JEC Group have brought together the international community of composites leaders and executives in our Composites Circle as an unique networking opportunity to meet with both peers and future partners.
Future developments in automotive design will depend on the availability of materials that allow further weight savings, can be efficiently processed into complex shape, and with sufficient load-bearing capability to push forward modular production. StructUre™ foam has the potential to become one of these materials.
(Published on August-September 2005 – JEC Magazine #19)
BY CHRISTOPH HOFFMANN, SALES MANAGER AUTOMOTIVE, FOAMPARTNER REISGIES GMBH, AND LEENDERT DEN HAAN, MARKET DEVELOPMENT MANAGER, FOAMPARTNER FRITZ NAUER AG
Because of the laws of aerodynamics, you have to streamline exterior automotive design in order to minimise air friction and reduce fuel consumption. The pursuit of comfort and aesthetics has had a similar effect upon the car’s interior (figure 1). A key factor determining the use of industrially manufactured semi-finished materials in the automotive sector is the ability to process such materials into complex-shaped, threedimensional parts within short cycle time and at reasonable cost.
Further structural weight reduction
The use of low-density materials like foam is almost unavoidable for reducing the fuel consumption of cars. Foam is used extensively in today’s cars and typically has two main functions: cushioning or acoustical insulation and noise reduction.
Using structural foam could result in further weight reduction. However, this type of foam is limited mostly to niche vehicles like sports and racing cars. The reason for this is that structural foam is typically rigid. Processing it into three-dimensional shapes requires time-consuming CNC-milling procedures or, in some cases, thermoforming - although, as foam by nature acts as an insulator, achieving a uniform heat gradient over thickness is extremely difficult when heating it.
New processing and production concepts
Soft, flexible foam can be processed efficiently using fast operating machinery. Processes like contour cutting, die cutting and shape profiling are well established. The FoamPartner group developed a new type of polyurethane foam called StructUre™ to combine the processing advantages of soft foam with the mechanical properties of rigid foam. This can be achieved by generating additional molecular cross-links in a post-treatment process and transferring the foam to the rigid state after processing and shaping in its soft state (figure 2).
For post-treating StructUre™ foam, the electron beam cross-linking process is a choice that offers many advantages for production. It takes place at ambient temperature, so there are no thermal stresses after cross-linking. It can be accurately adjusted and controlled, and the electron dosage is the only variable (figure 3). The material properties are optimised for combined strength and damage tolerance. Above all, the process is extremely efficient and takes only a matter of seconds. Continuous systems can now be used (figure 4). The high throughput enables large series production, typical for the automotive industry.
The future of modular automotive production
The current trend in automotive production is heading more and more towards the assembly of prefabricated modules. Such subassemblies, like front ends, dashboards and interior headliners, allow for easier access during production. They also allow for outsourcing parts of the production process and for easier implementation of local content when manufacturing lines are duplicated elsewhere in the world.
Lightweight sandwich structures could play an important role when it comes to breaking down automotive structures into smaller, load-bearing modules. The dimensional stability of sandwich structures facilitates quick and precise assembly. This concept has already been demonstrated for buses, where floor, roof, front and rear modules have been based upon sandwich design. Thin skins made of rapid-curing composites or aluminium can be processed into class-A surfaces and load-bearing, damage-tolerant StructUre™ foam that is efficiently shaped and processed could be used with these as core material.