Ultrasonic welding of thermoplastic polymers has been practiced industrially for many years without being fully understood. This study includes an analysis of the energy dissipation mechanisms responsible for the formation of ultrasonic welds in PMMA including viscoelastic loss and by plastic deformation.

The physical effects contributing to the formation of an ultrasonic weld in glassy thermoplastics are identified and used in the derivation of a classification for all welding techniques for these materials.

Ultrasonic welds were studied using high speed photography, the measurement of polymer chain orientation and residual stress, the measurement of contact dynamics at the initiation of welding and the influence of polymer chain interdiffusion by reference to simple thermal welds. A description of defects present in an ultrasonic weld is given and this is extended to a proposed scheme for defects in welds made using all welding techniques.