Attention! Bend Allowance and Bend Reduction are two measurements that relate the bent of the curved length of a sheet of metal to the flat length. And it’s also the first step in understanding how sheet metal parts are processed.

What is the Bend Allowance?

The Bend Allowance is the distance between the bend lines or in other words the arc of the bend as measured along the neutral axis of the material. This is due to the fact that the workpiece will be deformed and stretched after bending, so the workpiece will increase in length compared to the original length.

Why should we calculate the Bend Allowance?

When you want to create a flat pattern, you'll need to subtract from the desired part size in order to achieve the right flat size.

What is the Bend Reduction(BD)?

So what is the Bend Reduction indeed? The bend deduction (also known as the bend compensation) describes the amount of stretching on the outside surface of the metal sheet. The BA is equal to the difference between the lengths of the mold lines and the total length.

When flattening a 3D model, the bend deduction represents the amount that must be subtracted from the workpiece length to account for any stretching that occurs during the bending process.

Bend Reduction(BD)= 2×OSSB−BA

PS: OSSB mean: Outside Setback This is the distance from the tangent point of the bend radius to the intersection of the extended outside edges of the flanges.

How do you calculate bend allowance?

The Bend Allowance Formula considers the geometry of the bend and the properties in your metal when determining the Bend Allowance. You will need your Material Thickness, Bend Angle (B), Inside Radius (IR) and K-Factor. The Material Thickness is measured in decimal, not gauge numbers

Bend Allowance Calculation:

The bend allowance calculation formula is:

Bend Allowance Chart

Conclusion

When working with fabricated sheet metal, bend deductions are one of the most important aspects. Missing this step can cause havoc to your formed parts. If you do it correctly, you will have an accurate measurement that you and your customers will love. This article is a great resource and we hope that you enjoyed it. Keep checking back for new articles on sheet metal forming and press brakes.