Punching Force Calculation Formula

For punching various forms of holes, such as circular, square or others, an appropriate strength is required. The given formula guides to the correct calculation of punch tonnage.

Punch strength(KN) equals Perimeter(mm)*Sheet Density(mm)*Shearing force(kn/mm2

To turn into metric tons divide the K/N result by 9.81

Here is the chart of some materials shearing force:

AluminumBrassLow Carbon SteelStainless Steel
0.17240.24130.34470.5171

In case of a square hole punch in not high carbon sheet of 3 mm with 20 mm side length the perimeter equals 20×4=80 mm, density equals 3 mm, shearing force is 0.3447 kn/mm2.

Punching strength kn is 80×3×0.3447, which equals 82.728 kn. Turned into tons 82.728 kn÷9.81=8.43

Punch and Die Clearence

In case of 12 top and 12.25 bottom mold usage the advisable gap is 0.25 mm. Inappropriate gap affects mold outwear, brings about roughs and additional act of cut, etc. The gap is determined by the sheet stuff and its density. In general in case of carbon steel sheets from12% to 18% of density is suitable.

Mold Gap Chart

Sheet Density                    Sheet Material


Mild SteelAluminumStainless Steel
0.8-1.60.15-0.20.15-0.20.15-0.3
1.6-2.30.2-0.30.2-0.30.3-0.4
2.3-3.20.3-0.40.3-0.40.4-0.6
3.2-4.50.4-0.60.4-0.50.6-1.0
4,5-6.00.6-0.90.5-0.7

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