Dear Muhammad,

ultrasonic generator converts the supply voltage into high frequency (ultrasonic) voltage, which is normally in the range of 20 to 35 kHz depending on the generator inner structure (please refer to the supplier data sheet in this regard). The central part of the converter is supplied with piezo-ceramic elements, which convert the high frequency electrical voltage into mechanical vibrations.

So if you need a certain frequency for the welding process you should choose the generator which can supply that. Then you can be sure that this frequency is the frequency of the welding horn.

You should know that what mostly affects the amount of the generated heat is the "amplitude" of the vibrations, which can be set up on the machine.

A successful joint (good bond) can be achieved by testing different parameters, such as amplitude of vibrations, welding time and the welding pressure for the material pairs you are using.

Regards,

Shima

The problem in your case probably may be due to insufficient ultrasonic amplitude of vibration. Because the wielding time and welding pressure may be manipulated easily and I believe that you must have tried these. The method to detect the transducer frequency is simply to use impedance analyzer. If you do not have the impedance Analyzer (expensive device), use function generator and remove the transducer connection. excite it with the function generator with 2 - 3 V only and use a 50 ohm (approx) in series during excitation. Now monitor the voltage across the transducer with the help of an Oscilloscope (DSO). Change the frequency of function generator from 20kHz to 35kHz and check the response. the transducer should indicate lower amplitude at the resonance which is obviously showing low impedance. Please note this freq (Transducer Freq). Now also check the welding excitation source frequency with an oscilloscope by using suitable probe (attenuator). Just make sure that these two frequencies should closely match in order to get the optimum ultrasonic vibration amplitude.

Hi,

let me give you some thoughts based my year long experience with Thermosonic Inspection (this a special NDT method using Ultrasound to excite vibration which transfers in heat at cracks etc. afterwards measured with thermocameras), We started first with conventional Ultrasound Welding Machines from e.g. Branson etc. Usually 20KHz with 2KW electrical power, somtimes tunable for some % of the center frequnecy. But you soon realize that fixed frequencies are bullshit. This puts us in a tricky situation. Usually the driver piezo stack is resonant so if you try to drive him with a different frequency, he looses amplitude or just makes what he wants - rings further on on his resonance frequency. So we had to look for different solution.

We had a lot of discussions with experts from Ceramic Industry - I attach some links of relevant industrial resources. It is worth to check through there as most academic papers did not really help us for designing market ready systems.

For checkint the effectivity of transducers - at the location, where you need the sound - in your case the weld spot - we took always a Vibrometer e.g. from Polytec (https://www.polytec.com/int/vibrometry/technology/) and sometimes our Thermocameras.

A scanning vibrometer may even give you an idea about the mode distribution over a full field. You can either check the surface of the piezo itself, the booster interface and of the horn or the sonotrode etc.

If you have non maybe you find a vibrometer in a neighbouring institute.

The vibrometer is the most efficient tool to really explore what ends up at the tip of your system - just where you need the energy for welding. The suggestion of an impedance analyzer does not meet the need to check the full path from the driver electronics via piezo, Interface, Booster, Interface, Horn, Interface, Material to Weld etc.

Be also aware:

acoustic impedance changes take place at each interface the sount is travelling through. If the acoustic impedance of two materials connected does not match (it is a product of material density and sound speed), you have losses because of reflection, which in turn can cause destructive interferences to damp the transitioning sound.

My advice is to modell the full soundpath with all meterial parameters, interfaces and geometries to optimize the acoustic path. Check also for a matching layer to let the sound get as good as possible into your material to be welded. The combination of materials you mentioned sounds not really perfect to me. You indicate silver as material for your piezo - I guess this only the contact surface, as silver is no piezo material. So a thin silver coating does not really influence the acoustic impedance. The impedance (mis)match has to be calculated between the Piezo Ceramic and the Booster (aluminum/silver) and the second interface towards the Titanium Horn, where again an impedance mismatch occurs (so is this combination really well selected?). Such problems we once discussed with Rittmeyer-Beri, really experts in this field. Check out their e.book, use the link i added.

The geometric form of the booster and the horn is also critical, so usually this is designed specifically for the welding problem - again some practical considerations you may find in the documents from Rittmeyer-Beri.

What you also need is a tunable power source well adapted to the capacitive load of your sonotrode. We for instance bought once an off-the-shelf power generator which was advertised as fitting best for our actuator, but after short use we saw smoke and fume and some burned semiconductors. So it turned out that the circut design was not hard enough to withstand the capacitive impedance load of the transducer array in our application. We had to carefully redesign the power supply. Here we needed real experts in this field.

Also some piezo material does not withstand high power of frequencies different from their Eigenfrequency. The material can show strange behaviour and fail after some time. So intensive discussions with manufacturers of ceramic raw material showed us the right selection. (therefore I have added some links)

Modelling is also a need to optimize the full path from electronics to the weld spot You will find solutions with Matlab, Comsol etc. Check the internet.

I add some links of other companies, which helped us too

There is a company in Germany (https://www.myathena.de) which also offers rather interesting information / support: the owner helds interesting lessons about this topic at the Technical University of Hannover, sadly his homepage is only in German.

Maybe this helps to reach you goal more efficiently.

Wolfgang Bisle

some links:

https://rittmeyer-beri.de/en/ especially https://rittmeyer-beri.de/wp-content/uploads/Lausige-Wellen-2017-en.pdf

https://www.piezosystem.com/products/piezocomposite/

http://www.noliac.com/contact/

https://www.unictron.com/piezo-elements/cleaning-welding-machining/

https://www.pi-usa.us/en/ + https://www.piceramic.com/en/ + https://www.physikinstrumente.com/en/

https://www.cedrat-technologies.com/download/CEDRAT_TEC_Catalogue.pdf

https://www.ceramtec.com/

Modelling / Software:

http://www.krell-engineering.com/fea/fea_info/fea_resonator_design.htm

http://www.mmech.com/atila-fem

https://sonicconcepts.com/software/