Calculate the punching force required to punch holes in sheet metal. Enter your hole shape, dimensions (diameter, side length, or perimeter), material thickness, and shear strength — and get back the punching force in kilonewtons and tonnage, plus a shear-adjusted force estimate.
Punching Force
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Punching Force (Tonnage)
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Force with 20% Shear Reduction
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Hole Perimeter
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Shear-Reduced Force (Tonnage)
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Punching force is the amount of force required to shear through a sheet metal workpiece to create a hole. Knowing the correct punching force helps you select a press with adequate tonnage capacity, preventing equipment damage, tooling failure, and inaccurate hole dimensions.
The standard formula is F = P × t × τ, where P is the perimeter of the hole (mm), t is the material thickness (mm), and τ is the shear strength of the material (MPa). The result is in Newtons. Divide by 1000 for kilonewtons, or by 9806.65 for metric tonnes (tonnage).
Typical shear strength values are: Mild Steel 200–250 MPa, Stainless Steel 300–400 MPa, Aluminum 70–100 MPa, Brass ~200 MPa, and Grey Cast Iron ~240 MPa. These values are approximately 60–80% of the material's ultimate tensile strength (UTS).
Adding a shear angle (bevel) to the punch face means not all of the perimeter is being cut simultaneously. This spreads the cutting action over a longer stroke, reducing peak force — typically by 15–30%. The calculator shows a conservative 20% shear reduction estimate.
It is common practice to apply a safety factor of 1.2 to 1.5 on top of the calculated force when selecting press tonnage. This accounts for material property variations, tooling wear, alignment imperfections, and other real-world variables.
Die clearance is typically 5–10% of the material thickness per side. Thicker materials require larger clearances to avoid excessive tool wear and burring. Insufficient clearance causes high punching forces and poor hole quality, while too much clearance results in excessive burring.
Yes. For rectangular and square holes, the calculator computes the perimeter automatically. For complex or irregular shapes, use the Custom Perimeter option — measure or calculate the total perimeter of your hole outline and enter it directly.
Sheet metal punching is widely used in manufacturing appliances (refrigerators, ovens), automotive chassis components, structural brackets, electrical enclosures, ventilation grilles, and any application requiring holes or cut-outs in flat metal sheets.