What V-die opening should I use?
For general air bending, choose a V-die opening of about eight times the material thickness for mild steel, ten times for stainless steel and high-strength steel, and six times for aluminium. The opening you choose also fixes the inner radius and the minimum flange length.
How is the recommendation worked out?
The opening follows the eight times rule adjusted per material, because stainless steel and high-strength steel spring back more and aluminium less. With the opening chosen, the inner radius is about 0.16 times the opening and the minimum flange is about half the opening plus the thickness.
| Quantity | Rule used here | Why it matters |
|---|---|---|
| Die opening V | 8t mild / 10t stainless and HSLA / 6t aluminium | Sets force, radius and minimum flange |
| Inner radius r | ≈ 0.16 × V in air bending | Must not be smaller than the drawing allows |
| Minimum flange | ≈ V/2 + t | Shorter flanges will not sit on the die shoulders |
| Force | F = 1.42 · σb · L · t² / (1000 · V) | Must stay inside the tooling and machine ratings |
What standard V-die openings are available?
Press brake dies are supplied in a standard series of openings. Choose the nearest standard size to the calculated value rather than an arbitrary width.
| Standard openings (mm) |
|---|
| 4, 6, 8, 10, 12, 16, 20, 25, 32, 40, 50, 63, 80, 100 |
When should I deviate from the eight times rule?
Use a narrower opening when the drawing demands a tight inner radius or a very short flange, and a wider one when the material is thick, high strength, or has a cosmetic surface that must not be marked. Each deviation changes the force, so re-check the tonnage.
- Narrower than 8t: tighter radius and shorter flange, but higher force and more marking risk.
- Wider than 8t: lower force and less marking, but a larger radius and a longer minimum flange.
- Below 6t: check the punch tip load rating, because the tip takes the concentrated force.
- Cosmetic surfaces: consider a urethane or anti-mark die before widening the V.
Related technical pages
V-die opening selection chart
Full table of opening against radius, minimum flange and tonnage.
Tonnage calculator
Calculate the force for a specific thickness, length and opening.
Minimum flange calculator
Check whether the flange on the drawing can actually be formed.
Press brake dies
Die types, including single-V, 2V, multi-V and urethane.
Next step
Tell us the material, thickness and the radius on the drawing and we will confirm the die opening and the tooling needed.
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