Roll Forming Line Automation

The typical order is: uncoiler, straightener, punching and notching stations, forming stands, cut-off and runout table or stacker. Punching is done in one of two ways: with pre-punching a servo feeder indexes the strip into the press and the press hits while the strip is stopped, and a loop pit absorbs the speed difference to the continuous forming section; with a flying punch the press rides on a carriage with the strip and punches without stopping the line.

There are three cut-off strategies. Stop-to-cut lines slow down and stop for every cut; the design is simple but throughput drops on short parts. Pre-cut lines cut the strip flat before forming; no profile-specific die is needed, but part ends can flare in forming and gaps form between parts. Post-cut flying lines cut the formed profile with a profile-matching die or a saw on a carriage synchronized to line speed; since the line never stops, this gives the highest throughput.

Because holes are positioned relative to part length, punching and cutting must share the same measurement. The controller tracks every part along the line using the position from the measuring wheel or the servo feeder: several parts can be between the punch station and the cut-off. The next order's hole pattern can then start before the current order's last cut, with no scrap at the order change.

The forming section is usually driven by one or more AC motors through a gearbox or chain. On flying cut-off and flying punch lines the main drive sets line speed and the cut and punch axes follow it. On stop-to-cut lines the main drive has to stop quickly and at the same position for every cut, so closed-loop vector control with an encoder is used.

In the ONX architecture the servo feeder, flying punch and flying cut-off axes and the forming main drive are brought together in one controller running CODESYS SoftMotion on CODESYS Control RTE on an industrial PC. The measuring encoder, servo and AC drives and remote I/O share one time base over EtherCAT; the punch and cut carriages are coupled to the measuring axis with electronic cams.

Part tracking, hole patterns and the production list run in the same controller; the list is entered from the operator panel and every part's length, hole pattern and quantity are stored with the recipe. The uncoiler's tension or loop control follows the same line speed reference.

The punching and cut-off axes of a roll forming line are built on the same synchronization platform ONX Control uses in its flying saw, flying punch and cut-to-length applications; field footage of those applications is on the related solution pages.

A typical picture on older roll forming lines: a contactor-switched main motor, cut-off triggered by a limit switch, a fixed-die punch press and part length set by hand for every order. In a retrofit the roll stands and dies are usually kept; the main drive moves to an AC drive with encoder, a measuring wheel is added, cut-off and if needed punching are converted to servo or flying operation, and the production list moves to the panel.