Electric servo precision for tube bending
Actuated by servo motors, this new breed of CNC machines boasts as many as 15 motion axes on some models.
Traditional tube (and pipe) bending machines have relied on hydraulic power to generate the forces needed. A relatively recent trend is bringing electric servo power to tube bending for precision, energy efficiency, and other benefits. “All-electric” (AE) bending machines handle tubes of increasingly larger diameters and wall thicknesses.
AE bending machines incorporate a multi-axis motion system actuated by servo motors to control tube position and torque throughout the bending process.
AE machines use power only during actual tube bending, unlike traditional machines that require continuous pressurization of the hydraulic fluid. Electric servo control allows slower bending speeds “to achieve optimal material flow and shaping, not possible with hydraulics,” according to Unison, Ltd.—a U.K.-based company and reputed pioneer in the all-electric bender arena. Several other manufacturers offer AE benders along with hydraulic machines (see more online).
Software-based control simplifies bender setups and allows storage of parameters for quick reconfiguration to different parts, virtually eliminating scrap. Some machines include laser measurement to enhance bend angle accuracy and minimize errors due to material hardness variations between batches of tubes. Bending of small batches, essentially down to one part, becomes feasible. All-electric benders avoid potential hydraulic circuit surges, run more quietly (typically 55-60 dB) and produce minimal heat. The various benefits can add up to potential cost savings versus a hydraulic bender.
Applications include aircraft, automotive, and shipbuilding industries. Multiple bends, complex shapes, and precision requirements are prevalent especially for aircraft tubing and involve a wide range of diameters. U.K.-based GKN Aerospace is one user of Unison all-electric benders for tubes up to 115-mm (4.5 in.) OD. GKN cites bends “made to 1 mm 3D envelope accuracy”— even as tight as 0.3 mm for some military aircraft applications—with all-electric bending technology.
In Nov. 2009, Unison announced capability to bend tubing up to 175 mm (~7 in.) OD. Said to be the largest AE tube bending machine built to date, it can generate bending torques up to 165,000 Nm (121,700 lb-ft).
“Expanding the scope of all-electric machines to seven-inch diameters provides the means for new classes of user to improve their production processes—allowing radical improvements in machine setup, operator skills required, minimum batch sizes, and post-bend testing operations [among others],” says Unison’s CEO Alan Pickering. Unison tube benders are available in the U.S. from Horn Machine Tools Inc.
Unison’s motion control system and servo motor supplier is Baldor Electric Co. Unison recently standardized on Ethernet-compatible drives and controls, using Baldor’s Ethernet Powerlink products. These include NextMove e100 machine controller and either MicroFlex (1- or 3-phase) or MotiFlex (3-phase) drives—depending on power needs. MotiFlex is applicable in centralized and distributed “intelligent drive” systems. One Baldor Ethernet Powerlink controller can manage systems with up to 16 interpolated axes.
While not the answer for every tube bending application, all-electric bending technology is likely to expand widely from its European origins.
Frank J. Bartos, P.E., is a Control Engineering consulting editor. Reach him at firstname.lastname@example.org .