22) What is the correct frequency for each element of the acoustic stack?

FAQ: If I want to prepare the optimum transducer + booster + horn assembly for 20 kHz, I assume their individual central frequency 20 kHz. Is that so? If I use a horn that is proper for 20 kHz, whatever the central frequency of transducer + booster is, the overall frequency is measured as 20 kHz. Is there a problem to use that in ultrasonic welding? For example, Fc_transducer = 20.45 kHz, Fc_tranducer+booster = 20.75 kHz and Fc_transducer+booster+horn = 20.00 kHz. Should I observe local heating or any other discrepancy? Mr. F.D.

Although your logic makes sense, ultrasonic welding systems are driven at anti-resonance frequency and not at central frequency. In addition, you are combining two single frequency elements (horn and booster) with a transducer that has a frequency range. Below find some recommendations based on our experimental observations and measurements of the most updated equipment.

The converter frequency range [Fr-Fa] should include the stack nominal frequency (20.00 kHz). The most common is to find the converter's Fr closer to the nominal frequency rather than Fa. A stack with a high or low frequency converter may work and be acceptable, but with lower efficiency and higher heating than a proper tuned one. The converter mechanical quality factor (Qm) must be equal to or higher than 250.

The converter+booster frequency range [Fr-Fa] should be within the “converter alone” frequency range. The converter+booster Qm must be equal to or higher than 700.

The converter+booster+horn frequency is mainly determined by the converter and should be equal to the nominal frequency +/- 0.25% (e.g. ±50 Hz for 20.00 kHz welders). The Qm should be higher than 1000.

Learn more about testing converters and acoustic stacks.