the upper and lower dies are aligned.

High-pressure bending is prohibited if the die is not properly aligned.

9. Bending Program Settings

Hydraulic CNC bending machines typically employ a programmed production method.

A complete bending program usually includes:

Material parameters
Slab thickness
Workpiece length
Bending angle
Bending radius
Die information
Back gauge position
Bending sequence
Motion parameters for each axis
Pressure or bending force
Speedparameters
Compensation parameters

10. Bending Angle Settings

For example, to process a workpiece with a 90° bend.

The target angle should be entered in the program.

However, please note:

The angle definition displayed by the CNC system must be consistent with the specific system.

Different systems may have different definitions for angles, interior angles, exterior angles, and coordinate directions. Therefore, a trial bend should be performed when using a new system or program for the first time.

11. Back Gauge Settings

The back gauge is a crucial mechanism for controlling bending dimensions.

During operation:

Input target dimension
System calculates corresponding axis position
Back gauge moves automatically
Operator checks actual position
Place sheet metal
Make sheet metal fit tightly against the stop finger
Perform bending

For complex workpieces, different stop positions should be set according to the bending sequence.

12. Trial Bending Operation

A trial bending operation must be performed before formal mass production.

Recommended procedure:

Program Input → Dry Run → Single-piece Trial Bending → Dimension Inspection → Angle Inspection → Parameter Correction → First-piece Confirmation → Mass Production

Key points to check during trial bending:

Bending angle
Bending length
Relationship between hole position and bending line
Inner radius
Appearance
Surface indentation
Dimensional relationship between multiple bends.

13. Standard Bending Operation Procedure

The following procedure can be followed during formal production:

1) Read the drawing

Confirm:

Material
Thickness
Total length
Bending dimension
Bending angle
Bending direction
Quantity
Appearance requirements

2) Check the program

Confirm that the program is consistent with the current workpiece.

3) Check the mold

Confirm that the mold model is consistent with the program.

4) Place the sheet metal

Place the sheet metal stably on the worktable.

5) Align the back gauge

Make the reference edge of the sheet metal contact the back gauge.

6) Initiate Bending

Operate the machine using the hand or foot control devices according to the equipment design requirements.

7) Complete Bending

The slider returns to the safe position.

8) Remove the Workpiece

Use appropriate handling methods based on the workpiece’s weight and dimensions.

9) Inspection

Check dimensions and angles.

10) Mass Production

Mass production begins only after the first piece is confirmed to bequalified.

14. Precautions During Bending

1) Overloading is Strictly Prohibited

The bending force must not exceed the equipment’s rated capacity.

Especially note: The tonnage of a bending machine does not mean that it can be used for any length, any material, or any V-groove.

Bending force is related to the following factors:

Material strength
Sheet thickness
Bending length
Lower die V-groove
Bending method
Bending radius

2) Avoid Uneven Loading

Long workpieces should have their force distributed as reasonably as possible.

Severe uneven loading may lead to:

Die damage
Abnormal slider force
Worktable deformation
Decrease in equipment accuracy

3) Hands Must Not Be Placed in Dangerous Areas

During slider movement, it is strictly forbidden to place hands, fingers, or other body parts between the upper and lower dies.

4) Touching Moving Parts is Prohibited

During equipment operation, the following must not be touched:

Slider
Back gauge
Die
Hydraulic cylinder
Coupling
Other moving parts

15. Handling Bending Springback

Metal sheets typically exhibit a certain degree of springback after bending.

For example, if the target angle is 90°, the material may spring back to 92° or other angles after pressure is released.

The degree of springback is related to:

Material type
Material strength
Sheet thickness
Bending radius
V-groove width
Bending method

Common adjustment methods:

These can be achieved by:

Modifying the bending angle.
Adjusting the bending depth.
Adding compensation.
Modifying the mold.
Changing the V-groove.
Optimizing the bending sequenc.
Improving the final angle.

In actual production, stable process parameters should be established based on trial bending results.

16. Bending Quality Inspection

Quality inspection should be performed on both the first piece and batch products.

1) Dimensional Inspection

Used:

Vernier calipers, steel ruler, depth gauge, height gauge, coordinate measuring machine, special inspection tools. Inspect critical dimensions.

