Plastic welding small parts - best method?

[muddybrown]

Hello,

I have been working on a small plastic part that consists of two smaller pieces and a membrane. You can think of it as two 1-2mm thick plates with a hole in the middle (face dimension ~ 50mm x 15mm) requiring adhesion around the top and bottom edges (edge is roughly 2mm wide) with membrane sandwiched in between. The membrane is made of some type of cellophane-like material. The two sandwiching pieces are made of transparent material, preferably Polystyrene.

I have no prior experience with polymer and need help and suggestions. What would be the best method of welding such small parts? I would like to avoid solvent or adhesive methods. I am looking at heat-welding and ultrasonic-welding. I have no clue which is better for my application. Cellophane membrane seems to have high melting temperature.
If I can weld membrane directly onto one of the frames, then that would be more ideal so I don't need to weld the top piece. Though, I would like to purchase a machine that can do both (membrane-ps as well as ps-ps and ps-membrane-ps).

If you have any suggestion on what method works the best, that would be very helpful, and maybe the price range. I'm looking for something small, such as hand-held type ultrasonic or tabletop heat welder. I don't mind spending money, except I don't want to buy these expensive machines just to "try it out". Want to be sure. If you have a suggestion on a method, I would like to know why and how it works.

Any help will be greatly appreciated!

 

[patprimmer]

It is very difficult to weld dissimilar materials.

It is quite difficult to weld film to plate, but it depends on thickness of film and quality of weld required.

You absolutely need to know the actual materials to be welded.

You need to specify if the weld needs only to be in a few spots or if it needs to cover the complete surface area. You also need to know if it simply locates pieces so they don't move around, if it needs structural integrity or if it needs an hermetic seal.

Regards
Pat
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[muddybrown]

Thanks patprimmer!

I would like to look into welding PS-PS, no membrane (I'll secure the membrane mechanically). The weld can be at few spots around the perimeter of the PS frames instead of the edge length, though it could be either way. The spot/stitch must be less than 2mm in width.
The product will not have any major force applied on them, so basically, I need the top and the bottom frame to be simply joined (though I don't want anything breaking simply by touching it..).

Thank you for your input!

 

[patprimmer]

How will you be making the PS part ie how much design freedom do you have. Can you incorporate holes and dowels that can be hot staked to hold the parts together.

Regards
Pat
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[muddybrown]

Thank you again!

PS will be injection molded during production (right now, machined parts). There is freedom to adjust the design, however, holes will be less than 2mm in diameter and the smaller the better.

Can these hot-stake holes be any shape, like rectangular 1mm x 2mm? I am not familiar with hot staking..

Thank you so much for your help

 

[patprimmer]

Yes they can be any shape,

If you design it correctly with both holes and stakes on one part they can be done in one mould so that the holes in the mouldings line up with the stakes if you flip the part over.

Regards
Pat
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[muddybrown]

Great! I will look into your suggestion.

Do you know anything about ultrasonic welding of small plastics? How do they compare to heat stakes? Costs, ease of use, product appearance, etc. Are there hand-held hot stake machines?

Thank you

 

[patprimmer]

Ultrasonic welders make great heat stake machines

Regards
Pat
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[muddybrown]

Thank you so much for all your input.

I found table top type and hand held type ultrasonic welders. What are the major differences as in performance for small welding application such as mine? I would like to test using a hand-held version, since they seem to be slightly cheaper, but if this is a bad choice (as in they are not suited for small application, etc.) then I would go with the other type. I am looking at Branson and SharperTek handheld versions.

Also, are Thermal Assembly Welders much cheaper than ultrasonic?

Thanks!

 

[patprimmer]

I have given you as much as I can. From here you need to approach suppliers for demonstrations and recommendations.

Regards
Pat
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