Colloquia

Summary

The use of thermoplastic composites (TPCs) is increasing in the automotive industry due to their potential for weight reduction, being well-suited for automated high-volume production, and providing opportunities for recycling. In this research a structural thermoplastic continuous fiber composite high-volume ready part was designed, using a cross-car beam (CCB) as a case study. The goal was to provide an overview of the challenges in the analysis and implementation.

The state-of-the-art of materials and manufacturing processes for TPC automotive parts were analyzed. Overmolding, which is press forming followed by injection molding, combined with blank manufacturing utilizing a pick-and-place process has demonstrated the capability to produce composite parts with a high degree of automation and within the required cycle time for high-volume manufacturing of automotive parts. It also allows for a high level of function integration. A market analysis identified both polyamide-6 (PA6) and polypropylene (PP) to have potential for automotive applications.

A composite CCB has been designed based on the overmolding production process. Simulations based on stiffness requirements have been done to compare a composite CCB with different layups to an aluminum CCB, the current standard for lightweight CCBs. The use of carbon fiber enabled weight reduction, however, this came at a high cost. Achieving weight reduction with glass fiber (GF) was challenging due to its relatively low stiffness. Substantial weight savings with GF were only achieved by lowering the eigenfrequency requirement for composites, leveraging the high damping characteristics of thermoplastics. Even with the lowered eigenfrequency requirement, the cost per kg of saved weight exceeded what is acceptable in the automotive industry.

Compared to metals the use of composites can also significantly increase the lead time of part design and simulation. Additionally, simulating a composite part is more challenging and thus costly, especially when it comes to strength and crash simulations. These hurdles currently limit the adoption of composites for structural parts. Thus, more research and simulation tools are required.

In conclusion, the aluminum CCB was found to be the better option compared to the investigated composite CCBs as it has a lower cost, easier design optimization and crash modeling, all at a minimal weight penalty.  Whilst it can also take advantage of the function integration provided by the overmolded ribs. Based on the challenges found in implementing TPCs as structural parts, the focus could be put on replacing other less structural metal parts with TPCs.