### Bending Basics 2015

#### Grand Unifying Theory of Bending on a Press Brake

##### September-December 2015

The Grand Unifying Theory of Bending on a Press Brake pt 1

Press brake guru Steve Benson proposes a new theory of bending, altering some long-held labels and definitions and introducing new formulas. Those long-held definitions worked well, but these new definitions and formulas may help a press brake technician become even more accurate in predicting how a part will form.

The Grand Unifying Theory of Bending on a Press Brake pt 2

Radius bends—defined here as any bend with an inside radius greater than 125 percent of the material thickness—require careful calculation, not only because of their significant springback but also because of the tooling these bends require. This includes the use of relieved dies.

The Grand Unifying Theory of Bending on a Press Brake pt 3

In this installment of the Grand Unifying Theory of Bending, press brake guru Steve Benson describes bending calculations for aircraft tooling. He also covers the basics of bottoming.

The Grand Unifying Theory of Bending on a Press Brake pt 4

This month Steve Benson summarizes his grand unifying theory of radius, bend deduction, and die selection with a review and complete rundown of the bend calculations, from estimating springback to working the bend functions.

You can use some common rules of thumb to predict the inside bend radius when air forming and the results you get are usually close enough, but with the help of a few online calculators, you can get even closer.

Using the 20 percent rule works well when calculating the floated radius in an air form, but what about the radius at different bend angles? To calculate this, we start with geometry to find the arc length and radius at different bend angles. We then manipulate these results by factoring in real-world bending conditions.

Forming aluminum on a press brake
June 2015

Air bending soft aluminum has such a low tensile strength that it doesn’t take much for a narrow punch tip to penetrate the surface and turn the bend sharp.

How an air bend turns sharp
May 2015

Why do air bends in cold-rolled steel turn sharp at an inside radius that’s about 63 percent the material thickness? It has to do with the relationship between forming forces and a material’s tensile and yield strength.

To ensure you always work within the tonnage limits of your press brake and tooling, first, calculate how much tonnage you need. Second, identify your tooling’s load limits. Third, calculate the sinking tonnage limit, which, if exceeded, can embed tooling into the ram or bed. Fourth, determine your press brakes’ centerline load limit.