17) How to measure ultrasonic welders’ amplitude of vibration?

FAQ: How manufacturers of ultrasonic welders perform the vibration max amplitude measurement? Of course, it is not possible to drive the converter to max power when unloaded, that is, it's likely that we would use up to 10-20% of maximum power at no-load condition. So, I was wondering how manufacturers consider the point of max amplitude that they declare ... i.e.: 30-50 microns at 20kHz. Mr. L.S.

In general, the procedure consists in driving the converter at maximum voltage (generator limit) and evaluating the amplitude of vibration at no-load condition using laser sensors. Since ultrasonic welding converters operate at antiresonance frequency (at maximum impedance), the power consumption will be low (the lower the better the converter and higher the Qm). However, if you are driving at resonance this approach does not work and we do not know how an equivalent amplitude test would be done.

FAQ: I work in a blow fill seal department and in our process, we use ultrasonic knives (Dukane, 20 kHz, knife/horn: 120µm amplitude) to cut parison tubes. For a long time, we have thought about a good test method to be certain that our ultrasonic knives are in a good condition. However, at this moment we don’t know what the output of the stacks is. I was doing a little bit research and read about a tool (SonicSniffer®) when visiting your website Can this tool be used for testing/troubleshooting? If the tools are suitable, are there other options? Mr. N.V.

It is unfeasible to verify the ultrasonic stack condition by measuring the amplitude of vibration on routine basis because of the high frequency involved. As far as we know, only laser interferometers and optical sensors are able to measure power ultrasonic devices amplitude of vibration properly, but they are expensive and impractical at the production floor. In your case, you have an additional complication because you lack a good optical target, since the knife termination is not a flat surface.

Our approach and suggestion are that you should evaluate the stack condition indirectly by its frequency and mechanical quality factor (Qm). There is a right frequency with tight tolerance (at 20 kHz the typical tolerance is ±50 Hz) and a minimum Qm (250 for converter alone and 1000 for full stack). The amplitude of vibration is directly proportional to the Qm.

The stack operational frequency with the knife running is measurable by the SonicSniffer, deviations indicate the need for preventive maintenance in order to avoid failures. The maintenance basically consists in cleaning the joints surfaces and reassembling the stack with the right torque. If the preventive maintenance is not enough, you need to troubleshoot the stack parts to identify the defective part (whether it is the converter, the booster or the knife). The TRZ Analyzer can be used to test each part frequency and mechanical quality factor (Qm) to perform the troubleshooting. TRZ® Software has preprogramed criteria to assist with the performance of this task. Furthermore, our test instruments include online training and remote support to assist you and speed-up your learning curve.

Learn more about testing converters and acoustic stacks.