Wood Welding

No additives are used to create the connection in wood welding. By the generation of energy by friction, focused on the interface of the pieces to be connected, a transformation of the wood structure by pyrolysis is obtained. The result is a sticking material which ensures the connection in form of an adhesive layer. A circular motion is applied to the parts to be welded. Since the process is controlled by the generation of heat due to the frictional movement, the parameters, which are influencing the generation of heat are of great importance: These are on the one hand, the machine settings such as for example the welding pressure, the frequency and the amplitude of the frictional movement; in addition, the material properties such as moisture content, orientation of the annual rings, density, the species of wood, etc. play an important role. The interfacial temperature defines the physical properties of the interface, which undergoes various «states of aggregation» (solid, liquid, gaseous) during the process of welding. The thermal decomposition of the material leads to the formation of newly formed chemical compounds. Examinations of the microstructure of the interfacial region give an indication how adherence between the welded parts happens.
(summary and the first picture from website of the laboratory for timber construction at EPFL)