BIZOMAT MAKEOS · Fabrication
Press Brake Bending Force
What tonnage does this V-die bend need, and is the press brake big enough?
Bending force for air bending in a V-die from length, thickness, tensile strength and die opening, with force per metre and comparison with the press brake capacity.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bend length | mm | Length of the bend line. |
| Material thickness | mm | Sheet or plate thickness. |
| Tensile strength | MPa | Ultimate tensile strength of the material. |
| V-die opening | mm | Width of the V-die opening (often about 8 × thickness for air bending). |
| Die factor | 1.0 gives the handbook approximation F = L T² UTS ÷ W; many press brake makers use about 1.33 for air bending. Bottoming and coining need several times more. | |
| Press brake capacity | kN | Rated tonnage of the press brake (1 t ≈ 9.81 kN). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Bend length
- What it is
- The length of the bend line along the part, which is the length of punch and die in contact with the sheet.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force rises in direct proportion; force per metre does not change.
- Get it right
- Use the length actually bent; a short part bent in the middle of a long die still loads only that length.
What this means: Material thickness
- What it is
- The thickness of the sheet or plate being bent.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force rises with the square of thickness.
- Get it right
- Measure the actual thickness; small increases matter.
What this means: Tensile strength
- What it is
- The ultimate tensile strength of the sheet, from its mill certificate or material specification.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 3000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 450 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force rises in direct proportion.
- Get it right
- High-strength grades need much more force than mild steel of the same thickness.
What this means: V-die opening
- What it is
- The width of the V-shaped opening in the lower die, measured across the top edges of the V.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 24 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A wider opening lowers the bending force but gives a larger inside radius.
- Get it right
- Measure across the die shoulders, not the depth of the V.
What this means: Die factor
- What it is
- A multiplier on the basic air-bending force formula that allows for die and material effects. The guide explains what different values represent; press brake makers publish their own.
- Units and format
- Enter a plain number with no unit. The form accepts 0.5 to 10. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.33 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force rises in direct proportion.
- Get it right
- This tool covers air bending; bottoming and coining need far more force than any air-bending factor gives.
What this means: Press brake capacity
- What it is
- The maximum force the press brake is rated for, from its nameplate or manual.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 1000000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only changes the utilisation and the pass or fail line.
- Get it right
- Enter kilonewtons; one tonne-force is about 9.81 kN.
Method and formulas
- F = k × L × t² × UTS ÷ V.
- Force per metre = F ÷ L × 1000.
- Example: 2000 mm of 3 mm, 450 MPa sheet in a 24 mm die needs 448.88 kN.
Limitations
- Air bending in a V-die; bottoming and coining forces are much higher.
- Long bends near full capacity can deflect the beam and bed; check the maker’s load-per-length limit.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check press brake tonnage before quoting a bend
- Choose a V-die opening
- Compare materials and thicknesses
Who it is for
- Fabrication supervisors
- Manufacturing engineers
- Estimators
What you get
- Bending force
- Force per metre
- Utilisation of the press capacity
- Die opening to thickness ratio
Interpreting the result
- Do not concentrate full tonnage on a short length; follow the maker’s maximum force per metre.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1346–1353. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Press brake force and punching force
In Sheet Metal Parts by the Numbers
What it covers: Estimate air bending force from a manufacturer's formula converted to SI, see how bottoming multiplies it, estimate punching force from cut perimeter, and why small holes break punches.
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