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.
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.