Manufacturer's tips and tricks for sheet metal bending

Even though widespread, sheet metal bending remains a manufacturing area which can go wrong and become a bottleneck in production. Many factors should be considered by a manufacturer. There are several technical issues to evaluate with the bending radius and air bending, once sorted, it will be easier to decide whether new tooling should be acquired.


Radius Does Matter

Regardless of method—air bending, bottoming, or coining—the inside bend radius is at the heart of precision sheet metal bending. Without it we will not be able to calculate the values for K factors, bend allowance, outside setbacks, and bend deductions. The inside radius of a workpiece matters—big time.

The punch radius is obvious: It’s the radius of the punch tip. Die radius usually refers to the radius of the die shoulder on either side of the die opening. Also it can be the radius at the bottom of the V die.

When air bending or bottoming, a sharp corner at the bottom of the V is still technically a “radius.” However, you may be coining, in which case you would be using a die with a noticeable radius at the bottom of the V. That radius should match the outside radius of the bend, like how a stamping die works.

How a Radius Forms

Just how the radius is created varies greatly with the bending method. If I use a punch with a nose radius equal to the inside radius I want to achieve, then I can bottom-bend or air-form the part. This is a “perfect” bend.

In an air bend, what matters most is the width of the die opening, as the radius will be floated as a percentage of that width. The percentages vary by material type. The correct die width will give you the bend radius you need.

The second-most important consideration in air forming is the punch nose radius. You do not want a radius on the punch nose to be larger than the natural radius floated in the part, and you do not want a punch nose radius less than what’s known as a sharp bend, or the minimum inside radius that’s possible without creasing the center of the bend.

This coining setup will lead to problems. The radius at the bottom of the die should not be smaller than the outside bend radius.

Depending on your desired inside radius, you can use these concepts to pick the appropriate die opening and punch radius for the job. The closer you can get the punch nose radius to the naturally floated radius, the more consistent and stable the bends will become, both dimensionally and angularly.

Air Bend Tooling Considerations

If you’re air bending, know that the included die angle, die radius, and the radius at the bottom of the die have no effect on the floated inside radius of the workpiece, which again is a function of the die width. Know, however, that bottoming cannot be performed or even attempted on these tools. Acute dies are meant solely for air forming.

Combining any acute-angle die with the tonnage pressure of bottoming would create so much side thrust on your die that it would split your tool down the middle.

Tooling Is a Consumable

I have watched many a fabricator buy a new, state-of-the-art press brake only to continue to use the same old beat-up tooling and outdated methods—then question why their new, state-of-the-art press brake isn’t living up to expectations!

Press brake tooling should always be viewed as a consumable item; it’s long-lasting, for sure, but it does not last forever. It wears out. The amount of extra time your operator will spend attempting to correct for issues directly related to worn-out tooling will far surpass the costs of new, high-quality tooling.

Along with supervisors, managers, and executives (who may not want to spend the money), operators and technicians are just as culpable in hindering the adoption of new tooling, bending methods, and machines. Occasionally a job may require a special tool, but you can use adapters (traditional planed to precision, or precision to traditional planed) to fit it on a new press brake. It often boils down to human nature and having to move out of our comfort zones.


IMA Information

Italian Machinery Association engineers have many years of experience in the bending market, having a broad knowledge of the bending machines of various kinds, bending techniques and tooling. No matter what requirement a bending customer might have, our experts are ready to provide the best advice and offer press brakes from Italian manufacturers Euromac and Vimercati, as well as the press brake tooling.

These are both hydraulic and electric kinds, as well as universal combined equipment with different tonnages.

Our catalog’s range of press brakes from our members can satisfy needs of any manufacturing, from a small job shop to an automated multi-tasking plant.

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