Stamping Press Tonnage Calculator for Blanking and Piercing
Choosing the wrong press size is expensive either way: too small risks stalling and broken punches, too large raises the hourly rate you quote. This calculator applies the standard perimeter x thickness x shear strength relation and adds stripping, forming and a margin.
Your numbers
Outside perimeter cut at the blanking station.
Sum of all hole and slot perimeters that cut at the same stroke.
Other cut length in the same stroke, such as notching or cutoff.
Staggered punch lengths or ground shear angle reduce peak force. 0 for flat punches.
Typically 5 to 20 percent of cutting force; higher for tight clearance or thin stock.
Add bend, coin or draw load from another station that hits at the bottom of the same stroke.
Your results
Shear strengths are approximate typical values for common tempers. Use the mill certificate shear or 0.75 x ultimate tensile strength for the real lot. This is an estimate, not a press selection certification.
Required tonnage vs material thickness
Sweeps Material thickness from 0.02 to 0.125, holding your other inputs fixed.
Check press loads against your work center master
Optional: flag jobs routed to presses that are too small, straight from your ERP routing and work center data.
Optional. The tool and every export work without this. No spam.
How to use it
Enter every cut length that happens in the same stroke: the blank outside, pierced holes and notches. A progressive die has many stations, so sum only the stations that bottom out together. Choose a material, set the thickness, and leave shear reduction at zero unless the die uses stepped or angled punches. Add any forming or coining load that occurs at the bottom of the stroke. The output shows peak working load and the press capacity to specify after your safety margin. Use the chart to see how load climbs as you move from thin to heavy gauge.
The formula and its assumptions
Cutting force in pounds equals cut perimeter in inches times thickness in inches times shear strength in pounds per square inch. Dividing the kip result by 2 gives short tons. Shear strength is roughly 0.75 times ultimate tensile strength for many steels and 0.5 to 0.7 for aluminum depending on temper. Stripping force is a fraction of cutting force. Shear reduction of 10 to 30 percent is a common design target for large blanking dies. Real peak load also depends on clearance and punch condition, so the margin matters.
- Short tons (2,000 lb) are used; multiply by 8.896 for kN.
- Dull tooling can raise the force by 20 to 50 percent.
- Do not rely on rated tonnage alone for off-center loads; check the bed-length rating.
Common mistakes
The most common error is adding the whole die perimeter even when stations are staggered in time, or the opposite, ignoring forming load that lands with the cut. Another is using tensile strength instead of shear strength, which overstates the load by about a third. Running a press near its rated capacity every stroke shortens its life, which is why most shops keep a 20 to 30 percent margin. Finally, tonnage is not the only limit; energy per stroke and the eccentric load limit often decide the press for deep draws and wide dies.
Frequently Asked Questions
What is the blanking tonnage formula?
Force in pounds equals the cut perimeter times material thickness times the material shear strength in psi. Divide by 2,000 for short tons. For 14 inches of cut in 0.060 inch low carbon steel at 40,000 psi shear, that is about 16.8 tons.
How much safety margin should I use?
Twenty to thirty percent is common. Use more for thin gauge on stiff alloys, dull tooling risk, off-center loading or when one press runs many different jobs. Never size to exactly the rated capacity.
Why include stripping force?
The material grips the punch after the cut and the stripper must pull it free. That load is usually 5 to 20 percent of cutting force and occurs on the upstroke, but many shops add it to the sizing load for a conservative result.
Does shear reduction really cut the tonnage?
Yes. Stepping punches by about half the material thickness, or grinding a shear angle, spreads the cutting over a longer part of the stroke and lowers the peak. The total work is similar, so energy per stroke does not fall the same way.
If press capacity and hourly rates live in a routing table in your ERP, we can connect this check to the work center master so the estimate flags overloaded presses automatically.
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