Thursday, July 28, 2011

What Amplitude is needed to weld my plastic components?

What exactly is “Amplitude” and why is it important?  Amplitude is the peak-to-peak movement, or expansion/contraction, of an ultrasonic tool stack.  Each component can multiply the amplitude that comes from the transducer, the amount of increase or decrease is called "Gain".  The total gain of the stack components determines the final amplitude at the working face of the ultrasonic horn, where part contact is made.  The ultrasonic tooling stack includes the transducer, booster and horn.  Some applications do not require a booster and the horn is attached directly to the transducer.   These are usually multi-head automotive applications or packaging applications.

Some customers have tried to save money by not purchasing the correct booster for their particular application.  Making sure the ultrasonic tooling stack is producing enough amplitude is one of the most important factors to successfully welding parts. 

Yes, there may be a setting or two that can be adjusted in the ultrasonic welding system, like adjusting the pressure, but that doesn’t mean that the material at the joint area is actually co-mingling.  If parts are not welded properly, they probably won't pass inspection or may even break apart in your hands.  Worse yet is the possibility of your customer returning parts due to poor quality.  Insufficient amplitude is often evidenced by not only weak welds but also incomplete welding where the melt around the interface is not completely present.  A weld detail, e.g., energy director, may show signs of embedding into the mating surface instead of melting.  If you have a weld time that is less than .1 seconds and your process seems to produce erratic results, then possibly your amplitude is too high and a reduction needs to be made.

A chart is included that shows some amplitude requirements of basic materials.  Use the example as a guide for your current resin and ultrasonic tooling stack to see if you have enough amplitude for your application. Generally speaking, amorphous plastics require less amplitude than semi-crystalline materials.  

Click to enlarge
Dukane’s application engineers can assist you in calculating the proper amplitude for your ultrasonic welding application and quote the proper booster to match up with the horn.



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