Press brake bending chart by material: force, V-die, inside radius and minimum flange

01 — The chartFive numbers for every bend.

A bending chart answers one question: with this sheet, which V-die do I use and how much force does it take? For every thickness × die pair it gives five numbers:

• the bending force in t/m, tonnes per metre of bend;
• the recommended die for that thickness;
• the inside radius Ri the die leaves on the part;
• the minimum flange B, the shortest leg the die can still hold;
• and, by difference, the alternative dies, narrower or wider.

It applies to air bending at 90°, which covers the vast majority of work. The PG chart starts from S235 steel with UTS ≈ 420 N/mm², the same basis as the tooling makers’ charts.

02 — How to read itFrom the thickness to the red cell.

In the PG chart the dies are in rows and the thicknesses in columns:

1. find the thickness in the top row;
2. go down the column to the red cell: that is the recommended die;
3. read the force in t/m in the cell; on the same row, to the left, you find V-die, inside radius and minimum flange;
4. multiply the force by the bend length in metres.

The recommended die is about 8 times the thickness from 1 to 12 mm and about 10 times from 15 mm up. Below 1 mm the ratio has to rise, because the smallest dies are V6 and V8. The inside radius is about V/6, 16% of the die opening; the minimum flange about 0.7 × V.

03 — The materialSame bend, different force.

Force grows with the strength of the material. To go from S235 to another material you multiply by a coefficient k. The PG coefficients come from the material database of the ESA CNC we fit on our press brakes: k is the strength of the material divided by that of S235.

So you don’t have to do the sum in the workshop, the PG chart exists already multiplied for each of these materials: one sheet per material, to hang next to the press brake.

04 — Three examples3 mm, 2.5 m bend, V25 die.

• S235 steel: 24 t/m × 2.5 m = 60 t.
• Stainless AISI 304: 24 × 1.57 ≈ 37.7 t/m; × 2.5 m ≈ 94 t.
• Aluminium 5754: 24 × 0.59 ≈ 14.2 t/m; × 2.5 m ≈ 35 t.

Same sheet, same die: from aluminium to stainless the force almost triples. That is why choosing the press brake always starts from the hardest material you really work, not from the most frequent one.

05 — The mistakesFour errors that cost.

• Die too narrow: at 3 mm the V20 needs 30 t/m instead of 24, 25% more, and marks the part.
• Flange shorter than the minimum: with the V25, below 17.5 mm the sheet slips into the die. Either use a narrower die and accept more force, or use dedicated tooling.
• Radius forgotten in the flat pattern: the inside radius is set by the die, not the punch. With the V25 it is about 4.2 mm, and that is the value for the flat-pattern calculation.
• Hardox treated like steel: wear plates do not follow the mild-steel chart. They need wider dies, 12–18 times the thickness, and the minimum radius given by the steel maker.

06 — The chartYour material’s sheet, by email.

These values are for choosing machine and tooling. On the machine the ESA CNC recalculates the force with its own material database, and a real batch can differ by a few per cent.

07 — FAQThe quick answers.