Frequently Asked Questions
Ultrasonic joining (which is used extensively in the plastics industry), has been used for bonding ceramic-metal combinations such as alumina/aluminium, alumina/stainless steel, zirconia-steel and glass ceramic (cordierite-based)/copper. Typical applications include batteries, thread guides, textile cutting equipment and heavy-duty electrical fuses. A limitation of the technique is that only thin films or sheets of metal can be joined to the ceramic. Soft, malleable interlayers are needed to join ceramics to hard metals such as steel.
Ultrasonic joining requires an ultrasonic transducer assembly operating at about 20kHz coupled to a sonotrode. The sonotrode tip is placed in contact with the workpiece under a clamping load of 1-10Nmm-2. Heat generated is localised at the interface, creating a temperature of up to 600°C when using aluminium interlayers.
During bonding, the shear stress in the metal exceeds its elastic limit: plastic deformation of the metal, coupled with rupture of surface oxide films brings atomically clean metal into contact with the ceramic. Mechanical keying then occurs, along with some chemical interactions to provide a bond.
The advantages of the process are:
- Short joining times (less than one second);
- Non-critical surface preparation (in contrast to almost every other ceramic joining process);
- Lack of melting and intermetallic formation.