Calculator Input
Example Data Table
| Material | Thickness | Bend Length | V Die | Angle | Estimated Tonnage |
|---|---|---|---|---|---|
| Mild Steel | 2 mm | 1000 mm | 16 mm | 90° | About 8.3 tons |
| Stainless Steel | 3 mm | 1200 mm | 24 mm | 90° | About 28.7 tons |
| Aluminum | 2.5 mm | 800 mm | 20 mm | 90° | About 7.8 tons |
Formula Used
The calculator estimates bottom bending force using this practical press brake formula:
Force kN = 1.42 × Material Strength × Thickness² × Bend Length ÷ V Die Opening ÷ 1000
The result is then adjusted by bend angle, tooling factor, and safety factor. Metric tons are calculated as:
Metric Tons = Force kN ÷ 9.80665
A smaller die opening increases force. A thicker sheet increases force sharply. Higher tensile strength also raises the required press brake capacity.
How to Use This Calculator
Select the unit system first. Use metric for millimeters. Use imperial for inches.
Choose the sheet material. Select custom when your shop has a tested tensile value.
Enter thickness, bend length, die opening, bend angle, tooling factor, and safety factor.
Press the calculate button. The result appears above the form and below the header.
Review metric tons, short tons, kN, tons per meter, and recommended die opening.
Use the chart to see how bending force changes as bend length changes.
Export the result as CSV or PDF for estimating, production planning, or job records.
Bottom Bending Tonnage Guide
What Bottom Bending Means
Bottom bending is a press brake method. The punch pushes sheet metal into the die. The metal reaches the bottom of the die. This gives better angle control. It also needs more force than air bending. The force depends on material strength, thickness, bend length, die width, and bend angle.
Why Tonnage Matters
Correct tonnage protects the press brake. It also protects tools and operators. Too little force can leave poor bends. Too much force can damage tooling. It may also overload the machine frame. A calculated estimate helps with safer setup.
Material Strength Effect
Stronger metals need more force. Stainless steel usually needs more force than mild steel. Aluminum usually needs less force. Custom strength is useful for special alloys. Always use real material data when it is available from the supplier.
Thickness and Die Opening
Thickness has a major effect. The formula uses thickness squared. That means a small increase can raise tonnage quickly. The V die opening also matters. A wider die lowers required force. A narrow die raises force and creates a tighter bend.
Safe Shop Planning
Use a safety factor for real shop conditions. Tool wear, grain direction, coatings, and machine condition can change results. Check your machine rating. Compare the calculated force with the press brake capacity. Leave a safe margin. This calculator gives a strong estimate. Final setup should follow your tooling guide.
FAQs
1. What is bottom bending tonnage?
It is the press brake force needed to bottom bend sheet metal. It depends on material strength, sheet thickness, bend length, die opening, angle, and safety allowance.
2. Is bottom bending stronger than air bending?
Bottom bending usually needs more force than air bending. It gives better angle control because the sheet is pressed deeper into the die.
3. Why does thickness affect force so much?
Thickness is squared in the formula. Doubling thickness can greatly increase required tonnage. Always check machine capacity before bending thick material.
4. What die opening should I use?
A common starting point is about eight times material thickness. This calculator shows that value, but tooling charts should guide final selection.
5. Can I use this for stainless steel?
Yes. Select stainless steel from the material list. It uses a higher strength value, so the estimated tonnage will increase.
6. What is a tooling factor?
A tooling factor adjusts the estimate for punch shape, die style, friction, and forming method. Use 1.00 for a normal setup.
7. Why add a safety factor?
A safety factor allows for real shop variation. Material batches, tooling wear, coatings, and operator setup can change actual force.
8. Is this result a final machine setting?
No. It is an estimate for planning. Always follow the press brake manual, tooling chart, and workplace safety rules before production.