HygroShape

Shaped by nature

HygroShape is the first concept for self-forming furniture. The project represents a paradigm shift in design and manufacturing processes for wood: By using material programming, a previously untapped potential of wood as a renewable material is activated, enabling more sustainable processes and applications. This brings with it a new material and design language in which the natural qualities and properties of wood are directly reflected in form and function.

May 23 2022

Material programming for 4D wood manufacturing 

Wood is a highly programmable material where a change in volume and stiffness correlates with a change in moisture content. This hygroscopic phenomenon is rooted in the structure and chemical composition of wood's cell walls. When wet, the cell walls expand and contract again when dry, with the intensity of the effect depending strongly on the direction of the fibres. 

These properties are well known to the wood craftsman, as they can lead to large, unwanted deformations when drying is uncontrolled. In contrast, programmed self-forming deliberately harnesses these forces to produce strong, predictable changes in shape that are driven directly and solely by the material. 

"Hylo H" is the prototype of a self-formed piece of wooden furniture by the project team of the Institute for Computer-based Design and Building Manufacturing at the University of Stuttgart. © ICD University of Stuttgart

The HygroShape concept developed by the project team at the Institute for Computer-Based Design and Building Production at the University of Stuttgart is based precisely on this deliberate use of hygroscopic shrinkage, which occurs naturally in freshly harvested wood. A comprehensive digital material model, which is based on the physical-mechanical properties of the wood, enables the calculation of this shrinkage behaviour. 

In combination with computer-aided design methods, a specific material syntax is developed from this. This syntax determines the internal composition and moisture content of the multi-layered timber components and thus physically programs a planned forming sequence into the material. 

This approach to material programming in manufacturing aims to create a new way of manufacturing where digital design is instinctively linked to material properties. This creates a process that enables greater use of natural materials with higher variability, while capitalising on previously neglected features. 

We spoke to Dr. Ing. Dylan Wood of the University of Stuttgart, who developed the HygroShape concept together with his colleagues Laura Kiesewetter and Prof. Achim Menges.

HygroShape is based on the targeted use of hygroscopic shrinkage, as occurs naturally in freshly harvested wood. © ICD University of Stuttgart

HygroShape is the first concept for self-forming furniture. How long did you work on the development?  

We have been studying self-shaping wood for over 6 years in our institute. Previously, we have deployed the concept for shaping large-scale plates for curved CLT for building components, for example, in the Urbach Tower. We have only now applied the technology at the furniture scale. 

Material programming in wood manufacturing is a novelty. The fact that you can programme wooden boards to bend in a precisely predetermined way is not familiar to everyone. What is the technique behind it? 

All pieces of wood will deform hygroscopically; it's a feature inherent to wood and many natural fiber-based materials. The key here is that we have discovered a specific syntax for arranging multiple boards in two layers, leading to a predictable bending.

We call this material programming because we use a computational model to calculate the physical arrangements and sort out which boards go where; after that, the material can compute its own shape over time. 

The project represents a paradigm shift in design and manufacturing processes for wood. What possibilities and potential do you see for HygroShape in the furniture industry? 

For furniture, the most significant advantage is that the physical shape emerges so directly from the material. Not only do you not need anyone to assemble the chairs, but you don't need any hardware or additional parts. Everything is contained in the relatively simple-looking flat sheet. 

This approach is inherently ecological. With one material, we get all the different parts of the chair and many manufacturing steps, simply through clever use of what wood has to offer.

From a design perspective, it's about looking at how we can get the best from natural, regenerative materials like wood. Working with raw, natural materials can be challenging, but it's the future.

Self-forming by air-drying from compact, flat configuration into stable, curved geometry. © ICD University of Stuttgart

However, HygroShape is not only an innovation for the furniture industry? The construction industry can also benefit from the process. To what extent can HygroShape promote sustainable construction? 

Self-shaping and the ability for a component to assemble itself in situ is an aspect that grows in value with scale. Curved geometry is a valuable tool for building material-effective structures.

Still, it's more difficult for humans and machines to shape bigger things. It's not so far-fetched to consider that with HygroShape, we could flat pack and self-shape parts for an entire building. 

This would have major implications, not just in saving material, but also in dramatically reducing the transport volumes, the number of on-site workers, the amount of heavy equipment needed on a building site, etc.

The implications are enormous if we embed shaping actions directly into the parts. At the same time, the technology opens new options for wood materials with a range of higher performance geometries that we are now cost-prohibitive to produce at scale. 

Dr. Ing. Dylan Wood is part of the project team at the Institute of Computer-based Design and Building Construction at the University of Stuttgart. Together with his colleagues Laura Kiesewetter and Prof. Achim Menges, he developed the HygroShape concept. © ICD University of Stuttgart

Author: Bernadette Trepte

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