Robotic cell automates welding of electricity generators

Citation

(1999), "Robotic cell automates welding of electricity generators", Industrial Robot, Vol. 26 No. 5. https://doi.org/10.1108/ir.1999.04926eaf.007

Robotic cell automates welding of electricity generators

Robotic cell automates welding of electricity generators

Keywords Robotics, Welding

In January this year, one of the very few plasma TIG (tungsten inert gas) robot welding systems in the UK started producing AC generator stators at the Stamford factory of Newage International (see Plate 6). What makes the installation remarkable is that the company has taken this quantum step forward in technology despite never having used a robot before.

Plate 6 Part of the twin-station, robotic cell for plasma TIG welding AC generator stators at the Stamford factory of Newage International

The twin station cell, based on a standard Comau SMART 2 articulated-arm robot, took over from manual MIG (metal inert gas) welding and has resulted in dramatic quality and cost benefits. Productivity per head has doubled from ten to 12 stator cores per shift to 23, helping to keep product costs down. Undiscounted payback calculations show that the £179,000 investment will be recouped in just over 18 months.

The former MIG process had major drawbacks including excessive fume production. It was also labour intensive and required a high level of operator skill to achieve consistent weld quality. In addition, the spatter produced needed dressing.

The major difference with plasma TIG welding is elimination of the filler wire, saving £12,600 annually on this consumable alone; and it is virutally fume free. The process is easier to automate as there is no need for torch cleaning stations and no risk of wire misfeeds. A tungsten electrode is used to weld and fuse together the coated electrical steel laminations using a highly concentrated arc at a temperature of 30,000°C. The plasma gas ensures deep penetration forcing the arc into the base metal to produce a stronger weld more quickly. Even so, total heat input is lower so the heat affected zone in the area around the weld is smaller.

The six-axis, floor mounted, computer controlled robot with 15kg wrist payload and 1,455mm reach has been interfaced with two existing core build fixtures which have each been fitted with a rotary drive to index the core packs through 360°. Migatronic supplied the 320 Amp welding source, water-cooled torch and tungsten electrode sharpener, while the PLC system with touch-screen diagnostics was based on OMRON components.

Main contractor was The Welding Centre; and systems integrator, Sciaky, built the cell and orchestrated its commissioning including installing the guarding, carrying out craneage modifications and fitting the existing fume extraction equipment on the robot arm to remove the smoke created by lamination press lubricant being burnt off.

Core pack building from steel laminations is still manual and the assembled packs are loaded on to the mandrel of the rotary fixtures by hand. From this point the welding operation is fully automatic. The fixture has proximity detectors underneath which recognise the size of the core pack which has been loaded. It then orientates to the correct angle for the first weld.

The outer guards have already closed and now an internal cell guard opens to allow the robot access, the torch is positioned, the arc struck and the first weld is completed, straight along the outside diameter of the core pack from one end to the other. The weld torch returns to pilot arc, the fixture indexes to the next weld position, and so on until the core welding is complete.

The robot then returns to its neutral position in the centre, the fixture is offloaded and the next core pack, which has been assembled within the time that the first was being welded, is immediately mounted in the other workstation to continue operation without interruption. Increased production anticipated in the foreseeable future may therefore be accommodated without any additional provision.

The cell was justified based on the production of the main stator cores for Newage International's HC4 and HC5 AC generators rated from 200 to 825 KVA for industrial and marine use. There are four variants of each of the two sizes which can be welded at either station. Programming is straightforward using the Comau C3G Plus cell controller, according to Nick Swann, Group Leader - Manufacturing Engineering at the Stamford factory.

A further benefit of the stronger plasma TIG welds is that they enable structural design changes in the stators which have saved a further £30,000 per year. Extensive tests have shown that electrical losses from the core are lower in addition to the mechanical advantages.

There are many makes of robot on the market and it is always interesting to know why one is chosen in preference to the others. Nick Swann advised that Comau was prepared to embrace the new plasma TIG technology, could supply a system physically capable of handling the heavy stators, and at a price which was 30 per cent less than the next best quote. He also commented that Comau UK and Sciaky have a proven partnership and he had seen successful installations in automotive plants. Lastly, and perhaps most importantly, he describes Comau UK's support, both on-site and over the telephone, as "second to none".

Despite being a first-time robot user, Newage has plans to increase its use of automation. Larger HC6 and HC7 stator welding is in view as well as progression on to rotor core production where potential earth faults can be eliminated. Other key manufacturing processes may follow.

Contact: John D'Angelillo, UK Manager, Comau UK Limited, Unit 3, Hortonwood 32, Telford, Shropshire TF1 4EU. Tel: +44(0) 1952 670396; Fax: +44(0) 1952 670398.