Talk Composites - The Forum for Advanced Composites

Advice for hand laying on a car bonnet

http://www.talkcomposites.com/Topic40526.aspx

By jameslawson - 11/13/2022 1:34:15 AM

So I have laminated small car interior trims with carbon fiber in the past, however now I'm embarking on a much more ambitious challenge..

I want to wrap the middle of my car bonnet in the V style carbon fabric. I bought a spare second hand bonnet which is made from aluminium and is sort of flexible.

My plan is to palm sand the paint off, prep the middle area, spread on some base coat, hand lay the fabric, vacuum bag it for a perfect flat result before then painstakingly applying the resin coats.

Is there anything I should be reconsidering or not doing here with this plan? I have always used the XCR epoxies but I'm worried about the heat resistance.. it doesn't get super hot but the car runs a pretty warm inline 6. Will the XCR resin stand up to this or do I really need to go with the high temp epoxies which have that unfortunate yellow look to them?

Here's a mockup I made in photoshop.. ideally I'll overlap the middle, then when its complete my bodyshop who's going to paint it will presumably use filler to blend between the epoxy and aluminium to create a seamless transition before painting the main and power dome section.

 

Many thanks - I really appreciate any advice that can be provided. In my mind this is just one huge panel that I need to hand lay, but I will only have around 2-3 weeks to complete this in due to garage space so I want to try and prepare for everything.
By Hanaldo - 11/30/2022 5:49:43 AM

I wouldn't bother with an oven cure on body panels. The panels will post-cure in their working environment, and with skinned parts you have plenty of resin on there to cut and polish into once that has taken place.
Just skin the bonnet, fit it to the car, and use it for several months (preferably through summer). Once it has seen a good bit of sun and engine bay temps, you'll notice the fibre print through to the surface and you'll get a bit of rippling. It will happen quite quickly if the weather is warm. But once it has been exposed to those conditions a few times, you can then take it off the car again, flat the surface down with 800 grit, and then move through to 1200>1500>2000>2500>3000, and finally compound to bring it back to a full gloss.

After that, you shouldn't see the print through come back unless it is exposed to a temperature higher than its Tg again. On a 30 degree day, a carbon bonnet can easily see in excess of 80 degrees. So it may never stay completely flat. But in all honesty, in my experience it is that initial shrinkage that is the worst, and after that it doesn't print too badly even if the bonnet gets up to 90-100 degrees. It's not as bad a problem as you might think.