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Tonnage Calculation

The tonnage required for punching any shape hole in a material is given by the following formula:

Required Tonnage = L x G x S where:-
L” is the total length of the cutting edge
G” is the material thickness
S” is the shear strength of the material
Hence required tonnage.

Example 1: For a 50.mm square in 2.mm mild steel
L = 50 x 4 = 200 G = 2 & S = 0.345
Hence required tonnage.
T = 200 x 2 x 0.345 = 137.95 KN

Punches with Shear
The tonnage required for punching with shear is given by the formula:-T = L x G x S x FWhere “F” is the shear factor (see ‘Calculating the effect of shear”)

Example 2: For a 3/8” x 3” Slitting Tool with 3/16” Shear Cutting ¼” Hard Aluminium
F = 0.63 (from graph below)
L = 2 (3/8 x 3) = 2.25 G = 0.25 S = 12 F = 0.63
Hence required tonnage:
T = 2.25 x 0.25 x 12 x 0.63 = 4.25 ton

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Recommended Clearances

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Please Note Measurements in mm

This is a recommended guide. If any problems or queries arise please contact F.M. Tool & Gauge for our expert advice.


Shear is used on punches to reduce tonnage and noise whilst punching.
A full shear can reduce the tonnages by up to 50%.

Rooftop Shear:

  • Ideal when punching at high loads
  • Avoid excessive side loading by

Taking large cuts (over 75%)

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Inverted Rooftop:

  • Very effective
  • Easy to produce and regrind
  • Avoid sharp corner in the centre, as this

provides a stress point, making the tool more susceptible

Concave:

  • Best for nibbling
  • More difficult to regrind

Than inverted rooftop

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Four Way Shear:

  • Ideal for large squares
  • always avoid sharp inside corners, as these encourage breakage

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