What you need to know about roll forming

Roll forming is a metal bending operation. This is the fundamental principle of the roll forming process. A common mistake that is made when running a rollforming machine is to roughly adjust the first forming passes to get an approximate shape, and then use the last several stations to force the metal into the final shape. An approach like this combines coining, stretching and extruding, and results in a part that is full of internal stresses. If the metal is thin, the part becomes "alive." A test to check if a light gauge profile was formed too fast in the last several rollforming stations is to hold a long piece of the profile by one end and slowly rotate it. If it is alive, it can suddenly snap into a twist along its length.

Roll Forming Machine

Internal stresses within a live section are not consistent, causing problems in secondary operations, like curving or bending. Two pieces that are roll formed by different operators using the same set of tools can look the same, but behave differently. One person adjusted all the forming passes so each pair of rolls did its share of the work, while the other used the last passes to crunch the metal into shape.



Although a rare exception, sometimes the operator cannot obtain a good cross-section without excessive pressure in the last driven passes because of a poor roll design. In other words, the rolls are not capable of forming the product. An experienced operator can determine the capability of a set of roll tooling by setting the roll gaps to do pure bending, and closing them slightly to compensate for the springing apart of the roll spindles under load. The set of tools will have a different capability for each material and material thickness combination that is processed. If the correct shape must be forced into the profile at the end of the forming machine, then part consistency will be difficult to maintain, and will show up in statistical checks or secondary operations.