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What is vibration welding of thermoplastics?


Vibration welding, also known as linear friction welding, is a commercially used process that can be applied to almost any thermoplastic material. The automotive industry is a major user and applications include bumpers, fuel tanks, engine air intake manifolds and other under-bonnet components.

At the start of the process, the parts to be joined are brought into contact under an applied load. Next, one of the parts is vibrated in a linear reciprocating motion whilst the other is held stationary. This generates frictional heat at the joint line and causes local melting and some displacement of material into the weld flash. Finally, vibration is stopped, the parts are aligned and the joint is allowed to cool under load to consolidate the weld.

Frictional heat, which must be sufficient to melt and flow the plastic at the weld interface, is generated by a combination of time, pressure, and amplitude and frequency of vibration.

Most industrial applications of vibration welding involve linear joints that are too long for ultrasonic welding. Weld times for large joint areas range from around 5-15 seconds, making vibration welding about four times faster than the hot plate technique. Alignment of the finished parts is consistently good.

There are a couple of disadvantages of vibration welding: high capital cost of equipment and difficulty with welding three-dimensional joints (which are impossible if they incorporate a seal).

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