The joining of composite materials: the best of both worlds

Over the past several years, lightweight construction has undeniably become a driving force in many areas of transportation.

Automotive design engineers have responded to a shift in consumer demands for more energy efficient vehicles. Using lightweight materials in the structure of vehicles is one way to meet consumer demands. Carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP) are two notable lightweight construction materials that offer high stiffness and strength, while allowing for the manufacture of very thin structures.

Great challenges for joining technology

Although these two technologically-advanced composites offer the lighter weight needed in many designs, CFRP and GFRP present joining technologies with even greater challenges than high-strength sheet metals do, since composite materials must be connected to other components in many areas.

Challenges arise in welding, screwing and riveting – the classical joining methods found in automotive production. The matrix of fiber composite materials is a bonded composite. Punching these materials by screwing or riveting damages the laminar structure, which is vital to the material's strength and stability. In addition, the punched hole must be sealed using a complex process to prevent delamination of the material. When joining CFRP to metal, there is also a high risk of corrosion.

For stable joints and efficient processes, the laminate should remain intact. Ultrasonic welding can be taken into consideration as an alternative, but has serious disadvantages. It is very power-consuming and suitable for thermoplastic matrix materials only. Therefore, thermal methods are rarely used, while forming techniques cannot be used because of the material's low ductility.

Bonding prevents material destruction

An easy and productive method to join composite material to other components is bonding. It is a non-destructive and component-saving joining method, demonstrating both high material flexibility and good resistance to dynamic forces. Bonding allows a high degree of automation with short cycle times for faster production, a top concern in many industrial manufacturing environments.

Collaboration enhances quality production

For the joining of composite materials to other materials, the assembly specialist Böllhoff and the adhesive expert DELO have developed a new method that uses stud welding as its basis.

To prevent complex drilling of holes, screwing or riveting, threaded bolts are bonded to fiber composite materials instead of being welded. The combination of bolt and base is called ONSERT. What makes this technique so special is its speed and effective energy balance.

This article appeared in the March–April 2018 issue of Reinforced Plastics. Log in to your free materialstoday.com profile to access the article.