Table of Contents

## Optimum Bending radius

There should have a bending radius for sheet metal bending, it should not be too large or too small, and should be chosen appropriately.

If the bending radius is too small, it will cause cracking at the bend position;

If the bending radius is too large, it is easy to rebound.

However, you can use V grooving machine to groove first, and then bend. In this way, you will get a smaller bending radius.

The optimum bending radius of different thicknesses of various materials (bend inner RADIUS) see table below:

Metal |
Annealing Condition |
Cold Hardening State |
||

The corresponding position of bending direction and fiber direction | ||||

Vertical | Parallel | Vertical | Parallel | |

08, 10 | 0.1t | 0.4t | 0.4t | 0.8t |

15, 20 | 0.1t | 0.5t | 0.5t | 1.0t |

25, 30 | 0.2t | 0.6t | 0.6t | 1.2t |

45, 50 | 0.5t | 1.0t | 1.0t | 1.7t |

65Mn | 1.0t | 2.0t | 2.0t | 3.0t |

Aluminum | 0.1t | 0.35t | 0.5t | 1.0t |

Brass | 0.1t | 0.35t | 1.0t | 2.0t |

Soft Brass | 0.1t | 0.35t | 0.35t | 0.8t |

Semi-rigid Brass | 0.1t | 0.35t | 0.5t | 1.2t |

Phosphor bronze | / | / | 1.0t | 3.0t |

The data in the table above is the preferred data for reference only. In fact, the rounded corners of press brake are usually 0.3, and a small number of the rounded corners of the press brake punch is 0.5.

For ordinary low carbon steel plate, anti-rust aluminum plate, yellow copper, purple copper etc, the inner radius 0.2 is no problem, but for some high carbon steel, hard aluminum, super-hard aluminum, the use of 0.2 radius will lead to bending fracture or the outer radius crack.

## Factors that may affect the bending radius

What are the factors that may affect the bending radius of the sheet metal?

There are sheet metal thickness, sheet metal material, top punch radius, bottom die, bending force, working temperature etc.

Based on personal experience, I hope this article will be useful to readers.

**Bending Angle**

**Bending Angle**

The bending angle of the sheet metal is the key factor affecting the bending allowance.

For example, if bending the sheet metal with large radius, more bending allowance will be deducted; if bending acute angle, less bending allowance shall be deducted.

**Sheet Metal Thickness**

**Sheet Metal Thickness**

In actual work, it is found that the thicker the material, the larger the bend radius.

We know that the thicker the plate, the greater the bending force and the larger the vee opening of the lower die.

So, what is the factor that affects the bend r angle?

**Sheet ****M****etal ****M****aterial**

**Sheet**

**M**

**etal**

**M**

**aterial**

The bending allowance of different plates of the same thickness are different, with slight differences, which proves that the material properties affect the bending radius.

The material has a property that resists bending and may directly affect the bending radius.

The material has an effect on the bending radius, but it has little effect on our actual use.

We can customize the bending allowance table for different materials.

**Top Punch Radius**

**Top Punch Radius**

The radius of normal bending mold is not larger than r1, and the minimum radius of the punch cannot be less than 1.

There is little effect on the bending without requirements for the bending radius.

For the sheet metal bending with special requirements and the bending radius is less than 1 or much larger than 1, it is not determined by the radius of the top punch.

Therefore, the radius of the top punch directly affects the bending radius.

**Bending ****Force**

**Bending**

**Force**

The thicker the sheet metal, the greater the ability of the material to withstand bending deformation.

Then you need to adjust the bending force.

The bending force cannot be increased indefinitely and needs to be adjusted to the proper level.

The bending force is proportional to the thickness of the sheet metal and inversely proportional to the width of the notch of the lower die.

In the actual bending, the thickness of the sheet metal is set, and the width of the lower die slot is selected according to the thickness of the sheet metal.

Therefore, the bending force is a constant determined by other factors.

The bending radius can be ignored without considering the bending force.

**Bottom**** ****D****ie**

**Bottom**

**D**

**ie**

The width of the lower die slot is related to the thickness of the sheet metal, and there is a corresponding relationship.

In practice, the greater the thickness, the larger the bend radius.

For the same sheet metal thickness, the bending radius is also different for using different with of vee opening.

It turns out that the lower die slot is an important factor affecting the bending radius.

**Operating ****T****emperature**

**Operating**

**T**

**emperature**

Generally, the working environment temperature is room temperature, which can be ignored.

**Conclusion**

**Conclusion**

The bending force is involved in the change of the bending radius, but is determined by the thickness of the sheet metal and the width of the notch of the lower die.

Almost all factors affect the bending radius, we can only limit the factors affecting the bending radius according to the demand.

For example, when the workpiece doesn’t have requirement for the bend radius, just limit all factors and specify a specific bend factor table.

When the bending radius is required to be much larger than 1, modify the radius of the upper die, and customize a specific bending factor.

Do not change the width of the lower die slot, which will affect the bending radius and bending allowance.

It can also be used to modify the width of the lower die slot and change the bending allowance and bending radius.

WendyThanks for the information!! Can I check, if 2 sheets which are made of the same material, have the same thickness but different width, will that affect the amount of bending of the material if the same force is applied to it? Thank you!

ShaneSome other factors also need to be considered, such as the bottom dies used, bending method (air bending, bottoming, coining), etc. You can read more articles in the bending category to learn more about this.

NareshWhat will be the impact in terms of load bearing capacity if the radius is more for same thickness of sheet metal and same bend length.

For eg: Sheet metal of 2mm thickness – C bend

Bend dimension 50mm each and at center it will be 100mm.

If outer radius if i maintain 4R and another piece 6R

any load carrying capacity changes?

ShaneMaybe you can get some ideas from this post: https://www.machinemfg.com/calculation-of-sheet-metal-bending-force-in-air-bending/