Wood-processing employing a superimposition of ultrasonic vibrations.

Wood products enjoy constantly rising popularity on an ecologically sensitised market. Wood is a natural material and the ecological importance of forests as natural lungs is unquestioned. An economic utilization of wood secures the existence of forest enterprises, counteracts obsolescence and loss of protective function of trees, and conserves an environment worth living and attractive for the tourism. On the way from the tree to a finished product, e.g. a piece of furniture the material wood experiences different processes. Processing mainly consists of cutting or separation (e.g. sawing, planing, milling, sanding) and possible successive surface treatments. By-products like chips and microscopic particles like health-injuring dust are frequently produced, which can solely be thermally utilized in most cases. Desirably these processes are improved to produce fewer and larger chips. In addition, less waste means a better utilization of the raw material and thus an increased creation of value. In a global market with intensified competition with cheap production countries, it is important for Austria to produce high-quality wood products with little waste. Innovative wood processing techniques are therefore a contribution for active environment and nature protection. Improved wood processing procedures secure the competitive power of Austrian quality products. They create and secure jobs and support thereby a sustainable development. In the "Fabrik der Zukunft" - project "Wood processing with superimposed ultrasonic vibrations" the prototype of a new wood processing equipment has been developed at the Institute of physics and material sciences, department of material sciences and process technique at the university of natural resources and applied life sciences in Vienna. This equipment is based on the principle of a fixed blade, similarly to the tool in a hand held planer or a turning lathe. The workpiece passing the blade and is processed. The substantial difference of conventional and ultrasonic processing is the blade, which performs a harmonic oscillation at ultrasonic frequency in (or somewhat inclined to) the cutting direction. The knife performs about 20,000 oscillations per second, which is above the audible range and the vibrations cause no noise therefore. The vibration amplitude is relatively small and lies within the range of several ten micrometers. The equipment was built considering the aspect of energy efficiency. The mechanical structure is based on resonance principles, i.e. appropriate shape of the mechanical parts allows the generation of resonance vibrations. The necessary vibration amplitudes are obtained with small power input. High efficiency use of electric power was realized using a switching amplifier. A control unit adjusts the oscillating frequency depending on the actual loading conditions and makes semi-automatic operation possible.