TWI Industrial Member Report Summary 952/2010
by R Wise
Ultrasonic welding of thermoplastic polymers is a very widely used technology because of its speed and consistency. It is used in the mass production of products including automotive and medical devices, and the process equipment has evolved to permit welding parameters to become more and more tightly controlled. Alongside this, much work has been attempted to model the process so that the beat generated as a function of time can be calculated with the change in geometry of the specimens.
In consideration of ultrasonic welding of materials, two categories energy, glassy thermoplastic polymers (glass transition temperature is well above room temperature), and rubbery semi-crystalline polymers where the glass transition point is below room temperature. For the latter category, ultrasonic energy is usually absorbed immediately by the polymer which becomes hot very close to the point of application of the ultrasound. For the former category, the ultrasonic energy can propagate over relatively long distances in the material (several 10s of mm) before causing heating. The work described concerns an investigation into the mechanisms responsible for heat generation in glassy thermoplastic polymers.
Three types of experiment were undertaken, temperature measurement, high speed video and dynamic contact.
- Identify the main heating mechanisms present at different stages of ultrasonic welding in glassy thermoplastic.
- Measure the temperature at the weld interface during an ultrasonic weld polymethylmethacrylate (PMMA).
- Identify the main mechanism responsible for heating, particularly during the first 100 milliseconds of the ultrasonic weld in glassy, amorphous thermoplastics.