The research team led by Sergio Amancio from the Institute of Materials Science, Joining and Forming of Graz University of Technology (TU Graz) has successfully tested two techniques by which extremely strong joints can be achieved without using adhesives or screws. Called as AddJoining technique, in this a component made of polymer composite is attached to and printed directly onto a surface using a 3D printing process.
The techniques’ application to wood is patent pending and has potential applications in the aircraft, automotive, and furniture industries.
AddJoining Technique: Join Wood to Polymer
The AddJoining technique involves attaching and printing a polymer composite component directly onto a surface, in this case wood, using a 3D printing process. The printed material penetrates the wood pores, causing a chemical reaction similar to that of glue and wood. Mechanical load tests revealed that the resulting connections performed admirably.
“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.”
Gean Marcatto, who works on this process as a postdoc at the institute.
These successful tests were conducted on an untreated wood surface. Even more durable joints could be created by incorporating a micro- or nano-structure into the wood via laser texturing or etching, which increases pores and improves bonding surfaces.
“But we wanted to work with as few steps as possible and, above all, without chemicals. 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.”
Sergio AMANCIO, Univ.-Prof. Dr.-Ing., TU Graz
Joining technology and additive manufacturing
Wood is a renewable raw material that is both light and strong, making it ideal for use in vehicle manufacturing. To date, one of the most difficult challenges has been securely joining the wood to the other materials in the vehicle, such as metals and polymer composites. Combining technology and additive manufacturing allows wood to replace less sustainable materials.
The two novel manufacturing techniques are appropriate for their respective fields of application. Test materials included beech, oak, carbon fibre-reinforced polyamide and polyphenylene sulphide, as well as stainless steel 316L and Ti-64 alloys.
“Our motivation is clearly environmental protection,” explains Sergio Amancio. With new manufacturing processes, wood, a renewable raw material, could replace components made of energy-intensive or difficult-to-recycle materials.
Ultrasonic joining creates a stable spot joint.
Ultrasonic Joining uses a sonotrode to apply high-frequency vibration with low amplitude to a wooden component. When in contact with the base component, which in this case is a polymer or a polymer composite material, friction generates heat at the interface, melting the polymer part’s surface. Molten polymer infiltrates the wood’s naturally porous surface. This method produces a very stable spot joint through a combination of mechanical interlocking (because the melted plastic solidifies again in 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 ultrasonic energy joining technology.
Mechanical testing of these spot joints also yielded positive results. The joints could also be strengthened by pre-treating the wood surface with laser texturing.
In the future, the team hopes to collaborate with partners from the automotive, aircraft, and furniture industries to further refine the technologies.
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