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large piece need to be ultrasonic welded

I need a Sonotrod for a 450 x 155 MM freezer door in the refrigrator. It is 2 piece Gpps plastic injection door. We have 20Khz branson machines. they are telling us to weld 6-8 times by making 160 x 40 x 140 mm tall sonotrod off coarse it need to be tuned and calculated.
Why this can not be weld by one sonotrod? I like to get a controle of this calculation in our own hand rather than waiting outside help. How we can do it? What we need to test the frequency ? what we need to calculate the maximum size of sonotrod we can use?
Surjit Virdi

Hello Surgit,

As the size of a sonotrode increases it becomes more and more difficult to keep it vibrating in the correct mode of vibration. Ideally the dimensions should be such that the length (height) is exactly half a wavelength and all other dimensions significantly less than this, but some designs like block / blade horns can be pushed larger.

In your case with (I guess) a titanium sonotrode at 20kHz the half-wavelength is about 130mm, and the dimensions you've been given are reasonable as maximum values for a blade horn - attempting to increase the 160mm length will almost certainly result in unacceptable variations in vibration amplitude along the sonotrode. Having a single sonotrode to weld a workpiece 450mm x 155mm is simply impossible with current technology.

You can take control of the sonotrode design and manufacture yourself, but be aware that it's a difficult job and you have a lot of catching up to do before you can hope to approach the wealth of specialist knowledge and experience that the established manufacturers already have. Unless you're absolutely sure that you will have an ongoing need for this expertise, doing it yourself is unlikely to be cost-effective compared to simply buying the sonotrodes from Branson. At the very least you'll need finite-element analysis software to help with the design, specialist tuning equipment to test / tune the parts and of course the necessary expertise to use both. My sonotrode calculator does not analyse blade horns at present, although I would like to add at least some capability in this area in the future.


Chris - site owner, chief cook and bottle-washer.