Take clearance 9% of stock thickness.

Given data:

D = 6 cm = 60 mm

d = 2.6 cm = 26mm

t = 3.7 mm

τs = 350 N/mm2

Production of washer depends on

a. Blanking the outside diameter

b. Piercing the inner hole

Blanking pressure or force, $F_b = πDt X τ_s = π × 60 × 3.7 × 390 = 272 × 10^3N$

Piercing pressure, $F_p = πdt X τ_S = π × 26 × 3.7 × 390 = 117.87 × 103 N$

Total pressure required $F_T = F_b + F_p = 272 X 103 + 117.87 X 10_3 = 389.87 X 10_2$

For calculating dimensions of tools

Assuming

Clearance = 5 % of stock thickness on one side

Hence 10 % clearance on both sides

Blanking die diameter = 60 mm

Blanking punch diameter = 60 -10 % of t = 60 – 0.37 = 59.63 mm

Piercing punch diameter = 26 mm

Piercing die diameter = 26 + 10 % of t = 26 + 0.37 = 26.37 mm