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 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.

Table of Contents

## 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 100ton press brake. However, we recommend you to 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 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 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 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.

**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.

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:

KrunalHi

Detailing in website so use full

Thanks

MachineMfgglad you like it.

swetambarDear sir if i choose beding radius R15 but thickness of part is 5 mm, then which v opening i have considered and what should be the minimum length of “B”.

MachineMfgfor our standard designed toolings, the “B” is 28mm. You should note the bending angle also should be took into consideration. You can refer to the following article which will show you how to select press brake dies: https://www.machinemfg.com/choose-press-brake-die/

ArunC channel size is 2780mm/530mm/12mm.

Both side height is 75mm from bottom.And radius at bend is 38mm.

How much ton hydraulic press i can use and how many nos.of identical cylinders required in a row..

ArunC channel size is 2780mm/530mm/12mm.C channel to make length wise.Before bending size of plate will be 2780mm/680mm/12mm.

Both side height is 75mm from bottom.And radius at bend is 38mm.

How much ton hydraulic press i can use and how many nos.of identical cylinders required in a row..

AaaGreat article ! Just one question – #2 in the formula 1.42 figure – where is that coming from ? Many thanks ?

MachineMfgAnybody know this?

MRMI guess it comes from 650/450 that equals 1.44 by some error.

Giovane Maia RomanE de onde saiu esses 650 ?

And where did the 650 come from?

Laser klip og bukwell written, it is a good text with very useful substance

Bhaumik PatelDear Sir,

Detailing Mail S Good Enough For General Purpose, Will you can send Calculation formula In By Mail,

With Best Regards,

Bhaumik Patel

Giovane Maia RomanE de onde saiu esses 650 ?

And where did the 650 come from?

MachineMfgThis article will answer your question:https://www.machinemfg.com/calculation-of-sheet-metal-bending-force-in-air-bending/

Jaya PrakashExcellent …Nicely Explained. Thank You…..

ShaneGlad to hear that, and you’re welcome.