At Meppel in Holland truck producer Scania has built a very modern plant for the combined painting of metal and plastic parts. The factory is now supplying parts to Scania’s production facilities in both Western and Northern Europe.
A few years ago when Scania transferred its cab manufacturing operations from Meppel to Oskarshamn in Sweden, an extensive search began for new ways to make use of the 20,000 square metres of factory space that then became available. In 2005, following a detailed study, the decision was taken to remodel the factory to create a robot-assisted paint shop for vehicle parts. The aim was to utilize the major strategic and commercial advantages offered by the Dutch factory’s logistical proximity to Scania’s production facilities at neighbouring Zwolle, at Angers in Western France and at Södertälje near Stockholm in Sweden to provide in-house paint finishing.
Leading technology
Scania named the project “Prisma” and, in formulating the key requirements for the plant at Meppel, declared that the paint finishing process at the redesigned facility was to be as efficient as possible and as modern as necessary. Application of Scania’s Production System principles was to form the basis for this. Paint systems specialist Dürr, based at Stuttgart (Germany), was the turnkey partner selected to achieve the ambitious target of building an automated paint plant for metal and plastic parts in an installation period of just five months.
Automatic robotic paint application is the core element around which the plant has been built. A conscious decision was taken not to include an even higher level of automation – all other processes, such as loading and unloading of parts, are manual and thus cost effective.
The whole plant covers an area of 6,000 square metres spread over three levels. Wet systems are located on the ground floor and include everything, from supply systems for de-ionized water for the pretreatment plant to scrubber systems, sludge removal and waste water treatment. Audit lines and spot repair work stations are also located at this level.
The actual painting process is carried out in nine paint spray booths on the floor above. Each booth is equipped with two EcoRP7 type seven axis paint robots. A surface area of 8-10 m² per skid is painted on three lines operating in stop-and-go modus in a cycle time for the whole plant of 85 seconds.
One of the three lines is designated for the painting of cab parts, the other two for chassis parts. This involves painting a variety of materials such as EPDM, polypropylene and SMC (sheet molding compounds). Two flaming robots prepare polypropylene parts for painting; front end, and spoiler parts made of SMC are primer painted prior to their delivery to Meppel.
Curing and cooling processes take place on the top floor of the paint shop. Air handling equipment, such as air recirculation units for the spray booths and air supply units for general areas like the central clean room, is also installed on this level.
A regenerative thermal oxidizer (RTO), also designed and built by Dürr, handles the treatment of the exhaust air that is contaminated with several different solvents. The RTO, which has three tanks and a cleaning capacity of 20,000 Nm³ per hour, achieves a separation level of more than 99 per cent keeping emissions within the limits allowed under Holland’s strict environmental regulations.
Customized painting
Particularly challenging aspects in designing the paint shop were the vehicle production batch sizes of one and the application of more than 450 different color shades. Special EcoSupply P type automatic “piggable” paint supply systems were integrated so that paint consumption could be kept to a minimum whilst retaining the highest possible level of flexibility. These systems make it possible to supply exactly the quantity of paint needed for each application.
In place of air-assisted atomizers EcoBell2 type high rotation atomizers are used for application to assure maximum paint transfer efficiency and a high quality paint finish. Paint consumption is thus reduced and environmental sustainability increased.
Dürr’s offline EcoScreen 3D-OnSite system is used to program and set parameters for the robots. These offline programs are created in advance and installed on the robots in the paint lines – all that remains to be done on site is optimization of the painting parameters.
Almost 250 different trim and add-on parts are handled and, so as to keep skid variants to a minimum, Scania operates a modular skid loading concept: variant bits allow each skid and its specific load of individual parts to be assigned to different robot programs.
The positioning of the parts, or of their carriers, on the skids also has a significant influence on paint finish quality because the tolerances here are minimal. To ensure that high quality would be guaranteed, extensive experiments were carried out, at an early stage, together with the customer and with the manufacturers of the skids and carriers and of the paint materials, in the Technical Center at Dürr Systems GmbH, Bietigheim-Bissingen (Germany). Here a basis was found for exact positioning of the parts on the skid, and painting parameters were determined in relation to the cycle times that would later be required in production operation.
At present 40 units an hour are coming off the line at Scania. Real satisfaction has been expressed with the customer-oriented build of the plant to comply with Scania’s modern production principles. Wiebe Stork, Prisma Project Leader at Scania, sees the technical design strategy as the reason for this: “We utilize convincing technologies that really work without aiming at one hundred per cent automation. What we want, and indeed have, is stable work flow and high availability.”
Dürr is a mechanical and plant engineering group at the top of the world market in its areas of activity. It generates about 85 per cent of its sales in business with the automotive industry. It furthermore supplies sectors such as the aircraft, machinery, chemical, and pharmaceutical industries with innovative production and environmental technology.
The Dürr Group operates in the market with two divisions. The Paint and Assembly Systems division supplies production and painting technology, especially for car bodies. Machinery and systems from the Measuring and Process Systems division are used in engine and transmission manufacturing and in final vehicle assembly, among other areas. Worldwide Dürr has 47 business locations in 21 countries.
