Fraunhofer Researchers Develop a Variety of Solutions for Joining Metal Components with Carbon Fiber-Reinforced Plastics

In order to design lightweight vehicles, manufacturers have to integrate highly durable and lightweight carbon fiber-reinforced plastics with functional metal components.

Smart solutions to join carbon fiber-reinforced plastics and metal. (Image credit: Fraunhofer IGCV)

Now, researchers at the Fraunhofer Research Institution for Casting, Composite, and Processing Technology IGCV at the Technology Center in Augsburg have come up with a wide range of solutions for combining such kinds of different materials. At this year’s Hannover Messe, which will be held from April 1st to April 5th, 2019, the researchers will showcase their novel technology using an e-scooter demonstrator at Hall 17, Booth C24.

Whether it is bicycles, scooters¸ cars or buses, electromobility is certainly perceived to drive the future. However, one major barrier that is presently faced is how to boost the range of vehicles—a challenge that will rely on rendering vehicles as light as possible. The energy storage will last for a longer time if the transporter or vehicle is also lighter. In this field, carbon fiber-reinforced plastics, also known as CFRP, are the preferred materials because they are as sturdy as steel and yet about eight times lighter, and are also three times lighter than aluminum. The standard method is to develop separate components, for example, the vehicle frame using CFRP and subsequently joining them to the function-bearing metal parts with the help of adhesives or screws. To put it in simpler terms, CFRP can be used to manufacture components connecting transfer loads and long expanses, while metal is used to develop the attachment points and functional components for the steering mechanism, for instance.

Weight savings of up to 50%

Now, Fraunhofer researchers have developed a range of innovative methods to combine CFRP –based cast components with those made of traditional materials. Looking further than the fully proven foundry technology, plenty of possibilities exist in the latest manufacturing methods like 3D printing and additive manufacturing.

We’ve combined the various new joining techniques in an electric scooter demonstrator. The goal is to cut down on the number of mechanical attachment points and simplify the joining process as much as possible. There’s a lot of potential in combining metal and CFRP components, with a potential weight saving of up to 50 percent depending on the part.

Dr-Ing Daniel Günther, Project Lead, Fraunhofer IGCV.

Clamping technique to join rear-wheel support

Metal is traditionally used to make the rear-wheel support of an electric scooter, because this support contains plenty of parts that are important for its functioning. In order to make it as lightweight as possible, the researchers developed the part from extremely durable steel, improving the topology so that the material is fully limited to the places it is required to support the functioning.

To develop the component, the team used an additive manufacturing method in which a laser beam is used to create components from metal powder. With the help of a screwing system, the rear-wheel support is joined to the CFRP footboard, making it convenient to take out and disassemble for maintenance purposes.

Adhesively bonded hybrid steering head

The scooter’s steering head is a hybrid component, with an aluminum base frame connecting to the handlebars at the front and the footboard behind. This steering head of the scooter contains many parts that are essential to its functioning, with a considerable area to bridge in-between. The required rigidity is ensured with the use of CFRP parts. Adhesive bonding is used to fuse the two entirely different materials.

In terms of a baseline load, we assumed a person weighing one hundred kilograms performing jumps with the scooter. To support that sort of load using a pure aluminum cast part, you would need a huge amount of material to ensure sufficient rigidity.

Dr-Ing Daniel Günther, Project Lead, Fraunhofer IGCV.

In order to produce the part, Günther together with his team first examined the available installation space. In principle, if more room is used, it will translate to a larger cross-section of the component and thus lead to better rigidity. However, it is important to keep the material as thin as possible to make sure that the component does not turn out to be extremely heavy. One solution to this is to utilize CFRP along with cast metal. As an additional step, the investigators computed the load at different points of the component, and also the splices were accurately placed at the points with the least load. Thanks to the molding of the CFRP component, rigidity is ensured.

‘Fork’ system: The joining technology of the future

The fibers present inside the CFRP contribute to its durability and load-bearing capacity. Here, transmitting the force acting on a part so that it is taken in by these same fibers was the major challenge. Added to this, engineers have to make sure that all metal components are as securely fixed to the CFRP components as possible, without any cavities or gaps in between. In response to this, the team has developed a new, fully joining method, which can be best elucidated by studying the various components involved. In the case of the electronic scooter, a cylindrical piece—that is, a steel component developed through an additive manufacturing method—is joined to the handlebars.

The component’s bottom has a plate that serves as a base with tiny pins protruding from its surface. The team subsequently superimposes this base plate with the prepregs for the CFRP part made from fibers coated with arterial resin. Following this, a vacuum was applied and the temperature was increased. After enclosing the carbon fibers, the resin flows in the downward direction and closes the gap with the metal plate, stiffening to create an adhesive bond. Here, the resin not only adheres to the plate but the protruding pins are also enclosed and kept in place by the fibers. As a result, the components are interlocked and a solid bond is formed without requiring any screws or extra adhesives.

The technique is fast, industry-ready and can easily be scaled up for mass production,” stated Günther.

The e-scooter and the joining methods described in this study will be showcased by Fraunhofer researchers at the Hannover Messe from April 1st to 5th, 2019 at Hall 17, Booth C24. Those who are interested will have an opportunity to take a test drive and learn more about the design and development of the individual components.

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