Are you new to the world of press brakes and struggling to understand the concept of tonnage? Look no further! In this informative article, we will guide you through the ins and outs of press brake tonnage and how to calculate it.

From the factors that affect tonnage determination to the popular formulas used in China and other countries, we’ve got you covered.

Plus, we’ll introduce you to our very own press brake tonnage calculator that will make your life a whole lot easier.

But that’s not all – we also delve into the importance of bending radius and minimum bending edge, providing you with helpful tables and formulas to ensure your sheet metal bending is done with precision and accuracy.

And if you’re looking to hem or seam your metal, we’ve even included tonnage charts for mild steel and stainless steel.

So, whether you’re a beginner or a seasoned pro, this article is a must-read for anyone working with press brakes.

## What Is Press Brake Tonnage?

During the bending process, the force between the upper and lower die is applied to the material, which causes the material to undergo plastic deformation. The tonnage of work refers to the bending pressure or press brake tonnage during the bending process.

The factors affecting the determination of work tonnage include bending radius, bending method, die ratio to bending length, thickness, and strength of bending material.

**Related reading:** Press Brake Buying Guide

## Factors Affecting Tonnage Calculations

There are several factors that influence the tonnage calculations for a press brake. In this section, we will discuss three key factors: Material Type and Thickness, Die Width and V-opening, and Bending Angle and Length.

### Material Type and Thickness

The type and thickness of the material being bent play a major role in determining the required tonnage for a press brake operation. Different materials have varying strengths and properties, which affect the amount of force needed to bend them.

For example, thicker materials and high-strength metals, such as stainless steel or aluminum, will require more force to bend than thinner or softer materials like mild steel or copper. Moreover, the material’s tensile strength should be taken into account to ensure accurate tonnage calculations.

### Die Width and V-opening

The die width and V-opening are essential factors to consider when calculating the tonnage required for a press brake operation. Larger V-opening sizes require less force to bend a given material, while smaller V-openings need more force. Die width can also impact the tonnage calculation, as narrower dies may result in higher tonnage requirements due to increased pressure on the material during bending.

To ensure accurate tonnage calculations, operators should choose dies and V-openings suitable for the particular material and desired bend radius.

### Bending Angle and Length

Finally, the bending angle and bending length also affect the press brake tonnage calculations. The required force increases as the bending angle deviates from a 90-degree angle, meaning that acute or obtuse angles will demand more force to achieve the desired bend.

Additionally, longer bending lengths require higher tonnage as a greater amount of material is being bent, increasing the resistance to bending.

It’s vital to accurately consider all these factors while utilizing a press brake tonnage calculator to ensure precise and effective press brake operations (Scroll down to use the calculator). Properly calculating the required tonnage can help operators avoid damaging the machinery, material or creating inaccurate bends.

## Press Brake Tonnage Calculation

### Press Brake Tonnage Calculation Formula

There are currently two main formulas for calculating the tonnage of the press brake that are popular.

The first formula is commonly used in China and the second one in other countries.

However, regardless of which formula is used, the calculated required press brake pressure is basically the same. Let me introduce these two formulas separately below.

**Formula #1**

**P=650 S²L/V (σb=450N/mm²)**

where,

- P – Bending pressure, kN
- S – Sheet metal thickness, mm
- L – Sheet metal length, mm
- V – Width of lower die opening, mm

**Formula #2**

**P=1.42 σbS²*L/V**

- P – Bending force (KN)
- S – Plate thickness (mm)
- L – Plate width (m)
- V – Bottom die slot width (mm)
- σb – Tensile strength (Mpa)

If you would like to gain a deeper understanding of how the tonnage of a press brake is calculated, you can refer to an article on the subject.

**Related reading:** How To Calculate Press Brake Tonnage?

The above article goes into detail on how to determine the required press brake tonnage using three different methods.

Actually, there is a third formula for calculating the tonnage of a press brake, which we have developed into a calculator. You will read about this knowledge later in the content.

### Press Brake Tonnage Calculator

If you are looking to determine the size of the press brake you need and quickly calculate the required bending tonnage, we have a solution for you.

Our press brake tonnage calculator, also known as a bending load calculator, makes it easy.

Simply enter the sheet metal thickness, bending length, and our recommended vee opening width, and the calculator will display the required bending force.

Get started by using the press brake tonnage calculator we have provided for you.

You can use the following press brake tonnage calculator to determine the necessary bending force for your sheet metal bending.

The calculator provides both metric and imperial units.

**The recommended V-opening width for the bottom die**

S | 0.5-3mm | 3-8mm | 9-10mm | >12mm |

V | 6*S | 8*S | 10*S | 12*S |

### New Tonnage Calculation Method

If the width-to-thickness ratio (V/S) is not equal to 9, and the radius-to-width ratio is not equal to 0.16, the above calculator will not be valid.

