How to Choose a Press Brake V-Die Opening
To choose a press brake V-die opening, begin with material thickness, then check the desired inside radius, minimum flange, material strength and required tonnage. For 3 to 8 mm material, an opening near eight times thickness is a widely used air-bending starting point. It is not a universal setting: thin sheet, thick plate, high-strength material and special bend methods require different checks.
V-Die Opening Starting Chart
| Material thickness | Reference starting ratio | Example opening | What to verify |
|---|---|---|---|
| 2.6 mm or less | About 6× thickness | 1.5 mm → about 9 mm; choose the closest approved opening | Small flange, marking and tool radius |
| 3 to 8 mm | About 8× thickness | 3 mm → about 24 mm | Natural radius and available tonnage |
| 9 to 12 mm | About 10× thickness | 10 mm → about 100 mm | Plate strength, radius and machine capacity |
| 14 mm and thicker | About 12× thickness | 16 mm → about 192 mm | Use the exact plate-bending chart and tooling rating |
Source: Wilson Tool air-bending force chart. The chart states that its formulas are for reference.
How V-Die Opening Changes the Bend
Inside radius
In air bending, the material forms a natural radius rather than wrapping perfectly around the punch. Mate publishes starting factors of approximately 0.16 times the V opening for cold-rolled steel, 0.14 for aluminum and 0.21 for stainless steel. Material behavior varies, so confirm with the actual grade and a controlled test bend.
Required force
A narrower opening requires more force for the same thickness and bend length. Increasing the opening generally reduces air-bending tonnage, but it also increases the radius and minimum flange. Do not solve a radius problem by narrowing the die until the force is unsafe.
Minimum flange
The flange must span the die opening and remain supported on the shoulders. Manufacturer charts commonly list minimum flange alongside V opening. A widely used reference is about 0.707 times V for a 90-degree air bend, but tooling shoulder radius, angle and part geometry can change the requirement.
Surface marking
Die shoulders carry the bending load. A narrow opening can concentrate contact pressure, while wider openings change where the sheet slides. For prefinished parts, evaluate protective film, polished shoulders, larger radii or purpose-built low-mark tooling without exceeding the approved load.
How to Choose a Press Brake V-Die Opening Step by Step
- Confirm the bend method. This article's ratios and radius relationships apply to air bending.
- Record the actual material. Include grade, measured thickness, tensile strength and grain direction.
- Calculate a starting opening. Use the manufacturer ratio or chart for the thickness range.
- Check the target inside radius. Compare the natural air-bend radius with the drawing tolerance.
- Check the shortest flange. It must be long enough to remain safely supported.
- Calculate force for the full bend length. Apply the correct material-strength factor.
- Verify every rating. The machine, holder, punch and die all need adequate capacity.
- Make a controlled test bend. Measure angle, radius and flange before releasing production.
Worked Starting Examples
Example 1: 1.5 mm mild steel
A 6× starting ratio suggests about 9 mm. Standard tooling may offer 8 mm or 10 mm. Compare both options against the tooling chart: 8 mm may form a tighter radius and require more force, while 10 mm may need a longer flange and create a larger radius.
Example 2: 3 mm mild steel
An 8× starting ratio suggests about 24 mm. A 25 mm opening is a common nearby size. Mate's mild-steel reference formula, inside radius approximately 0.156 times V, would estimate about 3.9 mm. Treat that as a planning value and confirm on the actual batch.
Example 3: 6 mm stainless steel
An 8× starting ratio suggests about 48 mm, so a 50 mm opening may be evaluated. Stainless typically requires more force and may form a larger natural radius than mild steel. Use the stainless values in the approved chart; do not reuse a mild-steel tonnage result.
When the 8× Rule Is Not Enough
- The drawing calls for a radius that the natural air bend will not produce.
- The flange is too short for the suggested opening.
- The material is high-strength, abrasion-resistant or otherwise outside the chart basis.
- The part has holes, slots or cutouts close to the bend.
- The operation uses bottoming, coining, hemming or a special die.
- The bend is off-center, staged or concentrated over a short tool length.
In those cases, work from the part drawing and tooling manufacturer's application data. For the broader workflow, see the complete press brake tooling selection guide and the press brake tooling styles guide.
V-Die and Punch Options
The products below illustrate different formats. Confirm clamping style, height, angle, radius, opening and maximum load before ordering.
2017 Two-V Die, 60°
Two available openings in one Amada-style die; verify which face suits the application.
From $241 CAD
View Two-V Die →
3161 Self-Centering Die, 88°
A 10 mm single-V insert for compatible self-centering lower holders.
From $250 CAD
View Self-Centering Die →
1324 Gooseneck Punch, 86°
Return-flange clearance option for compatible Wila-style holders and approved dies.
From $503 CAD
View Gooseneck Punch →Send the machine and holder model, material grade, thickness, bend length, radius, angle, flange and part drawing.
Request Tooling Help or a Quote
Press Brake V-Die FAQ
What is the best V opening for a 90-degree bend?
There is no single best opening. For air bending, start with the approved thickness ratio, then check radius, flange and force. A tooling chart for the actual material is the final reference.
Does a wider V opening reduce tonnage?
Generally yes for air bending, but it also produces a larger natural radius and needs a longer flange. All three effects must be evaluated together.
Can one two-V die cover multiple thicknesses?
It can provide two opening choices, but each face still has a defined angle, radius, capacity and supported application range. Reorient and secure it only according to the manufacturer's procedure.
Should the punch radius equal the desired inside radius?
Not automatically. In air bending, the V opening and material often control the natural radius. A punch tip that is too small or too large can cause other problems; use the toolmaker's punch-tip guidance.
Calculate the Required Air-Bending Force
Enter material, thickness, bend length and V opening in the new metric/imperial calculator. It also estimates natural inside radius and minimum flange.