A φ 25 mm hole is pierced in at = 2.5 mm thick steel

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A φ 25 mm hole is pierced in at = 2.5 mm thick steel sheet having shear strength τ = 350 MPa. If the diametral clearance is given by the expression c = 0.0064 √τ, the die diameter (in mm), punch diameter (in mm) and punch force in (kN) respectively are

1. 25.0, 25.3, 171.8
2. 25.0, 24.7, 68.75
3. 24.7, 25.0, 171.8
4. 25.3, 25.0, 68.75

Correct Option: D

t = 2.5
τ = 350 MPa
d_hole = 25 mm
Punch dia = 25 mm
Clearance = 0.0064 × 2.5 × √350
≌ 0.3mm
Die Dia = Punch Dia + Clearance
= 25 + 0.3 = 25.3
Punching force = πDtτ = π × 25 × 2.5 × 350 = 68.72 KN