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Bud Carlson
Bud Carlson • Aug 21, 2016

Ultrasonic Welding

Is anyone here able to help me out with some questions about the ultrasonic welding process?

I am having a bit of a problem with solvent welding some polycarbonate parts that I had injection molded, so I've now turned my head in a different direction. I'm hoping UW is the answer to my problems...
We have used methylene chloride solvent bonding for PC with excellent optical and mechanical properties. The two bonding surfaces are first soaked in the solvent till a soft interface is got. the two parts are then pressed together and held under pressure for a few minutes. After this the joint is left free for about 24 hours before loading.
The soaking is important. Unless a softened interface is got the joint will be poor.
Bud Carlson
Bud Carlson • Aug 22, 2016
The issue that I am having I believe (what I'm told by an expert acrylic fabricator) is that the issue is moisture content - similar to when you bond acrylic under high humidity conditions. The PC apparently has a lot of moisture and thus it blushes almost immediately whenever any air gets in contact with the joint.

The joint is actually a lap joint so I'm not sure how I would achieve a soak time without exposing the PC to solvent on both sides of each part when only one side needs to be exposed. It's also a shape that is not very conducive to a dip-soak if that is what you are referring to. Then, clamping the parts would be tricky without marring the non-interface side.

What I'm considering at this point is a UV cured adhesive to achieve a seal (it must be water-tight, but not a pressure vessel) and then a smaller solvent weld to achieve joint strength. Then I may change the part material to PETG or possibly impact modified acrylic so that I can solvent weld without the blushing issue.

Ultrasonic welding is very cost prohibitive and seems to be a bit of "dark art"
Can't spell beer w/o EE
The joint is actually a lap joint so I'm not sure how I would achieve a soak time without exposing the PC to solvent on both sides of each part when only one side needs to be exposed. It's also a shape that is not very conducive to a dip-soak if that is what you are referring to.
We have done lap joins. Just paint the mating areas with methylene chloride and give enough time to soften the surfaces before pressing them together. The problem of blushes has more to do with the moisture in the pellets prior to molding. This is usually taken care of by the molder. The bins are provided with heaters to dry the pellets before molding. Dip soak is not what was recommended. A bit of trial and error may be involved.
Bud Carlson
Bud Carlson • Aug 23, 2016
If I even touch these parts with MC, they blush. That is the problem.
Bud Carlson
Bud Carlson • Aug 23, 2016
If that wasn't the case, I could just bond them with MC and wouldn't need to consider ultrasonic welding or UV adhesive, etc. The solvent bond is very strong, just not clear.

Perhaps I should tell the molder to dry out the pellets...

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