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An ultrasonic stack is compatible when its generator, converter (transducer), optional booster and horn are all built for the same resonant frequency, and when their electrical and mechanical interfaces and their power or amplitude ratings correspond. Four components carrying the same frequency label are not automatically a working stack. Accept a combination only when you hold each element's frequency and rating, its interface drawing, and a written statement of what the combination was actually run against.
Compatibility means the stack works as one resonant assembly driven at a single frequency: the converter, the booster (when one is used) and the horn are tuned to resonate at the same ultrasonic frequency, and the generator delivers a high-power electrical signal at that same resonance. Industrial ranges are commonly quoted at 15 kHz, 20 kHz, 30 kHz, 35 kHz, 40 kHz and 70 kHz.
A resonant match is the starting condition, not an acceptance test. The same stack principle serves two different joining mechanisms: metals are welded without melting the base metal, while thermoplastics absorb the energy and melt locally at the joint. A stack that resonates therefore tells you nothing yet about your joint design, the amplitude your part needs, or the weld you will actually get.
Keep frequency agreement as one line in the acceptance file, next to the interface drawings and the written statement of which combination was run together.
The generator must deliver its high-power electrical signal at the stack's resonant frequency, and what it can output has to suit the converter and horn attached to it. Frequency agreement is the entry requirement; drive capability, and the way the generator finds and holds resonance, decide whether the combination behaves on your press.
A generator listed in the RPS-SONIC catalogue is described as having an intelligent frequency-control system that tracks a resonance point. Ask for that behaviour in writing, because it is the part of the match you cannot read from a nameplate.
Start from the converter's own data: its nominal frequency and rated power must fall inside what the generator is designed to drive, its electrical connection must match, and the mechanical fit above and below it must be the one the stack was designed for. Then ask for evidence that this converter and this generator were run together.
A booster is optional: a stack can be converter and horn only. When a booster is fitted it sits between the converter and the horn, must be tuned to the same resonant frequency as both, and adds length that the press stroke, mounting height and tooling clearance have to accommodate.
The horn contacts the part, and it must be tuned to the same resonant frequency as the converter and booster while its mounting interface and geometry suit your joint. Horn design is application-specific, so the compatibility file needs a drawing and an amplitude rating for your horn, not only a frequency figure.
Yes — the converter, booster and horn must all be tuned to the same resonant frequency, and the generator must drive at that frequency. Matching nominal figures is necessary but not sufficient: the electrical and mechanical interfaces and the power and amplitude demand of your horn must correspond as well.
| Element | Function in the stack | What must correspond | Evidence to request before acceptance |
|---|---|---|---|
| Generator | Supplies the high-power electrical signal at the stack's resonant frequency. | Operating frequency equals the stack resonance; output suits the converter and horn fitted. | Datasheet with frequency and output rating, a description of its frequency control, and the converter and horn it is set up for. |
| Converter (transducer) | Converts the electrical drive into mechanical vibration at the tuned frequency. | Nominal frequency same as generator and horn; rated power consistent with the generator; connector and mounting interface identical to the drawing. | Datasheet, interface drawing, and a test record showing it running with this generator. |
| Booster (when fitted) | Sits between converter and horn and is tuned to the same resonant frequency. | Frequency, overall length for the press stroke, and both mating interfaces. | Booster drawing, stated frequency, and what the complete stack delivers at the workpiece with it in place. |
| Horn (sonotrode) | Transfers the vibration into the joint area. | Frequency, interface to the booster or converter, amplitude demand against stack capability, and geometry for your joint. | Horn drawing, frequency and amplitude rating, and a design-analysis summary where one is offered. |
Send the machine and the stack you already have, not just a frequency: machine make and model, generator nameplate data, the existing converter, booster and horn with part numbers and dimensions, and drawings or photographs of every interface. RPS-SONIC states that it asks for full machine information before supplying a component so that the part does not create a connection and matching problem. Treat that exchange as the start of the check, and still ask for the documentation that results from it.
Matching fixes the resonant frequency and the interfaces; it does not by itself establish weld quality, a safe noise exposure limit, or the right amplitude for your part. Those are separate questions answered by your own weld trials, by your EHS function, and by the limits the element manufacturers document.
Process first. Metals and thermoplastics are joined by different mechanisms under the same stack principle, so a compatible stack is only the delivery system for a joint design you still have to prove on samples.
Noise second. High-frequency sound can damage hearing, and enclosing the machine or using ear protection are the mitigations usually cited. Because the hazard includes airborne ultrasound, an ordinary audible noise reading does not settle the question: the US National Institute for Occupational Safety and Health recommends an exposure limit of 85 dBA as an 8-hour time-weighted average with a 3 dBA exchange rate, but that figure is a benchmark for audible occupational noise, not a limit for ultrasound. Ask your EHS function for a measurement and control plan covering the frequencies your machine produces.
Third, power safety. Any inspection, cleaning or component change on the stack starts with switching the generator off and disconnecting it from its power source, then following the manual's permitted access procedure.
Build the acceptance file before you accept the stack: one line per element with its frequency and rating, an interface drawing for each joint in the stack, and a written statement of which combination was run together. Then isolate the power before any fitting, re-check the operating point on your machine, and prove the joint on samples before production.
These are the questions engineers ask most often when a supplier proposes a generator, converter, booster and horn as one matched stack.
Sometimes such a pair runs, but the brand label is not the evidence. What matters is whether the converter's frequency and power rating fall inside what the generator is designed to drive, whether the connector and mechanical interface match, and whether the specific pair has been documented running together. Catalogues that group transducers by brand family, with figures such as 15 kHz 2600 W or 20 kHz 2000 W, describe what is offered for each item; they do not show that any cross-brand pair is qualified.
There is no universally best frequency. Industrial ranges are commonly quoted at 15 kHz, 20 kHz, 30 kHz, 35 kHz, 40 kHz and 70 kHz, and the stack must be built around whichever one you choose. Decide it with your horn and converter supplier using your part and joint data, then require the generator, converter, booster and horn all to be specified at that single frequency.
The hardware principle is shared, but the joining mechanism differs. In metals the weld is made without melting the base metal; in thermoplastics the material absorbs the energy and melting is local at the joint. That difference changes the tooling, the joint design and the amplitude you need, so ask for experience in your own material class.
High-frequency sound can damage hearing, and enclosing the machine or using ear protection are the mitigations usually cited. Because the hazard includes airborne ultrasound, an A-weighted audible reading alone does not answer the question. Ask your EHS function to measure the frequencies your machine produces and to set the controls, rather than copying a limit from a noise poster.
A booster is optional, and once fitted it becomes part of the resonant stack, so it must be tuned to the same frequency and its interfaces must fit the converter above and the horn below. Ask what the complete stack delivers at the workpiece with and without the booster, and stay within what the converter and horn are documented to take. If you need more than that, the horn or converter changes too.
No. The same nominal frequency is a necessary condition, not the test. The interfaces must mate, the generator must be able to drive that converter and horn, the amplitude demand must sit inside the stack's documented limits, and someone must be able to show the exact combination running together.
