[moved] Ultrasonic welding machine

[william2016]

Hi All
who can help me? i want to make a ultrasonic welding machine. and i meet two questions.
1: i haven't any circuit design information about 28KHz.
2: how to design a transducer apply for generater circuit and horn.
please help me.

 

[c_mitra]

Re: Ultrasonic welding machine

What kind of transducer you are planning? Piezoelectric or magnetostrictive?

 

[william2016]

Re: Ultrasonic welding machine

What kind of transducer you are planning? Piezoelectric or magnetostrictive?

Thanks for you help.
I want to use the ultrasonic welding of plastics with piezoelectric ceramic transducer.

 

[BradtheRad]

I'm thinking of an earphone used with old-fashioned pocket transistor radios. A coil next to a steel diaphragm, 1/2 inch diam. (Maybe the diaphragm is magnetized, one face north, the other face south.) Run AC through the coil. It moves the diaphragm back and forth. The sound travels to a tiny hole at the other end.

To do sonic welding, I think will require these changes:
* Multiply the power input. Make the coil able to carry a few watts.
* Mount the diaphragm so it has more flexibility to move back and forth.
* Seal around its edge, thus making it impossible for moving air on one side to cancel effects of moving air on the other side.
* The housing should be rigidly constructed so it does not vibrate. All sonic energy must be concentrated to the opening.
* Hold the opening near plastic pieces which are touching.

It could help to sweep through a range of frequencies, in case one is more effective on the physical substance being welded.

 

[william2016]

I'm thinking of an earphone used with old-fashioned pocket transistor radios. A coil next to a steel diaphragm, 1/2 inch diam. (Maybe the diaphragm is magnetized, one face north, the other face south.) Run AC through the coil. It moves the diaphragm back and forth. The sound travels to a tiny hole at the other end.

To do sonic welding, I think will require these changes:
* Multiply the power input. Make the coil able to carry a few watts.
* Mount the diaphragm so it has more flexibility to move back and forth.
* Seal around its edge, thus making it impossible for moving air on one side to cancel effects of moving air on the other side.
* The housing should be rigidly constructed so it does not vibrate. All sonic energy must be concentrated to the opening.
* Hold the opening near plastic pieces which are touching.

It could help to sweep through a range of frequencies, in case one is more effective on the physical substance being welded.

Thanks for you help.
Your explanation is mainly about work principle, please recommend circuit of ultrasonic welding, can you give me some examples.

 

[BradtheRad]

I think the diaphragm should be forcibly moved back and forth by true AC through the coil. This ought to be more effective than DC pulses (which force the diaphragm in one direction, then turn off to let it 'relax' back in the other direction).

I think either square waves or sinewaves are okay.

Oscillator circuits are easy to make. I think you can get by with a simple type whose frequency is adjustable. Then feed the output to a half-bridge, or H-bridge, which drives the inductor.

There is the type of oscillator whose frequency is derived from the inductor's behavior. It might be LC based. Its frequency is not easily changed. However I believe it is more important to be able to adjust the frequency.

 

[william2016]

I think the diaphragm should be forcibly moved back and forth by true AC through the coil. This ought to be more effective than DC pulses (which force the diaphragm in one direction, then turn off to let it 'relax' back in the other direction).

I think either square waves or sinewaves are okay.

Oscillator circuits are easy to make. I think you can get by with a simple type whose frequency is adjustable. Then feed the output to a half-bridge, or H-bridge, which drives the inductor.

There is the type of oscillator whose frequency is derived from the inductor's behavior. It might be LC based. Its frequency is not easily changed. However I believe it is more important to be able to adjust the frequency.

Thanks for your help.
My plan is here.First of all,I will design a circuit with 555 timing chip as a control of welding time, and this is easy for me.
Second, I realize the square wave oscillation of piezoelectric ceramic piece best,but how to make a circuit output square wave for 28KHz? That is difficult for me.Third, how to design a transducer or buy a suitable transducer to match to horn,that is i want to know.
Thanks!

 

[c_mitra]

I think either square waves or sinewaves are okay..

The same idea is used with a 50W speaker coil and a power oscillator.

But the setup may not be efficient to handle 100W power at 45KHz. But the truth is that I do not know.

- - - Updated - - -

I realize the square wave oscillation of piezoelectric ceramic piece best,but how to make a circuit output square wave for 28KHz?

This is actually the least of the problems. The transducer provides the C and you make a L to match the frequency of the transducer. This is the natural frequency of the transducer and it is easy to dump lots of power into the ceramic. When pressed against the plastic, about 60% of the energy is transferred to the tip and the plastic (sufficient to provide sufficient friction to melt the plastic and weld the sheet).

Most of the circuits for ultrasonic cleaners (about 100-200W) should work without major modifications. Most of the power is handled by 1 or 2 MOSFET. Rest are routine (but I am ignorant).

 

[BradtheRad]

First of all,I will design a circuit with 555 timing chip as a control of welding time, and this is easy for me.
Second, I realize the square wave oscillation of piezoelectric ceramic piece best,but how to make a circuit output square wave for 28KHz?

A 555 IC is suitable to generate pulses, at adjustable frequencies. Then its output biases a transistor half-bridge. A push-pull arrangement, with capacitor stack, can provide true AC through the coil.



I can't be sure this is the optimum set of values. The aim is to move the transducer (plate) back and forth a distance, very rapidly. The flux field needs to be strong, therefore you need to determine the right combination of Amperes and Henry value in your coil. This has to do with wire gauge, number of turns, etc.