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Tubular Structures made of Wood

When Weight, Aesthetics and Feel Are Called For

| Editor: Alexander Stark

The start-up company Lignoa manufactures three-dimensional tubular structures made of wood. In this interview, Managing Director Yves Mattern explains the manufacturing, properties and possible applications of this lightweight solution, which is still rarely used.

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The three-dimensional tubular structures can compete with many of the properties of aluminum. They are lighter and more ecological.
The three-dimensional tubular structures can compete with many of the properties of aluminum. They are lighter and more ecological.
( Source: K.Juschkat/konstruktionspraxis )

Mr. Mattern, you studied mechanical engineering at the TU Dresden until 2017. In 2018 you founded the company Lignoa together with your partner Philipp Strobel. Why lightweight construction with wood?

Yves Mattern: It all started with a wheelchair. For personal reasons, we wanted to enable wheelchair users to use not only a functional wheelchair, but also a beautiful, lightweight, sustainable wheelchair that suits their personality. And that idea caught on. That’s why Philipp Strobel and I started to work together in our hobby workshop. There was simply no technology available worldwide to produce curved lightweight profiles from wood. That's why we invented it ourselves. My professors at the Institute of Lightweight Structures and Plastics Technology (ILK) encouraged me to write every document, project or thesis on this topic. The lightweight design properties of wood quickly turned out to be excellent. With our process, we can show that these properties can be used primarily in the field of fibers - the W3T process was born.

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How exactly does the Wooden 3D tubing process work?

Mattern: For the production of a wooden tube structure, many layers of veneer are first layered on top of each other until the desired component thickness is acquired. Each layer has the same grain direction. The layers are then pressed and glued to form a blank. The blank is then cut into veneers to obtain saw veneers with a defined grain flow. These saw veneers are then pressed and glued again with a defined shape and the resulting product is divided into two parts, which in the following process serve as the shells. This is because the shells are milled out on their joining surface using a CNC milling machine which creates a cavity. The outer geometry is then formed by machining.

What must be considered when working with wooden tube structures?

Mattern: Depending on the thickness of the component, we must ensure that the veneers can be formed. Thus, there are minimum bending radii, which must be adhered to. Additional and function-integrative elements should be taken into account in the design phase, as these can be very easily integrated into the wood profile.

Is it also possible to incorporate weight optimizations?

Mattern: Above all, the profile dimensions, variable geometrical moments of inertia and the corresponding topology optimization determine the degree of lightweight construction in the design process. Topology optimization helps to calculate the wall thickness and the milling structure in detail, which significantly increases the degree of lightweight construction. The profile bending and the corresponding fiber orientation are also aligned as closely as possible to the stress curve.

What are the advantages over light metals?

Mattern: The veneers produced by the W3T process initially weigh 30 % less than a tube made of aluminum (alloy 6061-T6) with similar performances. In addition, it offers vibration damping properties, higher fatigue strength, lower thermal conductivity and, of course, a favorable design aspect. Since we are largely free in our choice of wood, new optics or a high degree of functional integration can be achieved in addition to an extremely good CO2 balance.

What are the disadvantages of these wooden tube structures?

Mattern: The procedure is still very young. Producing prototypes and small batches is very simple, but for large quantities machines have to be partly newly developed. In order to achieve a similar economic efficiency as with metal pipes, we still need some time. Creating media resistance is also not as easy as with metallic materials - but with an appropriate adhesive and coating this is usually no problem.

What are possible applications?

Mattern: Strollers, wheelchairs, bicycles and golf trolleys are products where the advantages of wood are very relevant and obvious. Moreover, door handles in cars, seat structures and armrests in aircraft, handles in trains are also components where the combination of weight, design and feel, or noise development always require a compromise without the W3T profiles.

Thank you very much Mr Mattern!

This article was first published by konstruktionspraxis.

Original: Dorothee Quitter / Translation: Alexander Stark

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