The basic process of ultrasonic welding can be described by the following steps:
1.The parts to be welded are placed in the anvil or fixture.
2.The horn contacts the parts to be welded.
3.Pressure is applied to keep the horn in contact with the welded materials and to hold them together.
4.The horn delivers ultrasonic vibrations to heat up the materials. The vibrations move less than a millimeter either up-and-down or side-to-side.
5.The materials are welded together.
6.The horn gets retracted and the welded materials can be removed from the anvil.
The welding times, applied pressures and temperatures are controlled by a computer or microprocessor within the welding apparatus. And what actually happens during the welding process depends on the nature of the materials. In metals, the ultrasonic vibrations are delivered parallel to the plane of the materials. The frictional heat increases the temperature of the metal surfaces to about one third of the melting temperature, but does not melt the metals. Instead, the heat removes metal oxides and films from the surfaces. This allows the metal atoms to move between the two surfaces and form bonds that hold the metals together.
The factors that vary in ultrasonic welding are the frequency of the sound waves (usually 20, 28 or 35 kHz), the pressure applied to hold the materials together, and the time over which the ultrasound is applied (fractions of a second to more than one second).