Roll forming is a metal fabrication process that involves the bending of metal strips to create a certain shape or design. It's one of the most simple and easy-to-understand metal forming processes there is; however, there are several components that go along with it.
Once you learn about these components and the role they play in the metal fabrication process, you'll understand exactly how your roll formed part is made.
Roll forming may seem like magic at first glance: You insert a coil of metal in one end, and a finished part pops out the other. But exactly what happens in the process to make that happen?
Let’s explore the mystery of this metal fabrication process by taking a closer look at 6 components of a roll forming line:
Roll forming starts with equipment that prepares the metal coils for bending. As the coils have been tightly wound for some time, minor correction is needed to remove coil set. Coil set is the tendency of the metal to stay coiled, plus a bit of material distortion.
Strip accumulators and slack loop stands contribute to roll forming’s highly efficient metal fabrication process. They allow the coil strip to stop long enough for a pre-punch press stroke while still allowing the roll form mill to run continuously.
Strip accumulators are used in high-speed operations where frequent stopping and starting will cause a loss of efficiency.
The accumulators temporarily store sections of metal strip, allowing the operations to continue while the loop straightens out. Timing needs to be accurate in order to feed another segment of “slack” at just the right time.
Before the metal is fed through the line, it may pass through one or more in-line punch presses. This is the first opportunity in the metal fabrication process to eliminate secondary fabrication steps by designing them into the roll forming line.
Digital controls and highly accurate coil feed systems allow operators to punch holes, notches, and slots in any number of uniform patterns. Depending on your project specifications, this may add no time at all to the production cycle.
The mill is the section of the roll forming line where the material is progressively shaped into its final form. A typical roll form mill consists of 10-24 pairs of roller die stands.
The mill is individually OR gang-driven to pull the ribbon of metal through the rollers. The rollers gradually form the ribbon into the finished shape. The flower pattern below illustrates the forming process of one particular series of rollers:
Once formed, the metal part is run through a series of straightening dies and side rollers to remove any lingering twist, bow, or camber. This step is absolutely necessary, as these distortions can easily ruin a perfectly good part.
The finished shape is cut to length in a flying cutoff press, which cuts the part to length without stopping the roll forming process. The flying cutoff press performs similarly to the slack loop at the beginning of the line. By accelerating the cut-off die at the same speed as the roll forming mill, very accurate length cuts are made. The part is then discharged onto a run-out table, so the operator can place it in protective crating for storage or shipment.
If secondary operations are required, your manufacturer may be able to complete those operations directly near the unloading end of the line. In the case of certain roll form suppliers, certain secondary operations could be free, if the cycle time to perform them is equal to or less than the time it takes for the next formed part to exit the line.
There are a wide variety of secondary operations available for roll forming, including:
From preparing metal coils to accounting for slack, the cutoff process, and all that happens in between, you now have a better idea of what happens “behind the curtain,” so to speak.
The roll forming process isn’t magic after all -- just some good old-fashioned metal fabrication.
Now that you understand how roll formed parts are made, feel free to check out our e-book on designing great rolled formed parts:
(Editor's note: This article was originally published in January 2016 and was recently updated.)