Neckarsulm, GermanyThe automotive industry has about 70 years of experience in the use of steel. For aluminum, it is closer to 17 years. But aluminum is being adopted increasingly due to its lightweight properties, and the automotive industry is very quickly having to acquire the expertise in its assembly plants to handle the material.
With the launch of its A2 model car, German car manufacturer Audi is the first to cross the volume barrier and bring aluminum into the realms of real production. Other aluminum-intensive models being built today include the BMW Z8 and Lotus Elise, but these are niche vehicles whose production volumes are low. At Audi's Neckarsulm plant, where the A2 is produced, capacity is 300 units per day, or 60,000 cars per year. Patented manufacturing techniques support the company's initiatives to develop aluminum-intensive vehicles.
For instance, Audi makes the side panel of the A2 as a single stamping. But, because aluminum cannot be deformed as far in one step as steel, it was necessary to refine the stamping process. Albrecht Reimold, manager of A2 production, explains that while Audi uses the same presses for both aluminum and steel, an innovative design of tools for deep drawing the single-piece aluminum side panel has been adopted. The design is based on a four-stage deep drawing process that overcomes the poor formability of aluminum, Reimold says.
Audi has patented manufacturing techniques that support the company's initiatives to develop aluminum-intensive vehicles.
Also patented is the fixture that holds parts for welding. Designed to accommodate and control expansion and contraction of the aluminum during the weld process, it prevents internal stresses and maintains accuracy. One side of the fixture is "fixed" while the other moves with the aluminum as it expands, and then retracts as it cools to bring it back to the required position.
Spaceframe construction. Welding, however, is just one of a combination of joining techniques used on the aluminum-intensive A2. Audi has based the A2 design around a spaceframe structure. The high-strength load-bearing frame is constructed principally from extrusions and high-pressure diecastings. This design, Reimold says, takes greatest advantage of the lightweight properties of aluminum, while optimizing cost factors. Extrusions are low-cost components while diecastings offer the potential to create a highly complex component that would otherwise require as many as eight or nine pressings to be joined together.
Assembling the spaceframe structure involves a combination of laser welding, seam welding, and self-piercing rivets. These processes are not new to the automotive industry, but Audi is the first to use them in volume production on an all-aluminum car. The main difficulty with implementation is the sensitivity of currently available aluminum alloys to variations in process parameters. "We have to be highly disciplined to ensure that parameters are maintained within the acceptable range," comments Reimold. He has already installed electronic control technology to keep the riveting process parameters on target, and plans similar systems for the various welding techniques. Until those are in place, it is necessary to carry out regular destructive testing of welds on sub-assemblies and even complete bodies to check their quality.
Suppliers help out. Alongside Audi's continued work to improve the manufacturing processes for aluminum, the aluminum producers are also enhancing the properties of available alloys. The current alloy is one that achieves full strength after a 30-minute curing cycle at a temperature of 205C. This requires Audi to provide a dedicated curing oven for completed A2 bodies to go through before passing on to subsequent paint and trim and final assembly operations. Next-generation alloys will not need dedicated curing ovens, predicts Reimold. They will reach full strength at the temperature of the paint-curing ovens.
A8 and the A2 spaceframe saving
The A8's Audi Space Frame, weighing only 249 kilograms (some 200 fewer than a steel bodyshell of the same type), set new standards in its market segment, but is surpassed in this respect by the A2's aluminium body, which weighs only 156 kilograms including add-on parts - 43 percent less than a comparable conventional steel body. Furthermore, the number of elements making up the A2's body is only 238, compared with 334 in the case of the A8. This has been achieved by combining various components into larger items - in most cases sections or multifunctional castings. For example, the A2 has a single-piece side wall frame, the first time such an item has been produced from aluminium.
At the same time, the degree of automation has gone up from 25 percent on the A8 to 85 percent on the A2, a value comparable with conventional pressed-steel body construction. The methods adopted allow up to 300 cars a day to be built. This must be compared with a maximum daily capacity of 80 in the case of the Audi A8.
An innovation not matched anywhere in the world is the laser-beam welding process used for the aluminium body elements. About 30 metres of laser weld seams are to be found in the A2. Joining techniques that had already been proved successful on the A8 are the use of self-piercing rivets and MIG welding. These methods succeed in keeping the dimensional tolerances of structural elements down to only ± 0.15 millimetre on the A2 - a benchmark value within the Volkswagen Group.
