An innovative new plasma-cutting machine for flue pipes by Techserv Cutting Systems, a specialist manufacturer of CNC profile cutting systems, uses advanced interpolated motion in the cutting system to dramatically increase production throughput. Helping to deliver the interpolated motion is a real-time machine control module from Baldor.
The machine cuts aluminum and stainless steel flue pipes at any angle, and holes of any shape or size, automating this aspect of manufacturing. Before the new design, elbow pipes, for example, were first cut into complex shapes from flat metal sheet, and then rolled and welded before assembly. This multi-stage fabrication process involved considerable movement of work pieces around the factory and was 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. 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 done in about 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 that 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 Baldor BSM series ac brushless servomotors driven by MicroFlex digital servo drives that use interpolation to secure a constant cutting rate regardless of the profile of the cut or diameter of the tube. The machine can handle a range of tube diameters, from 90 to 350 mm, with wall thicknesses up to 1.5 mm.
The tube cutter also uses three Baldor stepper motor driven axes. Two of the axes 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 for 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.
All five electrical axes are controlled by a NextMove ESB-2 real time machine control module that receives commands 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.
Said Techserv’s Technical Director, Mike Cowley, “The Mint programming language helps us develop motion control programs for custom applications quickly. Integrating the NextMove controller with our front-end CNC system was straightforward because it uses the same API naming conventions as ActiveX commands. As we need to change the scaling and speed of the machine’s servo axes on-the-fly to maintain a constant cutting rate, the controller’s fast interpolation capabilities provide an important advantage. We find the Mint’s ‘Hold-To-Analog’ command is especially useful, since it allows us to handle real-time control of the plasma arc entirely within the NextMove controller. We continuously monitor the arc voltage and the software interprets this analog value to automatically adjust the distance between the torch and the tube wall, thereby maintaining the constant plasma characteristics needed to ensure optimum cutting performance.”
Filed Under: Machine tool industry + subtractive manufacturing, Electronics • electrical, Motion control • motor controls, Software