TRZ® Analyzer main applications
The main applications of the TRZ® Analyzer are: ultrasonic horns tuning, ultrasonic welding stacks maintenance, converters repair, and transducers quality control. It is also used in receipt inspection and ultrasonic products development.
Horns and sonotrodes tuning
Frequency tuning of ultrasonic horns and similars is required for new parts to compensate for elastic properties variations and milling tolerances. For used and worn horns, it is required to compensate dimensional changes in order to extend their lifespan.
In the case of ultrasonic welding and cutting equipment, the horn frequency should match with the booster and converter ones for vibratation efficiency and spare parts compatibility. This is the same for medical and dental equipment, such as ultrasonic scalpels, scissors and scalers, ultrasonic polishing and ultrasonic grinding equipment.
Basic dimensional change for increasing and decreasing frequency.
The basic changes for horn tuning are to reduce its length to increase the frequency and to change the lateral dimensions to decrease the frequency. The Lateral dimensions reduction decreases the frequency, but with lower sensitivity than the length and with side effects in amplitude gain.
The tuning process consists in changing the horn dimensions by employing machine tools (lathe, milling and grinding) combined with TRZ® Analyzer measurements until the desired frequency is reached. Each dimension change should be minor and preceded by the TRZ analysis. To be measured, the horn must be connected to a converter and booster, as it would be in real use.
Frequency increase with length decrease along tuning of a 15 kHz block type horn. The target frequency was 15.000 kHz ± 0.050 and the final frequency tuned 14.950 kHz. The sensitiveness was ≈90 Hz/mm (2.3 Hz/mil).
The standard operation to tune a horn is to reduce its length because it is the easiest dimension to change and the frequency is more sensitive on this direction (≈ 100 Hz/mm for 20 kHz parts). A new horn or replica is usually machined lengthier to later tuning with length reduction, +4 mm (≈160 mil) is enough for 20 kHz horns. The change of lateral dimensions is limited to horns reconditioning; wear and facings reduce the length, thus increasing the frequency, which can be corrected to some extent by changing the lateral dimensions and moving the step position.
It’s worth to mention that is not possible to repair a cracked horn. You may tune the frequency, but the crack will keep both the mechanical quality factor and the performance low.
Ultrasonic welding stacks testing
To identify which stack element is not working properly, a progressive test should be performed: firstly, test the converter alone; secondly test the converter and the booster and lastly, the complete stack. At each step / combination, specific acceptance criteria should be applied for frequencies, frequency range, mechanical quality factor and impedances.
|Mechanical quality factor (Qm)||≥ 250||≥ 700||≥ 1000|
|Frequency range [Fr-Fa]||Should include the stack nominal frequency||Should be within the converter frequency range||-|
|Operational frequency (usually Fa)||-||-||Should be equal to or tighter than the stack nominal frequency ±0.5%|
Over the years we learned the typical deviations of malfunctioning ultrasonic stacks parts and condensed this knowledge within general guidelines and acceptance criteria. The guidelines have been summarized on the table above and the criteria programed on the TRZ® Software.
There are many ways manufacturers can align the stack parts frequencies and drive it, making impossible to define specific guide lines and criteria that would be perfect to all of them at the same time. In spite of that, the guidelines and criteria we offer herein and within the TRZ® Software are a good start that can be later refined by testing new parts and/or by requesting further specifications and tolerances from the manufacturers.
Before running the tests, ensure that the stack parts mating surfaces are flat, parallel and clean. A light coat of high temperature grease or a film washer on the mating surfaces is recommended. Any mating surface in bad condition should be reconditioned, because poor mating surfaces compromise both mechanical quality factor (Qm) and performance of the stack. Likewise, clean and check the studs and threads condition.
Converters testing (converter alone)
The mechanical quality factor (Qm) of converters must be equal to or higher than 250 regardless of the frequency, power or manufacturer. This number is a rule of thumb based on our experience.
Example of a converter in good conditions: the stack operational frequency indicated by the red dashed trace at 20 kHz is within the converter range [Fr-Fa]C indicated by the blue region.
You can understand the Qm as how many times the device oscillates after power is turned off (this is a rough approximation for illustration purpose only). A converter oscillating 800 times (Qm=800) vibrates more efficiently and dissipates a lower energy fraction than one oscillating 250 times (Qm=250). It worth to mention the Qm varies greatly from part to part and the higher the better.
The converter frequency range [Fr-Fa]C should contain the stack nominal frequency. In the first figure above, the stack operational frequency (20 kHz) is within the blue region, indicating the converter is ok with regard to this criterion. In the second figure, the stack operational frequency (20 kHz) is out of the blue region, indicating the high frequency of the converter. The operational frequency range may be anywhere between the converter Fr and Fa, however, the most common frequency should be close to Fr. 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.
