Free Engineering Tool
Calculate the blanking force and punch compressive stress for sheet metal blanking and punching operations — for circular blanks and general contours. Enter the punch diameter (or cut perimeter), sheet thickness and material shear strength; the calculator returns press force in kN, N and ton-force plus the punch face stress.
This is the first check our own tooling engineers run before quoting a new blanking or progressive die project. Getting the force right decides press selection, tool steel choice and ultimately part cost — and it protects the punch from failing in service. Use the material quick-reference to auto-fill shear strength, or enter your own value from the material certificate. For the presses and dies this calculation sizes, see ourmetal stamping services.
Enter the diameter (or perimeter), thickness and shear strength above …"the blanking force updates automatically.
Blanking shears a blank from sheet metal using a punch and die. The punch presses the sheet into the die opening, and the material fails in shear along the cut perimeter.
| Material | τf (MPa) | Die clearance c/t (%) |
|---|---|---|
| Low carbon steel | 320–400 | 6–9% |
| High carbon steel | 550–900 | 8–12% |
| Stainless steel | 520–560 | 7–11% |
| Copper (soft) | 250–300 | 6–10% |
| Copper (hard) | 180–220 | 6–10% |
| Aluminium (hard) | 130–180 | 6–10% |
| Aluminium (soft) | 70–110 | 5–8% |
τf is typically 80–90% of tensile strength. Die clearance c = (c/t)% × t. Smaller clearance improves cut quality but increases force and die wear.
A circular blank of D = 100 mm is punched from 2 mm steel with τf = 500 MPa. Blanking force F = π × 100 × 2 × 500 ≈ 314,159 N = 314 kN. Punch face area Ap = π × 100²/4 ≈ 7,854 mm², so punch compressive stress σc = 314,159 / 7,854 ≈ 40 MPa — far below tool steel yield strength (> 1000 MPa), so the punch is safe.
Blanking and piercing are the same shearing process — the difference is what you keep. In blanking, the punched-out piece is the product (a washer, bracket or contact); in piercing (punching), the hole is the feature and the slug is scrap. Both use a punch and die to shear metal, and both follow the same force formula F = shear area × shear strength.
Blanking force F = A × τf, where A is the shear area and τf is the material shear strength. The shear area equals the cut perimeter times the sheet thickness. For a circular blank of diameter D and thickness t, F = π·D·t·τf. For any general contour, F = P·t·τf where P is the total cut perimeter. Add 10–20% for progressive dies, dull tooling and press efficiency.
Shear strength τf is the stress at which a material fails in shear (sliding) rather than tension. For most metals it is approximately 80–90% of the tensile strength. For example, a low-carbon steel with 400 MPa tensile strength has a shear strength around 320–360 MPa. If you only know the tensile strength, multiply by 0.8 as a safe estimate.
Die clearance c is the radial gap between the punch and die, usually expressed as a percentage of sheet thickness. For mild steel it is about 6–9% of t. A smaller clearance gives a cleaner shear face but raises cutting force and die wear; a larger clearance reduces force but produces more rollover and a bigger burr. Optimal clearance depends on the material and the required cut quality.
Compute the punch compressive stress σc = F ÷ Ap, where Ap is the punch face area. For a circular punch, Ap = π·D²/4. The punch material must have a yield strength comfortably above σc to avoid plastic deformation. Tool steels typically yield above 1000 MPa, so σc values of tens to a few hundred MPa are usually safe.
Start from the calculated blanking force, then add a safety factor of 10–20% for progressive dies and dulling tooling, and leave headroom of about 30% below the press rated capacity for press longevity. Also sum the forces of all stations in a progressive die — the press must exceed the combined peak force, not a single station.
Send your drawing to shawn@balford.net — our tooling engineers will confirm the blanking force, die design and pricing within 24 hours.