Combination of the latest manufacturing technologies ensures highly resilient lightweight construction products

Material scientists are becoming more and more imaginative when it comes to increasing the strength and durability of components while at the same time reducing weight. For future vehicle designs, FOREL (Research and Technology Center for Resource-Efficient Lightweight Structures) has optimised standard seat-backrests. These components are exposed to extreme loads, particularly in accidents, and have to save human lives. With the innovative multi-component design and improved injection moulding technology, the team succeeded in optimising almost every aspect of the component as well as integrating it better into the process chain.

To this day, cars are generally still designed using the shell construction method. The steel chassis is partly supplemented with aluminium doors for weight reasons. Carbon fibre-reinforced components are currently found almost exclusively in non-structurally important components, which is mainly due to the high production costs. However, it is worth reassessing some individual parts of a modern automobile from the point of view of materials research, which is now well advanced.

This is exactly where FuPro comes in: The project dealt with how a car seat can be improved in many different aspects. For this, the team looked at ordinary seatbelt integral backrests that withstand car accidents and have to keep people in their seatbelts. The sheer forces involved have so far made it difficult to produce a cost-effective and similarly stable design from alternative materials.

The objective was the development and implementation of a manufacturing process for hollow profiles with complex geometry, including multi-component structures, using injection moulding technology. With this process, the team not only wanted to reduce the weight by 25 per cent compared to the serial part. In addition, the company's own integral backrest was to pass approval tests. Furthermore, the process had to be designed as suitable as possible for series production in order to be able to achieve high quantities for a potential market launch as well as to prove the maturity of the study.

The FuPro team calculated the greatest loads by means of structural-mechanical simulations and adapted the cast basic structure to the acting forces even before the first trials. With a few more iterations, the shape was further optimised.

Even if 3D printing would be able to promise potentially better results: The FuPro research team's process has made it possible to produce the entire injection moulding structure in just 90 seconds. Even the fastest additive manufacturing methods cannot keep up with this speed. To do this, the production time of the additional organic sheets used must be considered separately, which depends largely on the weaving and forming process as well as the material of the individual fibres.

Additive processes can melt metals together in the sintering process and achieve structures that would be inconceivable in the injection moulding process. For this reason, the process is particularly suitable for small series or concepts; however, it cannot compete with a process such as FuPro.

FOREL was able to reduce the weight of the process by approximately 30 per cent compared to the reference component, as the steel construction could largely be replaced by the lighter composite materials. At the same time, the number of used components is reduced. The backrest no longer consists of punched sheets and steel profiles, but only of the cast plastic, the hollow profile and an organic sheet. This reduces the assembly time and the number of pre-produced semi-finished products.

This is offset by the currently still higher production costs. Production is somewhat more expensive than that of ordinary integral backrests. Still, much less money has to be invested at the start. Bending tools, joining processes or welding equipment are not required. In case of components, which have to be manufactured to be weather-resistant, the corrosion protection can also be saved on.

FUPro's lightweight components and manufacturing technology can also be used outside the automotive market. Trains, as well as aeroplanes and many other individually movable components, will profit from this trend in the future. The adaptation of the manufacturing process for structurally integral components in terms of casting as well as the increased use of glass and carbon fibres not only reduces efficiency during production but also during operation. In addition, there are possible gains in terms of durability and material fatigue.