How to calculate bending force

#1. By the press brake tonnage chart

Calculation of bending force together with main bending parameters allows for the operator to choose correctly the necessary tools as well as to justify the maximum requirements for bend according to the specification of press brake.


S Sheet metal thickness                                                        α Degree of bending

V Die opening                                                                          B Minimal resting part

Ri Internal radius of bend                                                    F Bending force necessary to make the bend

TS Tensile strength of material, where:

* Mild steel 45 kg/mm

* Stainless steel 80 kg/mm

* Aluminum 45 kg/mm

Determination the V as die opening:

S (mm) ≤ 0,7 0,8 – 3,0 3,1 – 9,0 9,1 – 14,0 > 14,00 Radius bending
V S * 6 S * 8 S * 10 S * 12 S * 14 R * 2 + S * 2

Determination of Ri as internal radius of bend:

Ri = (5 x V) / 32

Determination of B as the minimal resting part:

α 30° 45° 60° 90° 120° 135° 165°
B V * 1,94 V * 1,31 V * 1 V * 0,71 V * 0,58 V * 0,55 V * 0,51

Considered tonnage and parameters for mild steel for 1 meter of bending:

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.refer to the chart Determination the VNow 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 “” stay is “330”.The unit of “330”” is “KN”.
Now we know that for bending the sheet metal with 4mm thickness and 1 m length, the required tonnage is 330KN.

lf bend the 4mm sheet in 3 meters, then the tonnage should be 330*3=990KN, which equals t0 101 tons,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. By the 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*S2*L/N (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, the method #1 to calculate the press brake tonnage are 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:

#2 Formula

Another press brake tonnage calculation formula is: P=1.42*σb*S*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 fnd out the tensile strength of the specific material, then you will get the required bending force by above formula.