Press Brake Bending Basics: Everything You Need to Know for Efficient Bending

Francis Pan

Have you no idea about purchasing a press brake machine? Don’t understand the principle of machine bending? Welcome to this beginner’s guide for press brakes!

You will learn about the basic bending content of a press brake from this article, including its definition, types, methods and techniques, operating procedures, and more basic content that beginners or operators need to understand.

Basic knowledge of press brake bending

Definition of press brake

A press brake is a machine that serves bending technology, and bending is a common metal processing technique that can bend metal sheets into specific shapes and process functional components. This technology is widely used in metal processing and manufacturing industries.

Press brakes play an indispensable role in modern manufacturing, as they reflect the technology and product quality of their manufacturing enterprises. Therefore, your purchasing choice is also crucial.

Types of press brakes

  • Divided by driving mode: manual press brake, hydraulic press brake, CNC press brake, servo electric press brake, and mechanical press brake.
  • Divided by control mode: manual press brake, semi-automatic press brake, CNC press brake

Definition of bending process for press brake

Bending technology refers to the process of manufacturing metal by applying pressure and bending moment to a fixed metal sheet through a mold on a press brake, thereby deforming it into a specific shape.

Common uses and practical application scenarios

The bending process of press brakes is usually applied in fields such as mechanical manufacturing, electrical control, transportation, and building materials. In daily life, from the shell of audio equipment to the box of electrical equipment, the participation of bending process is very important.

a metal piece of metal with a black rubber strip
press brake bending

Bending Methods & Techniques

Air Bending

Air bending is one of the commonly used processes in metal bending, which does not require direct contact between the metal and the die. The punch will push the metal plate into the die, but it will not fully contact the bottom of the die. This process utilizes the air gap at the bottom to place the metal on a V-shaped die for bending, and the depth of the punch pushing determines the angle of the metal bending.

Advantages and disadvantages:

  • This method saves a lot of work time by using the same set of press brake tools for different bends, and requires relatively low machine power, which can extend the machine’s usage time. But it will cause rebound after bending, so manual bending is needed to achieve the desired bending angle, which is why this technology cannot achieve particularly accurate angles.

Typical usage scenarios:

  • Air bending is widely used due to its flexibility. It is suitable for various fields such as automobile manufacturing, aerospace, and is generally used for small and medium-sized enterprises because it does not require frequent tool replacement, making it more suitable for this method.

Bottom Bending / bottom mold bending

Bottom bending is the process of completely pressing a metal sheet into the bottom of a die, so that it fully conforms to the shape of the die. In the bottom bending, there is no longer a gap between the metal sheet and the die, but a tight fit between the top of the punch and both sides of the die. The rebound phenomenon of bottom bending is significant, often requiring more bending force for recovery.

Advantages and disadvantages:

  • This method can better control the bending angle, reduce the number of angle adjustments, and also reduce rebound. However, there may be rebound when bending the bottom. To eliminate rebound, it is usually possible to use a die with a small angle for bending in advance, or to excessively bend with a punch to increase the tonnage, which can lead to wear and tear of the machine, punch, and die.

Typical usage scenarios:

  • This technology is the best choice for items with the same results and precise dimensions, generally used in the manufacturing of parts.

Coining Bending

This method involves applying strong pressure to push the metal downwards, causing it to deform, bend, thin, and then bend into the same shape as the die.

Advantages and disadvantages:

  • After this method of bending is completed, there is almost no rebound, and it can make the bending angles of multiple components the same, thus producing high-precision bending. However, due to the need for strong pressure, there are significant requirements for press brakes, punches, dies, etc., which generally lead to damage to these instruments.

Typical usage scenarios:

  • This method was originally used to produce coins. During the production process, a metal plate is pressed between two dies under strong pressure to ensure that the metal can completely fill the dies.

Three point bending

The three-point bending die requires a servo motor to accurately adjust the height of the bottom die. This method can only bend within the radius of the die, and as the depth increases, the bending angle will become smaller and smaller until it reaches the bottom of the die.

Advantages and disadvantages:

  • This method has high flexibility, can automatically adjust the height, and also has high accuracy, which can control rebound. But this approach will increase equipment costs and there are not many tools to choose from.

Typical usage scenarios:

  • This method is generally applied to the manufacture of high-precision instruments and tools, and can be used for multi size and multi angle plates.

Related technical reading : The Complete Guide to Press Brake Techniques:11 Types of sheet metal pressing process Explained

Air Bending and bottom d bending
Air Bending and bottom d bending

Press Brake Workpiece Preparation and Operation Process

Material loading, alignment, and fixation

Material loading:

Material loading is the process of placing metal sheets into a press brake, ensuring that the material and die centerlines are aligned during placement, which can avoid tilting and deviation during subsequent bending processes.