The history of the plant can be traced back to 1873, when the ingenious Swabians Christian Schmidt and Heinrich Stoll established a knitting machinery factory in Riedlingen, on the Danube. Seven years later they relocated the factory to Neckarsulm, and commenced production of penny-farthings under the "Germania" brand two years after. Their first low-level bicycles followed shortly afterwards. The company started to build motorcycles at around the turn of the century, and manufactured its first cars from 1905, under the name of the "Original Neckarsulm Motor Car". By 1914, now operating under the name of Neckarsulmer Fahrzeugwerke AG, its 1,200 workers turned out 27,000 bicycles, 3,600 motorcycles and 900 cars. Car production, however, ground to a halt during the Great Depression.
In 1946, "NSU Werke AG" rebuilt the factory that had been destroyed during the war and started to build cycles and motorcycles again. Thanks to the boom in motorised two-wheeled transport in the 1950s, the company soon grew to become the world's largest motorcycle manufacturer. Car production recommenced in 1958. The product range included such renowned models as the Prinz, NSU Spider and Ro 80. In 1969, AUTO UNION GmbH merged with the Neckarsulm-based NSU Motorenwerke AG to form AUDI NSU AUTO UNION AG. The Audi 100 was built at Neckarsulm. In the mid-1970s, the workers fought hard to save the plant. To make better use of the available production capacity, the Porsche 924 and 944 were assembled here. 1985 saw the company change its name to the present form of AUDI AG, with its head offices in Ingolstadt.
Neckarsulm - an overview of the plant
The town of Neckarsulm has 26,745 inhabitants. With 13,697 employees (figure correct as at December 31, 2001), Audi is the largest employer in the Heilbronn-Franconia region. Of this total, 10,774 are industrial workers and 2,242 office staff. There are in addition 681 apprentices employed at Neckarsulm.
251,057 cars in total were built at Neckarsulm in 2001, an increase of 10 percent on the previous year. 49,369 of the Audi A2 and 166,472 of the Audi A6 (including 55,915 A6 Avant models) were built, as well as 19,995 of the allroad quattro and 11,708 A8 models.
The site covers an area of 951,799 square metres, of which around 90 percent is developed.
The production facilities at the Neckarsulm plant include the Press Shop, Steel and Aluminium Body Shops, Paint Shop and assembly lines. Other facilities include Quality Assurance, Technical Development, tooling, training, dealer training and the service workshop. The arrangement whereby customers have been able to collect their own vehicle from the Neckarsulm Customer Centre goes back 15 years.
The Audi A2, including a version which does 100 km on only three litres of fuel, as well as the A6, A6 Avant, allroad quattro, A8 and long-wheelbase A8 and the sports models Audi S6, S6 Avant, Audi S8 and RS 6 (the latter being manufactured by quattro GmbH) are built here.
The Aluminium Centre is a special Technical Development facility at Neckarsulm. As far back as 1994, the Audi Group decided to concentrate its expertise in lightweight design at the Aluminium Centre. Around 100 employees work on a cross-disciplinary, simultaneous engineering basis on new production techniques and methods as well as aluminium bodies, and optimise products that are already in series production. It strives in particular to optimise material properties, components and processes for the large-scale use of Audi Space Frame technology. Suppliers, universities and institutes are also involved in the development process.
The first volume-production model with an all-aluminium body, the Audi A2, was created at the Aluminium Centre. This already represents the second generation of Audi Space Frame (ASF) technology. The ASF is a high-strength aluminium frame structure into which the large aluminium panels are integrated, thus assuming a supporting function. The body is around 40 percent lighter than an equivalent one made from steel, and the car's fuel consumption is thus lower. Audi created the first four-door, three-litre car in the guise of the Audi A2 1.2 TDI. ASF technology has been further refined and optimised for the new Audi A8.
Audi has already built over 200,000 cars with an all-aluminium body, including more than 100,000 of the Audi A8. Lightweight design is moreover finding increasing use in other Audi models, with aluminium components becoming ever more prevalent as an aspect of composite construction, for instance in the front lid of the A6.
There are 878 employees in Technical Development at Neckarsulm: 420 industrial workers and 458 employees on a collective pay scale. 278 of them are engineers. As well as the Aluminium Centre, the principal activities of the Neckarsulm plant include development work on petrol and diesel engines, sports engines for motor racing and the development of interior equipment.
An entirely new paint shop was opened at Neckarsulm in October 2000 following the completion of its third phase. The paint shop represents the largest capital investment in the plant's history, at around EUR 300 million.
