BIZOMAT MAKEOS · Fabrication
Punching Operation Plan (Force, Stripping, Punch Stress, Clearance)
What force does this punching operation need with stripping, is the punch strong enough, what die clearance should I use, and is the press big enough?
Plan of a piercing or blanking operation: cut perimeter for a round or rectangular punch, cutting force with a factor for tool wear (as the punching force tool), stripping force as a share of it, total press load for the punches working together, compressive stress in the punch against your allowable and the smallest round punch for the thickness, die clearance per side from your percentage of thickness, the die opening, and the energy per hit from the penetration before breakthrough.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Punch shape | choice | Round or rectangular punch. |
| Punch diameter (round) | mm | Diameter of a round punch. |
| Punch length (rectangular) | mm | Length of a rectangular punch. |
| Punch width (rectangular) | mm | Width of a rectangular punch. |
| Punches cutting together | Number of punches that cut at the same moment. | |
| Sheet thickness | mm | Sheet thickness. |
| Shear strength of the sheet | MPa | Shear strength of the sheet (often about 0.7–0.8 of tensile strength). |
| Wear (dull tool) factor | Allowance for punch and die wear (as in the punching force tool). | |
| Stripping force share | % | Force to strip the sheet off the punch as a share of the cutting force (your value; typically 5–20%). |
| Allowable punch compressive stress | MPa | Allowable compressive stress for the punch steel and hardness (your value). |
| Die clearance per side | % of t | Clearance between punch and die on each side as a share of thickness (your value for the material and edge quality). |
| Penetration before breakthrough | % of t | Share of the thickness the punch enters before the slug breaks out. |
| Press capacity | kN | Rated capacity of the press. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Punch shape
- What it is
- Whether the punch is round or rectangular, which decides how the cut perimeter and punch face area are worked out.
- Units and format
- Choose one of 2 options from the list: Round; Rectangular.
- Example
- The form opens with “Round” selected as a worked example. Choose the option that matches your case.
- Get it right
- Only the size inputs for the chosen shape are used; the others are ignored.
What this means: Punch diameter (round)
- What it is
- The diameter of a round punch, which gives the length of the cut edge and the punch face area.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger punch raises the cutting force but lowers the punch stress.
- Get it right
- Used only for a round punch. The die opening is this diameter plus twice the clearance per side.
What this means: Punch length (rectangular)
- What it is
- The longer side of a rectangular punch face, which with the width sets the cut perimeter and face area.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer punch raises the cutting force.
- Get it right
- Used only for a rectangular punch. Corner radii are ignored.
What this means: Punch width (rectangular)
- What it is
- The shorter side of a rectangular punch face, measured at right angles to the punch length.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A wider punch raises the cutting force but lowers the punch stress.
- Get it right
- Used only for a rectangular punch; narrow punches carry the highest compressive stress.
What this means: Punches cutting together
- What it is
- How many punches cut through the sheet at the same moment in one press stroke. Their forces and energies add.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 200. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The press load and energy rise in direct proportion.
- Get it right
- Count only punches that cut together; punches stepped in length cut one after another.
What this means: Sheet thickness
- What it is
- The thickness of the sheet being punched. It also sets the clearance and the penetration distance, which are entered as shares of it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cutting force rises in direct proportion to thickness.
- Get it right
- Measure the actual sheet rather than relying on nominal gauge.
What this means: Shear strength of the sheet
- What it is
- The shear strength of the sheet material, the stress at which it parts in shear along the cut edge.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 2000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cutting force rises in direct proportion to it.
- Get it right
- Use shear strength, not tensile strength; take it from the material data sheet or tests.
What this means: Wear (dull tool) factor
- What it is
- A multiplier on the theoretical cutting force to allow for punches and dies that have worn dull between sharpenings.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting force, stripping force and press load rise in direct proportion.
- Get it right
- Use your shop’s value; 1 means a sharp tool with no allowance.
What this means: Stripping force share
- What it is
- The force needed to pull the punch back out of the sheet after the cut, as a share of the cutting force.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 50%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger share raises the total press load.
- Get it right
- Type the percentage itself. It is added to the cutting force for the press load.
What this means: Allowable punch compressive stress
- What it is
- The compressive stress the punch steel can carry at its hardness, used for the punch stress check and the smallest round punch.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 5000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the tool steel supplier for the grade and hardness; slender punches may also need a buckling check.
What this means: Die clearance per side
- What it is
- The gap between punch and die on each side, as a share of sheet thickness. It sets the die opening and affects edge quality.
- Units and format
- Enter a number in % of t: % of t. The form accepts 1 % of t to 20 % of t. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 % of t as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- This is per side, not total: the die opening is the punch size plus twice this clearance.
What this means: Penetration before breakthrough
- What it is
- How far the punch enters the sheet before the slug breaks free, as a share of sheet thickness. It sets the energy needed per hit.
- Units and format
- Enter a number in % of t: % of t. The form accepts 10 % of t to 100 % of t. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 % of t as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy per hit rises in direct proportion to it.
- Get it right
- Type the percentage of thickness. Harder, less ductile materials break out sooner.
What this means: Press capacity
- What it is
- The rated force of the press, compared with the total cutting plus stripping load of all punches.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check that the press can deliver this force at the height in the stroke where the cut happens.
Method and formulas
- Perimeter: π d (round) or 2(a + b) (rectangular); cutting force F = perimeter × t × τ × wear factor (as the punching force tool).
- Stripping = share × F; press load = (F + stripping) × punches.
- Punch stress = F ÷ punch area; smallest round punch d_min = 4 t τ × factor ÷ σ_allow.
- Clearance per side = share × t; die opening = punch + 2 × clearance; energy per hit ≈ F × penetration × t.
- Example: a 20 mm hole in 2 mm sheet takes 45.239 kN plus 4.5239 kN stripping; the punch runs at 144 MPa.
Limitations
- Flat-faced punches; shear angles on the punch or die lower the peak force.
- Clearance shares vary by material and the edge quality wanted.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a press for a piercing tool
- Check a small punch for crushing
- Set die clearance for a material thickness
Who it is for
- Press tool designers
- Sheet-metal engineers
- Press operators
What you get
- Cutting, stripping and total press force
- Punch stress and smallest round punch
- Clearance, die opening and energy
Interpreting the result
- When the punch diameter nears the sheet thickness, the punch itself becomes the weak link.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1338–1346. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · Library collection
Press tools and dies: how sheet metal parts are blanked, pierced and formed in volume
What it covers: How press tools work, punch and die clearance, estimating press force, single, compound, progressive and transfer dies, strip layout, forming and springback, press safety and when tooling pays.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Punching Operation Plan (Force, Stripping, Punch Stress, Clearance) calculator