Free to use, provided as-is. No warranty or guarantee of accuracy or fitness for purpose. This is an idealised axial column model and an engineering aid only — it does not replace tool design judgement, punch-maker data or trial. AbarTech Ltd accepts no liability for outcomes arising from its use.
Piercing force, punch compressive stress, Johnson–Euler buckling capacity and the maximum unsupported punch length for a single punch. Includes a minimum punch size check and a stripping load estimate.
| Material | Shear τ | |
|---|---|---|
| Hot-rolled mild steel (tonnage-chart basis, 50 000 psi) | 345 MPa | |
| ASTM A36 structural steel (60 000 psi) | 414 MPa | |
| Type 202 stainless (1.8 × the mild-steel basis) | ≈ 620 MPa |
| Spring steel strip (EN 10132-4) | UTS | |
|---|---|---|
| C75S / C67S annealed, skin passed (max) | ≤ 640 MPa | |
| 51CrV4 annealed (max) | ≤ 700 MPa | |
| Hardened & tempered, lower end | 1200 MPa | |
| Hardened & tempered, mid range | 1500 MPa | |
| Hardened & tempered, upper end (C75S) | 1900 MPa |
Spring steel buttons switch to Estimate from UTS with τ ≈ 0.8 × UTS. Annealed values are specification maxima, so they give a conservative force. Hardened-and-tempered strip spans 1200–1900+ MPa, so use the value on your certificate.
Basis values used in a published punch-maker tonnage chart. They are typical, not specified minima. Material certificates vary, and work-hardened or high-strength stock can be much higher.
| Family | Shear ≈ × UTS |
|---|---|
| Mild steel | 0.70 – 0.80 |
| Stainless steel | ≈ 0.90 |
| Aluminium alloys | ≈ 0.50 |
| Copper alloys | 0.50 – 0.90 (alloy dependent) |
| Steels, general approximation (incl. spring steel) | ≈ 0.80 |
Common planning assumptions from metal-forming practice. Using UTS directly in place of τ over-estimates the force, which errs on the safe side for the punch.
Stripping is the separate load case on the return stroke, when the stock grips the punch and has to be pulled off. It puts the punch in tension. Punch section, thickness and shear strength are taken from Tab 1.
Free piercing punch calculator from AbarTech Ltd, Dyserth, North Wales. It works out punching force from cutting perimeter, stock thickness and shear strength, then checks the punch as a column. The Johnson parabola covers short and intermediate punches and the Euler curve covers slender ones. From that it gives the punch's buckling capacity, the factor of safety at your current unsupported length and the longest unsupported length that still meets your target. It also covers round, rectangular, obround and custom sections, the minimum punch diameter relative to thickness, and the stripping force for stripper spring sizing. Built from hands-on experience designing press tooling and special-purpose wire-forming and retaining-ring production machinery.
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