Please review the updated method for calculating the bending force on a press brake machine.

Use the following bending force calculator instead.

**Download Excel:**Press Brake Tonnage Calculator Excel Version

## Bending Radius

During sheet metal bending, a bending radius is required at the bending point, which should not be too large or too small, but should be selected appropriately. If the bending radius is too small, it is easy to cause cracking at the bend point, while if the bending radius is too large, the bending may rebound.

### Bending radius chart

The optimal bending radius (inner bending radius) for various materials of different thicknesses is shown in the table below.

Minimum bending radius value (mm)

Material Science | Annealing state | Cold work hardening state | ||

Corresponding position between bending curve direction and fiber direction | ||||

vertical | parallel | vertical | parallel | |

08, 10 | 0.1t | 0.4t | 0.4t | 0.8t |

15, 20 | 0.1t | 0.5t | 0.5t | 1.0t |

25, 30 | 0.2t | 0.6t | 0.6t | 1.2t |

4550 | 0.5t | 1.0t | 1.0t | 1.7t |

65Mn | 1.0t | 2.0t | 2.0t | 3.0t |

Aluminum | 0.1t | 0.35t | 0.5t | 1.0t |

Copper | 0.1t | 0.35t | 1.0t | 2.0t |

Soft brass | 0.1t | 0.35t | 0.35t | 0.8t |

Semi hard brass | 0.1t | 0.35t | 0.5t | 1.2t |

Phosphorus bronze | / | / | 1.0t | 3.0t |

The data in the table above are optimal and for reference only. In fact, the rounding of the bending blade of the manufacturer is usually 0.3, with a few bending blades having a rounding of 0.5.

For ordinary low carbon steel plates, rustproof aluminum plates, brass plates, copper plates, etc., an inner rounding of 0.2 is generally sufficient. However, for some high carbon steel, hard aluminum, and super hard aluminum, this type of bending rounding can lead to bending fractures or cracking of the outer rounding.

### Bending radius calculation formula

The following formula can be used to calculate the press brake bend radius:

**R=5*V/32**

## Min Bend Edge Size

### Minimum bending edge calculation formula

The calculation formula for the minimum bending edge is different for different bending angles, which can be found in the table below.

165° | 135° | 120° | 90° | 60° | 45° | 30° |

0.51×V | 0.55×V | 0.58×V | 0.71×V | 1×V | 1.31×V | 1.94×V |

### Minimum bending height reference table

**L-bending**

Reference table for inner bending radius R and minimum bending height of cold-rolled thin steel plate materials:

Serial number | Material thickness | Width of concave groove | Punch R | Minimum bending height |

1 | 0.5 | 4 | 0.2 | 3 |

2 | 0.6 | 4 | 0.2 | 3.2 |

3 | 0.8 | 5 | 0.8/0.2 | 3.7 |

4 | 1.0 | 6 | 1/0.2 | 4.4 |

5 | 1.2 | 8 (or 6) | 1/0.2 | 5.5/4.5 |

6 | 1.5 | 10 (or 8) | 1/0.2 | 6.8/5.8 |

7 | 2.0 | 12 | 1.5/0.5 | 8.3 |

8 | 2.5 | 16（14） | 1.5/0.5 | 10.7/9.7 |

9 | 3.0 | 18 | 2/0.5 | 12.1 |

10 | 3.5 | 20 | 2 | 13.5 |

11 | 4.0 | 25 | 3 | 16.5 |

**Z-bending**

The minimum bending dimension L for Z-bending of sheet metal with different thicknesses is shown in the table below:

Minimum height of z-bend:

Serial number | Material thickness | Width of concave groove | Punch R | Z-bend height L |

1 | 0.5 | 4 | 0.2 | 8.5 |

2 | 0.6 | 4 | 0.2 | 8.8 |

3 | 0.8 | 5 | 0.8/0.2 | 9.5 |

4 | 1.0 | 6 | 1/0.2 | 10.4 |

5 | 1.2 | 8（6） | 1/0.2 | 11.7（10.7） |

6 | 1.5 | 10（8） | 1/0.2 | 13.3（12.3） |

7 | 2.0 | 12 | 1.5/0.5 | 14.3 |

8 | 2.5 | 16（14） | 1.5/0.5 | 18.2（17.2） |

9 | 3.0 | 18 | 2/0.5 | 20.1 |

10 | 3.5 | 20 | 2 | 22 |

11 | 4.0 | 25 | 3 | 25.5 |

**Press Brake Tonnage Chart**

The press brake tonnage chart below can assist you in determining the necessary bending force with ease.

For instructions on how to read a press brake tonnag chart, please refer to this post.

