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Sheet metal bending
Sheet bending force calculator: thickness, steel grade, die opening and press check
The calculator works out the air bending force of a sheet on a press brake from the thickness, steel grade, bend line length and die opening. It chooses the die opening itself, shows a force range with an allowance for strength scatter, checks the press (our 2000 t one or yours) and, if the force is not enough, tells you which opening is needed. It is an estimate, not a data sheet.
Contents
Bending force calculator
Choose the steel grade, enter the thickness and the length of the bend line. The calculator picks the die opening itself, and the press can be chosen from the list or set by you.
This is an estimate. The die opening series is generic, not a list of our tooling; the 2000 t press is taken from the data on the sheet bending page. For an order we confirm the force, tooling and radius against the material and the drawing.
Request a bending calculationHow to use it
- steel grade: the list has the grades of DSTU 8539:2015 (former GOST 27772-88) and three grades of EN 10025-2; for another metal choose «own tensile strength» and enter it in MPa;
- sheet thickness and bend line length: the length is entered in metres, for a multi-sided pole section it is up to 12 m;
- die opening: «choose automatically» uses a practical rule (6, 8, 10 or 12 thicknesses depending on the sheet thickness) and the nearest value of the series; you can choose your own;
- press: «our 2000 t press» checks the force, bed length and thickness; «your own press» lets you enter the force and bed length; «no press check» only calculates the force.
What the calculator does
The tensile strength is taken from the sheet table by thickness: for one grade the value differs between ranges, for example up to 10 mm and above 20 mm. If the grade table has no value for your thickness, the nearest range is used and a separate line says so.
The result gives two numbers: the force at the minimum tensile strength from the standard and the force with a +20 % allowance for the strength scatter of a real batch. The press counts as enough if it is enough even with the allowance; «at the limit» means the sheet passes at the minimum strength but not with the allowance.
If the press is not enough, the calculator looks for the smallest die opening at which the sheet will pass, shows the nearest value from the series and the radius that results. For a sheet that passes, it shows the maximum bend line length on this press.
Below the result is a table: how the force, the radius and the press verdict change with a narrower or wider die. It is the quickest way to see whether to increase the opening.
Examples
The die opening in the examples is automatic. All examples are for air bending to about 90° and for a 2000 t press with a 12 m bend length; the tensile strength is the minimum per DSTU 8539:2015 (former GOST 27772-88).
| Sheet | Die opening, mm | Force, t/m | Total, t | With +20 %, t | Press used |
|---|---|---|---|---|---|
| C245, 6 mm, 3 m | 50 | 40.2 | 121 | 145 | 6 % |
| C245, 10 mm, 6 m | 80 | 70.7 | 424 | 509 | 21 % |
| C345, 10 mm, 12 m | 80 | 93.7 | 1124 | 1349 | 56 % |
| C345, 16 mm, 12 m | 200 | 81.0 | 972 | 1166 | 49 % |
| C345, 25 mm, 12 m | 320 | 120.2 | 1443 | 1732 | 72 % |
| C345, 25 mm, 6 m | 320 | 120.2 | 721 | 866 | 36 % |
How it is calculated
The force is calculated by the simple air bending formula: F = (1 + 4·s/A) · σв · L · s² / A. Here s is the sheet thickness, A is the die opening, L is the bend line length and σв is the tensile strength; if σв is in kgf/mm² and the dimensions are in millimetres, F comes out in kilograms-force, and after dividing by 1000 in tonnes-force. The same formula and a numerical example are analysed in the article Sheet bending force calculation.
The calculator takes the approximate inside radius for air bending as 0.16 of the die opening and the smallest flange as 0.7 of the opening. These are practical guides that depend on the material and the tool.
The die opening series in the calculator is generic (8–400 mm), not a list of our tooling. The parameters of the 2000 t press (12 m bend length, sheet up to 25 mm) are taken from the page Sheet bending on a 2000 t press.
What the calculator does not take into account
- bend angle: the calculation is for an angle of about 90°; a sharper angle needs more force, a more open one less;
- springback and the minimum radius: the calculator does not give them, see the article on sheet bending on a 2000 t press;
- the real tensile strength of the batch: it is taken from the metal certificate, while the calculator takes the standard minimum and shows a +20 % allowance;
- the condition of the sheet: cleaned burrs, the hardened zone removed after thermal cutting, the rolling direction;
- bottoming and complex sections: that is a different mode with a larger force.
What to send for an exact calculation
For an order we confirm the force and tooling against the material and the drawing. It is enough to send the steel grade and thickness, the bend line length, the angle and the inside bend radius or «the minimum possible», and the number of parts. If there is no drawing yet, KM and KMD design will help, and bending, cutting and welding are done within steel fabrication. The service requirements are on the page sheet metal bending.
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Bending force calculator: frequently asked questions
How do you calculate the bending force of a sheet on a press brake?
By the air bending formula F = (1 + 4·s/A) · σв · L · s² / A: sheet thickness, die opening, bend line length and the tensile strength of the steel. The calculator does this and adds a press check.
Which die opening should I choose?
A practical rule: about 6 thicknesses for thin sheet up to 3 mm, 8 thicknesses for 3–10 mm, 10 thicknesses for 10–12 mm and 12 thicknesses above 12 mm. A narrower opening gives a smaller radius but a larger force and a risk of cracks; a wider one gives a smaller force, a larger radius and more springback.
Why does the calculator give two force values?
The first is calculated at the minimum tensile strength from the standard, the second with a +20 % allowance for the strength scatter of a real batch of metal. If the press passes on the first but not on the second, it is «at the limit», and it is better to take a wider opening or check the sheet certificate.
Is a 2000 t press enough for a 25 mm sheet 12 m long?
By this estimate, for C345 steel at the automatic die opening of 320 mm the force is about 1443 t, and about 1732 t with the +20 % allowance, that is 72 and 87 % of the press. The final decision is made by the press data sheet, the material and the tooling.
Related products: Sheet metal bending · Steel structure design (structural and detail drawings) · Custom steel fabrication
More on this topic: Sheet bending force: what it depends on and how to estimate it, using a multi-sided pole section · Bending Sheet up to 12 m Long on a 2000 t Press: Capabilities and Examples · Flat pattern calculator for bent sheet parts: blank length from sizes, radius and K · Flat pattern of a bent part: blank length, K-factor and bend deduction
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