BIZOMAT MAKEOS · Fabrication
Press Brake Set-up: Die, Radius, Flange and Tonnage
Which V-die should I use for this bend, what inside radius and minimum flange will it give, and is the press brake big enough?
Air-bending set-up for a press brake: the die opening from a chosen multiple of thickness (rounded up to a common die opening), the inside radius that air bending produces (a share of the die opening), the shortest flange that still spans the die, the bending force by the handbook-style formula (as the press brake force tool), force per metre and the press capacity check.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thickness | mm | Sheet thickness. |
| Tensile strength | MPa | Tensile strength of the sheet. |
| Bend length | mm | Length of the bend. |
| Die opening as a multiple of thickness | Die opening as a multiple of thickness (about 6–8 for thin sheet, 8–12 for plate). | |
| Inside radius ÷ die opening (air bending) | Inside radius produced by air bending as a share of die opening (about 0.15–0.16 mild steel, 0.2 or more for stainless and aluminium). | |
| Minimum flange ÷ die opening | Shortest flange as a share of die opening (so the flange still bridges the die). | |
| Bending factor | Air-bending factor in the force formula. | |
| Press capacity | kN | Press brake rated force. |
| Die rating (force per metre) | kN/m | Load rating of the die per metre of length. |
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: Thickness
- What it is
- The thickness of the sheet or plate being bent, which sets the die opening through the chosen multiple and drives the bending force.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 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
- Force rises with the square of thickness, and a thicker sheet may step up to a wider die.
- Get it right
- Measure the actual sheet; nominal gauge numbers do not always match the real thickness.
What this means: Tensile strength
- What it is
- The ultimate tensile strength of the sheet material, from the mill certificate or material standard.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 2000 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 is directly proportional to tensile strength.
- Get it right
- Use tensile strength, not yield strength; the force formula is written for tensile strength.
What this means: Bend length
- What it is
- The length of the bend line along the press brake, usually the full width of the flange being formed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 20000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total force is proportional to length; force per metre does not change.
- Get it right
- Use the length actually bent in one hit, not the length of the part or the tooling.
What this means: Die opening as a multiple of thickness
- What it is
- How many sheet thicknesses wide the V-die opening should be. The tool multiplies it by thickness and rounds up to the next common die opening.
- Units and format
- Enter a plain number with no unit. The form accepts 4 to 16. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger multiple picks a wider die: less force, a larger inside radius and a longer minimum flange.
- Get it right
- The die actually used can be wider than multiple × thickness because of the rounding up; check the die opening in the results.
What this means: Inside radius ÷ die opening (air bending)
- What it is
- The inside bend radius that air bending produces, expressed as a fraction of the die opening. It depends on the material and tooling.
- Units and format
- Enter a plain number with no unit. The form accepts 0.05 to 0.4. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.16 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The inside radius is this fraction times the die opening.
- Get it right
- Type it as a fraction of the die opening, not of the thickness; your own test bends are the best source.
What this means: Minimum flange ÷ die opening
- What it is
- The shortest flange that still bridges the die shoulders during the bend, expressed as a fraction of the die opening.
- Units and format
- Enter a plain number with no unit. The form accepts 0.4 to 1.2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.7 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The minimum flange is this fraction times the die opening.
- Get it right
- Type it as a fraction of the die opening; a flange shorter than this falls into the die and bends badly.
What this means: Bending factor
- What it is
- The dimensionless factor in the air-bending force formula that allows for die geometry and how the sheet wraps the punch.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 2. 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 is directly proportional to this factor.
- Get it right
- Use the factor that goes with this formula from your tooling supplier or handbook; bottoming and coining need far more force than this formula gives.
What this means: Press capacity
- What it is
- The rated force of the press brake, from its specification plate or data sheet.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 100000 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
- It does not change the bending force, only the capacity check.
- Get it right
- Machines are often rated in tonnes force; convert to kN before entering.
What this means: Die rating (force per metre)
- What it is
- The load the die can carry per metre of bend length without damage, stamped on the die or given in the tooling catalogue.
- Units and format
- Enter a number in kN/m: kN/m. The form accepts 0.000001 kN/m to 100000 kN/m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 kN/m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the force, only the die rating check.
- Get it right
- Compare per metre, not total: a short bend can overload a die locally even when the press has spare capacity.
Method and formulas
- Die opening = multiple × t, rounded up to a common opening (6, 8, 10, 12, 16, 20, 24, 30, 35, 40, 50, 60, 80, 100, 120, 160, 200, 250 mm).
- Inside radius ≈ share × die opening; minimum flange ≈ share × die opening.
- Force F = k L t² UTS ÷ V (as the press brake force tool); force per metre = F ÷ L.
- Example: 3 mm sheet on a 24 mm die bends to about 3.84 mm inside radius with 224.44 kN.
Limitations
- Air bending rules of thumb; bottoming and coining need several times more force.
- Radius and flange shares vary with material and tooling.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a die for a new sheet-metal part
- Check the minimum flange a die allows
- Confirm press brake tonnage before bending
Who it is for
- Press brake operators
- Fabrication supervisors
- Sheet-metal designers
What you get
- Die opening chosen
- Inside radius and minimum flange
- Bending force, force per metre and checks
Interpreting the result
- A wider die lowers force and raises the inside radius; a narrower die does the reverse.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1346–1353, 1383–1386. Topic reference; no source tables or recommended settings are reproduced.
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Open the Press Brake Set-up: Die, Radius, Flange and Tonnage calculator