The renewable raw material wood offers a climate-neutral, lightweight, and durable option, making it an appealing choice for vehicle manufacturing. However, joining wood with other materials, such as metals and polymer composites, has been a challenge.
Led by Sergio Amancio, a research team at the Institute of Materials Science, Joining and Forming of the Graz University of Technology (TU Graz), including Gean Marcatto, Awais Awan, Willian Carvalho, and Stefan Herbst, has successfully tested two techniques to create incredibly strong joints without the use of adhesives or screws. These patent-pending techniques have the potential to revolutionize industries such as aircraft, automotive, and furniture manufacturing.
Two revolutionary manufacturing techniques have found their own unique niches. Using materials such as beech, oak, carbon fiber-reinforced polyamide and polyphenylene sulfide, stainless steel 316L, and Ti-64 alloys, researchers are driven by a clear focus on environmental sustainability. Sergio Amancio emphasizes the potential for wood, a renewable resource, to replace components traditionally made from energy-intensive or difficult-to-recycle materials.
The AddJoining technique involves attaching a polymer composite component directly onto a surface, specifically wood, using 3D printing. The printed material seeps into the wood pores, triggering a chemical reaction reminiscent of glue bonding with wood. The resulting connections have exhibited remarkable strength in mechanical load tests.
“After the joint fractured, we were able to find polymer in the wood pores and broken wood fibres in the polymer, which suggests that the fracture occurred in the wood and polymer, but not at the joint,” explains Gean Marcatto, who works on this process as a postdoc at the institute.
These remarkable tests were conducted on untreated wood surfaces. By implementing a micro- or nano-structure into the wood using laser texturing or etching, we can significantly enhance the durability of joints. This process increases the pores and improves the bonding surfaces, leading to exceptionally strong and lasting results.
“But we wanted to work with as few steps as possible and, above all, without chemicals,” says Sergio Amancio, explaining the underlying idea. “We can use this technology particularly well with complicated 3D geometries because the components are printed directly onto the surface – in whatever geometry is required.”
In Ultrasonic Joining, high-frequency vibration with low amplitude is expertly applied to the wooden component using a sonotrode. As this component comes into contact with the base component – in this case, a polymer or a polymer composite material – the resulting friction generates intense heat at the interface, causing the surface of the polymer part to melt. The molten polymer then infiltrates the naturally porous surface of the wood, creating an exceptionally stable spot joint through a combination of mechanical interlocking (due to the melted plastic solidifying within the wood) and adhesion forces.
“This technique is particularly suitable for large components and 2D structures since we achieve a precisely localized spot joint,” explains Awais Awan, who dedicated his doctorate to joining technology using ultrasonic energy.
These spot joints have undergone rigorous mechanical testing, yielding impressive results. Furthermore, the joints can be further reinforced by pre-treating the wood surface through laser texturing.
In the future, the team is eager to collaborate with partners from the automotive, aircraft, and furniture industries to further refine these groundbreaking technologies.
