What this calculator does
Punching force is the area of material being sheared multiplied by its shear strength. A 30 mm round hole, perimeter 94.2 mm, through 2 mm steel at 310 MPa needs 58.4 kN, or about six tonnes.
It is the perimeter that matters, not the hole area, which catches people out. A long slot can need far more force than a round hole of the same area, because it has much more edge to shear. Two small holes need the same total force as one hole of their combined perimeter.
The formula
The sheared area is the hole perimeter multiplied by the material thickness, which is the cylindrical surface the punch cuts through. Multiplying by the shear strength gives the force. The figure is the theoretical maximum with a flat punch face; angled or sheared punch faces cut progressively and reduce the peak load substantially.
| Term | Meaning |
|---|---|
| Shear strength | Roughly 0.6 to 0.8 of tensile strength for most metals. Mild steel is around 310 MPa. |
| Perimeter | The cut edge length. For a round hole it is π times the diameter. |
| Shear angle | Grinding the punch face at an angle so it cuts progressively, lowering peak force. |
| Stripping force | Additional force to withdraw the punch, typically 5 to 20% of the punching force. |
The inputs explained
| Field | What to enter |
|---|---|
| Hole perimeter (mm) | Hole perimeter in millimetres. For a round hole it is π times the diameter; for a slot, add all the edges. |
| Material thickness (mm) | Material thickness. |
| Shear strength (MPa (N/mm²)) | Shear strength in MPa. Mild steel is about 310; aluminium around 210; stainless around 450. |
When to use it
Sizing a press
The press tonnage must exceed the punching force with margin, and this is the figure to compare against.
Checking a multi-hole tool
Punching several holes at once multiplies the force, which can exceed the press capacity.
Comparing materials
The same hole in stainless needs roughly half again the force of mild steel.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much force for each thickness?
The same hole through a range of material thicknesses.
| Material thickness | Punch force needed | In metric tonnes-force | In pounds-force |
|---|---|---|---|
| 1 mm | 29.2 kN | 2.98 t | 6,565 lbf |
| 2 mm | 58.4 kN | 5.96 t | 13,130 lbf |
| 3 mm | 87.6 kN | 8.93 t | 19,695 lbf |
| 5 mm | 146.0 kN | 14.89 t | 32,824 lbf |
Questions
Why does the perimeter matter rather than the area?
Because punching shears the material along the edge of the hole, not across its face. The sheared area is the perimeter times the thickness. A long thin slot has far more perimeter than a round hole of equal area, and needs proportionally more force.
What shear strength should I use?
Roughly 0.6 to 0.8 of the tensile strength if you do not have a shear figure. Mild steel is around 310 MPa, aluminium about 210 and stainless steel around 450. Use the actual material specification for anything near the press limit.
How can I reduce the force needed?
Grind a shear angle onto the punch face so it cuts progressively rather than all at once, which can cut peak force by a third or more. Staggering punch lengths in a multi-hole tool achieves the same effect by spreading the cuts over the stroke.
Do I need to allow for stripping force?
Yes, for the press and tool design. Withdrawing the punch from the material takes an additional 5 to 20% of the punching force. The press must handle both, though they occur at different points in the stroke.
For flat pattern development, see the bend allowance calculator. For material weight, see the metal weight calculator.