01 — The engineA real table, not a textbook formula.
This calculator doesn't run a generic formula: it runs the PG SRL technical table — the same one working inside our configurator — with the tonnage per linear metre already tabulated for every thickness × V-die pair, on reference mild steel (UTS≈400 N/mm²). The calculation is:
- t/m is the specific force of the die opening: shop-floor experience turned into numbers, not handbook constants.
- L is the bend length in metres. A 2.5 m bend counts as 2.5.
- k is the material coefficient: 1.0 mild steel, 1.5 stainless, 0.45 aluminium — average values, a specific alloy can swing ±15%.
The physics underneath is still the handbook one — force grows with thickness squared and drops with die width (F ∝ UTS·S²/V) — but the pure textbook formula, with its literature constant, underestimates by about 15% the force we actually measure on the shop floor: friction, tooling tolerances and real materials don't live in book constants. That's why we trust the table.
02 — The V-dieThe real rules for choosing it.
The rule the table applies (and that you'll find preselected in the calculator):
| Thickness | Recommended V | Why |
|---|---|---|
| under 1 mm | 10 – 13 × S | minimum die sizes exist (V6, V8): the ratio goes up by necessity |
| 1 – 12 mm | ≈ 8 × S | the right compromise between force, radius and flange |
| 15 mm and up | ≈ 10 × S | heavy plate: wider to contain force and cracking |
In the calculator you can also pick the other dies available for your thickness: a V narrower than recommended marks the part and raises the force, a wider one lowers it but enlarges inner radius and minimum flange — if your part has a short flange, the wide V won't fit it.
03 — Radius and flangeThe two geometric consequences of the V.
In air bending the inner radius is not set by the punch: it's set by the die opening. In the table the inner radius ≈ V/6 and the minimum flange B ≈ 0.7 × V — the shortest leg the die can grip: shorter bends need dedicated tooling (narrow blades, 88° tools).
04 — SpringbackWhy you always bend "a little further".
When the force is released, the sheet elastically recovers part of the deformation: that's springback. It grows with the material's yield-to-modulus ratio and with the radius-to-thickness ratio — which is why stainless and high-strength steels "come back" more than mild steel. On the shop floor it's compensated by overbending. The typical ranges shown by the calculator:
| Material | Typical overbend |
|---|---|
| Mild steel (S235–S275) | 0.5 – 1.5° |
| Austenitic stainless (304/316) | 1 – 3° |
| Aluminium | 1.5 – 3° |
| High-strength steels (S700+) | 3 – 6° |
The numerical controls on our press brakes compensate springback in the machine with automatic angle correction — the ranges above help you understand the phenomenon, they don't replace the correction.
05 — LimitsWhat this tool does not tell you.
- Acute angles (≤60°): force grows beyond the table — case-by-case evaluation.
- Coining: the calculator applies an indicative ×4.5 factor, but literature ranges from 3× to 10× depending on geometry and material.
- Hemming: the folded edge is formed in two stages (air pre-bend at ~26-35° with a sharp punch, then flattening of the leg outside the die). The factor on the air bend is ×1.9 up to 2 mm and ×3 above, aligned with tooling makers' benchmarks. Typical of fine architectural sheet metal: 0.6-1.5 mm, 3 mm max. For a fully closed hem (double thickness) the force reference is coining.
- Coatings (galvanised, pre-painted): +5-10% apparent strength.
- Bends longer than the machine: that's a tandem configuration.
You have the parameters. Now the machine.
Take force, length and material into the configurator: in 7 steps you get a press brake sized on your actual work, with a quotation. Or write to us with two lines about the part you bend: we reply within 24 hours.
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