What you need to know about roll forming

Many companies that form a variety of shapes and have a choice of machines that can be used often switch the rolls from one machine to another. The operator usually has no input in choosing the machine, because its selection is treated as a production/scheduling problem. However, the person who does the scheduling does not know that forming rolls are designed for a machine with a specific horizontal center distance, and running them at any other distance will affect how well they work. This basic principle explains why operators are heard to say: "This set of rolls works on Machine A, but we have problems when running it on Machine B." The term "horizontal center distance" is the most misunderstood phrase in roll forming. It refers to distance from the centerline of one forming station to the next

Roll Forming Machine

Does changing the rolls to a machine with a different horizontal center distance mean they will not work? Not necessarily. However, if the horizontal distance is shortened, it is possible that one or more portions of the metal strip will be stretched going from one forming station to another and be permanently wrinkled. The term for this case is "forming too fast."

If the horizontal distance is increased, there is a chance that the profile will spring open between some passes. Wherever a profile opens, the next station must close it back to its original position in addition to doing its share of the forming. It usually is not possible to close the profile to its original position because of localized work hardening of the metal. This phenomenon is called "losing control of the section."

Each metal has a different set of formability characteristics, which includes springback. A set of roll tooling that is designed for a low carbon steel might not work on one of the stainless steels or any metal that has more springback. As a guideline, the only way to determine how much lengthening or shortening the horizontal machine center will affect the performance of a set of forming rolls is to try the rolls at different horizontal distances using the metal in question.



The trend in rollforming is to reduce the thickness of the metal in the part, and maybe change the metal. As a result, the formability of the metal changes. The Purchasing Department orders the new raw stock, and the Sales Department notifies their customers of the availability of an improved product. The Production Department receives notification, so it can plan for a change in volumes for its products.

The operators, however, are not told of the change to the product. Thinner material, with different formability, is brought to the roll forming line, and the operator is expected to produce parts at least as good as the ones they have been making. None of the people involved in making the change is aware that a change in metal thickness affects the performance of the roll tooling.