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.
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.