Expert talk: Interview with Stefan Kienzle

Together with Heinrich Flegel, Stefan Kienzle manages the Materials, Manufacturing and Concepts Center, which is part of Daimler Research and Advanced Engineering, and has offices in Sindelfingen and the Ulm Research Center.

Mr. Kienzle, it was in your Center that the foundation was laid for the introduction of flexible roll forming as a low-cost body-in-white production technique. A pilot facility for this system is now operating at the Sindelfingen plant and is scheduled to begin manufacturing series production components in 2009. What are the next milestones you’re aiming to achieve here?

We plan to make the technology more flexible in terms of materials, geometries, cross-sections, and wall thickness. We’ve already run some successful tests here. Right now, for example, we’re working on varying the wall thickness of existing profiles in order to be able to use less material in those areas our simulation experts say will subjected to weaker forces. This is known as “load curve optimization,” and it can help further reduce weight. We need to enhance precision here. The facility will be able to deliver the full scope of its effectiveness with future model series featuring wheelbases with a greater range of lengths, because we can produce sill components of varying lengths while using only one machine.

In addition to passenger car sill components, key applications will include space-frame type cabin concepts for trucks, vans, and buses. Flexible forming technology makes it relatively easy to shape even the highest-strength steels available today. This in turn opens up the possibility for new lightweight construction applications.

The close cooperation of all development and production departments has been very impressive at the Sindelfingen pilot facility. Can you give us other examples of such extensive and productive cooperation in the field of materials technology, collaborative efforts by research/advanced engineering, development, and production departments?

The integration of “old research” into development has made us much more efficient in all areas, from the body-in-white to powertrains. For example, all lightweight body-in-white design projects for upcoming model series are developed to conceptual maturity through close coordination among all departments. When it comes to the powertrain, for instance, all departments coordinate with one another and then select materials for the cylinder bores, because such materials play a key role in reducing CO₂ emissions.

The fundamental philosophy behind the integrated “Materials, Manufacturing and Concepts” approach is to validate the advantages and manufacturing feasibility of new materials, and to assess them through use in specific components.

Although materials technology plays a major role in vehicle construction, it's hardly noticed by the public. What benefits does proper material selection offer customers, who may not even be aware of these advantages?

Increasing demands in terms of, for example, crash safety and noise emissions can be met only by using optimized materials. Lightweight materials make a major contribution to increasing fuel efficiency, which is something customers notice directly in their wallets. New materials provide comfortable interior temperatures in both winter and summer, for example, and harder paint coats enable customers to run their vehicles through the car wash much more often without jeopardizing its appearance. As you can see, there are a large number of material technologies that provide our customers with direct benefits.

With the issue of CO2 in the public spotlight, lightweight engineering is becoming more and more important. The flexible roll forming method makes it possible to process extremely high-strength steel, which if utilized can significantly reduce weight. Do you believe there’s further potential to be tapped with lightweight metals and steel, or have we reached the end of the line?

Innovative leaps here will become less dramatic. We will be seeing even stronger steel variants, which will further reduce wall thickness and contribute to lightweight engineering. The next generation of vehicles will include cold-rolled steel materials in the 1,000 –1,200 MPa tensile strength class, as opposed to the current level of the order of 340 MPa. So you can see what type of achievements are being made here. However, as we move toward steel with extremely low wall thickness, we’re going to run into a problem over the long term with the competing goal of structural noise reduction, for example, which is why I expect to see a certain amount of consolidation in this area.

Aluminum will be playing a more important role in the outer body layer – in terms of its use as a material for structural components, we’re going to have to play close attention to the additional costs it generates. With aluminum, we can expect to see a delayed development similar to that of steel, ultimately leading to advanced high-strength aluminum.

Magnesium is already being used today in certain areas where the higher additional costs associated with lightweight construction potential can be justified. We determine where to use lightweight construction by dividing our vehicles into so-called light material zones.

Roll forming technology has now become the norm for longitudinal components, and its use will also remain limited to such elements.

Plastics and fiber composites are giving metals some tough competition. Do you think the former will continue to push the “old materials” out?

As we all know, competition is good for business – and the dynamic development of steel over the last few years confirms this. In structural terms, vehicles need to fulfill demands related to rigidity and safety, and steel will always have a role to play here, especially with high volume models and the business framework that goes with them. Steel’s modulus of elasticity, for example, is three times higher than that of aluminum, which is why steel offers the best possible protection for the occupant cell.

In my opinion, the competition among materials will continue between polymers – reinforced with fibers as well – and aluminum and magnesium. It’s also interesting to note the growing number of applications for plastics, in particular carbon fiber-reinforced materials in the wind power and aviation industries. We’re looking forward to seeing what impact this will have on automobile design. In any case, Mercedes-Benz is already one of the few automakers that have a vehicle with a carbon fiber structure in its portfolio – the SLR.