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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.
Roll-formed sections may have advantages over 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.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 time for one product to take shape can be represented by a simple function: , where is the length of the piece being formed, is the number of forming stands, is the distance between stands, and is the velocity of the strip through the rolls.
In general, roll forming lines can run from or higher, depending on the application. In some cases the limiting factor is the punching or cut-off applications.
Lubrication provides an essential barrier between the roll dies and the work-piece surface. It helps reducing the tool wear and allows things to move along faster. This table shows the different kinds of lubricants, their application, and the ideal metals to use them on.
| Nonferrous | Chlorinated oils or waxes, mineral oils | Spray, wiping roller |
| Ferrous | Water-soluble oils | Wiping, drip, spray |
| Stainless steels | Chlorinated oils or waxes | Wiping roller |
| Polished surfaces | Plastic film | Calendaring, covering, spraying |
| Pre-coated materials | Film or forced air |
The effects of the process on the material's properties are minimal. The physical and chemical properties virtually don't change, but the process may cause Work hardening, Crazing, or thinning at bends when discussing the mechanical properties of the material.
The cost of roll forming is relatively low. When calculating the cost of the process things such as setup time, equipment and tool costs, load/unload time, direct labor rate, overhead rate, and the amortization of equipment and tooling must be considered.
Safety is also a bit of an issue with this process. The main hazards that need to be taken into consideration are dealing with moving work-pieces (up to ), high pressure rolls, or sharp, sheared metal edges.
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