Competitive and sustainable thermoplastic composites for automotive applications

The growth in the use of lightweight composite materials in the automotive industry is subjected to meeting challenges such as sustainability. The first rel­evant applications of composite materials in electric vehicles such as the BMW i3, 7 Series and others show great potential for weight re­duction, but they are based on thermosetting composites and processes with limitations in terms of sustainability.

Competitive and sustainable technologies for lightweight automotive components

To achieve lightweight composite auto­motive components in a competitive and sustainable manner, Tecnalia is developing the following enabling technologies and solutions:  
• Thermoplastic composites based on low-cost raw materials;
• Competitive multi-material and hybrid solutions containing composite and metal or composite and plastic both with glass fiber (GF) or carbon fiber (CF).
• Multi-material solutions with good impact behaviour and high toughness along with conventional body in white (BIW) bond­ing solutions of thermoplastic composite reinforcement on metal;
• Zero or minimal scrap processes thanks to a combination of processes with over­moulding;
• Competitive, fast and automated manu­facturing technologies with cycle times of around 2 min.;
• Flexible automated processes that allow variable thickness and customized stack­ing;
• Thermoplastic composite technologies that facilitate recyclability. In this context, three technologies developed by Tecnalia are described below.

T-RTM technology by in situ polymerization

The CAPROCAST T-RTM (Thermoplastic Resin Transfer Moulding) technology was developed and patented by Tecnalia. In this process, the melted monomer of polyamide 6 (PA6) with its catalytic system, providing a 3K (three-component) system, is directly injected and polymerized in the mould to produce the polyamide material and the moulded part at the same time, as shown in Figure 1. The low viscosity of the melted monomer, caprolactame, and the fast reac­tivity of the 3K system allow fast processing to produce thermoplastic composites with good mechanical properties in a fast and competitive way.

The main advantages of this technology are the following:  
• Low-cost raw materials (matrix), i.e. matrix cost<2 €/kg;
• Competitive and fast manufacturing with injection time about 5 second and a cycle time of 2-3 minutes;
• Improved recyclability of the composite thanks to the thermoplastic PA matrix;
• 3K system for in situ polymerization of three components, caprolactam + catalytic system (initiator and activa­tor). This 3K system is characterized by:  
– A liquid catalytic system at room temperature,  
– No need for premixes which means a long life of the material in the machine,  
– Have the possibility to easily adjust the recipe for more reactive or slower formulations;
• “One-shot” manufacturing of complex parts.  

For the industrial implementation and scaling of this technology, Tecnalia is working with industrial machine manu­facturers and with end users to validate the technology and the material’s properties according to the requirements of the auto­motive sector.
Figure 2 shows another advantage of this technology, the one-shot manufacturing of complex parts that combine highly-re­inforced areas, with the corresponding reinforcement preforms, and areas with ribs or other complex polyamide details.

In line with the previous concept, Figure 3 shows the one-shot manufacturing of a battery box cover defined and designed by Faurecia during COSIMO project, which also combines highly-reinforced areas with reinforcement preforms and complex polyamide ribs. Tecnalia’s 3K material  which the Research Center collaborated with Krauss Maffei to adapt the RTM machine to this specific technology.

Zero-scrap forming of customized stacks (Tecnalia/Gonvarri/Fill)

In collaboration with the Austrian company Fill and companies in the transport sector value chain, Tecnalia developed and vali­dated a manufacturing process for thermo­plastic composite components that offers great flexibility in part design based on automated stacking. The process allows the production of components with zero scrap, variable fibre thicknesses and orientations, and the possibility of combining different tape materials.
Figure 4 shows the main equipment for the first part of the process based on this fast and flexible tape laying technology.

Figure 5 shows the different steps of the process: fast tape laying, 2D consolidation, 3D thermoforming in the press and over­moulding of the details/ribs and the pe­rimeter frame to finish the part without the need to trim any excess material, therefore providing a zero-scrap process and elimi­nating the need for trimming operations. In short, the main advantages of this tech­nology are the following:
• Competitive, fast and automated manufacturing technologies with cycle times of 1-2 minutes and a deposition time per layer about 10 seconds;
• Competitive hybrid solutions to combine GF or CF composite with plastic;
• Low-cost raw materials (tapes) and process;
• Maximum optimization with variable thickness and customized stacking;
• Minimum or zero scrap thanks to the combination of tape laying and forming with complementary overmoulding.

Additional details of the development con­ducted together with Gonvarri (Gestamp group) for an automotive BIW component are shown below, including the forming process simulation (Figure 6), the possible integration of local reinforcements by combining different tape materials (Figure 7), the manufacture of the corresponding demonstrators and the validation of the final prototypes (Figure 8).

Metal-thermoplastic multimaterial composite solutions

Tecnalia also developed a new multimate­rial solution within the framework of the Circular-TP European project financed by the EIT Raw Materials programme.
The objective was to develop thermoplastic composite BIW reinforcements for B-pillars or others similar to those in Figure 9, to rein­force the metal bodywork so that the weight of the metal structure can be reduced and, at the same time, the conventional joints of the metal parts are maintained (see Figure 10).

For this, a material combination is used to provides good ductility and recyclability due to the use of thermoplastic materials. In summary, this technology offers the following advantages:
• Competitive composite/steel multima­terial;  
• Good in-service and impact behaviour with high toughness
• Robust and validated processes: press forming and welding of thermoplastics; conventional metal joining technologies maintained for the BIW;
• Recyclability of both thermoplastics and steel.  

The main steps of the manufacturing pro­cess used for the thermoplastic composite reinforcement are shown in Figure 11 and 12, including the tape laying and forming processes (Figure 11), the process used to join the composite reinforcement to the metal structure (Figure 12) and an exam­ple of an omega demonstrator (conceptual model equivalent to a B-pillar).

Conclusions

Tecnalia developed and successfully demonstrated several processing solutions for lightweight automotive structures to make the transition from thermoset to ther­moplastic composites in an efficient and competitive way. These advanced processes are based on recyclable thermoplastics such as T-RTM or tailored tape laying and forming with UD thermoplastic tapes combined with plastic overmoulding and metal-composite multimaterial solutions. This article has been published in the JEC Composites Magazine N°146.

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