Press Brake Tonnage Calculator
Required Force
*Calculated for air bending with a 1.45 factor.
Understanding Press Brake Tonnage Calculation
In metal fabrication, determining the correct tonnage for a press brake is critical for both safety and precision. Tonnage represents the amount of pressure required to bend a specific piece of sheet metal over a V-die. Applying too little force results in an incomplete bend, while excessive force can damage the machine frame, tools, or the workpiece itself.
The Press Brake Tonnage Formula
The standard formula used for calculating the force (P) required for air bending is:
P = (1.45 × Rm × L × t²) / (V × 1000)
- P: Force in Metric Tons
- Rm: Tensile Strength of the material (N/mm²)
- L: Length of the bend (mm)
- t: Material thickness (mm)
- V: Die opening width (mm)
Common Tensile Strengths
| Material Type | Tensile Strength (N/mm²) | Correction Factor |
|---|---|---|
| Aluminum (Soft) | 200 – 250 | ~0.5x Mild Steel |
| Mild Steel (ST37 / A36) | 420 – 450 | 1.0x (Baseline) |
| Stainless Steel (304) | 650 – 750 | 1.5x – 1.7x Mild Steel |
The Rule of Eight (V-Die Selection)
For standard air bending of mild steel up to 6mm thick, a common engineering rule of thumb is to choose a die opening (V) that is 8 times the material thickness (t). For thicker materials (over 6mm), the ratio is often increased to 10 or 12 times the thickness to reduce the required tonnage and prevent cracking.
Critical Safety Considerations
Never exceed the maximum tonnage rating of your press brake or your specific tooling. Remember that "bottoming" or "coining" requires significantly higher force (often 3 to 5 times more) than air bending. This calculator is designed for air bending calculations only. Always verify your setup with your machine's specific load charts provided by the manufacturer.