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How many tons (how big) press brake do you really need? Or how to calculate press brake tonnage?

The answer is the same.

For determining the hydraulic bending force or the tonnage of the press brake that is required to bend the sheet metal in a specific thickness, you have totally the following THREE methods:

**By the press brake tonnage chart****By the bending force calculation formula****By the press brake tonnage calculator**

Only after the tonnage of the press brake is confirmed, then you can spend your time taking other factors (press brake components, toolings, controllers, etc) into consideration before making your decision to purchase the press brake.

In this article, we will show you how to determine the required bending force by your sheet metal.

## 1. Press Brake Tonnage Chart

The following press brake tonnage chart is used by many press brake manufacturers both in China and abroad countries.

We know that many press brake suppliers are using a different chart, but most of them are similar and the final result will almost the same.

So just take one of them as your reference.

**Note:** if there are no special requirements for the bending radius, the slot width V should be 8-10 times plate thickness.

The tonnage as shown in the above press brake tonnage chart is calculated based on the sheet metal with the tensile strength **σb=450N/mm²** and **length L=1m**.

Now you have the bending force chart, the question is how to find the press brake tonnage in the above chart?

First, you need to know what does “S” “V” “B” “R” means in the above chart.

Check out the following pictures you will understand what do they mean.

- P = Bending force
- S = Thickness of sheet
- V = Vee opening of the bottom die
- B = Min bending flange
- R = Inner radius

Let’s say the thickness of your metal sheet S=4mm, generally the vee opening of the bottom die is 8 times the thickness of the sheet.

However, for the thicker plate, the vee opening should be bigger.

The following recommend vee opening of the bottom die can be your reference.

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

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

Now we back to the chart, find the S data in the chart which is “4”, and now we know the “V” should be 4*8=32. And you can see that the intersection of the row and column where the “S” and “V” stay is “330”. The unit of “330” is “KN”.

Now we know that for bending the sheet metal with 4mm thickness and 1m length, the required tonnage is 330KN.

If bend the 4mm sheet in 3 meters, then the tonnage should be 330*3=990KN, which equals to 101 Ton.

Here we come to the conclusion: you should choose at least 100 ton press brake.

However, we recommend you choose the bigger tonnage like 120Ton because if the press brake works in full load for a long time, the service life of the machine will be shortened.

**2. Bending Force Calculation Formula**

Except for the bending chart, you can also use the bending force formula to calculate the required bending force by yourself.

### #1 What Is The Bending Force Calculation Formula?

The press brake bending force calculation formula is:

**P=650 S²L/V (σb=450N/mm²)**

- P: bending force (KN)
- S: plate thickness (mm)
- L: plate width (m)
- V: bottom die slot width (mm)

**For example:**

Plate thickness S=4mm, width L=3m, σb=450N/mm²

Generally slot width V=S*8

Therefore P=650*4²*3/4*8=975 (KN) = 99.5 (Ton)

The result is very close to the data in the bending force chart.

As you can see, method #1 to calculate the press brake tonnage is based on the mild steel material.

What if the material is stainless steel, aluminum or brass?

It’s simple, multiply the results calculated by the above formula by the coefficients in the following table:

Material | Coefficients |

Mild Steel | 1 |

Stainless Steel | 1.6 |

Aluminum | 0.65 |

Brass | 0.5 |

### #2 Tonage Calculation Formula

Another press brake tonnage calculation formula is:

**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)

**For example:**

Plate thickness S=4mm, width L=3m, σb=450N/mm²

Generally slot width V=S*8

Therefore P=1.42*450*4²*3/4*8=958.5 (KN) = 96 (Ton)

For bending the sheet metal with different materials, the key point is to find out the tensile strength of the specific material, then you will get the required bending force by the above formula.

The tensile strength table below can be the reference:

Material | Soft (N/mm²) | Hard (N/mm²) |
---|---|---|

Lead | 25 – 40 | – |

Tin | 40 – 50 | – |

Aluminum | 93 | 1710 |

Aluminum Alloy Type 4 | 230 | 480 |

Duralumin | 260 | 480 |

Zinc | 150 | 250 |

Copper | 220 – 280 | 300 – 400 |

Brass (70:30) | 330 | 530 |

Brass (60:40) | 380 | 490 |

Phosphor Bronze / Bronze | 400 – 500 | 500 – 750 |

Nickel Silver | 350 – 450 | 550 – 700 |

Cold Rolled Iron | 320 – 380 | – |

Steel .1% Carbon | 320 | 400 |

Steel .2% Carbon | 400 | 500 |

Steel .3% Carbon | 450 | 600 |

Steel .4% Carbon | 560 | 720 |

Steel .6% Carbon | 720 | 900 |

Steel .8% Carbon | 900 | 1100 |

Steel 1.0% Carbon | 1000 | 1300 |

Silicon Steel | 550 | 650 |

Stainless Steel | 650 – 700 | – |

Nickel | 440 – 500 | 570 – 630 |

**New Bending Force Calculation Formula**

In free bending, the opening width V of the lower die selected is 8 to 10 times the sheet thickness S.

And the press brake manufacturers always list the corresponding values of the die width V and the inner diameter r of the bending workpiece on the bending force parameter table.

Generally **r=(0.16~0.17)V**

However, when the inner radius r is not (0.16-0.17)V, then the above two calculation formula is not applied any more.

Then you should refer to the new calculation method to calculate the necessary bending force or press brake tonnage.

The following is the calculator:

**3. Press Brake Tonnage Calculator**

Finally, I strongly suggest you use the following press brake tonnage calculator because this is probably the best and easiest way to calculate the required bending force.

**Further reading:**

There is one similar press brake bending chart made by one European professional press brake toolings manufacturer.

This can also be your reference, below is it:

**Related reading:** How to Calculate Bending Force in Air Bending (Sheet Metal)?

Nakulhello sir,

I need to be perform bend with inner radius of r 47 bend angle is 90 degree , material is ss 304 with 3 mm thickness , could you please suggest best suitable die. I have 260 t machine .

ShaneSure, I will send an email to you.