After alignment, the metal plate will be fixed in place with the help of a back gauge system or fixture, ensuring that it will not move during the bending process.

Material alignment:

  • Alignment method: Use a mechanical positioning ruler or CNC back gauge to accurately position the sheet metal, with priority given to using precision ball screws/servo motors to control the error of repeated positioning within ± 0.05mm.
  • Alignment requirements: Ensure the parallelism of the board to the left, right, front, and back, and the angle error should not exceed the design tolerance (commonly<0.5 °).

Attention: If encountering high-precision workpieces, auxiliary equipment such as laser alignment and stop gauges can be used to reduce manual errors.

Material fixation:

  • For lightweight boards: manual pressure clamps or vacuum suction devices can be used to reduce board deviation
  • For heavy-duty boards: hydraulic or pneumatic pressure feeding devices can be used to achieve long-term positioning and fixation, avoiding angle misalignment caused by board movement.

Tool Settings

  • Die and punch selection: Select the matching die and punch based on the bending radius of the required part and the characteristics of the metal material.
  • Punch: It is necessary to consider the bending angle and minimum edge size to ensure that the finished product will not deform due to tool interference. If necessary, narrow punch or special section punch should be selected.
  • Adjust the angle and stroke: adjust the bending angle, bending force and stroke in advance to meet the needs of different parts.
  • Travel setting: Travel setting: According to the size of the V-mouth of the lower die and the thickness of the material, adjust the maximum downward displacement of the slider through CNC to protect the mold and prevent damage caused by “dead bending”.
  • Calibrate control system parameters: Based on specific part dimensions, calibrate the parameters of the control system to ensure that the bending of the material is within the specified tolerance range.

Bending process monitoring and parameter control

angle control:

  • High end models: usually equipped with laser real-time angle measuring instruments or bending adaptive systems, which can automatically feedback and correct bending angles with an accuracy of ± 0.25 °.
  • Ordinary models: rely on experience correction and first piece measurement, manually adjust angle compensation according to different material batches.

Strength control:

  • Hydraulic CNC pressure regulation: Based on material thickness, elongation, and tool type, the CNC system automatically allocates reasonable bending pressure, greatly reducing the risk of tool damage.

Travel monitoring:

  • Y-axis reproducibility: The Y-axis repeatability accuracy of high-end CNC press brakes can be better than ± 0.005mm.
  • Sliding block dynamic adjustment: CNC real-time compensation for small stroke deviations caused by temperature rise/load changes, achieving batch stable production.

Bending operation process

Program call and confirmation: The operator calls up and verifies the process program, checks the installation of the tool and the position of each section of the blocking material, and prepares to start after confirming that there are no errors.

Strict two or three person operation standards (for large-sized/heavy-duty boards): one person is responsible for control, and two people collaborate to support materials and assist in positioning.

Start and feed: Gradually lower the slider to the top of the sheet, adjust the pressing speed through CNC, automatically apply pressure and complete the forming after bending, and the slider will automatically return to zero after releasing the pressure.

Bending Calculations

How to calculate the bending force (tonnage)?

The core formula is σ max=Mmax/W (to calculate the maximum bending normal stress) and 1/ρ=M/(EI) (to calculate the curvature radius)

  • Mmax: Maximum bending moment on the section (Newton meters, N · m).
  • W: The flexural section coefficient (also known as section modulus) depends on the shape of the section.
  • σ max: The maximum normal stress (in megapascals, MPa) that the material can withstand at this point, reflecting its bending resistance

How to calculate Bend Deduction?

The calculation formula for bending deduction is:

BD=2 x (bending radius+material thickness) x tan (bending angle/2)

How to calculate Bend Allowance?

Bending allowance=bending angle x (π/180) x (inner bending radius+(K factor x total material thickness))

The K factor refers to the neutral layer, which is neither stretched nor compressed during the bending process of the sheet metal. The K value represents the ratio of the distance from the center layer to the inner surface of the sheet metal to the total thickness of the material.

Basic terms for bending

The introduction of the following terms will help you better understand the relevant drawings and operating procedures in the future.

Bending radius

The bending radius refers to the radius formed on the inside of the material during the bending process, and its radius is determined according to the thickness of the material, generally speaking, the radius is 3 times the thickness of the material. If the radius is too small, cracking will occur, and if it is too large, it will affect the effect of bending.

Bending angle

The bending angle refers to the angle formed by the plate after bending, and the general angle is 90° or 180°. Effective bending angles must be precisely set in combination with practical use.

