Method to Retain a Small Disk within plastic

[CPosner]

I am trying evaluate methods to permanently retain a small disk, .75" x .125" in some plastic.

I have come up with 3 ideas, but not so sure of the cost effects and manufacturability of each.

Insert disk and sonic weld cap on...Needs to be strong bond.

Drop Disk into slot and Glue/Sonic weld cap to retain

Snap Latch..No so sure about designing these still.

I'd like to permanently retain the disk. I think Molding it in would also be nice, but the disk has a 170degF limit. Don't know the cost of that either..I can possibly substitute for high temperature material.

So I have 4 Options..Need good retention strength. Water tight would be a plus, but Do I have to be concerned if this is brought on an air plane and increased pressure differential causes a break at the seal? Something I have to analyze. Also, I need to be able to predict the sonic weld strength. Mostly thinking out loud here.

Thanks

 

[esqrkim]

You cannot insert mold the disk unless you're willing to live with a small openings to the disk. It looks like making it water tight is not essential. I'd go with the snap fit disk method. It's clean. Straight forward in terms of tooling and molding. No post op. Hey, what more could you ask for? It's not worth throwing this idea out just to make it have a "plus" feature.



**My comments are my opinions, and results are not guaranteed**
Eugene Kim

http://www.eeksolutions.com

 

[patprimmer]

Your sonic welded design sounds best to me. Done properly it will be watertight even under adverse conditions, but it does need god design and good processing.

You might also spin weld it.

Adhesives will work with the right materials. Take PVC pipe for plumbing systems for instance.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CPosner]

Thanks for the replies.

I'm kind of torn between the snap and welded cap. Welded cap Introduces another step in the process and another tool, making the Snap more viable, but the I like the aesthetic of the cap. I think I will need to review. Also, I can use a Disc with a hole in the center..and maybe use a "push-in" snap cap to retain the part.

But the center hole needs an undercut for the push-in snap cap. I'll have to think about that..

 

[MikeHalloran]

If you're willing to use two parts, you could make it from two identical parts. Just trim off two opposite tangs, and the cover becomes self- conjugate. One up, one down, both snap over the disc with two tangs each.



Mike Halloran
Pembroke Pines, FL, USA

 

[esqrkim]

CPosner:

Is having a pleasing aesthetics a design requirement? Is it a company goal or a personal goal?

If it's a company goal, then no one should have any issue about spending the extra money on tooling, molding, and assembly. The "push-in" snap cap or some form of molded cover as MikeHalloran suggested sounds good. By the way, for molded-in disc option, it would require at least two holes on either side of the disc package. More holes may be needed depending on what it would take to hold the disc in place during the molding op. You may even have to settle for the less productive vetical molding with operators hand-loading the discs.

If meeting an aesthetic requirement is a personal goal, during a design review, how would you justify the extra costs to produce the more asethetically pleasing part?


**My comments are my opinions, and results are not guaranteed**
Eugene Kim

http://www.eeksolutions.com

 

[CPosner]

Aesthetics is a personal goal and also a company goal, though in the end, performance is everything. We will decide, but cost is a driving factor in the parts and what designs we will end up with.

Another option is to screw-fix the disc into the part. I think that may be the most economical method, but not those most aesthetic.

 

[patprimmer]

If it has to stay waterproof long term, and if a high reject rate for the encapsulated component is not acceptable, I would stick with the first design and ultrasonic or solvent welding.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Pud]

I would guess that the money saved in tooling cost by going ultrasound welding (i.e. straight open and shut tooling, simple cavities) would buy you a second hand welder and tooling.

Agree with above that it would be the neatest solution by far.


Cheers


Harry

 

[bvanhiel]

I would use a disk with a hole and slide it over a post in the plastic. Heat stake it down and your done. An additional tool/step, but a simpler one than an ultrasonic weld and more secure than a snap.

-b

 

[patprimmer]

-b

That doesn't sound real watertight.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CPosner]

Watertight isn't the most critical issue, just a benefit. The disc is nickel plated, and I am currently testing these in sea water for corrosion. If my samples corrode/break down, then watertight will be the only option.

 

[MikeHalloran]

I don't trust ultrasonic welds.
Solvent bonding is better, imho.
Or just gob the cavity full of hot melt.



Mike Halloran
Pembroke Pines, FL, USA

 

[Pud]

Assuming it's possible to solvent bond - or even CA glue.

If it's ABS or similar, then no problem - apart from getting solvent/glue on the outside and ruining any aesthetic finish required. There is also these days the health and safety aspects of using solvents. Not loved by all.


Rgds


Harry