How to Perform Closed Bending in Sheet Metal Processing?

When I first started working in sheet metal processing, I thought it was impossible to complete close bending, unless I use a professional die (it seems very difficult).

Later, I had the opportunity to contact some sheet metal parts, that is, closed bending design, which was processed by the press brake machine.

I analyzed it with my partners and thought that sheet metal closed bending can still be done.

Today I write it down for everyone to study together.

I share three options that I think are feasible, which are listed below.

Not all closed bends are the same. According to my memory, I temporarily draw the closed bend diagram. See the figure below:

closed bend diagram

The first method:

The picture above is the sheet metal part I saw at that time. It is a door panel on the chassis cabinet.

This design plays a reinforcing role, which is equivalent to adding a square tube.

The key point of this closed bending is a row of long circular holes in the figure. Why?

Because of this row of long round holes, ordinary bending punch and die can be used to finish the bending and no need for special dies.

The specific steps is shown in the figure below.

Closed bending method

Steps for closed bending

The first step to the third step are normal bending, and the bending master with certain experience can fold it out.

The fourth step is to use the long round hole on the sheet metal part because the strength of that piece is the weakest.

The position of the long round hole can be bent manually or pressed 45 degrees by the bending machine.

The fifth step is completed with a bending machine. Pay attention to bending interference.

When the fifth bend is finished, the bending deformation in the fourth step can be flattened manually. You can knock it with a hammer or press it with a flattening die.

An experienced bending master said: the bending is uneven because the bottom is closed, there will be cracks without excessive deformation.

Yes, in fact, there will be gaps after repair. At this time, when the two sides are welded together, they will not open. After completing all the above steps, the goal can be basically achieved.

The second method:

If it is not done well, the bending effect is not good. There will be deformation and depression at the long round hole, and the effect is not very satisfactory.

If it is a plastic sprayed part, it doesn’t matter much. It can be repaired before plastic spraying.

What about stainless steel parts or sheet metal parts without surface treatment? The network God also drew the processing method of reverse bending without opening a long round hole in advance.

As shown in the figure below, the third step is not folded to 90 degrees, the fourth step is to bend in place with a gooseneck punch, step 5 press the angle that is not folded in place in step 3 with the bending punch.

Closed bending method

Finally, use the flattening die to make it looks good.

The third method:

There is another method, that is, grooving before bending.

There may be some sheet metal factories that haven’t contacted the grooving, and I only contacted it later in my work.

Simply put, at the position of the bending line, use the method of grooving to process a groove. It is necessary to leave some thickness, which can not be grooved completely. Generally, it is OK to leave 0.4 times the plate thickness.

Because after grooving, this bending line is easy to bend.

The third step in the figure above can bend to 90 degrees at one time, and the following steps are not needed.

Because the last bend has been grooved, it can be bent manually or shaped and bent with a rubber hammer.

Relatively speaking, the bending steps are simple, but the groove needs to be made first.

In addition, the rounded corners of the last bend after grooving will be smaller than those of the previous three bends, and the appearance effect is different.


So many closed bending methods of sheet metal are introduced, and each method has its own limitations.

Here is just to develop ideas, hoping to draw inferences from one example.

In addition, there are many different forms of closed bending or different sizes. The above methods are limited and may not be applicable. Problems need to be analyzed in detail.

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