Example of the simplest formula for calculating punch tonnage

It is very important to select the tonnage of the press and punch in the stamping die. Too much tonnage will waste costs, and too small tonnage will affect the quality of stamping parts. Tonnage calculation is required for reasonable selection of punch. The simplest calculation formula is as follows:

Punch tonnage=blanking force+pressing force+stripping force+forming force

Blanking force

P=T * L * K (unit: N)

Note: P blanking force, T material thickness, L blanking perimeter, K shear strength

(Shear coefficient of SECC, SPCC and SGCC is 330, and that of SUS is 660)

Example:

How much force should be used to punch a square hole with a length * width of 700 * 500 for a cold rolled sheet with a material thickness of 1mm?

Answer: P=T * L * K

T=1mm、L=（700+500）*2=2400mm、K=330

P=1*2400*330=792000N=79.2t

Pressing force and stripping force

Generally, the pressing force does not need to be calculated accurately. It is usually calculated according to the size of the blanking force, which is about 30% of the die blanking force.

When selecting tonnage, the size of stripping force can be ignored. In design, about 5% of the blanking force is generally taken.

Forming force

P1=0.43 * T * L1 * K1 (unit: N)

Note: P1 forming force, T material thickness, L1 bending length, K1 tensile strength

(SECC, SPCC, SGCC tensile coefficient is 300~350, SUS tensile coefficient is 350~400)

Although the calculation of punch tonnage is related to several forces, the blanking force is the main force, and the calculation of other forces can be ignored. In addition to its material, hardness and perimeter, the size of blanking force is also closely related to the size of blanking clearance and the level of machining accuracy.

Therefore, the calculation of tonnage is actually an approximate value, which is not very accurate, nor can it be completely accurate. When selecting tonnage, 20% of the calculated tonnage value is often added as the reserved force to prevent insufficient blanking force from affecting the stamping parts.