Ultrasonic Welding

Ultrasonic welding uses ultrasonic energy at high frequencies (20 - 40 KHz) to produce low amplitude mechanical vibrations. The vibrations create heat through friction on the joining surfaces of the thermoplastic materials. The material will melt and under pressure, during the cooling cycle, a bond is created.  A major advantage of Ultrasonic welding is the speed. A weld cycle is typically between 0.1 and 1 second.

When a thermoplastic is subjected to ultrasonic vibrations, sinusoidal standing waves are generated in the material. Part of this energy is dissipated by intermolecular friction, resulting in the localized build-up of heat at the interface of the materials. The weld quality depends highly on the geometry of the part and the ultrasonic absorption characteristics of the material.

The distance between the energy source and the welding surface is important, as this will determine the total amount of energy absorption.  Certain geometric features may be designed into the part (e.g. energy directors) which will direct energy more efficiently to the welding surface.

 

Advantages

  • Welding speed cycle (0.1 - 1 second)
  • Easy to automate
  • Quick tooling changes

Disadvantages

  • Size restriction (10" x 12")
  • Tooling cost
  • Special design features required
  • Limited material compatibility