Along with the growing product range and the increasing proportion of aluminium-bodied vehicles, the demands on the paint shop had continued to rise. The third phase of the new paint shop permitted the introduction of segmentation: there are separate operations for each model line. The result was greater flexibility in the filler, top coat and patterns line. The 7,000 square metre paint shop is likewise ideally equipped to adapt to future technologies, including for the protection of the environment.
quattro GmbH has its head offices in Neckarsulm. A fully-owned subsidiary of AUDI AG, it was established in 1983. quattro GmbH became a vehicle manufacturer in its own right in 1996, and successfully entered the segment of high-performance vehicles in 1999 with its first own model, the Audi RS 4. It has around 230 employees, of whom 100 work in production and logistics. Its administration, development and production activities are based in Neckarsulm, whereas sales and marketing operations are controlled from Ingolstadt. quattro GmbH generated revenue of EUR 99 million in 2001.
The activities of quattro GmbH are not limited to the production of independent high-performance vehicles such as the RS 6. Other important areas of business include customisation (under the "Audi exclusive" label), supplying sports packages such as the current S line versions of the A2, A3, A4, A6 and TT, tuned vehicles, exclusive accessories and an extensive range of lifestyle articles.
Occupying a total of around 10,700 square metres of floor space, including 3,500 square metres for RS production, quattro GmbH is able to respond swiftly and flexibly to the dictates of the market and to specific customer requests. It is moreover capable of assembling various different vehicle models in parallel.
For production of the RS 6, quattro GmbH is supplied with partly assembled basic vehicles from the S6 production line. The final assembly and quality assurance processes can handle up to 20 vehicles per day in two shifts (with scope for stepping up output to around 35 vehicles a day if a third shift is worked). Saloon and Avant versions of the Audi RS 6 are available.
Environmental protection at Neckarsulm
As a company with operations worldwide, it is the objective of AUDI AG to uphold individual mobility. The group bears responsibility for the ongoing improvement of the environmental compatibility of its products and production plants, and for demonstrating an environmentally responsible approach towards natural resources; bearing this in mind, advanced technologies are deployed on the basis of their combined ecological and economic impact. AUDI AG makes these technologies available worldwide and enables their implementation along the entire process chain.
The significance of this specifically for the Neckarsulm plant is that it became the first premium-segment German plant to submit itself voluntarily for accreditation as part of the EU Eco-Audit and Management Scheme in 1995. The plant was accredited for the third time on this basis in September 2001. This was followed by VDA 6.1 certification in 1999. Water-soluble fillers and basecoats, as well as low-solvent two-pack clear coats, have been in use at the paint shop since 1995, thus cutting solvent emissions by around half. The paint shop moreover no longer discharges any waste water from the production process into the sewerage system.
In 2000, Audi developed a method of recovering and recycling material lost during the spray-painting process. Less material is now used, and toxic waste is avoided.
In the press shop, too, all metal trimmings which occur when steel panels are being cut are reprocessed. Unused raw materials are compressed using baling presses and returned to the steel works for reprocessing.
To optimise a car's operating phase from an ecological viewpoint after it has left the plant, Audi treats innovative materials and technologies as a priority. Lightweight design techniques using materials such as aluminium, magnesium and plastic significantly reduce the vehicle's weight, thus cutting its fuel consumption and emissions. This is particularly true of out-and-out lightweight designs based on the ASF principle, but also of composite-design Audi models.
There is a saying among actors that light entertainment is the hardest of all. The same principle applies in automotive engineering: treat the matter of vehicle weight too lightly and you will ultimately find it all the more difficult to achieve your objectives." The words of Dr. Franz-Josef Paefgen, Chairman of the Board of Management of Audi AG, echo the guiding principles of auto industry specialists across the world. And Audi has been treating the subject lightly: literally. For Audi is the company that in 1994 took the technology plunge by starting production of the all-aluminum luxury A8 sedan.
The guiding principle of the significant A2 project is efficiency. That covers everything from aerodynamics the most aerodynamically efficient version has a remarkably low Cd of 0.25, with standard versions recording 0.28 to powertrain and production. The range includes the introduction of a "three-liter" version that is claimed to achieve an average fuel consumption of 3.0 liters/100 km (78 mpg), joining sister company Volkswagen's similarly capable Lupo.
"The A2 model series is our vision of progressive mobility in the 21st century. The A2 combines innovative technology with distinctive design, and its light weight opens up new horizons in terms of both dynamic performance and economy," said Paefgen. Audi has invested more than DM 300 million in plant and buildings for the A2, providing maximum capacity for a 60,000-a-year build. The A2 marks major innovations for Audi, with the necessity of developing what it describes as entirely new or modified techniques, procedures, tools, and production methods for the world's first volume-built aluminum body.
