Ultrasonic Welding Question

Hello everyone,

I’m currently working on a project where I am looking at using ultrasonic welding to fix a cover cap in place. The cover cap will hide fixings, PCBs etc and give a clean finish. I don’t have loads of experience with ultrasonic welding so was just wondering if anyone on here did and would be able to help me out with a few questions.

Firstly, is it feasible to weld a cap like this in place as one of the the final assembly steps? I can’t give much detail about the product but it will contain electrical components so I didn’t know if the frequencies generated by the welding could have an impact on those. I’ve seen a few videos of people welding housings together but they tend to be empty and can’t really find much information about it.

Secondly, I’ve been lead to believe that it’s possible to create a watertight seal using the correct type of joint, has anyone had any experience with this?

If it’s not feasible then I’ve got a few other options that I can explore so it’s not the end of the world but I just thought I’d see what you experts thought :slight_smile: Thank you in advance!!


  1. I believe it would be highly unlikely damage would occur. But you obviously need to test the finished good to confirm. UL/CE testing should uncover any problems.

  2. Yes, watertight seals can be made. But it is entirely dependent on your design and the resulting horn design.

For high volumes, it hard to beat the throughput of ultrasound. For lower volumes, adhesives are an option.

The damage depends on the PCB design. If there are a lot of surface mount parts with small footprints, it could be a problem. As iab said though, it’s usually OK.

A watertight seal is possible. A mold-maker with experience can help you get the right parting line for this, and there are guides. (Try googling, “ultrasonic welding guide”). Again, as iab said, there are alternatives. Again, your supplier should be able to help you out on this, but here are some thoughts:

  • Ultrasonic welding works best on planar parting lines. It also works best when your design is fairly box shaped to direct the vibration into the joint.
  • I have seen ultrasonic welders for low volume here in Montreal. They are hand operated (they look like drill presses).

Thanks iab and Ray for coming back to my questions.

I’ll double check with the guys working on the PCB design and see what components will end up mounted on the PCBs. I’m glad it wasn’t a completely ridiculous question though, I couldn’t tell if I was just being overly cautious!

The design of the area that I’m looking to seal is all in one plane with a pretty simple shape so I don’t think it should be a problem. I’ve been reading through a few guides over the weekend and it seems possible so that’s one thing off the list.

Thanks again for the help, hopefully I’ll get to share the work in the future and let you know how it goes :slight_smile:

One thing I notice about your question is this is the final step in assembly. In the past when I have ultrasonically welded it has always had to be backed by a conductor. I don’t know if there are other ways to do it. But as a final assembly step that might be a problem. Outside of that, I agree with the above comments.

Thanks Singletrack, I’ll do some more research into that and see if there is any way around this. Although it’s looking more and more likely that we will be going down a different route. Still, it’s good to have the knowledge locked away for the future!

No need to be backed up by a conductor. Check Branson Ultraconics Branson | Welding & Cleaning Equipment | Emerson US

Thanks for sharing the link Dan, that’s super helpful. Sorry for the delayed thanks, I didn’t get a notification about the reply :slight_smile:

Also consider hot plate welding which plasticizes the material locally, creating a good bond without vibration. The drawback is that to completely hide the flash, an added flange is needed. Or consider friction welding which happens at lower frequencies. If the frequencies near those in FCC vibration testing, you almost have a free extra validation test, right.

Thanks for these extra processes to consider Ralph. I’ll keep them in mind too :slight_smile: