Ultrasonic vibratory lapping
Ultrasonic vibratory lapping (older: ultrasonic drilling ) is a cutting production process with a geometrically undefined cutting edge for the production of geometrically complex workpieces from materials that tend to break brittle. According to DIN 8589, vibratory lapping is assigned to lapping . In contrast to other lapping processes, it is not used for the fine machining of workpieces that have already been largely created by other processes, but for the creation of new shapes only through vibratory lapping.
A high-frequency electrical energy is converted into mechanical vibrations of the same frequency by means of a piezoceramic sound transducer . The amplitude of the longitudinally vibrating sound transducer is only 5 µm. There is therefore another unit between the mold and the sound transducer, consisting of an amplitude transformer and a sonotrode (also known as a drill pipe), which amplifies the amplitude to 20–40 µm. The four mentioned interconnected elements together form a vibrational system that is operated in resonance .
The process is based on the fact that the mold vibrating in the ultrasonic range (19-22 kHz) hammer the grains into the workpiece surface, creating micro-cracks and finally removing fragments. This process takes place mainly in the direction of movement of the ultrasonic vibration. If possible, the use of rotating tools is also recommended, as the removal is much higher here. The grains are in a liquid or paste ( lapping agent ). This mixture is continuously flushed or pressed into the gap between the mold and the workpiece, the gap should be approximately twice as wide as the average grain size.
Because of its good breakability and thus self-sharpening, the choice of grain material is almost without exception boron carbide , which takes up about 25-35% by weight of the lapping agent and is usually between 50 and 60 µm in size. Since the mold is subject to the same stresses as the workpiece, it must be made of a material that is either harder than the workpiece material or has sufficient resistance to abrasion. Steel materials are therefore predominantly used, since the impact of the grains mainly leads to elastic and plastic deformation .
The main area of ultrasonic vibrating lapping is to carve out the finest three-dimensional contours from materials such as ceramic , graphite or glass . Recesses with a diameter of less than one millimeter can be machined into workpieces that are thinner than 200 µm. A typical product is the graphite electrode for die sinking EDM .
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- Wilfried König , Fritz Klocke: Manufacturing process 3, removal and generation. Springer-Verlag: Berlin, Heidelberg 1997, ISBN 3-540-63201-8 , pp. 129-152.
- Alfred Reichard (Ed.): Manufacturing technology 1. Verlag Handwerk und Technik: Hamburg 2000, ISBN 3-582-02311-7 , p. 212.