Prof. Dr.-Ing. Ulf Breuer: Continuous fibre-reinforced thermoplastics – Ground-breaking technologies in automotive construction

Figure 1: Fibre-reinforced polymers (FRP) offer outstanding lightweight construction properties, which is why they can contribute to improving product performance in nearly all industry sectors.

Against the backdrop of internationally progressing industrialisation and ­urbanisation, environmentally compatible and sustainable economies and ­innovations in key areas are the key challenges of the 21st century. The topic “Complex materials and new materials” incorporated in the research initiative of Rhineland-Palatinate is an important focus for this. Advanced fibre-reinforced thermoplastics are the key to decisive innovations in transportation and traffic organisation, the energy sector and the health sector.

Fibre-reinforced polymers (FRP) are increasingly used in German key industries due to their enormous lightweight construction potential and contribute significantly to environmenttal compatibility and economic efficiency of products in relation to innovative mobility concepts. Current primarily used thermoset fibre-reinforced polymers require elaborate and often economic­ally inefficient manufacturing processes; they are not fusible and therefore have a very limited recyclability. Innovative thermoplastic fibre-reinforced polymers, called thermoplastic composites (TPC), overcome these disadvantages and make it possible to overcome established constructive limits of conventional materials and improve the performance of a multitude of products in a variety of different areas of application. However, full exploitation of this potential is dependent on further research and development.

Figure 2: Mechanic capacities of FRP in comparison (left), display of possible weight savings for CFRP (right).

The possible leap in development with TPC becomes evident when the mechanical performance of these materials is compared to that of traditional lightweight construction materials. Figure 2 clearly shows that carbon-fibre-reinforced polymers (CFRP) are significantly more effective than high-strength metals due to their high rigidity and strength as well as their low material density. This makes it possible to save material on components, especially when the fibres are practically endless and only limited by the size of the component itself and when the options for aligning the fibres in accordance with the component stress are exploited correctly. Based on this, a component made of CFRP can weigh, depending on its application, just one-quarter of the steel version of the component. This weight advantage results in fuel savings, lower emissions and range advantages in transportation.

Figure 3: Global demand for carbon-fibre-reinforced polymer (in 1000 t) * estimate source: CCeV Marktbericht 2015.

Increasing use of FRP in automotive manufacturing is what drives the development, among other things. BMW uses FRP not only for electric vehicles but also in large-scale production (7 series). Audi, VW, Porsche and other OEMs are also successively expanding their lightweight construction centres in order to increase the use of FRP in large-scale production. There is also extremely high potential for growth in the supplier industry, as suppliers can use new production technologies to expand their product portfolios. The wind energy market also leads to a boost in development. It shows stable growth rates and Germany is one of the main export countries for wind turbines.

Figure 4: Injection mould bearer for use in the automo­tive sector, a joint development of Audi AG, Bond-Laminates GmbH, Jacob Plastics GmbH, KraussMaffei Technologies GmbH, LANXESS Deutschland GmbH and the Institute for Composite Materials in Kaiserslautern; Federal Ministry of Education and Research (BMBF) funding code 02PU2351

The use of FRP is reach­­ing its limits despite these impressive figures, which are mainly defined by the fact that FRP is usually based on thermoset polymers in large-scale production, which irreversibly chemically crosslink. Thermoset polymers are established on the market, but their broader application is limited by

• high costs of continuous fibre-reinforced
• semi-finished products,
• comparably long cycle times and
• severely limited reusability of the material.

Despite their technological superiority over conventional materials, FRPs are frequently not used today as their use is not yet economically sensible. For this reason, the high manufacturing costs in particular have to be reduced. According to a current study by the VDI, the greatest need for research is seen in recycling, simulation, design, connection technology, joining surface treatment and non-destructive quality assurance.

Figure 5: Thermoplastic tape laying head which allows for optimal component production with continuous fibre reinforcement (Institut für Verbundwerkstoffe, Kaiserslautern)

Figure 6: Efficient joining technology based on fully automatised induction welding (Institute for Composite Materials, Kaiserslautern)

Thermoplastic composites (TPC) are the key to exploiting the full technological potential. Unlike with thermoset polymer, ther­­mo­­plastic com­­­­po­­sites can be for­­med or re­­turned to a molten state when introducing heat. This means they can be:

• molten,
• welded,
• re-formed,
• recycled and
• produced in short cycles and therefore on a large scale.

Thermoplastic semi-finished products can also be stored for an unlimited period of time. Together with the advantages mentioned above, this opens up possibilities for processing methods and combinations which are highly attractive economically. Nonetheless, they are currently only available in relatively few applications on mass markets. With the right development approaches such as those adopted in Rhineland-Palatinate, gaps in research and development can be closed. Then the advantages outweigh the disadvantages, TPCs will be able to compete with conventional materials on a broad scale and will be available for environmentally friendly, economical, lightweight and safe automobiles of the future.

Prof. Dr.-Ing. Ulf Breuer
The author studied mechanical engineering in Darmstadt, Manchester and Kaiserslautern and received his doctorate in 1997. After that, he worked for the German Aerospace Center (DLR) and for Airbus. Since 2010, he has been a professor at the TU Kaiserlautern and managing director of the Institute for Composite Materials GmbH.