Tech Briefs
Producing BMWs at Dingolfing

BMW's Dingolfing, Germany, facility. The windshield of a 5 Series sedan is installed by robot at BMW's Dingolfing plant. Aluminum welding of the BMW 5 Series rear axle. BMW 5 Series powertrain and front axle assembly at Dingolfing. 3 and 5 Series sedans in final assembly at Dingolfing. An employee hand-finishing leather steering wheels at BMW's Dingolfing production facility.

BMW is the first to admit that its success did not come easily. The company was not required, however, to learn from others how important it is to be flexible—for flexibility has always been one of BMW's outstanding features. That philosophy has seen its history range over aircraft engines, motorcycles, and cars; the company's blue-and-white badge is a stylized aircraft propeller. Today its extensive product line extends from the 5.0-L V8-engined Z8 two-seat sports car to the C1, a 125-cm³ (7.6-in3) roofed scooter that brings a new dimension to city transport.

BMW has production plants in Germany, Austria, South Africa, and the U.S. Its largest is Dingolfing, 100 km (62 mi) from Munich in Lower Bavaria, where production started in 1973, although the first cars manufactured in the city were the strangely named little Goggomobiles produced by Hans Glas GmbH in the 1950s. In 1967 BMW, looking for larger production facilities and trained autoworkers, took over Hans Glas. Three years later, BMW decided to build a new car plant at Dingolfing and in another three years the first examples—the first generation 5 Series 520i—were driven from the factory on Sept. 27, 1973.

Today Dingolfing forms Plant Complex 2 of BMW AG that comprises plants 2.1, the old Glas factory where suspension components are now manufactured; 2.2, the central parts store; 2.4, automobile production; and 2.5, parts production. The company states that it would be impossible to build complete cars or motorcycles in Dingolfing or at any of BMW's other individual production facilities. Accordingly, it is only the network of BMW plants that provides a really rational production system. Dingolfing supplies all of BMW's assembly plants with chassis components, gets engines from Munich and from Steyr (Austria), and plastic bumpers, instrument panels, and propeller shafts from Landshut. Numerous activities of the company are now organized in independent division or business units, plants, and locations interacting and in some cases offering their products to external customers. The press and stamping shop, tool and die production, laboratory services, plant catering, and engine and chassis production—as well as body fittings plus various other divisions—act as independent profit centers.

Dingolfing, Mun-ich, and Eisenach comprise the Die Production Division of BMW. At Dingolfing some 600 workers are involved in this area, manufacturing tools and dies for metal part and panel production, including hoods, trunk lids, and side panels. These employees also make facilities and complete production systems subsequently used in body-in-white (BIW) production, as well as models for the development of future production cars and prototypes. The Tool and Die Production Division at Dingolfing makes about 1500 tools, dies, calibration gauges, and models a year, and together with Munich and Eisenach provides up to 40% of BMW's total requirements in this area, the remainder coming from suppliers.

The Dingolfing press shop processes some 1000 t (1100 ton) of sheet metal every day. It has five press lines with 65 individual presses, plus nine multi-stage presses, most under automatic control. Panels are pressed in optimum batch-sized stock covering a minimum of four and a maximum of 45 production days. According to BMW, the time to retool a particular press for a panel change has been steadily reduced and now stands at an average of 70 min on presses without a removable tray and about 3.5-20 min on presses equipped with the tray. On average 37 retooling processes take place every day at Dingolfing. Spot quality checks are made using computer-aided metrology systems.

The body shop at Dingolfing is equipped with laser welding systems and a high level of automation. For the 5 Series sedan, robots perform 96% of the spot welding. The welding robot population is about 500. Total production area at Dingolfing's Body Shop is some 85,000 m² (915,000 ft²). An electronic data-management system is in place for individual bodyshell identification and specification detailing. Bodyshell mass is about 350 kg (770 lbs). Some 80% (by mass) of the 5 Series' body panels are hot-galvanized steel. BMW says that more than 60% of its employees in the Dingolfing Body Shop are metalworking specialists and 80% of the workers in bodyshell production are skilled mechanics.

BMW pays great attention to body protection. Before the first four layers of paint can be applied, the BIW must be pre-treated to make its surface clinically clean. To do this, bodies are dipped vertically into one of 11 paint baths at the Dingolfing plant, finally being covered with a layer of zinc phosphate. The trade name used to describe this technology is VERDIB (vertical dipping of car bodies).

Four layers of paint are applied to BMWs. The first is applied in a bath of water-soluble paint being, as BMW puts it, "cemented" onto the body by a cathodic dip process. This builds up the 20-µm (790-µin) thick primer that, in conjunction with the zinc phosphate layer, provides most of the rust proofing (inside and out) and allows the paint to stick to the body. The next layer, which measures 30 - 40 µm (1180 - 1575 µin), is filler applied electrostatically by high-speed rotation sprays. The topcoat applied as the "outer skin" of the body is sprayed on in two steps both with metallic and non-metallic paint. The "basic" paint provides the desired color in the first layer, the clear coat is then sprayed on after a short drying phase before the entire car goes into a hot chamber for drying. The clear coat is to a thickness of 35-45 µm (1380-1770 µin).

It has been almost 10 years since BMW began a powder-based clear coat development project. Once proven, powder-based clear coat technology was introduced at Dingolfing, the company claiming an industry first for such a production application. The first powder-painted cars entered pilot production in 1996. Solvent free, powder-based clear coating cuts emissions. By 1998, all standard colors on 5, 7, and 8 Series BMWs produced at Dingolfing—about 1000 cars a day—used powder clear coat technology. Car bodies pass through the paint shop at the rate of one every 93 seconds at 6.2-m (20.3-ft) separation.

In the paintshop, the underfloors—particularly wheelarches and sills—are given a PVC coating applied "airless" and then burnt on to the body. The coating is generally 0.5-1.5 mm (0.02-0.06 in) thick, but in some areas is 4 mm (0.16 in) thick. The body is sealed with PVC applied to all seams and joints, some of this work necessitating manual application. A bituminous compound is melted into appropriate areas of the body as an anti-resonance system, and wax preservatives are applied to various areas.

The assembly area at Dingol-fing involves a total workforce of about 6000 working in two halls subdivided into three main levels and producing 1250 units per day of 3, 5, and 7 Series cars. Pre-assembly of individual groups and components takes place on the ground floor. These are complete vehicle systems such as the engine (with attachments), front axle, rear axle, doors, bumpers, and instrument panel. These are then allocated to the respective vehicle and fitted on the first floor, an efficient feed being ensured by delivery systems conveying the right unit to the right car at the right time. The body fittings division on the second floor fits seats, headrests door linings, etc. Leather-covered components are assembled on this floor.

Robotization is used where appropriate in final assembly, including application of glue for the windshield and rear window. A robot installs the 25-kg (55-lb) wiring harness. However, BMW regards the assembly of cars as likely to remain generally labor intensive "for quite some time to come" because of the need for special skills and care and a "feel for quality" by the worker. The sheer number of variants and complicated joining procedures would appear to make any further automation largely impossible for the time being.

Stuart Birch