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How can I monitor the quality of ultrasonically welded thermoplastic components?


Frequently Asked Questions

There are no non-destructive methods for inspecting ultrasonically welded thermoplastic components. Therefore, it is important that welding process parameters are monitored and controlled. Since the advent of microprocessor control, the majority of ultrasonic welding machines are able to monitor key parameters such as weld energy, weld time, material displacement and welding power. Some even have statistical process control (SPC) software, allowing up to 200,000 welding records to be collected and stored. This is useful for monitoring trends and deviations in welding data when large batches of components are involved.

When an ultrasonic welding machine is initially set up for welding, it is important to define a component acceptance criterion. This will usually be a particular strength, leak criteria or appearance. Once this is defined, a batch of components, typically 50 to 100, should be manufactured and the welding parameters monitored, for example, if the component is welded using time, the weld energy and weld displacement can be monitored. The results can then be used to set the welding limits on the machine. For example, if the weld time was 300m sec and the energy required to produce an acceptable welded component was between 50J and 60J, then these energies could be set as the 'weld energy limits'. Any welded components produced outside these limits can be visually inspected and either returned to the production line or rejected.

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