Roulage (technique)

Roll forming, also spelled roll-forming or rollforming, is a type of rolling involving the continuous bending of a long strip of sheet metal (typically coiled steel) into a desired cross-section. The strip passes through sets of rolls mounted on consecutive stands, each set performing only an incremental part of the bend, until the desired cross-section (profile) is obtained. Roll forming 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 often used to develop or validate the roll designs and optimize the forming process to minimize the number of stands and material stresses in the final product. Roll-formed sections may have advantages over extrusions of a similar shapes. Roll formed 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. Roll forming machines are available that produce shapes of different sizes and material thicknesses using the same rolls. Variations in size are achieved by making the distances between the rolls variable by manual adjustment or computerized controls, allowing for rapid changeover. These specialized mills are prevalent in the light gauge framing industry where metal studs and tracks of standardized profiles and thicknesses are used. For example, a single mill may be able to produce metal studs of different web (e.g. 3-5/8" to 14 inches), flange (e.g. 1-3/8" to 2-1/2") and lip (e.g. 3/8" to 5/8") dimensions, from different gauges (e.