INNOVATIVE PLASMA CUTTING MACHINE FOR FLUE PIPES

An all-in-one real-time machine controller manages five motion axes and I/O to simplify the development of this advanced new plasma tube cutter.

An innovative new plasma cutting machine for flue pipes has been developed by Techserv Cutting Systems (Dewsbury, England), a specialist manufacturer of CNC profile cutting systems. Advanced interpolated motion of the cutting system is used to dramatically increase production throughput – using an economic real-time machine control module from Baldor Electric (Fort Smith, AR), a leading marketer, designer, and manufacturer of industrial electric motors, mechanical power transmission products, drives and generators. Baldor is a member of the ABB Group (Zurich, Switzerland).

Capable of cutting aluminum and stainless steel flue pipes at any angle, as well as holes of any shape or size, the plasma tube cutter completely automates this aspect of manufacturing. Until now, for example, elbow pipes have traditionally been produced by first cutting complex shapes from flat metal sheet, which are then rolled and welded before assembly. This multi-stage fabrication process necessarily involves considerable movement of work pieces around the factory and is very time-consuming.

The new cutter dispenses with the need to pre-cut complex shapes. Instead, the flat metal sheet is first rolled into a tube and seam welded, then each tube is successively loaded into the machine. The entire cutting operation is handled autonomously; a simple angled cut takes a matter of seconds. Cutting the angled end pieces for an elbow pipe and then assembling them – a task that previously took about 15 minutes in total – can now be accomplished in around 4 minutes.

The tube being cut is mounted in the machine with its top end held in a rotating pneumatically-driven clutch assembly. The plasma cutting torch is moved up and down as the tube rotates, at a rate which determines the severance angle or the size and shape of the hole being cut. Both the main rotational axis and the plasma torch height axis are powered by BSM series AC brushless servomotors driven by MicroFlex digital servo drives, and employ interpolation to secure a constant cutting rate regardless of the profile of the cut or diameter of the tube. The machine can handle a wide range of tube diameters, from 90 to 350 mm, with wall thicknesses up to 1.5 mm.

The tube cutter also uses three stepper motor driven axes. Two of these control the position of a pair of guide rollers, which support the tube during the cutting process and are driven closer together or further apart depending on the diameter of the tube. They also move aside automatically during the tube reload phase to facilitate operator access. The third stepper-driven axis dynamically varies the distance between the plasma torch head and the wall of the tube during the cutting process, to provide optimum performance.

All five electrical axes are controlled by a NextMove ESB-2, a compact real-time machine control module which receives commands direct from an on-board PC-based CNC system developed by Techserv specifically for tube profile cutting applications. The CNC system software runs under Windows XP, with all operator information presented on a large touch-sensitive full color HMI.