How to Calculate Press Brake Bending Force?

What size press brake do you actually need in terms of tonnage, and how can you calculate the press brake tonnage? The answer to both questions is the same.

There are three methods for determining the hydraulic bending force or the tonnage of the press brake required to bend sheet metal of a specific thickness:

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

Once you have confirmed the tonnage of the press brake, you can then consider other factors such as press brake components, tooling, controllers, etc. before making a purchase decision.

In this article, we will guide you in determining the required bending force for your sheet metal.

Press Brake Tonnage Charts

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

Although different suppliers may use slightly different charts, the final results are usually comparable, as most of them are similar.

Therefore, you can use any of them as a reference.

Note: If there are no specific requirements for the bending radius, the V-slot width should be 8 to 10 times the plate thickness.

How to Read Press Brake Tonnage Charts?

The tonnage indicated in the press brake tonnage chart is based on a sheet metal with a tensile strength of σb=450N/mm² and a length of L=1m.

Now that you have the bending force chart, the next step is to understand how to locate the press brake tonnage in the chart.

To do this, you first need to know the meanings of “S,” “V,” “B,” and “R” in the chart.

Please refer to the accompanying images to comprehend their meanings.

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

Assuming your metal sheet has a thickness of 4mm, the general rule is that the V-opening of the bottom die should be 8 times the sheet’s thickness.

However, when dealing with thicker plates, a larger V-opening is necessary.

The recommended V-openings listed below can serve as a reference:

Let’s consider a metal sheet with a thickness of 4mm.

Typically, the vee opening of the bottom die should be 8 times the thickness of the sheet. However, for thicker plates, the vee opening should be larger.

To determine the required press brake tonnage, we need to refer to the press brake tonnage chart.

First, find the row with a thickness value of “4” and then determine the corresponding vee opening value of 32 (4 * 8).

The intersection of the row and column where the “4” and “32” values meet indicates a tonnage of 330 KN.

If we need to bend a 4mm sheet that is 3 meters long, the required tonnage would be 330 * 3 = 990 KN, or approximately 101 tons. In this case, we recommend choosing a press brake with a tonnage of at least 100 tons.

However, it is better to opt for a larger tonnage, such as 120 tons, as the service life of the machine will be longer if it operates at full load for extended periods of time.

Bending Force Calculation Formula

In addition to using the bending chart, you can also calculate the required bending force using the bending force formula.

#1 What Is The Bending Force Calculation Formula?

The press brake bending force calculation formula is:

P=650S²L/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 obtained using the bending force formula is very similar to the data in the bending force chart.

Note that method #1 to calculate the press brake tonnage is based on mild steel material.

If the material is stainless steel, aluminum, or brass, you can easily adjust the calculation results by multiplying them with the coefficients listed in the following table.

#2 Tonage Calculation Formula

Another press brake tonnage calculation formula is:

P=1.42σbS²*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=1.424504²3/48=958.5 (KN) = 96 (Ton)

The key to bending sheet metal with different materials is to determine the tensile strength of that specific material, then calculate the required bending force using the above formula.

The tensile strength table below can be the reference:

New Bending Force Calculation Formula

In air bending, the opening width V of the lower die is typically chosen to be 8 to 10 times the thickness of the sheet, S.

Press brake manufacturers often list the corresponding values of the die width, V, and the inner diameter, r, of the bending workpiece on their bending force parameter table.

As a general rule, r=(0.16~0.17)V

However, when the inner radius is not equal to (0.16-0.17)V, the above calculation formula is no longer applicable.

In these cases, you must refer to a new calculation method to determine the required bending force or press brake tonnage.

The following is the calculator:

Press Brake Tonnage Calculator

Finally, I highly recommend using the press brake tonnage calculator as it is likely the best and most convenient method for calculating the necessary bending force.

• Press Brake Bending Force Calculator

Further reading:

There is a similar press brake tonnage chart created by a professional European press brake tooling manufacturer.

This can also serve as your reference. Here it is:

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