Estimate the force for a conventional 90° air bend. All lengths are in millimetres; force is shown in metric tonnes-force.
Estimates only: confirm material tensile strength, bend geometry, machine capacity and the rated load of every punch, die and holder—including short segments. Not for bottoming, coining, hemming or high-strength plate setup approval.
For ordinary mild-steel air bending, start around 8 × thickness. Thinner sheet may use around 6 × thickness after checking the tooling and bend requirements; thicker plate often needs 10–12 × thickness. These are starting guides, not universal minimum safe openings.
| Thickness (mm) | 6 × thickness — narrower reference | 8 × thickness — usual starting point |
|---|---|---|
| 0.8 | 4.8 mm | 6.4 mm |
| 1 | 6 mm | 8 mm |
| 1.5 | 9 mm | 12 mm |
| 2 | 12 mm | 16 mm |
| 2.5 | 15 mm | 20 mm |
| 3 | 18 mm | 24 mm |
| 4 | 24 mm | 32 mm |
| 5 | 30 mm | 40 mm |
| 6 | 36 mm | 48 mm |
A narrower V increases force and marking; the required inside radius and flange length can rule it out. For mild steel, the natural inside radius is roughly 0.16 × V. Check the actual die’s minimum flange specification; about 0.7 × V is a preliminary 90° reference only.
Stainless, aluminium temper, grain direction and high-strength grades need material-specific checks. Ask Carter if you need a smaller V than the usual starting point.
Select a sheet thickness, then tap a V-opening to use it in the calculator. Multiply tonnes per metre by bend length in metres for total force.
Shows V-openings within the 6–12 × thickness reference window. A displayed number does not certify a safe tool combination.
Force increases with material strength, bend length and thickness squared, and falls as the V-opening widens. This reference model uses F = 55 × S² / V × L / 1000 × Rm / 450, giving metric tonnes with S, V and L in mm and tensile strength Rm in N/mm². Check actual material properties and tooling limits before use.
HEMMING REFERENCE
Force in metric tonnes per metre of hem. S is sheet thickness; A is the overall open-hem height; 2S is the nominal closed-hem thickness.
| Sheet mm | Height A mm | Tonnes/m |
|---|---|---|
| 0.6 | 3 | 9 |
| 0.8 | 3 | 12 |
| 1 | 3.5 | 15 |
| 1.25 | 3.5 | 17 |
| 1.5 | 4.6 | 22 |
| 2 | 5.5 | 30 |
| 2.5 | 6.5 | 55 |
| 3 | 8 | 70 |
| Sheet mm | Height 2S mm | Tonnes/m |
|---|---|---|
| 0.6 | 1.2 | 23 |
| 0.8 | 1.6 | 32 |
| 1 | 2 | 40 |
| 1.25 | 2.5 | 50 |
| 1.5 | 3 | 63 |
| 2 | 4 | 80 |
| 2.5 | 5 | 90 |
| 3 | 6 | 100 |
| Sheet mm | Height A mm | Tonnes/m |
|---|---|---|
| 0.6 | 3 | 15 |
| 0.8 | 3 | 20 |
| 1 | 3.5 | 25 |
| 1.25 | 3.5 | 26 |
| 1.5 | 4.6 | 38 |
| 2 | 5.5 | 50 |
| Sheet mm | Height 2S mm | Tonnes/m |
|---|---|---|
| 0.6 | 1.2 | 35 |
| 0.8 | 1.6 | 50 |
| 1 | 2 | 60 |
| 1.25 | 2.5 | 80 |
| 1.5 | 3 | 95 |
| 2 | 4 | 130 |
Total force = tonnes per metre × hem length in metres. For example, 1 mm sheet at 45 kgf/mm² needs 40 t/m for a closed hem: a 500 mm hem gives a 20-tonne reference load.
These reference values apply to the strengths and hem geometries shown. Check the material, tooling and machine load limits. The air-bending calculator does not calculate hemming force.
Hemming tools may also be listed as edge-flattening, flattening-punch or safety-edge tooling. Find these in the tooling catalogue under Hemming & joggle tools, then contact Carter to confirm the right profile for your machine and material.
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