**See also:**

- Air Bending Force Chart: The Most Authoritative Data From Amada
- Download Press Brake Tonnage Chart (in PDF)

**Data of V, R, B**

Below press brake tonnage chart is from Amada:

## Hemming & Seaming Tonnage Chart For Mild Steel & Stainless Steel

Hemming is a type of bending that requires a higher amount of tonnage compared to standard air bending.

The following tables illustrate the tonnage needed for hemming and seaming operations.

**Hemming & Seaming Tonnage Chart For Mild Steel**

Note: Required tonnage is given per 1-meter length

**Hemming & Seaming Tonnage Chart For Stainless Steel**

Note: Required tonnage is given per 1-meter length

## Bending Rebound

**Bending rebound angle:**

Δα = b – a

where:

b – Actual angle of the workpiece after the rebound

a – Angle of the die

**Size of rebound angle:**

The rebound angles for 90° single angle air bending are shown in the table below.

Material | r/t | Thickness t（mm） | ||

<0.8 | 0.8~2 | >2 | ||

Low carbon steel | <1 | 4° | 2° | 0° |

Brass, σb=350MPa | 1~5 | 5° | 3° | 1° |

Aluminum, zinc | >5 | 6° | 4° | 2° |

Medium carbon steel, σb=400-500MPa | <1 | 5° | 2° | 0° |

Hard brass, σb=350-400MPa | 1~5 | 6° | 3° | 1° |

Hard copper, σb=350-400MPa | >5 | 8° | 5° | 3° |

High carbon steel, σb＞550Mpa | <1 | 7° | 4° | 2° |

1~5 | 9° | 5° | 3° | |

>5 | 12° | 7° | 6° |

**Factors affecting rebound and measures to reduce rebound:**

- Material strength: The rebound angle is proportional to the yield point of the material and inversely proportional to its elastic modulus E. For sheet metal parts with high precision requirements, low carbon steel should be selected as much as possible to reduce rebound, and high carbon steel, stainless steel, etc. should be avoided.
- Relative bending radius r/t: The larger the relative bending radius r/t, the smaller the deformation and the greater the rebound angle Δα. This is a very important concept. The bending radius of sheet metal should be as small as possible, considering the material performance, which is conducive to improving accuracy. It should be noted to avoid designing large arcs, such as the example shown below, which can cause difficulty in production and quality control.

## Safety Considerations

When using a press brake tonnage calculator, it is important to consider safety factors in order to prevent accidents and protect operators. In this section, we will discuss two key aspects: avoiding overloading and proper maintenance.

### Avoiding Overloading

One of the main safety considerations when calculating press brake tonnage is ensuring that the machine is not overloaded. Overloading can cause damage to the equipment, and in extreme cases, it can lead to serious accidents. To calculate tonnage limits, apply a safety factor to your calculations.

Some tips to avoid overloading include:

- Regularly updating the tonnage calculator with the latest material properties
- Using a calculator that considers the material type, die opening, bend length, and material thickness
- Consulting with experienced operators or engineers when in doubt

### Proper Maintenance

Proper maintenance is another essential safety consideration when using a press brake. Regular inspections and maintenance ensure that the machine is in optimal condition and can accurately perform calculations.

Some tips for proper maintenance include:

- Following the manufacturer’s guidelines for regular maintenance and inspections
- Checking and calibrating measuring devices to ensure accurate tonnage calculations
- Inspecting the tooling and dies for wear or damage

By taking into account safety considerations such as avoiding overloading and ensuring proper maintenance, operators can work with a press brake confidently and efficiently.

## FAQs

**1. What is the formula for brake press tonnage? **

There are two formulas for press brake tonnage calculation, one is **P=650 S²L/V (σb=450N/mm²)** and the other one is

**P=1.42**.

*σb*S²*L/V**2. How do you calculate press brake machine load? **

You can use these two formulas **P=650 S²L/V (σb=450N/mm²)** and

**P=1.42**or use the press brake tonnage calculator to calculate press brake machine load.

*σb*S²*L/V**3. How big of a press brake do I need? **

The size of the press brake you need depends on the maximum length and thickness of the material you intend to bend. A larger brake is needed for longer or thicker material. It’s also essential to consider the complexity of the bend (simple or complex, acute or obtuse) as it could impact the tonnage required.

**4. How do you read a press brake tonnage chart?**

In this post, we write an example to teach you how to read a press brake tonnage chart. You can read it to learn the details.

## Conclusion

I believe that by reading this article, you will clearly understand how to choose the right tonnage for a press brake.

It’s important to know that if the machine’s tonnage is too large, it will be a waste of money; if the tonnage is too small, it won’t be able to do the job. We hope that our press brake tonnage calculator can assist you in selecting the appropriate press brake for your needs.