Bend deduction is a critical aspect of press brake bending.
The size of the workpiece, as depicted in a graphic design drawing, is different from its size in the bent state.
During bending, the tension stretches the outer material, causing it to elongate, while the inner material is compressed.
The neutral axis remains unaffected by pressure or tension, hence, its length remains unchanged.
As a result of these changes, the size of the workpiece after bending is different from the size of the flat pattern.
To correct the bending point and flange length, it’s necessary to calculate the bend deduction, which represents the amount to be subtracted from the workpiece size after bending.
In simpler terms, Bend Deduction (BD) refers to the extent to which the sheet is stretched after the tension applied during bending is released.
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 required to calculate the bending deduction are the material thickness, the bending angle, the inner radius and the K-factor.
The K-factor, i.e. the ratio of the distance between the neutral line and the material edge to the material thickness, is determined by the material thickness and the bending method.
The formula for the K-factor is:
K = t/T
where t is the distance from the neutral line to the edge of the material and T is the thickness of the material.
The K-factor usually ranges between 0.3 and 0.5.
We present the formula for calculating the bending allowance:
If we know the bending allowance (BA) and the external setback (OSSB), we can quickly calculate the bending deduction.
BD = 2 – OSSB – BA
The formula for the external setback (OSSB) is:
When we know these parameters, the bend deduction calculation formula can also be:
Where K stands for the K-factor, R and IR both stand for the inner radius, T for the material thickness, B for the bending angle and MT also for the plate thickness.
The calculation of bend deduction is crucial in the preparation of sheet metal bending. Accurate calculation results are necessary to produce precise bending workpieces.
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