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Ultrasonic welding uses high-frequency acoustic vibrations to join plastic or metal without bolts, nails, welding materials or adhesives. It is automated and creates visually attractive seams but is limited to small components due to cost. As technology improves, more materials can be joined.
Ultrasonic welding is an industrial technique in which two pieces of plastic or metal are joined seamlessly through high-frequency acoustic vibrations. One component to be welded is placed on a stationary anvil, with the second component placed on top. An extension (“horn”) attached to a transducer is lowered onto the top component and a very rapid (~20,000 KHz) acoustic vibration is applied to a small patch of weld. Acoustic energy is converted into thermal energy by friction and the parts are welded together in less than a second.
Ultrasonic welding is unique in that no connecting bolts, nails, welding materials or adhesives are needed to join the two parts together. This saves significantly on production costs and creates visually attractive (i.e. unnoticeable) seams in product areas where appearance is important. Because ultrasonic welding is a largely automated process, all a technician has to do is pull a lever and the weld is complete. The disadvantage of ultrasonic welding is that it is applied only to small components: watches, cassettes, plastic products, toys, medical instruments and packaging. The chassis of an automobile, for example, cannot be assembled with ultrasonic welding because the energies involved in welding larger components would be prohibitively expensive.
Ultrasonic welding technology appeared in the early 1990s and has been developing rapidly ever since. As technology improves, the range of materials that can be joined using this technique increases. At first, only inflexible plastics could be welded because their material properties enabled the efficient transmission of acoustic energy from one part to another. Nowadays, less rigid plastics such as semi-crystalline plastics can be welded because large amounts of acoustic energy can be applied to the weld zone. As technology matures and becomes more versatile, large classes of historical techniques for joining materials together are likely to be obsolete.
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