Wood-processing employing a superimposition of ultrasonic vibrations

Project description/ tasks

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 increase 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 for 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.

The ultrasonic equipment developed within the "Fabrik der Zukunft" - project served to cut different woods and wood composites including spruce, beech and MDF. The substantial advantage of ultrasonic assisted cutting is the pronounced reduction of forces. The additional kinetics of the knife may reduce the necessary cutting forces to less than half compared with conventional cutting. At large vibration amplitudes and slow cutting speeds, the measured cutting forces in beech and spruce were 20% and 30%, respectively of the values measured without superimposed ultrasonic vibrations. At vibration amplitudes of somewhat more than 10 micrometers, which may be realized easily, the necessary cutting force decreases to approximately 50% of the initial value. However, the reduction of cutting forces depends substantially on the cutting velocity. Cutting experiments with MDF show that the vibration amplitude (in micrometers) should be about 25 times the cutting velocity (in meters per second), to approximately halve the cutting force. The cutting direction additionally influences the obtained results. Cutting spruce in longitudinal and in tangential direction, reduced cutting forces were found, however, the effect was larger for longitudinal cutting.

Surfaces produced with ultrasonic assisted cutting are in general similar to the surfaces produced with conventional cutting. Surface roughness and wettability were comparable after cutting with a sharp knife. At large magnifications, however, small impacts of the knife and micro-reels are visible on surfaces produced by ultrasonic cutting. Measurements of the surface free energy show changed base component and surface chemistry affected by ultrasonic cutting. Measurements of the surface free energy show changed base component and surface chemistry affected by ultrasonic cutting may be concluded therefore.

Superimposing ultrasonic vibrations on tools is a promising new and technically feasible method for wood processing. The application of this technique is energy efficient and reliable. Layout similar to the developed equipment may be used or it can be adapted to already existing wood processing equipment. In both cases, knowledge accumulated within this project may be used.

• Azade, T.: "Wood Vibrations", Industriemagazin 6, 2003.
• Sinn, G., Beer, P., Zettl, B., Mayer, H.: "Influence of Ultrasonic Vibrations on Low Speed Cutting of Spruce Wood", Proceedings of the 16th Intern. Wood Machining Seminar, August 24.-26. 2003, Matsue, Japan

Project manager:

Ao. Univ. Prof. Dipl.-Ing. Dr. Herwig Mayer
Institut für Meteorologie und Physik

Contact

Dipl.-Ing. Gerhard Sinn
Institut für Meteorologie und Physik
Türkenschanzstraße 18
A 1180 Wien
Tel.: +43 1 4705820 DW48
Fax: +43 1 4705820 DW60
E-Mail: gerhard.sinn@boku.ac.at