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Blanking force and press capacity for washer

Short answer

Cut perimeter = π(50+20)=219.9 mm. Punch force = perimeter×t×τ = 219.9×1.5×320 = 105.6 kN. Press capacity = 1.2×105.6 ≈ 126.7 kN. Work per stroke = force × penetration × t = 105.6×0.4×0.0015 = 63.3 J.

A washer of 50 mm outer diameter with a 20 mm centre hole is to be blanked from 1.5 mm thick strip. The shear strength of the material is 320 MPa. Calculate (a) the total punch force when blanking and piercing are done in one stroke, (b) the press capacity if a 20% allowance is provided, and (c) the work done per stroke if the punch penetrates 40% of the thickness before fracture.

Given: outer D = 50 mm, hole d = 20 mm, t = 1.5 mm, τ\tau = 320 MPa.

(a) Punch force

The force equals the shear area times the shear strength. The shear area is the perimeter cut times thickness.

Cut perimeter=π(D+d)=π(50+20)=219.9 mmF=perimeter×t×τ=219.9×1.5×320=105,558 N\begin{aligned} \text{Cut perimeter} &= \pi(D + d) = \pi(50+20) = 219.9\ \text{mm} \\ F &= \text{perimeter}\times t\times\tau \\ &= 219.9\times 1.5\times 320 = 105{,}558\ \text{N} \end{aligned}

(b) Press capacity

Fpress=1.2×105.56=126.7 kNF_{press} = 1.2\times 105.56 = 126.7\ \text{kN}

A 150 kN standard press would be selected.

(c) Work done

Approximate work per stroke: W=F×p tW = F \times p\,t, where p = 0.4 is the fraction of thickness penetrated before fracture.

W=105,558×0.4×0.0015=63.3 JW = 105{,}558\times 0.4\times 0.0015 = 63.3\ \text{J}

Note on shear: a shear angle on the punch lowers the peak force, but the work stays about the same.

Answer: (a) F = 105.6 kN; (b) press capacity = 126.7 kN (use 150 kN press); (c) W = 63.3 J.

✓ Answer checked by Claude Opus 5.5 (high effort)

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