Lightweight construction has been given all the weight such an important topic deserves at Audi: for 17 years now, Audi has been undertaking intensive research and development work into aluminium as a material, and has built up unrivalled know-how in using this lightweight metal. Dr. Werner Mischke, AUDI AG's Director of Technical Development, comments: "Our lead over competitors in this area is at least five years." Among the products that provide evidence of this are the Audi A8 and the Audi A2, two cars that sell successfully and have all-aluminium bodywork. But Audi's use of weight-saving materials grows all the time in other ways as well, tailored blanks, plastics or magnesium for add-on components and applications in the engine, transmission or running-gear areas. The policy can be summed up as "intelligent use of mixed construction principles to reduce vehicle weight".
The notion of building lightweight cars with the aid of innovative materials goes back many years. As early as 1913, NSU produced its 8/24 car with a body entirely made of aluminium. In 1923, Audi announced a six-cylinder all-alloy engine. In the same year, it experimented with a streamlined aluminium car body for its Type K model. Later, in 1954, the Auto Union looked into the possibility of saving weight by using plastic for the car's body.
In the years that followed, weight-saving construction remained one of the key competence areas of the Ingolstadt-based automobile manufacturer. In 1980, for instance, Audi developed an upper midsize research vehicle using plastic elements as body reinforcements. This was followed in 1984 by the legendary Audi Sport quattro, which had a high-tech outer skin made from a composite fibre material. 1984 was also the year in which Audi began to study aluminium intensively again; in due course, an aluminium body based on the Audi 100 was developed.
At the 1991 German Motor Show (the 'IAA') in Frankfurt, the four-ring badge was seen on the Audi quattro Spyder, a sports coupé that was received most enthusiastically, much of the sensation it caused being due to its aluminium body. Only a short time later, at the Tokyo Motor Show, another futuristic sports-car design study was unveiled, the Audi Avus quattro, with an eye-catching body in aluminium polished to a high gloss.
Close observers of the automobile scene judged these exciting new moves to be clear evidence that Audi was planning to make greater use of aluminium in its production models. As it transpired, a partnership had been in existence for some years already with the Aluminium Company of America (Alcoa), aimed at developing an aluminium-bodied car to production readiness. The policy was formulated as follows: a systematic weight-saving construction concept, particularly as far as the car's body was concerned, would lower fuel consumption significantly without calling for any sacrifices in comfort, performance or safety.
Audi Space Frame and A8
In the autumn of 1993 the German Motor Show was once again chosen to reveal the results, in the form of the Audi ASF aluminium design study. This vehicle made use of entirely new construction principles that amounted to far more than mere substitution of aluminium for steel as the structural material. The Audi Space Frame principle created a high-strength aluminium framework into which the larger sheet aluminium elements were integrated and performed a load-bearing function. The extruded aluminium sections o the frame were linked by pressure die-cast nodal elements.
New manufacturing technologies had to be developed for the new construction principle, and also improved light alloys and process techniques. In addition to welding and adhesive bonding, self-piercing rivets were used as a joining technique for the first time in the automobile manufacturing industry. More than 40 patents and patent applications were ample evidence of the sheer novelty of the ASF concept. In 1994, at the Geneva Motor Show, the ASF concept car was translated into series-production form: the Audi A8 with its all-aluminium body celebrated its world première - a milestone in automobile construction.
The Aluminium Centre
The A8 is built at the company's plant in Neckarsulm. This location in the German State of Baden-Württemberg soon established itself as the centre of Audi's aluminium know-how. At the end of 1994, the Group grouped together its competences in weight-saving construction and invested the equivalent of some eight million Euro in the construction of an Aluminium Centre. This now employs more than a hundred people, who are solely concerned with the development of production vehicle built in aluminium. Dr. Wolfgang Ruch, the
Director of the Aluminium Centre, explains: "We are particularly concerned with optimising the material properties, components and processes used in high-volume production according to the ASF technological principle. Suppliers, colleges of advanced technology and other institutes are all involved in this activity."
The Audi A2 and the second ASF generation
This development work has clearly been crowned with success: in 1997 Audi exhibited its Al2 design study, a vision of an aluminium car suitable for high-volume production. It took only two years more for this vision to become reality: in 1999 production of the Audi A2 began in Neckarsulm and with it the second generation of ASF technology - the first car to be produced in volume with an all-aluminium body. Its success was due in no small way to the invaluable experience already gained by Audi from series production of the all-aluminium A8 model. The new second-generation ASF vehicle consists of 60 percent sheet aluminium, 22 percent aluminium castings and 18 percent extruded aluminium sections. Audi's development partner for the A2 in the aluminium area was Algroup Alusuisse (now Alcan).
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.
Weight-saving construction methods for the 'three-litre' car
Like the A8 in 1994, the Audi A2 received the European Aluminium Award in 2000 for its innovative concept. In the same year, this model was awarded the German Industry Innovation Prize for its developed version of the ASF technological principle. Furthermore, Audi went a step further and added the first four-door hatchback in the world with a fuel consumption of only three litres per 100 kilometres to its A2 programme. The A2 1.2 TDI actually weighs 135 kilograms less than the already low figure recorded by the A2 1.4 TDI: just 855 kilograms. Its fuel consumption (total according to 93/116/EG) is precisely 2.99 litres of diesel oil per 100 kilometres. One of the methods adopted to achieve this weight reduction is the use of innovative lightweight materials for even more of the car's components.
In this way the running gear, for instance, has been reduced in weight by more than 80 kilograms. The frame to which the axle is attached, the lateral suspension control arms and the suspension struts are made of aluminium, as are the front disc brake calipers and the rear brake drums. The A2 1.2 TDI also has lightweight forged alloy wheels and special tyres which weigh only 4.9 kilograms each thanks to the use of aramid fibres to provide the necessary strength in the tyre carcass. Lightweight forged alloy wheels, incidentally, are now standard equipment on most Audi models. Further weight-saving measures applied to the A2 1.2 TDI included aluminium shock absorbers, front seats in lightweight foam and a rigid rear seat back of sandwich construction, which alone cuts the weight by 19 kilograms.
150,000 aluminium cars
In July this year, Audi reached a new milestone in its successful history of weight-saving car construction by producing its 150,000th aluminium car. The total is made up of more than 93,000 Audi A8s and almost 57,000 A2s. Nor will we have to wait much longer to see Audi's next aluminium car: in 2002 the successor to the current Audi A8 will be launched, and will once again be of aluminium construction, using a developed version of the ASF concept.
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