When I started working in sheet metal processing, I believed that it was impossible to achieve precise bending without using a professional die, as it seemed to be a challenging task.
However, later I had the opportunity to look at some sheet metal parts with closed bend designs that were processed using a press brake.
After analysis with my colleagues, I realized that closed sheet metal bending was possible after all.
So I'm writing this for everyone to learn.
I'd like to share three viable options I discovered.
It is important to note that not all sharp turns are the same. Based on my memories, I created a diagram of a closed curve, as shown below:
The first method:
The image above shows the sheet metal piece I found back then. It is a port panel in a chassis cabinet.
This design serves a reinforcement purpose, which is similar to adding a square tube.
The critical aspect of this closed flexure is the row of long circular holes in the figure. This is because of these long round holes, punches and regular bending dies can be used to complete the bending process, without the need for specialized dies.
The specific steps are demonstrated in the figure below.
Steps for Closed Pushup
The first and third steps involve normal bending, which a skilled and experienced bending master can perform.
In the fourth step, the long round hole in the sheet metal part is used as it is the weakest point in terms of strength. The long round hole can be bent by hand or pressed at a 45 degree angle using a press brake.
The fifth step is completed using a press brake, taking care to avoid interference with the bend.
Once the fifth bend is complete, the bending deformation from step four can be flattened by hand by hitting it with a hammer or using a flattening die.
According to a qualified bending master, uneven bending may occur if the bottom is closed, and excessive deformation may result in cracking.
True, after repair, gaps may appear. However, when the two sides are welded together, they do not separate. By following all the steps described above, the desired result can usually be achieved.
The second method:
If not performed correctly, the bending results will be unsatisfactory, with deformation and depression in the long round hole.
For sprayed plastic parts, this is not a major concern as they can be repaired before being sprayed with plastic.
However, for stainless steel parts or metal sheets without surface treatment, there is another method that can be used, known as reverse bending without pre-opening the long round hole. This method is shown in the following figure:
In the third step, instead of bending at 90 degrees, the bend is made in place using a gooseneck punch in the fourth step. In the fifth step, the angle that was not bent in step three is pressed with a bending punch.
Finally, use a flattening die to achieve a desirable appearance.
The third method:
There is another method, that is, grooving before bending.
Some sheet metal factories may not have implemented the channel in their processes and it may be added later in the work process.
In simple terms, a groove is processed at the bend line position using the grooving method. It is important to maintain some thickness and not completely groove. Typically, leaving 0.4 times the board thickness is sufficient.
The groove makes bending along this line much easier.
As shown in the figure above, the third step can fold up to 90 degrees at once, eliminating the need for subsequent steps. Because the last bend has been grooved, it can be bent by hand or shaped and bent with a rubber mallet.
Although the bending steps are relatively simple, the channel must be made first.
Additionally, after channeling, the rounded corners of the last fold will be smaller than those of the previous three folds, resulting in a different appearance.
Conclusion
A variety of methods for closed sheet metal bending have been introduced, each with its own limitations.
This information is intended to provide inspiration and encourage further exploration.
Furthermore, there are various closed fold shapes and different sizes, so the methods mentioned above may not be suitable in all cases. A detailed analysis is necessary to resolve any issues that may arise.
