Press Brake Tonnage Calculator
Bending force in kN and tonnes for air bending, plus minimum flange and the natural inside radius for the die.
Results
What this tool does
Air bending force depends on four things and not one of them is the machine: the strength of the material, the square of its thickness, the length of the bend and the width of the V die underneath. Because thickness is squared, going from 2 mm to 3 mm more than doubles the tonnage. The die opening is the lever you actually control on the shop floor, and widening it is the cheapest way to bring a job inside the capacity of the press you have.
Formula
F = 1.42 Rm t² L ÷ V (air bending)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
rm | Tensile strength | N/mm² |
tt | Material thickness | mm |
vv | V die opening | mm |
lb | Length of the bend | m |
FK | Bending force | kN |
FT | Bending force | t |
MF | Minimum flange | mm |
IR | Inside bend radius | mm |
FM | Force per metre of bend | kN/m |
Worked example
- Tensile strength450 N/mm²
- Material thickness3 mm
- V die opening20 mm
- Length of the bend2 m
- Bending force575.1 kN
- Bending force58.64 t
- Minimum flange12.60 mm
- Inside bend radius3.20 mm
- Force per metre of bend287.6 kN/m
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.
Frequently asked questions
How do I choose the die opening?
The usual shop rule is a V opening of six to eight times the material thickness for sheet up to about 3 mm, and ten to twelve times for thicker plate. A wider V cuts the tonnage sharply — the force is inversely proportional to it — but it also increases the inside radius and the minimum flange you can still bend, so it is always a compromise between the machine you have and the part you need.