The Basic Formula
Required blanking force is approximately the product of the part's cut perimeter, the material thickness, and the material's shear strength: F = P × t × τ, where P is perimeter (mm), t is thickness (mm) and τ is shear strength (N/mm²). Fine blanking also adds V-ring and counter-pressure forces on top of the basic shear force, so total required press tonnage is meaningfully higher than the shear force alone.
Why Fine Blanking Needs More Tonnage Than Stamping
- V-ring (impingement) force clamping the material around the cut line
- Counter-pressure (ejector) force supporting the part during the cut
- Main blanking force to shear the profile
- Safety margin for material variation and multi-up tooling
Rule-of-Thumb Tonnage Bands
| Part Class | Typical Press Tonnage |
|---|---|
| Small connector/lock/motorcycle components, thin gauge | HF200 – HF320 (2,000–3,200 kN) |
| Mid-size automotive flanges/gears | HF400 – HF500 (4,000–5,000 kN) |
| Transmission/turbo parts, thicker gauge | HF650 – HF800 (6,500–8,000 kN) |
| Large structural stampings | HF1000 – HF1200 (10,000–12,000 kN) |
These bands are general guidance only. Send your part drawing for an exact tonnage calculation.