Overview of the Roll-Forming Process

Roll-forming is a continuous bending operation in which a long strip of sheet metal (typically coiled steel) is passed 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 similar shape.

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"), flange (e.g. 1-3/8" to 2-1/2") and lip (e.g. 3/8" to 5/8") dimensions, from different gauges (e.g. 20 to 12 GA) of galvanized steel sheet.
 
Roll-forming 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 roll-forming 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 roll-forming lines incorporate only one of the above punch or cut-off applications, others incorporate some or all of the applications in one line.
 
The process of roll-forming is one of the simpler manufacturing processes.

It typically begins with a large coil of sheet metal, between 1 in. and 20in. in width, and 0.004 in. and 0.125 in. thick, supported on an un-coiler. The strip is fed through an entry guide to properly align the material as it passes through the rolls of the mill, each set of rolls forming a bend until the material reaches its desired shape. Roll sets are typically mounted one over the other on a pair of horizontal parallel shafts supported by a stand(s). Side rolls and cluster rolls may also be used to provide greater precision and flexibility and to limit stresses on the material. The shaped strips can be cut to length ahead of a roll-forming mill, between mills, or at the end of the roll-forming line.
 
The geometric possibilities can be very broad and even include enclosed shapes so long as it is the same cross-section throughout. Typical sheeting thicknesses range from 0.004in. to 0.125in., but they can exceed that. Length is almost unaffected by the rolling process. The part widths typically aren't smaller than 1in. however they can exceed 20in. The primary limitation is profile depth, which is generally limited to less than 4in and rarely larger than 6in due to roll-imparted stresses and surface speed differentials that increase with depth.

Tolerances can typically be held within ±0.015in. for the width of the cross-sectional form, and ±0.060in. for its depth.