Robots are four times faster at polishing

Citation

(2001), "Robots are four times faster at polishing", Industrial Robot, Vol. 28 No. 6. https://doi.org/10.1108/ir.2001.04928faf.003

Robots are four times faster at polishing

Robots are four times faster at polishing

Keywords: Polishing, Robots

Following the successful installation of Motoman systems for robotic arc welding and more recently plasma welding and cutting, one of Europe's leading stainless steel catering and sanitary ware equipment manufacturers, W&G Sissons, has embarked on a far-reaching programme to automate polishing at its Sheepbridge, Chesterfield factory (Plate 3).

The first cell, based on two Motoman six-axis articulated-arm robots, entered service in January of this year (2001). Patrick Mason, production engineer in charge of the project, is planning to ensure that the polishing of all bowls, WCs and other products manufactured in batches over 20-off will be automated within the next two years.

Plate 3 The Motoman robotic polishing cell at Sissons, Sheepbridge, set up to polish stainless steel bowls at both stations

Speed is perhaps the main benefit of robots over hand polishing. A WC which used to take 70 minutes to polish to a grained finish by hand now takes 18 minutes including six automatic tool changes. If a mirror polish is required, the saving is even greater – 30 minutes by robot compared with three hours manually. A further companson was cited, whereby a 500mm x 400mm stainless steel bowl which used to take 24 minutes to polish is now completed in six. The success in polishing this and other similar bowls has allowed a reduction in the work previously subcontracted.

Not only are the robots faster at polishing, but they are also capable of operating "lights out" overnight. In six hours, the unmanned cell can polish 100 bowls and stack them for packing the following morning. Similarly, a batch can be run unattended on Saturday ready for Monday morning.

Continued Mr Mason: "The list of advantages of robotic polishing seems almost endless. For example, if six hand polishers are deployed on a product batch, we have to ensure that they polish to the same standard, which is difficult and requires a high level of developed skill.

"However, the finishes are consistent when robots are used. The reason is two-fold: first, the cycle is exactly reproducible each time; and second, robots can handle considerably larger tools than is possible by hand so there is much less overlapping between passes and sometimes none at all. Consistency of finish is a particular advantage if we have a large number of units going to one customer for a large project; or, say, a washroom is fitted with a range of our products that are viewed together but manufactured at different times.

"Hand polishing is by its nature repetitive heavy work, ideally suited to robotic application. In addition, dust and fumes generated in the polishing area are not a problem for a robot but there are Health and Safety issues when operators are involved, requiring efficient dust extraction plus individual safety equipment".

Robotic polishing consumables are more environmentally friendly as they are dry abrasive wheels, whereas, hand polishing involves the use of abrasive granules in a matrix of fat, predominantly of animal origin. The latter tend to be dirty in use, whereas, debris from the former is simply extracted through ducts at each robotic workstation. Moreover, unlike hand polishing tools, robotic consumables do not have to be dressed and prices are generally lower.

Over 50 product variants are polished in the new Motoman cell. It is the result of a joint development by the equipment supplier and Sissons, which supplied the initial concept layout, jigs and fixtures and carried out its own integration. The cell comprises two Motoman UP-130 robots, one serving a rotary table and the other a fixed table. The robots not only handle the products into position, polish and unload them, but also exchange suction heads, abrasive tools and consumables automatically.

Additionally, there are two infeed and two outfeed stations for products; and a 24-position rack for housing tools, consumables and suction heads on two levels. Tools on the top have dedicated positions for each robot, but as they both share the lower positions, a safety cube for collision avoidance has been set up in the software. Programming is via a hand held pendant and is assisted by pull-down menus and icons.

Control is provided by the latest Motoman XRC unit which synchronises the movements of robots and peripherals. Advanced motion control optimises acceleration, deceleration and speed for circular and corner movements. Likewise, inertial compensation via the path control function maintains accuracy during high speed movements.

A typical production polishing set-up at the Chesterfield factory is as follows. Robot 2 fitted with a suction head picks up a WC from the first infeed station and places it on table 1 (rotary) for robot 1 to polish in an 18 minute cycle. Robot 2 then handles a bowl from the second infeed station onto table 2 (fixed), automatically exchanges the suction head for an abrasive tool and polishes the bowl in a six minute cycle. The suction head is selected again and the finished bowl is taken to outfeed station 2. The bowl cycle is repeated twice more before robot 2 is required to remove the polished WC from the rotary table and transfer it to outfeed station 1, whereupon the sequence starts again.

Sissons is said to be the only manufacturer in Europe to take the polishing tool to the job, rather than the product to the tool. Patrick Mason says that the former configuration suits the large variety of Sissons products as well as the preponderance of internal as opposed to external polishing. Another first for the company is the use of fully reprogrammable robots rather than dedicated automatic polishing plant.

For more details contact: John D'Angelillo, Managing Director, Motoman Robotics (UK) Ltd, 1 Swan Industrial Estate, Banbury, Oxfordshire OX16 8DJ, UK. Tel: +44 (0)1295 272755; Fax: +44 (0)1295 267127; E-mail: johnd'angelillo@motoman.co.uk; Web site: www.motoman.se