Building the BMW 7 Series

Whether it be market share or profits, the model line up or share prices, BMW grows exponentially.

Whether it be market share or profits, the model line up or share prices, BMW grows exponentially. It simply does not know the word "downturn" or "recession." Last year, for example, it saw a 60% increase in profits to just under $3 billion. It is predicting that sales will rise from 906,000 units to around 1 million in 2002. A key part of this success is the production side of the company. Last year BMW increased its capital expenditure by 26.4% to $3.1 billion as part of a major product offensive investment from which many of its worldwide network of plants benefited. However, one particular plant in Germany has been in receipt of some special attention.

Located about 100 kilometers east of Munich, the Dingolfing plant is the biggest production facility within the BMW Group. Approximately 21,000 people are employed producing up to 1,300 units a day, or 280,000 vehicles a year. Since production commenced there in September 1973, around 5.3 million cars have been made, including versions of the 3, 6, and 8 Series, every generation of the 5 and 7 Series, and the painted body for the Z8 Roadster. However, it has been the arrival of the new 7 Series, which entered series production in July 2001, that has brought new levels of investment worth around $2-billion in a 5-year period spanning 1999-2004.

One of the principle areas of investment has been in the press shop, where 1,200 employees produce parts on 79 presses six days a week, 24 hours a day in three and four shifts from Sunday 7:30 pm to Saturday 3:30 am. In the autumn of 1999, one of the largest vacuum transfer presses in the automotive industry was installed at a cost of just over $40-million. With a length of 90 meters and a maximum press force of 9,500 tonnes, it is able to produce 13 parts a minute; it can process 4.5 x 2-meter blanks. Among other things, this press makes possible the production of a complex side panel from one single piece of sheet steel.

Another trend setting item to be found in the stamping shop, which employs 325 people, is the internal high-pressure forming process–unique to BMW, claims the company–which has been in operation since spring 2000. When applying this method, a water-oil emulsion is pressed into tubes that are then formed into body parts by the closed tool with a locking pressure of up to 5,000 tonnes. Inside the tubes a pressure of up to 400 bar is built up. The end result is the production of complex and high-strength components, such as the rear axle, allowing a reduction in the number of body parts.

A great deal of attention has also been paid to the body-in-white process and the body shop itself, home to around 2,800 people and 250 robots. Where there are more than 100 body variants for the 5 Series, there are just four for the 7 Series–left and right-hand drive with and without sunroofs. The introduction of a stretched version later this year will double the variants.

82% of the 7 Series' body-in-white consists of high-strength steel, with the rest made up of aluminum. A total of 480 steel sheet and aluminum parts with a thickness ranging from 1 mm to 2.25 mm are welded, bonded and bolted in the body assembly shop. Altogether, there are around 5,750 welding spots, 150 running meters of adhesive and weld seams of an overall length of more than four meters.

The body shop also features the world's first inline measuring units that consistently monitor the serial production processes as well as carrying out a 100% check of the dimensions by means of temperature compensated measuring robots. Four flexible inline measuring units check the front and rear ends and underbody at 62 measuring points and the body carcass at 105 measuring points. More flexible than previous systems, it takes just 2 hours for the reprogramming should the body's measuring points need to be changed. A central database for all future inline measuring units is in the planning stage in order to ensure a more efficient documentation in addition to process monitoring and control.

The paint shop, which has around 1,500 people working on a three-shift system, also has a history of innovation, being the first to use powder-based clear coat technology in series production. However, in October last year, it saw another industry first when it commissioned the so-called rotational dipping system (RoDip) for large-scale use. After the joining of the steel and aluminum components, the body-in-white has to be pre-treated–cleaned, degreased and phosphatized. To do this, the different body types are dipped and rotated at the same time. The RoDip system is very flexible, handling bodies up to a length of six meters and a weight of 700 kg. It also allows the operators to leave out individual baths and requires less space than comparable continuous pass plants. Additionally, the 360º rotational movement allows the body-in-white's cavities to be much better flooded and emptied. Before the body-in-white reaches the RoDip, though, it goes through the so-called "Bodywasher" where, rotated through 360°, it undergoes a type-specific pre-purification during which it is intensively showered with jets of water. After that, it proceeds through a contour-controlled brush facility before it is dipped.

The new element in the assembly shop, where more than 6,500 produce up to 1,300 3, 5 and 7 Series cars a day in two shifts, is the customer-oriented sales and production process (KOVP). This has helped BMW reduce the processing time from the 28 days it was two years ago to the current total of just 12 weekdays. Day one is for the "freezing" of the binding order, the next six are for the preliminary planning and then two days are allowed for assembly. This allows three days for delivery of the car to the dealer (in Germany). As this method relies in the postponement of the allocation of the vehicle to the order of a specific customer, the vehicle and chassis type identification number is now applied by a robot no earlier than at the beginning of the assembly process. In the past, the vehicle was already allocated to a specific customer order at the beginning of the body-in-white assembly. The KOVP system will be gradually extended to the entire BMW network with the start of production of future models.

KOVP and modular construction also make greater demands on the suppliers than before. Fully pre-assembled door modules and front-end modules with integrated headlights and radiator grille are delivered precisely to the section of the assembly line at which they are needed.

In order to test the many electronic modules and 60+ control units, the CASCADE–Control Application Sequences for Coding and Diagnostic Execution–control system has been introduced into the assembly shop. Claimed to be a revolutionary system by BMW in the world of electronic bench tests, it is one of the first JAVA-implemented productive systems running under all operating systems that is able to determine any defects or the absence of faults. Using special software it virtually assembles a vehicle in accordance with the respective vehicle identification number upon receipt of the assembly order. All necessary data is read out from a database with virtual vehicle components that comprises all model and equipment-specific test criteria. After the identification of the vehicle at the respective CASCADE test bench, information is retrieved from the real vehicle, added to the test information and evaluated. This information can be assessed at any time and from everywhere. Its use, says BMW, enabled the 7 Series to go from concept to series production in two-and-a-half years.

While a great deal of thought has gone into the new 7 Series as befits BMW's flagship model, the same amount of thought, if not more, has gone into its production process. While the innovations that have been introduced into the Dingolfing plant will be of little interest to the proud owner of a new 7 Series, the end result is, and that at the end of the day is all that really matters.