2) Angle Inspection

Used:

Electronic angle gauge, digital angle meter, angle gauge, special inspection tools.

3) Visual Inspection

Inspect:

Cracks, indentations, scratches, deformation, burrs, mold marks, surface damage.

17. Common Bending Defects and Solutions

Reference Table:

Problems	Possible causes	Solutions
Bending angle too large	Excessive springback	Increase bending depth or perform angle compensation
Bending angle too small	Excessive compression	Reducing downward pressure
Inconsistent left and right angles	Abnormal stress or compensation	Inspecting the frame, die, and compensation system
Incorrect bending dimensions	Incorrect back gauge position	Inspecting the X-axis and stop
Indented marks on workpiece	Unsuitable mold	Replacing with a suitable die or implementing protective measures
Cracked workpiece	Insufficient radius or unsuitable material	Increasing the radius (R-angle) or adjusting the process
Twisted workpiece	Uneven material, mold, or stress	Adjusting the die and bending sequence
Gradually deviating dimensions after multiple bends	Inappropriate process sequence or positioning method	Optimizing the bending sequence
Unstable back gauge positioning	Machinery clearance or abnormal drive	Inspecting the transmission system and shaft parameters
Abnormal slider operation	Hydraulic system malfunction	Inspecting the hydraulic oil, valve assembly, pump, and sensors

18. CNC System Operation Precautions

When operating the CNC system, the following parameters must not be modified arbitrarily:

Machine tool parameters
Axis parameters
Servo parameters
Hydraulic parameters
Pressure parameters
Encoder parameters
Safety parameters
Manufacturer calibration parameters.

These parameters directly affect equipment accuracy and safety.

If modifications are necessary, they should be performed by trained technicians, and parameters should be backed up beforehand.

19. Shutdown Procedure

After normal production is completed, the hydraulic cnc bending machine should be shut down according to the prescribed procedure.

Recommended Procedure:

Complete the current workpiece
Return the slide to the safe position
Move the back gauge to the safe position
Clean the worktable
Clean the mold and surrounding area
Save the production program
Stop the hydraulic system
Turn off the CNC system
Turn off the main power supply
Record equipment usage
Maintain a record of equipment usage

After equipment shutdown, check for the following:

Oil leakage
Abnormal temperature rise
Unusual noise
Alarm
Mold damage
Electrical abnormality

20. Daily Maintenance

1) Daily Maintenance

It is recommended to check daily:

Hydraulic oil level
Oil pipes and connectors
Mold condition
Back gauge
Worktable
Lubrication points
Emergency stop device
Safety protection devices
CNC system alarms

2) Weekly Maintenance

Check:

Mold clamping mechanism
Bolt connections
Back gauge transmission components
Guide rails
Electrical cabinet
Fan and filter device
Hydraulic system operating status

3) Monthly Maintenance

Check:

Hydraulic oil condition
Hydraulic pipelines
Electrical wiring
Mechanical connections
Guide rail lubrication
Transmission system
Position detection elements
Compensation mechanism

4) Periodic Maintenance

Perform according to the equipment manufacturer’s specified cycle:

Hydraulic oil testing or replacement
Filter element replacement
Lubricating oil replenishment
Electrical system inspection
Hydraulic system pressure check
Accuracy testing
Axis positioning accuracy testing

21. Hydraulic System Maintenance

The hydraulic system is one of the core power systems of a hydraulic CNC bending machine.

Maintenance focuses include:

1) Hydraulic Oil

Use the hydraulic oil specified by the manufacturer.

Different hydraulic oils must not be mixed arbitrarily.

2) Oil Cleanliness

The hydraulic system is sensitive to contaminants.

Oil contamination may lead to:

Valve core jamming
Pump wear
Unstable pressure
Abnormal slider movement
Reduced system lifespan

3) Regular Leak Checks

If oil leaks are found in oil pipes, joints, or hydraulic cylinders, they should be dealt with promptly.

Never check for high-pressure oil leaks by hand.

22. Lubrication Maintenance

Lubrication should be performed at the specified lubrication points according to the equipment manual.

