Roll forming: how coil becomes a section

The process

1. Decoiling: the strip is drawn continuously from the coil.
2. Levelling: the curvature inherited from the coil is straightened out.
3. Forming: the strip passes through successive roller stations, each bending it a little closer to the final cross-section.
4. Operations: punching, dimpling, marking, cut-outs — typically in line, before or after forming, depending on the machine.
5. Cutting: the finished profile is cut to length.

Why forming is gradual

Because a sharp bend cannot be made in one step without damaging the sheet. Gradual forming:

• preserves the edge — it does not crack,
• gives accurate geometry, because each station makes a small deformation,
• produces predictable springback, which the tooling allows for.

The bend radius is matched to the steel grade and thickness. What cold forming does to steel.

What follows for design

The cross-section is fixed, the length is free

The roller line produces one given cross-section. Length, however, is arbitrary: cutting follows the program. So member length is not a cost factor in the way it is for technologies working from standard lengths.

Changing profile is a setup question

Another cross-section means resetting the machine, or a machine adjustable within its range. This affects production scheduling: members with the same profile are produced in one run.

The operation is part of the pass

Punching, dimpling and marking are made in the same pass. There is no separate workshop work, so connection details do not make production more expensive. Tools and machine operations.

The quality decided here

The accuracy of the cross-section determines the capacity of the structure. That is why flange and lip width, straightness and squareness are measured on the finished profile — not for cosmetic reasons. In-process quality control.

The point

The essence of roll forming is gradualness: it gives accurate geometry, and it lets every member have its own length at no extra cost.