Looking to punch holes through metal? Determining the required pressing force can be a daunting task. But fear not, because MachineMfg has got you covered with their comprehensive guide on press tonnage calculation.

In this article, you’ll learn how to calculate the required punching tonnage using the press tonnage calculation formula.

You’ll also discover how to convert KN to metric tons and how to determine the optimal punch and die clearance.

Plus, you’ll find a handy table for selecting the die clearance based on material and thickness.

Accurately calculating punching force is essential for optimizing the punching process, minimizing defects and material waste, and ensuring worker safety.

With this guide, you’ll have all the information you need to select the appropriate machine tools and dies, reduce punching force, and improve the quality of your punched holes.

Whether you’re a seasoned metalworker or a beginner, this article is a must-read for anyone looking to punch holes through metal with precision and efficiency.

## Press Tonnage Calculation Formula

If you need to punch round, square, or any other type of hole through a given metal thickness, you’ll need to determine the pressing force required to accomplish this task.

To calculate the required punching tonnage, you can use the following press tonnage calculation formula, which is also applicable for blanking force calculation.

**Press Tonnage (KN) = Perimeter (mm) * Plate Thickness (mm) * Shear Strength (kn / mm ^{2})**

Converted into metric tons: __dividing the result of KN by 9.81__

**Perimeter:**The total length of the continuous line forming the boundary of a closed geometric figure.

**Thickness:**The thickness that will be penetrated by the punching mold.**Shear Strength:**The physical properties of the plate, which are determined by the material of the sheet, can be found in the material manual.

Common materials’ shear strength are as follows: unit: KN/mm^{2}

Aluminum | Brass | Low Carbon Steel | Stainless Steel |

0.1724 | 0.2413 | 0.3447 | 0.5171 |

For various shear strength table, you can check out the following post:

e.g: If punching one square hole in the 3mm thickness low-carbon steel plate, side length 20mm, you will get:

- Perimeter = 20×4 = 80mm
- Thickness = 3mm
- Shear Strength = 0.3447kn/mm
^{2}

**Punch Force (KN)** = 80 x 3 x 0.3447 = 82.728 KN Convert into tonnage: 82.728 KN ÷ 9.81 = 8.43 Ton

For further information about shearing strength, including how to calculate it, you can refer to the Wikipedia article.

The formula mentioned can also be applied as the cutting force formula in press tooling or as the formula for determining the force required to punch a hole.

## Press Tonnage Calculator

How to calculate the force (tonnage) of a punch press machine?

I believe the following press tonnage calculator can be used to calculate the required punch force for your workpiece.

P.S: If you want to calculate hydraulic press tonnage, you can use our **hydraulic press tonnage calculator**.

## Punch and Die Clearance

The clearance between the punch and dies is a critical factor in the punching process, and it is represented by the total difference.

For instance, suppose you are using an ø12 upper die and an ø12.25 lower die. In that case, the optimal clearance should be 0.25mm.

If the clearance is not proper, it can reduce the die’s service life, cause burrs, and lead to secondary cutting. An irregular opening can also increase the demounting force.

Moreover, the die clearance depends on the material and thickness, and for carbon steel plates, it is recommended to use a value between 12-18% of the thickness.

**See also:**

If there are no special requirements for the CNC punch, you can refer to the following table for selecting the die clearance.

**Punch Press Die Clearance Table**

Thickness | Mild Steel | Aluminum | Stainless Steel |

0.8-1.6 | 0.15-0.2 | 0.15-0.2 | 0.15-0.3 |

1.6-2.3 | 0.2-0.3 | 0.2-0.3 | 0.3-0.4 |

2.3-3.2 | 0.3-0.4 | 0.3-0.4 | 0.4-0.6 |

3.2-4.5 | 0.4-0.6 | 0.4-0.5 | 0.6-1.0 |

4.5-6.0 | 0.6-0.9 | 0.5-0.7 | / |

## FAQs

**1. What is punching force?**

Punching force refers to the force required to pierce a hole in a sheet metal workpiece using a punch and die. Accurate calculation of this force is essential for process optimization, machine tool selection, and maintaining the quality of the final product.

**2. Why is it important to calculate punching force accurately?**

Accurate calculation of punching force is crucial for several reasons, including selecting the appropriate machine tools and dies, optimizing the punching process, minimizing defects and material waste, and ensuring worker safety.

**3. What factors influence punching force?**

The main factors that influence punching force are material properties (type, thickness, and hardness), punch and die geometry (size, shape, and clearance), and process parameters (stroke rate and lubrication).

**4. How can I reduce the punching force required in a process?**

To reduce the punching force, consider proper material selection, optimal punch and die geometry, appropriate lubrication, and controlled stroke rates.

**5. What are some practical applications of punching force calculations?**

Practical applications of punching force calculations include machine tool selection and design, process optimization, quality control and defect prevention, and worker safety.

**6. What software can be used for punching force simulation?**

Finite element analysis (FEA) software, such as ANSYS, LS-DYNA, and ABAQUS, can be used to simulate punching force and optimize the punching process.

**7. How does lubrication affect punching force?**

Lubrication reduces friction between the punch and the sheet metal, leading to a decrease in the required punching force. Adequate lubrication can also extend tool life and improve the quality of the punched hole.

**8. Why is die clearance important in punching force calculation?**

Die clearance, the gap between the punch and die, is a crucial factor in punching force calculation. If the clearance is too small, excessive force may be required, leading to tool wear and deformation. Conversely, if the clearance is too large, the hole quality might be compromised. Optimal die clearance depends on the material type, thickness, and punch/die geometry.

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