Ultrasonic plastic joining methods related to welding

Where the limitations of ultrasonic plastic welding make a job impractical, some other ultrasonic joining techniques may be applicable.

Staking

Ultrasonic staking is like a riveting application for moulded plastic components, but without the disadvantages of separate fasteners. It can join dissimilar plastics or metal to plastic. Typically one part has a number of plastic studs which fit through holes in the other part. A sonotrode is pressed onto the end of each stud, softening and reforming it, often into a dome shape (like a rivet head) that locks the other component in place. Depending on the shape of the components it may be possible to perform multiple staking operations simultaneously using a single sonotrode. In any case the operation is quick and simple since ultrasonic energy is transferred directly to the part being reformed.

Re-forming (swaging)

Where a staking process is not practical ultrasonic reforming may be an option - generally changing the shape of one part so it traps the other in place. Again one of the materials needs to be a thermoplastic; the other may be an incompatible plastic, metal or almost anything else. The exact nature of the reforming will depend on the application but a typical example would be reshaping the edge of a plastic container to trap a lid in place.

Insertion

Where a strong thread is needed in a plastic component ultrasonic insertion can be used to fit a metal bush. This is normally threaded internally with a knurled external surface. The insertion process involves pressing the bush into a hole in the plastic moulding which is initially too small. Vibrations transmitted through the bush to the plastic heat and soften it, allowing the bush to be pressed in without damaging the component. As the plastic cools it hardens around the bush, holding it firmly in place.