## What Is Bend Deduction?

Bend deduction is a necessary parameter in press brake bending.

The length in the graphic design drawing of a workpiece is different from that in the bending state.

During bending, the outside of the material is stretched to a longer length by tension, and the inside is compressed.

There is no pressure or tension on the neutral axis, so its length will not change. After bending, the size of the workpiece is different from that of the workpiece in a flat pattern.

Therefore, it is necessary to calculate the bend deduction, which is the amount to be subtracted from the bending workpiece size.

In this way, the correct bending point and flange length can be obtained.

In other words, bend deduction (BD) refers to the extent to which the tension applied to the sheet is stretched after bending.

Thus, the value of bend deduction is equal to the difference between the total flange length and the total flat length.

## How to Calculate Bend Deduction?

The parameters needed to know for bend deduction calculation include material thickness, bending angle, internal radius and K factor.

The K factor is determined by the material thickness and bending method and is the ratio of the distance between the neutral line and the material edge to the material thickness.

K=t/T

Where t is the distance from the neutral line to the material edge, T is the material thickness, and the K factor range is generally 0.3~0.5.

We have introduced the calculation formula for the bend allowance:

If we know the bend allowance (BA) and the outside setback(OSSB), we can quickly calculate the bend deduction.

BD=2 · OSSB - BA

The calculation formula of outside setback(OSSB) is:

When we know these parameters, the bend deduction calculation formula can also be:

Where K represents the K factor, R and IR both represent the inner radius, T represents material thickness, B represents the bending angle, and MT also represents plate thickness.

## Conclusion

The calculation of bend deduction is an essential factor in preparing sheet metal bending. Accurate results need to be calculated to obtain precise bending workpieces.

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