The parts to be joined are held together under pressure and subjected to ultrasonic vibrations, usually at a frequency of 20 or 40kHz. After a preset time, the ultrasonic vibration is switched off, welding pressure is maintained and the molten thermoplastic solidifies to form a weld. With weld times typically less than one second, the process is very fast.
Weld strength approaches that of the parent material, and with correct part and joint design, hermetic seals are possible.
Other benefits of ultrasonic welding include good energy efficiency, high productivity with low costs and ease of automation. The main limitation is that the maximum length of joint is around 250mm. This is due to several factors: power limitation of ultrasonic transducers; inability of ultrasonic horns to transmit very high powers; and amplitude control difficulties due to the fact that joints of this length are comparable to the wavelength of the ultrasound in the horn.
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