Rebound

Springback refers to the elasticity that occurs after the material is finished, which will lead to a larger bending angle. The thinner the material, the greater the rebound amplitude, and the bend angle is usually pre-set in advance to offset the rebound.

Common bending radius, bending angle, and springback adjustment points

  • Adjust bending radius: Choose a more suitable tool/smaller inner diameter/adjust V-mouth to change the plastic deformation ratio.
  • Adjust bending angle: Adjust the bending angle of the parts one by one through an angle measurement system or manual measurement.
  • Adjust rebound: Use the program to bend the workpiece slightly greater than the target angle, causing it to rebound back to the target angle.

Definition of V-shaped bending and U-shaped bending

V-shaped bending refers to the bending process of using a V-shaped die and punch to fix a metal sheet in a specific position in a V-shaped groove, causing it to form the expected angle or shape.

U-shaped bending refers to the process of processing metal sheet metal with a U-shaped tool to make its cross-section U-shaped.

press brake bending
press brake bending

Important factors affecting bending accuracy

Material Types

Different metal materials such as steel, aluminum, copper, and their alloys have different bending accuracies, resulting in different material characteristics.

Material Characteristics

The characteristics of sheet metal materials to be bent play a crucial role in affecting the bending accuracy of the press brake.

  • Steel: It has the characteristics of durability and hardness. But processing steel often requires a larger tonnage of bending force.
  • Aluminum: It has good flexibility, but its surface is prone to deformation and significant rebound phenomenon.
  • Copper and its alloys: have good plasticity and ductility, and are commonly used in more complex processes. But its material is not hard enough and is easily damaged.

Material thickness

The factor of material thickness is particularly important in the bending process of a press brake. The thicker the material, the greater the bending force required, and the machine used also needs to be adjusted and changed accordingly. If the bending force of the machine cannot reach the required material, the material will break or deform.

Material Hardness

The hardness of materials also profoundly affects the bending process. Hard materials often require strong bending force, while soft materials often require smaller bending force. The mismatch between material hardness and bending force can lead to bending failure.

Press brake tools

Selecting the correct punch and die:

  • Punching angle and radius: The punching angle and radius should correspond one-to-one with the required bending angle and radius. When selecting, punching angles with smaller shapes are more suitable for steep bending angles.
  • Die opening width: The die opening width should correspond one-to-one with the material thickness and the required bending radius. A wider V-shaped width is easier to bend thicker materials, while a relatively narrow V-shaped width is more suitable for thinner sheets. The opening of the die needs to be carefully selected to avoid material damage and ensure the accuracy of bending.
  • Tool material type: Tool material is also an important factor in the selection process. If you want to process high-strength metals, tools with hard alloy properties are very suitable. If you want to avoid surface damage to softer metals such as copper or aluminum, brass tools with protective coatings are a better choice.

Wear and maintenance of press brake tools：

  • Regular inspection: Regularly inspect the tools for any gaps, deformations, or cracks. If any are found, they should be replaced and repaired immediately to prevent accidents during the subsequent bending process.
  • Tool cleaning: Clean the tools in a timely manner to avoid oil stains and dirt, and keep them clean.
  • Proper storage: Arrange a fixed placement plan, store tools properly, and prevent tool damage.

Bending gap

Bending gap: refers to the gap between the punch and the lower die. If the gap is too large or too small, it can cause damage to the tool. The travel limit of the machine should be strictly set according to the V-port of the lower die.

Machine tool rigidity

The rigidity of CNC press brakes directly determines the straightness and consistency of long workpieces. The optimization of the host frame, slider material, and structure can effectively prevent deflection and improve machining consistency.

Multi segment bending deflection compensation

When processing long workpieces, the machine’s own deflection will cause the middle bending angle to be upward (horn mouth). Hydraulic/mechanical or electric deflection compensation functions (Y1/Y2 compensation) can be selected to automatically adjust the slider/worktable to achieve consistent overall angle.

Repeatability of operation

The manual bending error (angle, position) is significantly greater than that of the CNC press brake. By adopting the automatic angle detection and real-time compensation function in the automation system, the repeated positioning accuracy can be controlled to ± 0.2 °, far exceeding manual control.

Springback phenomenon and compensation

Rebound occurs when the material undergoes elastic recovery after the release of bending force. In materials with higher yield strength, the phenomenon of rebound is more pronounced.

Reason for rebound: The high elastic modulus/yield strength of the material results in elastic deformation recovery, which is a process variable that cannot be ignored.

Compensation strategy:

  • Excessive bending: Slightly bending beyond the required angle to compensate for rebound.
  • Material selection: Choose materials with lower rebound tendency.
  • CNC adjustment: Using a modern CNC system, it can dynamically adjust bending parameters in real-time to counteract rebound.

