Welding Technologies: Ultrasonics

For joining complex injection molded thermoplastic parts, ultrasonic welding equipment can be easily customized to fit the exact specifications of the parts being welded. The parts are sandwiched between a fixed shaped nest (anvil) and a sonotrode (horn) connected to a transducer, and a  low-amplitude acoustic vibration is emitted (Note: Common frequencies used in ultrasonic welding of thermoplastics are 20 kHz, 30 kHz, 35 kHz 40 kHz and 70 kHz). When welding plastics, the interface of the two parts is specially designed to concentrate the melting process. The ultrasonic energy melts the point contact between the parts, creating a joint. This process is a good automated alternative to glue, srews or snap-fit designs. It is typically used with small parts (e.g. cell phones, consumer electronics, disposable medical tools, toys, etc) but it can be used on parts as large as automotive instrument cluster.

Ultrasonic welding of thermoplastics causes local melting of the plastic due to absorption of vibration energy.

Ultrasonic welding can be used for both hard and soft plastics, such as semicrystalline plastics. Ultrasonic welding machines also have much more power now. The understanding of ultrasonic welding has increased with research and testing. The invention of more sophisticated and inexpensive equipment and the increasing demand for plastic and electronic components has led to a growing knowledge of the process.