Punch presses can also be used for bending parts. Special bending tools make it possible to produce flanges with bent angles of up to 90 degrees. Designers who know how to take advantage of these capabilities can design many sheet metal parts so that can be produced entirely on a punch press. This, in turn, enables sheet metal fabricators to eliminate not only this step but also the cost associated with the use of a press brake.

The bending process

Sheet metal bending tools work in a variety of ways. One involves the use of a roller that is set into the die. When the punch is lowered, it presses the workpiece up against the surface of the roller. The pressure created by the punch causes the roller to rotate, and movement of the roller then bends the sheet upward. In addition to simple bends, multiple bends and diagonal bend scan also be made. The dimensions of both the bend and the bent surface, however are limited.

Sheet metal bending techniques

Formed parts where process of sheet metal bending was used, are everywhere. Door hinges, computer housing, TV panel, etc. We come across them at every turn. A large number of these parts are fabricated using the following techniques.

AIR SHEET METAL BENDING

In air sheet metal bending, the punch presses the workpiece into the lower die without actually forcing the material up against the inside of the die. As the punch is lowered, the flanges of the workpiece are turned up, creating an angle at the point where the punch presses material down. The farther the punch presses the workpiece toward die, the smaller the angles becomes. The size of the angle is determined by the distance that the punch travels.

Advantages

Air bending is a standard technique for producing angles from 30 to 179 degrees. Air sheet metal bending is cheaper and more flexible then other techniques.

BOTTOM SHEET METAL BENDING (COINING)

In bottom bending, the punch presses the workpiece completely into the die below. Punch, workpiece, and die precisely fit one on the top of the other. At the same time, this means, that for each angle and shape different tool has to be used.

FOLDING AND HAMMING

Sheet edges are often folded over, or “hemmed” like a pair of trousers. This produces a bend whose two flanges are parallel. Hemming increases the rigidity of the finished part and provides edge protection. Interlocking hems are also frequently applied in lock seams for joining parts.