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The previous articles were about how the tool shape determines the type of profile that we need to form. Therefore, before defining which tools are going to be used, it is useful to identify which shape the customer needs to obtain.
In this article we are going to focus on punches needed to produce U-shaped profiles.
Gooseneck punches with a deep relief in the middle are usually the most suitable solution to bend U-shaped profiles with a press brake. The minimum possible width of the bent "U" profile (bottom leg) depends on the width of the inclined side of the punch, while the maximum height of the "U" (up-leg) depends on the relief depth and on the height of the punch.
However, bending "U" profile may not always require using a gooseneck punch: in many cases, a narrow straight punch might be enough to do the job.
Which is the right shape to choose then?
Tool shape according to the U-shaped profile to be formed.
To begin with, U-shaped profiles can be divided in 3 groups:
- square U-profiles;
- rectangular U-profiles (horizontal);
- rectangular U-profiles (vertical).
Let's analyze them.
1. Square U-profiles.
When bending square U-profiles, the return flange touches the center line of the punch. This happens because, being a square, the center line coincides with the diagonal of the square.
Therefore, it is necessary to use a punch where the center line is not "inside" the body of the tool, in the point where the third leg of the profile ends. This type of U-profile does not necessarily require a gooseneck punch, as long as the center line of the tool used is "outside" where it might interfere with the sheet metal.
For example, it is possible to use particular models of straight punches that are narrower or have relief areas on the back, to have more flexibility when bending return flanges. These are standard punches.
There are also models with a great relief area where a big portion of the center line is "outside”. In this case it is worth remembering that the deeper the relief, the less its tonnage capacity.
2. Rectangular U-profiles (horizontal).
When bending horizontal rectangular U-profiles (horizontal), the return flange never collides with the tool, as the base of the rectangle (bottom leg) is longer than its height (up-legs).
In this case, it is enough to check that the back of the punch does not collide with the end of the third leg.
3. Rectangular U-profiles (vertical).
When bending vertical rectangular U-profiles, the return flange always goes beyond the center line of the punch. This is a metalwork which necessarily requires using gooseneck punches: the deep relief in the middle of the punch body prevents the third leg from colliding with the tool.
The maximum height of the U-profile that can be bent depends on the depth of the relief, but remember that a deeper relief also means less tonnage capacity. Therefore, a tool with a lower strength.
The lever arm extends away from the fulcrum - the point where the punch body starts inclining - and, as a consequence, the compressive stress which tends to deform the tool increases. This is the reason why the punches used for U-profiles with a narrow base and long up-legs, have quite low tonnage capacity.
The width of the punch tip determines the minimum width of the U-profile base that can be bent. In other words, the base of the rectangle cannot be shorter than the width of the punch tip.
It is also worth remembering that the narrower the tip, the less the tonnage capacity.
The next article is going to focus on the relation between the height of the punch and the dimensions of the final product.
Anyway, aim at quality.
Whatever your product, make sure you always choose tools that meet these two greatest goals: obtaining a high-quality finished product, in the shortest possible time.
Eurostamp makes press brake tools of excellence. For 50 years we have been helping our clients, responding promptly and efficiently to any request, for standard or custom solutions.
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