Sheet Metal Bending Table
Sheet metal bending table — V-die selection and tonnage
Which die opening for which thickness, how much press force it needs, the inside radius you end up with, and the shortest flange you can form. Switch between metric and imperial.
The formulas, so you can check them
Force per metre (kN) = 1.33 × Rm × T² ÷ V
Inside radius = 0.156 × V
Minimum flange = (V ÷ 2) + T
Recommended die ≈ 8 × T, rounded to the nearest available
Rm = tensile strength in N/mm² · T = thickness · V = die opening. Mild steel is taken as Rm 450.
These are the standard air bending relationships. I have checked them against published press brake charts: 2 mm in a V16 comes out at 15.3 t/m against a published 15, and 6 mm in a V50 gives 43.9 against 43. Close enough to quote from, not close enough to skip a test bend.
Why 8 × T
Die opening is the decision everything else follows from. Too narrow and the tonnage climbs sharply, the tooling marks the material, and the outside of the bend can crack. Too wide and the inside radius grows, the bend line becomes harder to hold, and short flanges drop into the die.
Six to twelve times thickness is the usual working range, and eight is the default most shops reach for. The table uses 8×T rounded to the nearest standard die.
Material factors
Force scales directly with tensile strength. The calculator handles this; the table is mild steel.
| Material | Rm (N/mm²) | Force vs mild steel |
|---|---|---|
| Mild steel S235 / DC01 | 450 | 1.00 × |
| Stainless 304 | 600 | 1.33 × |
| Aluminium 6061-T6 | 310 | 0.69 × |
| Aluminium 5052 | 230 | 0.51 × |
What this does not cover
These figures are for air bending, the most common method. Bottoming needs several times the force, and coining several times more again.
They also assume a 90° bend. Sharper angles need more force. And they say nothing about springback — the table tells you the force to reach an angle, not the angle you will have once the punch lifts. That is covered on the springback page.