Metal inserts - Carbon fiber layup


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Trace Elliott
Trace Elliott
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Hello everyone,

I'm designing a drone, and I would like to be able to bolt two plates together (rather than use an adhesive, because if something breaks, I'd prefer to be able to change the piece that broke, rather than a whole assembly).
The plates would be 2-3mm thick, made by resin infusion.
To that effect (bolting plates together), I'd like to put a metallic insert in the lamination, prior to the infusion.
The insert would be a nut, essentially.
I know you can make the plate, then drill a hole and glue the insert, but I'd rather infuse the whole thing at once, if it's possible.

My question is: how do you put an insert in the fiber stack?
I read everywhere that you should have pins in the mould to accurately locate the inserts, but very little info on how to blend the insert in the fiber stack.

Should I spread the fibers apart? I'm thinking that won't look good
Should I punch a hole through the stack? Hello fibers everywhere...
Should I lay the first cloth and spread the others around the insert, and grind the first layer to reveal the insert?

If you have any ideas, please do tell :-)

Thank you very much!
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Dravis
Dravis
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I have actually conducted several tests of bonding in and laminating in metal fasteners (made from Grade 5 titanium) for a small shipyard that builds CF pre-fab parts for medium sized vessels.

I can tell you that there is a very small advantage in strength of the fasteners binding to the actual part, from laminating it inside (vac-bag) or infusing it into the CF laminate.  It is simply only cost effective in terms of the work you need to put into it, unless you need to produce a fair amount of copies of the same part.

Bonding the fasteners in with patches of cf fabric laminated on top retains 90 -95 % of the strength of an "infused in" fastener.

Bonding in a simple standard nut will not be very strong, its much better to have some threaded inserts made, that have a larger surface area to bond to and to spread the load over a larger area of the cf laminate.

I can give an example:   an M5 threaded insert machined as a flat disc 18 mm in diameter has more than 600% higher strength, compared to a standard M5 nut laminated into the CF sheet.

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Do not adjust our mind, theres a fault in reality :-)
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