The machine used to bend metal is called a press brake.
The lower part of the press contains a V shaped groove, called the die. The upper part of the press contains the punch that presses the sheet metal down into the die, causing it to bend. There are several techniques used, but the most common modern method is air bending.
In Air Bending the die has a sharper angle than the required bend and the upper tool is very precisely controlled during its stroke, pushing the material down the required amount to bend it. A general purpose air bending machine has a bending force available of around 25 tonnes per metre of length.
The opening width of the lower die is typically 8 to 10 times the thickness of the metal to be bent, the inner radius of the bend formed is determined by the lower die width. Typically, the inner radius is equal to 1/6th of the V width used in the forming process.
Press brakes usually have a back gauge to position depth of the bend along the workpiece, this backgauge can be computer controlled to allow the operator to make a series of bends to a component to a high degree of repeatable accuracy.
Simple machines control only the backstop, more advanced machines control the position and angle of the stop, the height and positioning of reference pegs used to locate the material. These machine also record the exact position and pressure required for each bending operation, allowing operators to achieve perfect 90 degree bends across multiple operations.
Roll Forming is a continuous bending operation, where longer metal pieces are fed through consecutive rollers, each set of rolls perform just an incremental part of the overall bend, until the desired cross-section profile is obtained.
Roll forming is ideal for producing components with long lengths, for producing open profiles or welded tubes. Roll forming is useful for producing longer lengths or large batches.
Production Lines
Roll-forming lines can be set up with multiple configurations, with sections to punch and remove parts in a continuous operation.
For cutting a component to length, lines can be established using pre-cut die’s where a single blank runs through the roll mill. Or post-cut die are utilised where the profile is removed after the roll forming process.
Features such as holes, notches, embossing, or shearing may be added using punching in a roll-forming line. These part features can be done pre-punch (before roll-forming), mid-line(during roll-forming) or a post punching application (after roll-forming).
Some roll-forming lines will incorporate only one of the above punch or cutoff applications others incorporate most or all of the applications in one line.
Profile Variation
In Roll Forming a variety of cross-section profiles can be produced, with each profile requiring a carefully crafted set of roll-tools.
Design of the rollers starts with a flower pattern, which is the sequence of profile cross-sections, one for each stand of rolls. The roll contours are then derived from the profile contours. Because of the high cost of the roll sets, simulation is often used for validating the designed rolls and to optimize the forming process. This minimizes the number of stands and the material stress in the final product.