FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY Machine re-building gets on track
With its enormous welding system repeatedly breaking down, a train manufacturer turned to HepcoMotion for a linear guidance system with a long rail length that could operate in a very dirty environment, under extreme and constant load
T
he DUO welding system used by a leading train manufacturer in Germany is enormous
at 30m long by 10m wide. Here, four robots are mounted on each of the two welding machines, two on the lower and two on the upper level. In a slow but constant movement, the robots weld aluminium assemblies up to 28m long to a wagon shell. The robots are mounted to individual rack-driven carriages, each driven by a motor, which run on two guide rails. The system, however, was old and was
repeatedly breaking down and Spie, the company responsible for the repair, maintenance and refurbishment of the machinery, had to visit the customer almost every week with two men working two or three shifts to maintain the machine. Günter Becker, deputy branch manager,
commented: “The problems we faced with the machine were multi-faceted. From a construction point of view, the key difficulty was that the existing welding system from the 1990s had been built with an inadequate drive and guidance system. These were not suitable for heavy loads or such a dirty working environment. The existing rail systems had also been mounted on milled surfaces that were not perfectly flat. In addition, the guide rails were heavily worn due to the loads they had seen.” As a result, the drive motors failed regularly and
the seams were not neat. Dirt particles also made their way into the recirculating ball bearings in the guide blocks for each welding robot, which accelerated wear and also contributed to the frequent blocking of the motors. To overcome the problem, the company
therefore needed a linear guidance system that would be capable of operating in a very dirty environment, under extreme and constant load, with a long rail length. It also needed to offer minimal maintenance and be able to be installed on the existing machine without interrupting production.
14 JUNE 2020 | DESIGN SOLUTIONS The plan was to swap the existing guides
one-by-one with a more appropriate system. Becker said: “Due to the very special
requirements of this application, only HepcoMotion came into consideration. To my knowledge, they are the only company that offer the flexibility to adapt to different sizes and lengths whilst coping with mechanical stresses and loads of the welding robots.” The rails, including carriages and bearings
specified by Spie, are from HepcoMotion’s proven GV3 system. Approximately 500m of single-edge slides were used in the new design; the upper slides in each assembly were supplied with a rack to drive the carriages by motorised pinion. Double-row bearings, which are made in a single piece, were used on the carriages. The one-piece design ensures no dirt can penetrate into the bearings; and the V-guide principle also ensures that dirt particles are transferred away from the running surface as the bearings move along the slide. The bearings have high load capacities, especially in the radial direction. In this case, this was of great importance as the mass of the welding robot and carriage is about 220kg. It was also important that the bearings could
be manually re-adjusted, without great effort, to take away any play that develops as a result
of wear from the continuous high load. Of benefit, HepcoMotion’s V guide systems
can be quickly and easily adjusted to remove any play that has occurred, thanks to the eccentric adjustment facility.
A TROUBLE-FREE SOLUTION To ensure production continued, work was carried out whenever a welding robot was not in use. “The old rails had to be disassembled and
the mounting surface fully cleaned so that 5,500 new holes could be drilled for mounting the new guidance system – and all by hand! HepcoMotion’s rails are supplied in a maximum length of 4m, but are easily joined to make the total 30m length of the system. “Alignment of each rail was of particular
importance to ensure a good join between teeth in the rack and to provide a smooth movement of carriage across each joint in the slides. With the assistance of a Leica laser tracker for surveying, we were able to accurately align the rails with a deviation of less than 50 microns per slide. This means the systems are running completely trouble-free,” explained Becker, who worked with his team to overhaul the machine over a period of five months.
HepcoMotion
www.HepcoMotion.com
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