Innovative materials in Audi's car production
But that is not all: in all Audi models the proportion of aluminium and other weight-saving materials continues to increase, particularly in the engine, gearbox and running-gear areas. Here are a few examples: the A8 (like the A4 and A6) has aluminium suspension components. On Audi's flagship model, weight-saving aluminium is also used for the wheel hubs, the front and rear wheel suspension control arms, all brake calipers, the shock absorber pivot mounts and the wheels. In Audi's new top-of-the-range engine, the W12, which is used to power the A8 L 6.0, aluminium is used extensively. The intake pipe, incidentally, is made from magnesium and secured with aluminium screws - another absolute innovation in the car industry.
Weight-saving construction methods are in any case applied systematically to Audi's engines. Such varied components as variable-length intake pipes, cylinder head covers and thermostat housings are made from glass fibre-reinforced plastic, and light alloys are also used extensively.
The three-cylinder 1.2 TDI engine used in the 'three-litre' A2 has an aluminium engine block and cylinder head. This engine weighs only 100 kilograms and is therefore one of the lightest passenger-car diesel engines available anywhere. The 3.0 V6 engine, the 2.0-litre inline four and the A2's 1.4-litre four-cylinder spark-ignition engine also have aluminium engine blocks.
The same applies to the 1.6-litre and 1.8-litre four-cylinder spark-ignition engines, which also have cast aluminium cylinder heads. Aluminium plays an important part in the V8 spark-ignition engines too. In the V8 3.3 TDI, Audi's most powerful diesel, the engine block is made of vermicular-graphite cast iron (GGV), a high-strength material that reduces the weight of this component by ten percent. Aluminium is used for the engine's cylinder heads.
Add-on body parts
The trend towards using weight-saving materials to a greater extent is also noticeable in the cars' add-on body parts. The A6, for instance, has an aluminium engine hood. Most Audi models have high-strength aluminium side intrusion protection beams in the doors, and TT Roadster owners who order a hardtop for their sports car will find that it is of sandwich construction, with a load-bearing aluminium frame surrounded by polyurethane foam and fibre glass mats.
Audi has also made successful use of magnesium. In addition to the air intake module on the W12 engine, which we have already mentioned, the intake pipe, sealing flanges and cylinder head covers on the V8 engine are also made from magnesium. Other applications for this light metal on production cars are the housings of Audi's multitronic continuously variable transmission and the five-speed manual-shift gearbox, parts of the adjustable steering column, the frame for the airbag steering wheel in all models, the ignition lock housing or the upper seat belt mounting loops in the A2.
Audi's multifunctional, weight-saving construction methods include the systematic use of thermoplastics and thermosets reinforced with natural fibres. This applies in particular to the polyamide and polypropylene thermoplastics, but Audi also makes use of thermoplastics and polyurethane matrix components reinforced with natural fibres for concealed areas of the interior trim. The rear side panel trims in the A3, for instance, consist of 75 percent flax fibre with an epoxy matrix. In the A4 Avant and A6 Avant, flax fibre with a polypropylene matrix is used for the load-area side trim, and in the A2 the door trims are made of flax fibre with a polyurethane matrix.
Intelligent use of mixed construction methods
All this indicates that Audi's engineers are certainly placing the emphasis on aluminium, but that they are also exploring quite different methods of systematic weight-saving. Professor Hans-Günther Haldenwanger, the Head of Materials/Processes/Recycling Development at AUDI AG, explains this as follows: "In addition to careful design of the vehicle package as a whole, the greatest potential for weight-saving is in the construction of concepts and modules using an intelligent mix of materials and methods." The new A4 is an example of how this maxim has been implemented by Audi in practice.
Priority for weight-saving on the A4
Audi's top-selling model is evidence that even a car with a load-bearing pressed-steel bodyshell can save weight most effectively if aluminium components are incorporated. The proportion of weight-saving materials, that is to say aluminium, magnesium and plastics, has risen steeply. Compared with the previous A4 model, the proportion of iron and steel has dropped by about 7.5 percent. Of the unladen weight of 1,310 kilograms, 716 kg of the principal construction materials are accounted for by these iron and steel, 237 kg by polymers and 191 kg by light alloys.
Steel none the less has a decisive role to play in the new A4. Large areas of the body structure - some 45 percent by weight - are made from extra-strong or ultra-high strength grades of sheet. So-called 'tailored blanks' are used for the front-end structure and the occupant zone in particular. This technique has the advantage that the tailored blanks, which are normally of large area, are made from metal rolled to varying gauges and can thus be of higher wall thickness in zones subject to particularly high loads. Weight saving and a stable structure can thus be combined in an effective manner. Ten large tailored blanks are used in the construction of the new A4.
Such a lead in the weight-saving area can only be achieved with a complex combination of different processes in the development and production areas. These processes must take effect long before the first prototypes are built: the optimum structure must be arrived at in the very earliest design phase. In the words of materials technology expert Professor Haldenwanger: "In the vehicle's definition phase, weight-saving conceptual and modular principles can save many kilograms of weight, whereas after this stage in the process only weight reductions of a few grams are possible." He has identified six different weight-saving design strategies:
High-strength steels, magnesium, aluminium (as alloy castings, extrusions or sheet), plastics, fibre-reinforced thermoplasts/thermosets or composite fibre and plastic materials are already a firm element in Audi's vehicle design practice. Professor Haldenwanger, with a team of some 20 highly qualified engineers at the Technical Materials Centre in Ingolstadt, is also conducting research into the use of materials such as titanium, ceramics or carbon for components and assemblies. All materials with weight-saving potential are undergoing tests at Audi.
Dr. Wolfgang Ruch, the Director of the Aluminium Centre, adds: "Whenever we consider using other materials for our models, we have to take their availability, cost, use in high volume and not least their suitability for recycling into account."
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