New base coat line in Neckarsulm

There was good reason to celebrate at the opening of the new base coat line at Audi in Neckarsulm: the newly built hall uses technologies that make the Neckarsulm site significantly more efficient and therefore fit for the future.

15,000 cubic meters of excavated earth, 2,600 drilled piles, 1,100 tons of steel and 13,700 cubic meters of concrete: after two years of construction, the new A22 building with a floor area of 12,000 square meters is complete. Audi is repositioning the Neckarsulm site in the area of surface technology and is investing heavily in modernizing and partially renewing the paint shop. On October 16, 2024, the inauguration was celebrated with more than 200 invited guests from politics, the press, Audi and its suppliers. Fred Schulze, Plant Manager at the Neckarsulm site: "By investing in the new facility, Audi is setting the course for continuing its move towards e-mobility and aligning the Neckarsulm site for a sustainable future. The construction project is an important milestone in the plant's development and part of a future-proof infrastructure for production."

Rainer Schirmer, Chairman of the Works Council, also praises the project: "With the refurbished paint shop, we have one of the most advanced facilities in the automotive industry with modern working conditions. This investment underlines our commitment to sustainability and ensures the future viability of our site."

In the new plant, both combustion and electric models are primed in a fully automated system, including all models produced at the Neckarsulm site and in the neighboring Böllinger Höfe, including the new Audi A5, the upcoming Audi A7, the Audi Sport models and current and upcoming all-electric models.

For the first time, pre-treatment will be carried out using a new thin-film process, eliminating the need for the previous phosphating process. The new process eliminates the need for several previously required process steps, such as activation and passivation, and can also be carried out at room temperature. In addition, no sludge containing heavy metals is produced and maintenance and disposal costs are significantly reduced. From an ecological point of view, the new pre-treatment process therefore realizes great potential savings in terms of waste, water and energy. In the new process, a 0.2 micrometer thin layer of zirconium and silicon compounds is applied to the base metal, which serves as an adhesive base for the subsequently applied cathodic dip coating in addition to providing corrosion protection.

Thin film pre-treatment

The process is called Oxsilan and was developed by Chemetall. Audi had already successfully used a comparable thin-film pre-treatment for all-aluminum vehicles in the past. Now an alternative to zinc phosphating on steel finally meets the car manufacturer's high standards. As the A22 building had to be integrated into the existing plant structure and the width was therefore limited to 77 meters and the length to 189 meters, corresponding adaptations had to be made to the plant technology. The pre-treatment system could not simply be set up in a straight line - this would have required a hall length of over 350 meters. For this reason, the car bodies first pass through the pre-treatment area, where they are cleaned and receive the Oxsilan coating before being turned around, so to speak, and fed into the parallel cathodic dip coating line.

All options for increasing efficiency and improving quality are also used in the cathodic dip coating process. For example, Dürr's RoDip technology moves the car bodies through the cathodic dip coating bath in a rotational movement to ensure complete and even coating of the car body, even in difficult areas. In addition, the power control of the anodes in the cathodic dip coating bath is adapted to the positions of the car bodies in the bath, which enables significant energy savings compared to a constant current supply.

Drying - rotated 90 degrees and from the inside

Audi opted for Dürr's new EcoInCure concept for the drying process. The car bodies pass through the dryer rotated by 90 degrees, during which a directed flow of hot air is generated around the car bodies and, above all, into the interior areas. As a result, complex sill structures are heated and, above all, warmed through much faster, so that the heating times are significantly reduced and the temperature distribution is more homogeneous at the same time. In addition, the temperatures that can be reached in the innermost areas of the sills increase, which is particularly important for structural bonding in car body construction. This is because they cure at the same time as the cathodic dip coating. In addition to the higher energy efficiency and the shorter overall length, which is advantageous in this application, the cross dryer is therefore very well suited for upcoming electric and hybrid vehicles with their more complex sill and body structures.

Ursula Noll, Head of Production Planning Paint Shop Corrosion Protection, summarizes: "The innovative thin-film technology in pre-treatment, combined with the new cross-drying process, makes a particular contribution to the efficiency and sustainability of the new basecoat. This enables us to significantly reduce our electricity and water requirements and make an important overall contribution to our Mission:Zero environmental program."

Saving energy with the top coat

The base coat building A22 is connected to the neighboring top coat building by a newly installed bridge over which the car bodies change halls. The company has also already carried out extensive restructuring and modernization work in the top coat. Audi has achieved energy savings of around 50 kilowatt hours per vehicle thanks to a new, dry paint mist separation process, which allows more than 90 percent of the filtered process air to be reused.

It is particularly noteworthy that Audi has now succeeded for the first time in achieving the company's very high internal appearance requirements without a filler application. In the new process, which is being used for the first time in Neckarsulm, the filler is replaced by a pre-zone paint, so that the previously necessary, complex and energy-intensive separate filler-drying process is no longer required. This saves up to 140 kilowatt hours of energy per vehicle.

With the modernization and conversion measures and the underlying concept in terms of sustainability, the Audi site in Neckarsulm is well equipped for the challenges of the future. In this context, the construction of the new base coat and the new hall represents another important milestone in the restructuring and modernization of the paint shop - a really good reason to celebrate.

CB