Common Mistakes & How to Avoid

Angle deviation caused by over bending

Reason for error: Failure to consider the characteristics and hardness of the material, and failure to adjust the processing angle in real time.

Avoidance strategy: Accurately calculate the bending force based on the characteristics of the material, use the automatic compensation function of the CNC system, and adjust the angle deviation in real time.

Inaccurate operation alignment and error superposition

Reason for error: The sheet metal was not placed correctly in the set position of the machine tool, and the sheet metal size calculation was incorrect

Avoidance strategy: Unified base positioning method, use pallet/follow-up support for long pieces, and regularly calibrate the back gauge.

Preventive measures for surface indentation, scratches, fractures, and other issues

Preventive measures: Regularly check the tool incision, keep the tool clean, use protective film if necessary, optimize the tool incision and radius, thereby reducing indentation and scratches. When processing high-strength sheets, process bending can be carried out to reduce the risk of fracture.

More about bending problem technology recommended reading: 10 Press Brake Bending Problems and How to Fix Them in Sheet Metal

Safety and maintenance recommendations

Training for operators

Press brake operators should receive formal and comprehensive training, such as operational skills, emergency response, safety protection, and other related skills.

Operators should receive regular training and inspections to ensure that their operational skills meet the standards.

Device authentication

Before use, the equipment must undergo quality certification, including certification of industry authoritative indicators such as OSHA 29 CFR 1910, ANSI B11.3, and other industry frameworks, to ensure compliance with international safety standards.

Standard compliance

All operators should strictly follow and understand the operating procedures.The operating system should comply with national industry standards and keep up with new industry changes in real time.

Common PPE (protective goggles, gloves, etc.) and use of protective devices

  • Wear impact resistant goggles to prevent splashing of metal objects and debris.
  • Use cutting resistant safety gloves and be sure to firmly secure them to prevent them from getting caught up in machinery..
  • Wear anti-static and flame-retardant protective clothing to prevent static electricity and sparks.

Regular machine calibration, hydraulic system inspection, tool maintenance and inspection process

  • Regular calibration of the machine: Use a laser calibrator to detect the position of the main slider (Y1/Y2 axis) and the back gauge (X/R/Z axis). If the error is ≤± 0.02mm, the parameters need to be automatically corrected. Regularly send machines to authoritative institutions for quality inspection to ensure the consistency of machine data.
  • Hydraulic system inspection: Check whether the oil temperature and level are normal, whether the oil is clean, and whether the system pipelines are blocked or damaged. If any are found, they should be reported immediately and repaired in a timely manner.
  • Tool maintenance and inspection process: Establish a press brake tool usage file, record the duration and frequency of tool usage daily. Regularly clean the surface of the tool, remove oil stains, and ensure that the tool is clean. If there is severe damage to the tool, it should be promptly recorded and replaced.

Recommended reading for related press brake maintenance technologies: Ultimate Guide to Hydraulic Press Brake Maintenance: Top Tools, Schedules & Expert Tips

Conclusion

This article introduces the basic knowledge of the bending process of the press brake, from the definition of the bending process to the subsequent process of the bending operation, which also includes many additional points that need to be paid attention to in the bending operation.

I hope these contents can help you have a more comprehensive understanding of basic bending knowledge!

FAQs

From the perspective of material type, material characteristics, and the required bending process, the following process can be considered: material → thickness → bending structure → V selection → punch selection → tool material → process matching.

Usually, “over folding” compensation is performed for angles: the angle set by the program is slightly smaller than the target angle, causing the metal sheet to rebound back to the target angle. A series of measurement methods such as material data and first piece bending can also be used for more accurate compensation.

Although the initial cost of a manual press brake is relatively low, it relies heavily on manual adjustment, so its accuracy is not high. Although the initial cost of CNC press brake is relatively high, its labor cost is low. Moreover, the accuracy of CNC brake press is higher than that of manual brake press. Therefore, if it is a large-scale production, CNC press brake is more recommended. If it is a small business, manual press brakes are more recommended.

Air bending is generally not in direct contact between the material and the die. This method is more suitable for those with larger angles and more materials, and it has less damage to the tool and higher flexibility. However, its rebound is particularly obvious.

The bottom bending requires the material to fully contact the die to form a specific angle, and its forming accuracy is relatively high, but it also damages the die relatively largely, and the equipment cost is also very high.

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Francis

Author introduction

My name is Francis Pan, and I am the foreign trade manager of RAYMAX. I have been engaged in the fields of metal manufacturing and CNC machinery for over 10 years. Welcome to visit our official website, I am more than happy to provide you with the best service and products.

Email：   [email protected]  | Wechat：  13645551070

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