|From Automobil Industrie Dezember 2001
In the eighth year of its existence, the Aluminium Centre at AUDI AG's Neckarsulm plant is working on both the new A8 and on other group projects. The team led by Dr. Wolfgang Ruch celebrated a master stroke when the A2, the first volume-built vehicle with an all-aluminium body, went into production. The Aluminium Centre's chief spoke to "Automobil Industrie" about Neckarsulm's technological lead in the field of lightweight design.
Dr. Ruch, the Aluminium Centre works on the development and application of aluminium technology in the car industry. What specific tasks does it perform?
Ruch: Our core skill extends over three major areas. The first area of expertise relates directly to the vehicle body. It involves its design and calculation. We define crash requirements, repair conditions, quality criteria and dimensional accuracy. The second area covers the material aluminium and the properties with which ideally it satisfies our product requirements. In other words, the right alloying elements, their corrosion resistance and long-term strength. The third aspect is production technology. The emphasis here is on the shaping and reshaping of aluminium semi-finished products, the joining of individual components, and apparatus and setup concepts for body production.
Is the A2 the Aluminium Centre's first brainchild?
Ruch: On the A2, we are using production technologies that evolved from the systematic refinement of A8 expertise. The question of production volume is of course also relevant. It significantly influenced the choice of production technology. Production operations for the A2 are geared up to a daily volume of around 300 vehicles, and in the case of the A8 about 80 a day.
If we compare the A8 and the A2 in terms of lightweight design, what degree of progress did you achieve between the first and second generations of aluminium bodies?
Ruch: Apart from the fact that the A2 is in a different league to the A8 in terms of volume and production totals, other differences between the two models are the production technology, the use of more advanced materials and the strategic objectives.
So what were the strategies in each case?
Ruch: In the case of the A8 we were seeking to demonstrate that the material aluminium is fundamentally suitable for body manufacturing and that it would become accepted by the market as regards the ease with which body repairs could be carried out. We had to show that an aluminium structure can be repaired just as easily as a steel body, without causing higher costs. In the case of the A2, the emphasis was on the production technology and on validating the processes for volume production. Our task specified that the degree of automation of an aluminium vehicle had to correspond to that of a conventional steel body.
On that basis, what did you change on the A2 compared with the A8?
Ruch: It would be simpler to ask what we didn't change: for instance, the alloy of the outer skin, the adhesive for the folds, punch rivets and other connecting elements. We changed everything else. We developed entirely new operating materials for punch-riveting and MIG welding, the latter including innovative torch cleaning and tool centre point (TCP) scanning to boost the reliability of the process. We invented new equipment components for stud welding. We achieved a dimensional accuracy of +0.2 millimetres on the profiles thanks to calibration by means of hydroforming. And we restructured the processes and alloys for the diecast parts in order to reduce their production tolerances further. Last but not least, we rethought the use of castings in the space frame: on the A2, the castings not only act as connecting elements between various surfaces, profiles and members; they also perform other functions. The castings take on the role of multifunctional large-scale castings.
And you have reduced the number of parts?
Ruch: Yes, the B-post is the most striking example; on the A8 it consisted of six sections, and on the A2 it is made from just a single element. The motto is "six into one". We will also be applying this "golden rule" to other components in future. At the same time, we have succeeded in integrating several functions. Take the longitudinal member, for instance, which has a ribbed pattern to absorb impact energy in a crash, but to which the suspension is also mounted. It also includes mounting points for the car jack. And the upper shell, again of a ribbed shape to absorb crash energy, is connected to the engine mounts and suspension strut bracket. The rear doors are hinged to the single-section B-posts. The belt reel mountings and deflectors are also mounted on the B-post.
What is the degree of automation of these two models?
Ruch: The degree of automation for the A8 is 25 percent. We were able to boost it to 85 percent for the A2. It is therefore on a par with the production of steel bodies.
Is the development of production technology a focal point of your work?
Ruch: Design work and the development of production technology take place hand in hand. Over 40 percent of our work focuses on production aspects and materials. At this point I should also mention the partners with which we are jointly promoting our technology. In contrast to steel construction, Audi buys in a whole range of parts for its aluminium bodies.
Do you mean your partnership with the aluminium producer Alcan?
Ruch: The company formerly known as Alusuisse, now Alcan, was very involved in the development of the A2. As a result, the company is the biggest supplier of aluminium parts for the A2. This aluminium specialist supplies us with castings, extruded sections and sheet panels. The only parts that we produce ourselves are the high-precision aluminium panel sections that determine the quality of the outer skin; we moreover regard this as one of our core skills. Although Alcan is our strategic technology partner for the A2, it is not our exclusive partner in the aluminium sector. We believe that a concerted effort by the aluminium industry is needed to support our production technology.
Was Alusuisse already involved in the development of the A8?
Ruch: We use an outer skin alloy on the A8 that was developed specially for us by Alusuisse. The same material is also used for the outer skin of the A2, and is supplied by Alcan from its mill in Sierre, Switzerland. The profiles and vacuum diecast parts of the A8 were developed together with Alcor.
So is the alloy used for the A8 and A2 the same?
Ruch: No, apart from the outer skin alloy and the profile alloy. We use an alloy optimised by heat treatment for the castings. We have created a process that guarantees optimised heat treatment. This renders the straightening process that was still essential for the A8's cast components unnecessary. This naturally has a positive impact on component costs. We have used a recycled alloy for the A2's inner skin alloy.
What problems were encountered during the launch of the A2?
Ruch: From a production viewpoint, the launch of the A2 was very successful thanks to systematic, methodical preparation of the production techniques and carefully planned training of our workers. The quality achieved was certainly on a par with any production launch of steel-bodied cars. This is evident from the fact that the A2 body serves as the benchmark for dimensional accuracy within the VW Group. We were soon able to rectify the problem that some purchased parts were not initially available in sufficient quantity.
Are there also partners outside the aluminium industry that you teamed up with for the development of the A2?
Ruch: There were for instance the Fronius and Dalex companies, with which we refined MIG welding, and the Schramberger Trumpf subsidiary Haas, which implemented its laser technology in our body manufacturing operations. Böllhoff and Tucker assisted us with other joining techniques, and in specific punch-riveting.
Does the Aluminium Centre also work for other VW Group brands, such as Bentley and Bugatti?
Ruch: We have unique expertise in aluminium here at Neckarsulm in terms of production, development, planning and quality. We obviously make this expertise available to the entire group. Whenever colleagues consult us on aluminium projects, whether from VW or from other group brands, we of course give them our support. For example, we are currently also working on non-Audi projects.
So far we have only talked about aluminium. Are you also working with other lightweight materials?
Ruch: We chose the all-aluminium body to achieve a maximum weight saving. Our expertise is clearly in aluminium, which is why we are called the Aluminium Centre. However, this does not mean that we are not interested in other materials. When we weigh up the relative advantages of various different materials, we have to consider their availability, their cost, their use in volume production and, last but not least, their suitability for recycling.
What are the next developments? What new technologies does the new A8 contain? What consequences will all this have on the new A6 planned for 2003?
Ruch: We now have over seven years of experience in aluminium technology. We are using concepts on the new A8 that did not yet exist when its predecessor model was created. In line with our findings from the development of the A2, we will further reduce the number of parts and increase the level of automation compared with the current A8. We will see ever more aluminium concepts in the deluxe segment and in the category of full-size cars. We are unable to comment on the extent to which these developments will also affect the new A6. However, one thing appears certain: the aluminium content of all our new models is rising sharply. And the aluminium content in the recently launched A4 rose to over 190 kilograms. This trend will continue.