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Some common sense about bending radius of bending machines


Press Brake bend radius, bend deduction, bend allowance, and K factor are important parameters in sheet metal processing.

Sheet metal processing is a comprehensive cold-working process for sheet metal materials (usually below 6mm).

Such as steel plates, aluminum plates, copper plates, and other metal plates.

Sheet metal processing techniques include shearing, punching/cutting/compounding, bending, folding, welding, riveting, splicing, forming (such as automobile body), etc.

Sheet Metal Bend Radius

The remarkable feature of sheet metal processing is that the thickness of the same part is consistent.

Sheet metal bending refers to the processing of changing the angle of sheet metal. Example, bending the sheet into a V shape, U shape, etc.

Generally, there are two ways to sheet metal bending:

One method is died bending, which used for sheet metal structures with complex structures, small volumes and mass processing.

The other is bending by the press brake, which used to process sheet metal structures with large structure sizes or small output.

What Is the Sheet Metal Bend Radius?

Sheet Metal Bend Radius

When the material is bent, the outer layer is stretch, and the inner layer is compress in its fillet area.

When the thickness of the material is constant, the smaller the inner radius, the more serious the tension and compression of the material.

When the tensile stress of the outer fillet exceeds the ultimate strength of the material, cracks and fractures will occur.

The tensile strength and bending radius of metal materials affect the bending quality of the workpiece.

Therefore, the structural design of the bending workpiece should avoid using too small a bending fillet radius.

The bending radius usually refers to the distance from the bending axis to the plate surface when bending metal plates, bars, etc., Which is generally called the internal bending radius.

The external bending radius is usually the sum of the internal bending radius and the sheet thickness.

What Determines the Sheet Metal Bend Radius?

Sheet Metal Bend Radius

Many factors affecting the bending radius, including material strength, materials thickness, lower die opening width, tonnage, etc.

In the process of bending, the plate will produce compressive stress and tensile stress, which will also affect the bending radius.

When the plate is bent, the inner side of the neutral axis is compressed, and a force resisting compression will be generated in the plate.

When the outside of the neutral axis is stretched, a tensile resistance force will be generated in the sheet.

When the workpiece is taken out, the residual compressive stress and tensile stress will cause the material to spring back, which makes the bending angle larger.

The greater the hardness and thickness of the material, the greater the spring back, which requires over-bending to obtain a smaller angle than expected.

In air bending, the inner radius is about 16% – 20% of the width of the die opening. For example, the common 60 KSI cold rolled steel is about 16%, and the stainless steel is 20%.

Generally speaking, if the material thickness is less than 6mm, the inner radius is equal to the material thickness.

The larger the opening of the V-shape die, the larger the bending radius.

On the same V-shape die, the greater the tensile strength of the material, the greater the inner radius.

Press Brake Bend Radius Calculation

The 8 rule is a rule of thumb applicable to the V-shape die opening, which means that the V-shape die opening should be 8 times the material thickness.

There is no perfect sheet metal bend radius formula, but within the specified bending force range, the inner radius roughly equal to the plate thickness can be calculated.

Of course, the change in material thickness will affect the accuracy. Some V-shapes die openings are 6-12 times the material thickness.

The thickness of the material is closely related to the inner radius of the bending.

When the material thickness is less than 6mm, the inner radius of bending is equal to the material thickness.

When the material thickness is greater than 6mm but less than 12mm, the inner radius of bending is generally 1.5 times the material thickness.

When the material thickness is less than 12mm, the inner radius of bending is approximately 3 times of the material.

This is just a rule of thumb. There are too many factors that affect bending, so it is difficult to be 100% correct.

When the thickness of the sheet is equal to the bending radius, the most perfect bending radius will be generated.

The bending state generated by this radius is very stable, its bending angle and size are consistent, and the spring back generated is the least.


Bend radius is an important factor in sheet metal bending, and the proper inner radius determines the bending quality of the workpiece.

Through the inner radius, we can also calculate important parameters such as bending allowance and bending deduction.

Improper inner radius will lead to deformation or even fracture of the workpiece. By reading this article, you can learn more about sheet metal bending,

The use of the KRRASS press brake can help you to manufacture more precise workpieces, and you can contact us to learn more about the press brake.


What Is the Minimum Bend Radius of Sheet Metal?

If the bend radius is smaller, the stress on the outside of the bend will be greater and the tension will be greater.

The plate will be deformed, cracked, or broken during bending. To avoid these problems, attention should be paid to the minimum bending radius.

Due to different bending methods, die and material characteristics, different workpieces may have different minimum bending radii, and it is difficult to calculate the correct value.

However, to obtain the most perfect bending workpiece, the inner radius should be set as close to the plate thickness as possible.

To select plates with high ductility, the greater the tensile strength and hardness of the material, the larger the radius is required.

What Is the Formula for Bend Deduction?

The bend deduction is the amount that the sheet is stretched during bending. Its value is the difference between the total length of the flange and the total flat length.

What Is the Formula for Bend Deduction

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