Free Engineering Tool
Estimate the air-bending force needed for a bend from sheet thickness, bend length, V-die opening and material tensile strength. Results are shown in kN, metric tons and US short tons.
Use this calculator to size the bending force before selecting a press brake or checking a tooling load limit. It is separate from blanking and piercing force: this page calculates the load created by an air-bending operation, not the force needed to shear a blank from sheet metal.
Press brake tonnage is the air-bending force required to form sheet metal, commonly called bending force or brake load. A practical estimate is F = 1.42 × Rm × t² × L ÷ (1000 × V), where Rm is tensile strength in MPa, t is sheet thickness in mm, L is bend length in mm and V is the selected V-die opening in mm. Mild steel commonly starts around 450 MPa and an 8t V opening, while stainless steel and aluminium move the input values in opposite directions. Bending force rises with thickness squared and bend length, so a full-bed bend can need much more capacity than a short strip. For shop planning, add a defined allowance before comparing the result with the press tonnage curve; 20% is a starting allowance, not a manufacturing guarantee. Zhejiang Balford Mechatronics Co., Ltd. evaluates press work at its 12,000 m² facility against machines rated from 25 to 350 t.
The V opening is within the common 6t-12t air-bending range.
This estimate is for air bending. Bottoming, coining, radius bending and special tooling can require substantially more force. Confirm the tooling load limit and the machine tonnage chart before production.
Air-bending force increases with material strength, thickness squared and bend length, and falls as the V-die opening becomes wider.
| Thickness t | Suggested V | Force per metre | Metric tons per metre | US short tons per metre |
|---|---|---|---|---|
| 1.0 mm | 8 mm | 79.9 kN/m | 8.1 t/m | 9.0 short t/m |
| 1.5 mm | 12 mm | 119.8 kN/m | 12.2 t/m | 13.5 short t/m |
| 2.0 mm | 16 mm | 159.8 kN/m | 16.3 t/m | 18.0 short t/m |
| 3.0 mm | 24 mm | 359.4 kN/m | 36.7 t/m | 40.4 short t/m |
| 4.0 mm | 32 mm | 639.0 kN/m | 65.2 t/m | 71.8 short t/m |
| 6.0 mm | 48 mm | 1,437.8 kN/m | 146.6 t/m | 161.6 short t/m |
Calculated for Rm = 450 MPa, a 1 m bend length and an air-bending factor of 1.42. These are estimates; use the tooling and press manufacturer's load charts for production limits.
A 1,000 mm bend in 3 mm mild steel, using a 24 mm V-die and Rm = 450 MPa: F = 1.42 × 450 × 3² × 1,000 / (1,000 × 24) = 239.6 kN, or about 24.4 metric tons and 26.9 US short tons. With a 20% allowance, the suggested working capacity is about 29.3 metric tons.
For air bending, a commonly used estimate is F = 1.42 × Rm × t² × L / (1000 × V), where F is force in kN, Rm is tensile strength in MPa, t is sheet thickness in mm, L is bend length in mm and V is the V-die opening in mm. Convert kN to metric tons by dividing by 9.80665, or to US short tons by dividing by 8.89644.
A wider V opening gives the material a larger lever and reduces the force needed to form the bend. It also generally increases the inside radius and springback. A narrower V raises tonnage, concentrates die pressure and increases marking or tool damage risk.
No. The result is an air-bending estimate. Bottoming and coining can require substantially more force than air bending and should be calculated from the tooling supplier's data or the machine manufacturer's tonnage chart.
The calculator lets you add an allowance to the working force. A common starting point is 20%, but the final allowance should also reflect material strength variation, tool wear, multi-hit sequences, off-centre loading and the press manufacturer's rated tonnage curve. Never rely on nominal press tonnage alone.
It is a useful first check for tooling and press selection, but not a substitute for the tool drawing or machine load chart. Send the part drawing and material specification to Balford if you want the bend route, tooling and process limits reviewed.
Include the material, thickness, bend length, V-die, radius and required angle. Send the drawing to shawn@balford.net. We normally reply within 24 hours, China Standard Time.