Development of the A2 body was carried out at Audi's Neckarsulm Aluminum Center based on experience gained via the Audi Space Frame (ASF) technology applied to the A8. However, the A2, which represents the second-generation ASF, comprises fewer but larger components, explained the company. It consists predominately of profiles and multifunctional large castings. A single-section side panel frame made from aluminum is also used for the first time in the car industry, according to Audi. Also novel are joining techniques for aluminum that involve a high degree of automation in volume production, with more than 30 m (98 ft) of seams being laser welded. Modular techniques are used in the car's assembly (the dashboard is a significant element of this), and Audi has simplified production line logistics by placing body production and final assembly in one building.
Audi's motto at Neckarsulm is "think light." It has been 15 years since the company started work seriously on aluminum with an eye to use it for production cars. Plant Manager Otto Lindner said it takes "immense technical expertise" and a comprehensive training program to build an aluminum car on an industrial scale. Audi has also made a major investment in automation, which accounts for a modest 25% of the A8's build but for more than 80% for the A2 said to be necessary to achieve consistently precise dimensional accuracy in high-volume production.
Said Lindner, "This requirement went hand-in-hand with the need for similarly high dimensional accuracy of the body's component parts. Unconventional approaches had to be adopted in the technical development process in order to satisfy this requirement."
The production flow of the A2 starts with panel sections produced in-plant arriving from the press shop, the body components given a pretreatment before being transferred to the upper floor of the A2 production hall. Once assembled, the bodies are transferred to the paint shop via a conveying bridge. They are painted together with the A8 and steel bodies for the Audi A6. Once painted, the bodies are moved back across the bridge to the ground floor of the production hall for final assembly.
Lindner singled out several elements of the A2 build and production process for particular mention: "The single section aluminum side panel is of particular interest. This proved a notable challenge. It is manufactured at our press shop via a four stage drawing process." Automation includes metal inert gas (MIG) welding and punch-riveting. MIG welding allows Audi to produce nodes via butt-welded joins to reduce production time. Punch riveting also allows higher joining speeds and is already used on the A8. "Five years ago, no one would have thought we would be able to weld aluminum automatically by means of a laser, but there are 30 m (98 ft) of laser-welded seams on the production A2; this is certainly unique within the car industry," said Lindner.
Other novel aspects of the A2 include multifunctional large castings such as a single-section B-pillar that previously would have comprised six parts. The A2's extruded sections see the use of a "hydroforming method for calibrating extruded sections," production of the entire section achieved in a single pass with close tolerances, including punching and stamping processes.
Lindner underlined the importance of workforce training. Production workers are involved in technology development processes at an early stage of the planning and implementation phase and "cross-divisional" teams have been formed to optimize processes before production start-up. He added that a comprehensive "launch-flanking" program is used to inform and motivate all workers who will be dealing with the product. The workforce will be about 1500 by 2001, with 500 in body production, 800 in assembly, and the remainder in the paint shop.
The five-door A2 will consist of petrol and turbodiesel (TDI) power units of 1.4-L capacity, each producing 55 kW (75 hp). Later there will also be an ultra-economy version capable of achieving 2.99 L/100 km (79 mpg) fuel consumption using the 1.2-L three-cylinder TDI engine already available on the Lupo. It produces 45 kW (61 aerodyForged aluminum wheels are fitted. Rear bench seat weight was cut by the use of "special materials and a sandwich principle." saving 19 kg (42 lb). The three-liter A2's suspension is some 80 kg (176 lb) lighter than that of the regular car.
The engine fitted to the A2 three-liter has an aluminum crankcase and a mass of 100 kg (220 lb). The A2's 0-100 km/h (0-62 mph) acceleration in 14.8 s and its top speed is 168 km/h (104 mph). It has an automatic stop-start function as a fuel economy aid, the engine restarting as the accelerator pedal is depressed. The car has an intelligent electrohydraulic gearchange mechanism, providing fully automatic or clutchless manual changes. In terms of smoothness of operation, it is the least successful aspect of the three-liter Lupo; it will be interesting to see if the A2 application is better. There is no torque converter. In automatic mode, the driver can select "Eco" for improved fuel consumption with earlier upshift points. The engine complies with EU III emissions regulations and the stricter German D4 regulations. Fuel consumption and emissions performance qualifies the A2 three-liter for tax concessions in Germany.