drivEcomp II – Development of a high-performance SMC for structural applications in electric drive systems

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In order to meet the targets of the Paris Agreement, CO2 emissions in all areas of mobility must be significantly reduced within the next few years. In addition to switching to electromobility and abandoning the use of fossil fuels, the energy efficiency of the used drive systems has to be optimized. Here, one research focus is on the development of new materials and manufacturing processes to achieve weight reduction at component level by fiber composite technology.

Compared to metallic materials, fiber-reinforced polymer composites (FRPC) often involve higher raw material and manufacturing costs. The higher manufacturing costs usually result from a low level of fully automated processes. For this reason, Sheet Molding Compounds (SMCs) were developed as early as in the 1960s. These compounds are based on polyester or epoxy resins, which are produced as flat semi-finished products from a resin paste and chopped fibers in a fully automated process. For component manufacture, the semi-finished product is cut to size, stacked to form the component weight and placed in a hot tool. Due to the heat effect in the press tool, the viscosity of the SMC decreases, it starts to flow and fills the tool. The flowing process of the material enables very complex geometries, such as ribs and webs to be formed, resulting in great design freedom for the components. SMC made it possible for the first time to manufacture FRPC components suitable for large-scale production that could compete with metallic components in terms of price. Since then, glass-fiber-reinforced SMCs have been used primarily as components exposed to low structural stresses, such as outer skin components in the automotive industry. In order to economically exploit the potential of FRPC for weight reduction in other areas, current developments aim at using SMC in structurally highly stressed components. To improve the mechanical properties of SMC, the reinforcing glass fibers are replaced by carbon fibers and the fiber volume fraction is increased.

In  project ‘driveEcomp II’, housing components of an electric traction motor - which are usually made of metals - are being developed as a SMC component. For the realization of this project, the design will be adapted to the advantages of SMC. Thanks to the great freedom of design, a load path-appropriate design can save material in places, where not required as well as integrating functions, such as an air duct. Another advantage of the SMC are vibration-damping properties which can reduce noise emissions from the engine.

The research activities of Leibniz-Institut für Verbundwerkstoffe within the project consist of developing the material and process technology. Since the component is exposed to very high dynamic and thermomechanical stresses during operation, a new SMC material must be developed. For this purpose, SMC semi-finished products are manufactured from various epoxy resin systems and carbon fibers, processed into test specimens and the mechanical and thermomechanical properties determined. Once a suitable material has been defined, the process parameters of the compression molding process will be optimized for the new material. The aim of the project is to produce functional prototypes of the bearing shield which will be tested in further functional tests under realistic conditions.  

Project partners:
Siemens AG
CirComp GmbH
Gustav Gerster GmbH & Co KG

The project ‘drivEcomp II - Advanced composite solutions for electric drives to increase the power density in ground-based mobility applications’ is funded by the Federal Ministry for Economic Affairs and Climate Action on the basis of a decision by German Bundestag (funding reference 19I20017D).

High-speed train Siemens Velaro (©Siemens AG, 2022)

Exploded view of a traction motor (©Siemens AG, 2022)

Schematic showing the production stages of a C-SMC semi-finished product

Microsection of C-SMC with 50 % fiber volume content

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