Some Press Brake Bending Techniques

Press brake bending is simple stuff: An arrow-shaped punch presses a sheet metal blank into a v-shaped die, thereby forming an angled bend. Or maybe, if we are getting adventurous, we could imagine something like a gooseneck punch making return flanges, but that is stretching it as far as it goes, right?

No, not quite. Press brake tooling has come a long way in recent years, and can do a lot more than it used to, and probably a lot more than you think. Some of the more interesting techniques include wiping, rocker dies, 3 way bending and elastomer bending.

A wiping operation consists of more than one movement, unlike simpler shaping methods. A special die set is used, where the bottom die has movable elements. As the punch moves down and executes the first part of the bend, the bottom element receives the blank and is pressed down on its springs. This motion activates an element on the back of the die, which now moves in and executes the second part of the bend. A good example of the application of this technique is the making of a radiused return flange: The blank is pushed down on the first, springloaded element, and the resulting downward motion bends the blank to a right angle with a radius at the bending point. The second element then comes into play and finishes the job by folding the edge of the blank over, creating a return flange in the process.

Rocker dies are essentially simple dies - with a twist: The top die has a built in 1-axis joint, which allows it to enter a bottom die with a partially obscured opening. This makes it possible to form a channel in one pass, even if the flange is very long - something that (depending on the shape of the part)might not be doable in a traditional channel die set. In that case, rocker dies provide the benefit of reduced setup time and fewer operations in order to shape the part.

The term 3 point bending is used about a special type of die set, in which the bottom die has an element which can be adjusted in height by a servo motor. The top die is buffered from the ram with a special hydraulic cushion to compensate for little variations in the thickness of the blank. Together, the two dies make it possible to attain extreme precision in the angles bent - down to 0.25 degrees. This type of tooling is expensive though.

Elastomer bending is especially interesting. Here, the bottom die isn't steel, but a flat piece of synthetic material which serves to wrap the blank around the punch, as it comes down. The resulting bend radius will be very close to the punch radius, as there is little springback. Also, the elastomer pad does not mar or scratch the blank.