Roll forming is a continuous bending operation with rotating tools in which sheet or strip metal is gradually formed in tandem sets of rollers until the desired cross-sectional configuration is obtained. During this operation, only the cross-section is modified, not the sheet thickness. Roll forming is ideal for producing parts with long lengths or in large quantities.

Any kind of shapes can be roll formed, simple and complicated ones. Some examples for roll formed profiles are: U and C channels, struts, door frames, sliding door rails, shutter profiles, trapezoidal profiles, corrugated sheet, screen doors, glass spacer bars, roller blinds profiles, glass shelves profiles, wall and roof cladding, roof bows and trusses, panels, gutters, purlins, fence posts, greenhouse profiles, grape stakes, logistic tracks, drawer slides, studs, beams, scaffolding profiles, beads, shelf racks, sheet piling, guard rails, seat tracks, bumpers, truck and trailer components, window guide channel, seal retainer, cross-members, heat transfer pipes, garage doors, rack beams, duct flanges, drywall profiles, cable trays.

The roll forming machine consists of a machine base with a set of roll forming stands, arranged in series. Mostly between 6 and 32 stands are needed, dependent on the complexity of the profile.

Each stand has a driven top and bottom shaft with force-fit tied roll tools. Often non driven side rolls with vertical axis are used, these side rolls are fastened on special auxiliary holders within or behind the stand. A common motor drives the top and bottom shafts of all stands via a gear box behind the machine. In order to allow adjusting the vertical position of the rolls, the shafts of the stands are connected to the gear box by using cardan shafts. If the gear transmission ratio between top and bottom shaft is 1:1, then the top and bottom rolls have the same working diameter (pitch diameter) in order to have the same circumferential speed at the profile web at least. Mostly however the transmission ratio 1:1.4 is used in order to have a larger top roll diameter (= bottom roll diameter x 1.4). This enables to produce profiles with larger vertical legs.

Each profile cross section needs a customized set of roll tools. First, after defining the final profile cross-section, the flower pattern has to be designed. This means, starting with the final section, the cross section of the profile in each stand is defined by unbending the arcs. Afterwards, the rolls have to be designed by deriving the roll contour from the profile contour in each stand.

A special roll forming problem is the longitudinal strain within the sheet (see below). To avoid remaining strain and unwanted deformations, it is necessary to check just in time, if the longitudinal stress does not meet or exceed the yield stress. During flower pattern creation, the stress can be checked approximately by the Stress of Band Edge Calculation or by the Profile Stress Calculation (PSA).

After completion of the roll design, the FEA method can be used for a final check. It also helps to evaluate if the designed roll tools are able to form the desired profile with the given allowances. The last step is to export the manufacturing data like parts list (sawing list) and the program for the CNC lathe.

Exactly this is the problem: if single points of the sheet cross-section are tracked, movements on curves with different lengths are observed. The result is different strain and stress of the material. As long as this occurs within the elastic bounds, strain disappears again after the profile leaves the final stand of the roll forming machine and the desired profile form can be obtained. If, however, the yield stress is exceeded, remaining strain arises. The local "too much" of material causes unwanted deformations like rippled edges, mostly in case of symmetric profiles. If the profile is unsymmetrical, twists around the longitudinal axis or curved profiles can result. When this occurs, time-consuming and expensive modifying of the roll tools is necessary.