Common lubrication points include:

Guide rails
Mechanical transmission mechanism
Back gauge screw
Bearings
Die-related moving mechanisms.

More lubrication is not necessarily better. Excessive lubrication may attract dust, forming contaminants and accelerating wear.

23. Common Alarm Handling Procedures

When an alarm occurs, do not immediately and repeatedly restart the hydraulic cnc bending machine.

It is recommended to follow these steps:

Read the alarm → Determine the alarm type → Inspect the site → Eliminate obvious causes → Reset → Low-speed test → Resume production

1) Servo Alarm

Key checks:

Motor
Driver
Encoder
Cable
Mechanical resistance
Axis movement obstructed

2) Hydraulic Alarm

Check:

Hydraulic oil level
Oil temperature
Hydraulic pressure
Pump
Valve group
Pressure sensor

3) Safety Alarm

Check:

Emergency stop
Safety light curtain
Protective door
Safety relay
Foot switch
Safety circuit

Safety protection should not be forcibly deactivated before the cause of a safety alarm is identified.

24. Emergency Shutdown

The equipment should be stopped immediately if any of the following occurs:

Abnormal and severe vibration of the equipment
Severe oil leakage
Abnormal loud noise
A clear crack in the mold
Workpiece dangerously stuck
Personnel entering a dangerous area
Smoke or odor from the electrical system
Abnormally high hydraulic system pressure
Safety device malfunction

Press the emergency stop button immediately. Disconnect the main power supply to the equipment if necessary. Do not restart the machine before the cause of the accident is determined.

25. Personnel Safety Requirements

Operators must comply with the following basic safety regulations:

Wear work clothes that meet workshop requirements.
Use necessary personal protective equipment.
Do not wear loose ornaments that could easily get caught in the equipment.
Do not perform maintenance while the equipment is running.
Do not cross over moving parts.
Do not place hands or tools between dies.
Do not turn off safety protection devices without authorization.
Do not overload the machine.
Do not use dies with cracks or serious damage.
Do not allow untrained personnel to operate the equipment.

26. Ten Prohibitions Safe Operation Of Bending Machines

Do not overload the hydraulic cnc bending
Do not use damaged dies.
Do not process under severe uneven load.
Do not put your hands between the upper and lower dies.
Do not perform maintenance while the equipment is running.
Do not turn off safety protection devices without authorization.
Do not arbitrarily modify core system parameters.
Do not pile up debris around the equipment.
Do not operate the equipment independently without training.
Do not force production when the cause of the malfunction is unknown.

27. Operational Techniques To Improve Bending Accuracy

1) Careful First-Piece Measurement is Essential

Don’t assume that a correct CNC program guarantees a qualified product.

First-piece measurement is a crucial step in stable mass production.

2) Maintain Material Consistency as Much as Possible

Use sheet metal of the same batch of products with:

Same material
Same thickness
Similar mechanical properties

3) Keep Dies in Good Condition

Wearing dies will affect:

Bending angle
Inner radius (R)
Dimensions
Surface quality

4) Optimize Bending Sequence

For complex workpieces, the bending sequence should be arranged reasonably to avoid:

Interference
Collision
Difficulty in positioning
Workpiece deformation
Inability to position subsequent bends

5) Utilize Compensation Appropriately

For long workpieces, mechanical or hydraulic compensation functions can be used depending on the equipment configuration to improve the consistency of angles along the entire length.

28. Bending Precautions for Different Materials

1) Q235 Carbon Steel

Q235 carbon steel sheet has good formability and is a common bending material.

Key considerations:

Sheet thickness
V-groove
Bending radius
Springback

2) Stainless Steel

Generally exhibits more pronounced springback and higher formability requirements than ordinary carbon steel.

Special attention should be paid during processing:

Die selection
Bending force
Surface protection
Springback compensation
Minimum bending radius

3) Aluminum Sheet

Aluminum sheet is relatively soft, but different grades have significantly different properties.

Consider:

Surface scratches
Cracks
Die indentations
Material orientation

4) High-Strength Steel

High-strength steel requires greater bending force, and springback is usually more pronounced.

