How do I check press brake tooling load?
Calculate the force per metre of bend from the thickness, die opening and material, then compare it with the rated load marked on the punch or die. Tooling fails when the load per metre exceeds its rating, not when the machine runs out of tonnage.
Why is the load per metre the number that matters?
A press brake can produce far more force than a punch or die can carry. The machine rating protects the machine; the tool's rated load per metre protects the tool. Exceeding it can crack or burst the tool, and the failure is sudden and dangerous.
How do I calculate the load per metre?
Use the air bending formula with a one metre bend length, which gives tonnes per metre directly: F = 1.42 · σb · 1000 · t² / (1000 · V), in kilonewtons, divided by 9.81 for tonnes.
| t (mm) | V = 6 | V = 8 | V = 12 | V = 16 | V = 20 | V = 25 | V = 32 |
|---|---|---|---|---|---|---|---|
| 1.0 | 10.9 | 8.1 | 5.4 | 4.1 | 3.3 | 2.6 | 2.0 |
| 2.0 | 43.4 | 32.6 | 21.7 | 16.3 | 13.0 | 10.4 | 8.1 |
| 3.0 | 97.7 | 73.3 | 48.9 | 36.6 | 29.3 | 23.4 | 18.3 |
| 4.0 | 173.6 | 130.2 | 86.8 | 65.1 | 52.1 | 41.7 | 32.6 |
| 6.0 | 390.7 | 293.0 | 195.3 | 146.5 | 117.2 | 93.8 | 73.3 |
What limits the load a tool can take?
The tool's section, the hardness of the steel, the heat treatment and the geometry of the tip. A sharp acute punch carries the highest load per millimetre because the force is concentrated on a narrow tip.
| Factor | Effect on the limit |
|---|---|
| Narrow punch tip | Lowers it, because the load concentrates |
| Short die section | Lowers it, because fewer segments share the load |
| High-hardness tool steel | Raises it, up to the point where it becomes brittle |
| Segmented tooling | Distributes the load if the segments are aligned and seated |
| Worn or damaged seating | Lowers it, because the load path is uneven |
Related technical pages
Tonnage calculator
Total force for a specific bend, not per metre.
Tonnage chart
Look-up table of tonnes per metre by thickness and opening.
Acute punches
Narrow-tip profiles, where the load limit is most easily exceeded.
Tooling hardness and steel grades
Why hardness and section decide the rated load.
Next step
Send us the part details and the tooling you intend to use and we will confirm the load per metre against the tool rating.
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