Punching Force Calculator for Sheet Metal
Punching force is the shear strength of the material multiplied by the cut perimeter and the thickness. This calculator gives the tonnage for round holes, estimates stripping force, and checks the result against a turret or punch press capacity.
Your numbers
Commonly about 0.7 to 0.8 for steels.
Ground-in shear on the punch face can cut peak force.
Your results
Planning estimate for round holes. For other shapes, use the total cut perimeter. Follow the tooling and press manufacturer's rated limits.
Punching force vs thickness
Sweeps Material thickness from 0.5 to 8, holding your other inputs fixed.
Manage tooling libraries alongside routings
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How to use the calculator
Enter the hole diameter, the number of holes struck at once, the material thickness and a tensile strength. Adjust the shear-to-tensile ratio if you have better data, and enter any force reduction provided by a shear angle ground on the punch. The tool returns total perimeter, shear strength, force in kilonewtons and tonnes, an approximate stripping force and the die clearance per side. Compare the utilization with the rating of the machine and the individual tool station.
- For multi-hit tools, count all holes struck in one stroke.
- For other shapes, enter an equivalent diameter that gives the same perimeter.
- Check the tool station rating as well as the press.
The formula
Punching force F = L x t x tau, where L is the cut perimeter, t is thickness and tau is the shear strength of the material. For a round hole, L equals pi times the diameter. Shear strength is commonly taken as 0.7 to 0.8 times tensile strength in steels. Because force is proportional to both thickness and perimeter, doubling thickness doubles the force, and a larger hole takes proportionally more. A shear angle ground on the punch spreads the cut over the stroke and lowers the peak load.
- Force rises linearly with thickness and perimeter.
- Shear angle lowers peak force but changes part flatness.
Worked example
A 12 mm hole in 2 mm mild steel, with 400 MPa tensile and a 0.75 ratio, has 37.7 mm perimeter and 300 MPa shear strength. Force is 37.7 x 2 x 300 = 22,620 N, about 22.6 kN or 2.3 tonnes. Stripping force is roughly a tenth of that. On a 30 tonne turret that is about 8 percent utilization, so the press is fine, although tools with many holes per stroke can multiply the load quickly.
- A 10-hole cluster tool in the same material is about 23 tonnes.
- Check the strike pattern when using large multi-tools.
Common mistakes
Forgetting the number of holes in a cluster tool, using too little die clearance, and treating tensile strength as shear strength are the common errors. Tight clearance raises both force and tool wear. Stainless and high-strength steels also work-harden, which increases wear on small punches. Record the punch, die and clearance used in the routing so the next job can reuse proven tooling.
- Do not overload small punches; check buckling limits for long thin tools.
- Do not punch holes smaller than the thickness without specialist tooling.
Frequently Asked Questions
How do I calculate punching force?
Multiply the cut perimeter by the material thickness and by its shear strength. For a round hole use pi x diameter. Divide the newtons by 9,807 to get tonnes-force. Add a safety margin when comparing with machine capacity.
What is the die clearance for punching steel?
A common starting point is about 10 to 15 percent of thickness per side for mild steel, with more for harder materials. Your tooling supplier's recommendation for the specific material should take priority over a rule of thumb.
What is stripping force?
It is the force needed to pull the punch out of the sheet after the cut. It is often estimated at about 5 to 20 percent of punching force and rises with tight clearance, poor lubrication and thicker material.
Does a shear angle reduce force?
Yes. Grinding a shear angle on the punch face spreads the cut over time and can reduce peak force noticeably. The trade-off is more part distortion, so it is used mainly for heavy or large punches.
If turret tooling, punch libraries and programs are managed in separate files, Netray can help tie them into your ERP routing and tooling data.
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