North Branch, MN--By applying a motion controller to a tube-bending machine, engineers created a bending system capable of compensating for steel's varying material characteristics.
Designed by engineers at Superior Engineering, the new machine bends the steel chassis frame for Polaris ATVs. Employing the new machines allowed Polaris to reduce labor costs in the chassis weld-assembly process.
Prior to the development of the post-form bender, lack of precision in the bends caused assembly problems. Varying mechanical characteristics--particularly in the modulus of elasticity--led to different amounts of "rebound" in the bent tubes. As a result, assemblers didn't always have the ρ0.020-inch part accuracy they needed. Welders compensated by adding extra weld material to ill-fitting parts. Although the extra welds strengthened the connections sufficiently, they raised labor costs.
The new machine solves that problem by bending the tubes, monitoring their rebound, then bending them again and again until absolute precision is achieved. It consists of a conventional bending fixture, an electric ram, a PLC, and an M-Cut motion controller made by Contrex Fenner Controls, Maple Grove, MN.
During operation, the ram's variable frequency ac motor turns a ball screw that pushes the frame tube. By counting the motor's turns, the motion controller monitors the linear distance of the push. The unit is programmed for an initial push of 0.50 inch. A pair of photoelectric sensors, made by Banner Engineering Corp., Minneapolis, MN, monitor the tube as it rebounds. If the sensors fail to sight the rebounded tube, the controller initiates subsequent pushes of 0.050 inch until the rebounded tube exhibits sufficient bend. During this process, the controller can call for as many as ten separate pushes. Most tubes, however, reach their precise bend angle in two to four pushes, says Arvid Johnson, design engineer for Superior Engineering.
Key to developing the new machine are several features inherent in the M-Cut motion controller. The first of them, says Johnson, is speed. "We need to make a very fast decision on whether to push the tube again," Johnson explains. "Polaris works with 30 second cycle times." Other key features include the ability to react to register marks (in this case, the photoelectric sensors serve as "register marks"), and the use of multiple pre-sets. The ability to react to register marks--unavailable in most motion controllers--make it possible for the controller to "know" when the tube reaches its desired bend. Multiple pre-sets enable the ram to make moves of varying lengths: say 0.50 inch on the initial push, and 0.050 inch on subsequent pushes.
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When Polaris switches to tubing of a different size, the controller's built-in user interface enables the machine operator to change motion parameters. "The built-in interface lets the operator easily dial up the changes," says Glen Gauvin, vice president of marketing for Contrex Fenner Controls. "So they don't need a laptop computer and a programmer to change the setup."
The result is a post-form bending machine that compensates for all of the varying material characteristics--modulus of elasticity, thickness, and tempering--that exist between lots of steel. "They needed a smarter machine--one that doesn't simply bend the steel the same amount every time," Gauvin says. "This system bends and checks, then bends again, until it gets it just right."
Additional details, bending machine...Arvid Johnson, Superior Engineering, 296 First Ave., North Branch, MN 55056, (612) 674-4427
Additional details, M-Cut controller...Glen Gauvin, Contrex Fenner Controls, Box 9000, Maple Grove, MN 5311-9000, (612) 424-7800