Other criteria are applied by the TRZ® Software in relation to the frequencies and respective impedances, however they are not strict because the frequencies and impedances of converters vary greatly with the device maximum power and from one manufacturer to another (users may and should perform refinement where possible).
Boosters testing (converter+booster)
If the converter fails on the previous step, you have found the problem or at least one of them. If the converter is ok, the problem is somewhere else and you can move to the next step by testing the booster. To test the booster, you need to connect it to a converter in good conditions (it can be the stack's own) with the proper torque and procedures recommended by the manufacturer.
The “converter+booster” mechanical quality factor (Qm) must be equal to or higher than 700 regardless of the frequency, power or manufacturer. This number is a rule of thumb based on our experience. We recommend to test the converter+booster also on the welding machine for the mechanical quality factor (Qm). Sometimes the booster problem is the damage on o-rings cushion, what may not be detectable unless the booster is fixed. This test is also important in developments to check if the booster nodal region is coinciding with the holding region (if not, the mechanical quality factor will decrease considerably).
Example of “converter+booster” in good conditions (blue chart) and the “converter alone” (gray chart). The converter range [Fr-Fa]C indicated by the blue region contains the converter+booster respective frequency range [Fr-Fa]C+B indicated by the red region.
The “converter+booster” frequency range [Fr-Fa]C+B should be within the “converter alone” frequency range [Fr-Fa]C (blue region), as exemplified on the first image above (the “converter+booster” range may be anywhere inside the converter range). The second image above illustrates a case of low frequency booster where the [Fr-Fa]C+B is not within the “converter alone” frequency range [Fr-Fa]C (the red box). The judgment is graphical/visual.
Other criteria are applied by the TRZ® Software in relation to frequencies and their respective impedances, however they are not strict because the frequencies and impedances of converters and boosters varies greatly with the device maximum power and from one manufacturer to another (users may and should perform refinement where possible).
If the “converter+booster” fails the previous step, the problem is the booster. If the “converter+booster” is ok, the problem almost certainly is the horn and you can move to the next step by testing the complete stack. Connect the horn to the booster with the proper torque and procedures recommended by the manufacturer.
The stack mechanical quality factor (Qm) should be equal to or higher than 1000, regardless of the frequency and power. The Qm equal to or higher 1000 is a rule of thumb based on our experience, we have never tested an acoustic stack working properly with Qm lower than 1000. When the horn is cracked, the stack mechanical quality factor decreases considerably.
Example of horn in good conditions, the stack frequency (Fa) is within the nominal operational frequency range indicated by the blue region at 30 kHz ± 75 Hz.
The operational frequency should be equal to the nominal one more or less than 0.5% (e.g. ±100 Hz for 20.000 kHz machines). The frequency tolerance may be tighter for high-grade equipment, ± 0.25 % is usual for well-known brands. In most cases the operational frequency is the antiresonance frequency (Fa), a few brands drive welding equipment at the resonance frequency (Fr) or between resonance and antiresonance frequencies; you can find it out by measuring the equipment with the SonicSniffer® non-contact frequency meter.
You can have bad stacks at the right frequency. It happens, for instance, when you have a wear (that increase the frequency) and poor interfaces (that decrease the frequency) simultaneously. In these cases, you will detect the problem by looking at the mechanical quality factor, which should be higher than 1000.
In an acoustic stack, or any resonant compound device, each part acts like a band pass filter and, if their frequencies are not aligned, the stack will have low efficiency. Low efficiency comes with over heating, overloading the generator and faster fatigue, making horn poor tuning the root of many problems in the power ultrasonic systems.
Ultrasonic transducers quality control and receipt inspection
The quality control of ultrasonic transducers and parts may be performed by the characterization of their frequencies, impedances and mechanical quality factor. To be approved, these parameters must be within the acceptance criteria.
Deviations indicate problems in the manufacturing and / or assembly of the parts and must be meticulously evaluated to avoid low performance and technical assistance problems. A transducer with characteristics outside these ranges can operate, but with low performance, overheating issues and reduced lifespan, besides the risk of damaging the generator and associated items, such as sonotrodes and boosters.
When a transducer or part is not approved, it can still be recovered by identifying and correcting the problem. Typical causes are dimensional deviations (frequency change) and assembly failures.
The acceptance criteria are determined based on the characterization of the average values and deviations of a pilot batch of reference transducers. When necessary, the ATCP can offer a customized consultation to assist the determination of acceptance intervals.
The TRZ® Analyzer is able to test reconditioned converters and parts by applying adjustable acceptance criteria.
The TRZ® Analyzer is an impedance analyzer able to test any piezoelectric device with regards to their frequencies, impedances and mechanical quality factor with the 1-200 kHz range (for instance, Langevin-type transducers and piezoelectric actuators).