# Punching Force Calculator for Sheet Metal

> Source: https://netray.co/tools/punching-force-calculator-sheet-metal
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Estimate the tonnage to punch round holes in sheet metal, including stripping force, die clearance and a machine capacity check.

## Category

manufacturing

## Industry

Sheet Metal Fabrication

## Audience

- Turret punch programmer
- Tooling engineer
- Fabrication engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Hole diameter

**Key:** d

**Type:** number

**Default:** 12

**Min:** 1

**Max:** 200

**Step:** 0.5

**Unit:** mm

#### Holes punched per stroke

**Key:** holes

**Type:** number

**Default:** 1

**Min:** 1

**Max:** 50

**Step:** 1

#### Material thickness

**Key:** t

**Type:** number

**Default:** 2

**Min:** 0.2

**Max:** 12

**Step:** 0.1

**Unit:** mm

#### Tensile strength

**Key:** uts

**Type:** select

**Default:** 400

**Options:**

##### Aluminum 5052 (about 230 MPa)

**Value:** 230

##### Mild steel (about 400 MPa)

**Value:** 400

##### Stainless 304 (about 600 MPa)

**Value:** 600

##### High-strength steel (about 800 MPa)

**Value:** 800

#### Shear strength as fraction of tensile

**Key:** shear_ratio

**Type:** slider

**Default:** 0.75

**Min:** 0.5

**Max:** 0.9

**Step:** 0.01

**Help:** Commonly about 0.7 to 0.8 for steels.

#### Force reduction from shear angle on punch

**Key:** reduction

**Type:** slider

**Default:** 0

**Min:** 0

**Max:** 40

**Step:** 5

**Unit:** %

**Help:** Ground-in shear on the punch face can cut peak force.

#### Machine capacity

**Key:** cap

**Type:** number

**Default:** 30

**Min:** 1

**Max:** 500

**Step:** 1

**Unit:** tonnes

**Outputs:**

#### Total cut perimeter

**Key:** perim

**Expr:** pi * d * holes

**Format:** decimal

**Description:** Millimeters sheared per stroke.

#### Shear strength

**Key:** shear

**Expr:** uts * shear_ratio

**Format:** decimal

**Description:** MPa.

#### Punching force

**Key:** kn

**Expr:** perim * t * shear / 1000 * (1 - reduction / 100)

**Format:** decimal

**Description:** Kilonewtons.

#### Punching force (tonnes-force)

**Key:** tonnes

**Expr:** kn / 9.80665

**Format:** decimal

**Primary:** true

#### Stripping force (about 10% of punching)

**Key:** strip

**Expr:** tonnes * 0.1

**Format:** decimal

**Description:** Rule of thumb; it varies with clearance and lubrication.

#### Die clearance per side (about 10% of thickness)

**Key:** clear

**Expr:** t * 0.1

**Format:** decimal

**Description:** Typical starting value in mm for mild steel; confirm with your tooling maker.

#### Machine utilization

**Key:** util

**Expr:** tonnes / cap * 100

**Format:** percent

**Primary:** true

**Chart:**

#### Punching force vs thickness

**Type:** line

**X:** t

**From:** 0.5

**To:** 8

**Steps:** 30

**Series:**

- tonnes

**Disclaimer:** Planning estimate for round holes. For other shapes, use the total cut perimeter. Follow the tooling and press manufacturer's rated limits.

## Content

**Intro:** 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.

**Sections:**

#### How to use the calculator

**Body:** 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.

**Bullets:**

- 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

**Body:** 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.

**Bullets:**

- Force rises linearly with thickness and perimeter.
- Shear angle lowers peak force but changes part flatness.

#### Worked example

**Body:** 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.

**Bullets:**

- A 10-hole cluster tool in the same material is about 23 tonnes.
- Check the strike pattern when using large multi-tools.

#### Common mistakes

**Body:** 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.

**Bullets:**

- Do not overload small punches; check buckling limits for long thin tools.
- Do not punch holes smaller than the thickness without specialist tooling.

**Cta:** If turret tooling, punch libraries and programs are managed in separate files, Netray can help tie them into your ERP routing and tooling data.

**Faq:**

#### How do I calculate punching force?

**Answer:** 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?

**Answer:** 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?

**Answer:** 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?

**Answer:** 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.

## Search terms

punching force calculator, punch press tonnage calculator, turret punch tonnage, shear strength punching force formula, stripping force punching, die clearance sheet metal, blanking force calculation, punch tonnage chart

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