Rollforming, is a continuous bending operation in which a long strip of coiled metal is passed through sets of rolls mounted on consecutive stands called passes, each set performing only an incremental part of the bend, until the desired cross-section profile is obtained. Rollforming is ideal for producing constant-profile parts with long lengths and in large quantities.
A variety of cross-section profiles can be produced, but each profile requires a carefully crafted set of roll tools. Design of the rolls starts with a flower pattern, which is the sequence of profile cross-sections, one profile for each stand of rolls. The roll contours are then derived from the flower pattern profiles. Because of the high cost of the roll sets, computer simulation is used to develop or validate the roll designs and optimise the forming process to minimise the number of stands and material stresses in the final product.
Cold roll formed steel sections may have advantages over extrusions of similar shapes. Rollformed parts may be much lighter, with thinner walls possible than in the extrusion process, and stronger, having been work hardened in a cold state. Parts can be made having a finish or already painted. In addition, the roll forming process is more rapid and takes less energy than extrusion.
Rollforming lines can be set up with multiple configurations to punch and cut off parts in a continuous operation. For cutting a part to length, the lines can be set up to use a pre-cut die where a single blank runs through the roll mill, or a post-cut die where the profile is cut off after the rollforming process. Features may be added in a hole, notch, embossment, or shear form by punching in a roll forming line. These part features can be done in a pre-punch application (before roll forming starts), in a mid-line punching application (in the middle of a roll forming line/process) or a post punching application (after roll forming is done). Some rollforming lines incorporate only one of the above punch or cut off applications, others incorporate some or all of the applications in one line.