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13th September 2018, Stuttgart

Tomorrow’s alternatives for proven adhesive technologies

Composites Europe from 6-8 November in Stuttgart will show the advantages and drawbacks of mechanical composite joining technologies such as crimping, gluing, riveting and screwing for the respective fibre composite.

Depending on the process, various factors have to be taken into account. During riveting, for example, the fibre layers are damaged by delamination during the pilot drilling. Drilling also weakens the component. Furthermore, the power transmission between the components to be joined is very limited locally. In bonded parts, the gap width can cause problems. Nevertheless, it is the standard process for joining fibre composites due to the uniform power transmission that makes optimum use of the material properties.

Mechanical joining technologies. © Composites Europe

What the individual processes look like will be demonstrated by the Institute for Welding and Joining Technology (ISF) at RWTH Aachen, Oxford Advanced Surfaces and Weiss Chemie + Technik at Composites Europe.

BMW focuses on adhesive technologies

For manufacturing the CRP body of its e-vehicles i3 and i8 BMW foregoes mechanical joining processes and relies exclusively on a special gluing technology, which has now developed into the standard process for these model series. This process is said to avoid mechanical damage to the carbon fibre reinforced plastic components thereby increasing component stability while saving costs at the same time.

The adhesion of the glue here is determined by the relevant surface priming. Due to the versatile properties of composites, this priming varies by application - in terms of both the matrix and the fibres used. On top of this, process parameters and materials also influence the adhesion quality and durability of the bonded connection. On account of this complexity, the research and evaluation of proven processes and new technologies for joining fibre composites and other hybrids are at the centre of numerous scientific studies.

Thermal direct joining

Experts at the Karlsruhe Institute for Technology (KIT) have developed a novel, strong and low-cost joining technology for gluing structural components. This hybrid process combines inorganic and organic adhesive layers and is therefore cheaper and more hard-wearing, according to the researchers. In joining technology this is particularly suitable for connecting structural components and therefore applicable in numerous sectors such as wind power, construction but also in automotive and mechanical engineering.

The Fraunhofer Institute for Material and Beam Technology (IWS) Dresden seeks to replace bonding processes entirely with the HeatPressCool-Integrative (HPCI) process. This so-called thermal direct joining presses laser-textured metal with thermoplastic components and heats them locally. In this way, the thermoplastic melts, penetrates the textures and adheres to the surface. Joining guns specifically developed for this purpose are said to produce strong connections within seconds.

Fibre lasers for contact-free joining

For the form-fitted and substance-bonded connection of fibre-reinforced thermoplastics (organic sheeting) with metal, the IWS experts have also developed the so-called slot-web principle. The organic sheeting only serves as a web plate, a metal sheet as a slot plate. A fibre laser is used for bonding. It makes for a very finely adjusted heat input and heats the protruding part of the fibre-reinforced web plate - contactless and at the precise position. The 2D and high-frequency beam deflection by means of scanner lenses allows uniform heating of the plastic.

The Fraunhofer Institute for Manufacturing Engineering and Applied Material Research (IFAM) in Bremen has developed a test line for the automated bonding of fibre composite boards for aircraft construction partnering with CFK-Valley Stade for a project. The process is designed to save costs over conventional methods and is also important for all industries that require lightweight, dimensionally stable and low-cost components.

Combining 3D printing and organic sheeting

With this move, the project partners say they have succeeded in replacing the so far manual frame assembly by filling the slot in a completely automated process. With a view to future mass production, the required drive intelligence has also been provided for. With the help of the decentralised concept even a high number of drives can be concentrated on a small footprint and adjusted and efficiently controlled in a modular way with little wiring.

In the LightFlex project scientists from the Fraunhofer Institute for Production Technology (IPT) in Aachen focus on a combination of 3D printing and organic sheeting from unidirectional semi-finished parts. To optimise the load-bearing capacity the 3D printed components are joined with a fibre composite component. For this, custom-sized organic sheets are used which are produced on a so-called PrePro line with a near-net shape. This approach minimises cut-off waste and results in marked savings considering the high energy consumption involved in carbon fibre production, the scientists explain.

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