Equipment capacity and process parameters must be recalculated based on the actual strength of the material.

29. Bending Force Estimation

The actual bending force of a V-bend is related to factors such as the material’s tensile strength, plate thickness, bending length, and V-groove width.

In engineering practice, the bending force can be estimated using appropriate bending force calculation formulas.

Typically, the following formula can be used:

F ≈ C × σ × L × t² / V

Where:

F—Bending force

σ—Material strength parameter

L—Bending length

t—Plate thickness

V—Width of the lower die V-groove

C—Coefficient related to the bending method and unit.

In actual production, the ability of the equipment to process the bend cannot be determined solely based on empirical formulas.

For critical operating conditions, the bending force table provided by the press brake manufacturer should be used for confirmation.

30. Summary of Standard Operating Procedures for a Bending Machine

The entire production process can be summarized as follows:

Start-up Inspection

↓

Start the CNC System

↓

Start the Hydraulic System

↓

Return to Reference Point

↓

Check the Die

↓

Input/Recall the Program

↓

Check the Backgauge

↓

No-load Run

↓

Place the Sheet Metal

↓

First Piece Trial Bending

↓

Dimension and Angle Inspection

↓

Parameter Correction

↓

First Piece Confirmation

↓

Batch Production

↓

In-process Spot Check

↓

Production End

↓

Equipment Cleaning

↓

Shutdown

↓

Maintenance Record

31. Daily Inspection Checklist for Operators

Inspection Items	Inspection Items	State
Power Supply	Voltage and power supply normal	□
Emergency Stop	Functional operation normal	□
Safety Devices	Light grating/protective device normal	□
Hydraulic Oil	Liquid level normal	□
Hydraulic System	No obvious oil leakage	□
Hydraulic Pump	No abnormal noise	□
Mold	No cracks or severe wear	□
Workbench	Clean and free of foreign objects	□
Backgauge	Normal operation	□
CNC System	No abnormal alarms	□
Guide Rails	Normal lubrication	□
Electrical Cabinet	No abnormal heating or odor	□

32. Precautions for Long-Term Equipment Shutdown

If the equipment is to be shut down for an extended period, necessary protective measures should be taken.

These include:

Cleaning the equipment
Cleaning the molds
Applying rust prevention treatment
Checking the hydraulic oil
Checking the electrical cabinet
Preventing moisture
Preventing dust from entering
Regularly checking the equipment status.

When restarting, do not immediately begin full-load production. A comprehensive inspection, power-on test, low-speed operation, and no-load operation should be performed first.

33. Operator Training Recommendations

New operators are recommended to be trained in the following stages:

Stage 1: Safety Training

Master:

Emergency stop
Safety areas
Danger areas of the molds
Safety devices
Emergency handling

Stage 2: Equipment Familiarization

Understand:

Frame
Slider
Worktable
Hydraulic system
Back gauge
CNC system
Molds

Stage 3: Basic Operation

Learn:

Powering on
Returning to zero
Program call
Parameter input
Back gauge operation
Single-step operation

Stage 4: Actual Bending

Completed under the guidance of experienced personnel:

Die installation
Sheet material positioning
First piece trial bending
Dimensional inspection
Parameter correction

Stage 5: Independent Production

Independent operation is only permitted after passing an assessment.

34. Conclusion

The correct operation of a hydraulic CNC bending machine is not simply a matter of “inputting the angle, placing the sheet material, and pressing the switch.”

Truly stable and efficient bending production requires integrating equipment, dies, materials, programs, positioning, bending force, springback compensation, bending sequence, quality inspection, and equipment maintenance.

In actual production, it is recommended to establish a standardized management process:

“Equipment Inspection → Process Preparation → Program Verification → Die Confirmation → First Piece Trial Bending → First Piece Inspection → Mass Production → In-Process Sampling Inspection → Equipment Maintenance”

For equipment equipped with multi-axis CNC systems, automatic compensation, servo back gauge, robot loading and unloading, or automatic bending units, corresponding CNC system operation, automation operation, mold management, fault diagnosis, and maintenance sections should be added to this basic manual to form a complete internal “Hydraulic CNC Bending Machine Operation and Maintenance Manual”.