Hood Project - Confirmation of Process & Materials

General Composites Discussions Composites Talk
#1

Hello, I’m new here and have mostly been using the forum for research. Now I am getting ready to move forward collecting materials for making my mold and composite piece. I’m looking for confirmation of the materials I’m choosing and whether or not I’m missing something or if I just plain out don’t need something or outright, quite possibly, going at it all wrong.
The plug is a hood for my car. That much I’ve taken care of so far. Next for me is to create the mold. I’m looking to design this thing to be strong due to the size of the mold, storage of the mold, and I may be making multiple products with the mold. So I will be framing and supporting it for durability. I’m more concerned with making sure that the layup process is correct.

The Mold
1)Coat plug with a releasing agent.
a. I’ve heard that Carnauba Paste Wax is great for such tasks.
2)Put down a “Face Coat” (a gel coat I believe)
a. A resin for the face mold that is super tough and polishes nicely and does not have any fiber in it.
b. I believe a polyester gel coat is what I’m looking for here.
3)Lay the fiber glass for the mold
a. Would 4 layers be sufficient for strength and durability?
b. Are there any issues with using a general fiberglass resin here in terms of chemical reactions with the polyester gel coat?

Laying the product (wet lay)
1)Coat the mold with a releasing agent
2)Put down a gel coat for the top coat
3)Follow with an epoxy resin and layers of Carbon fiber.
4)Since this is a hood I will be doing an outside piece and bonding it with an inside piece.
5)I was intending on doing 3 layers of a standard 6oz 2x2 twill weave for each piece
a. Will this be enough strength for a hood on a car that will definitely reach speeds as high as 150mph?
b. Mind you that there is little exterior modification to the hood and the understructure of the hood will be unmodified to maintain OEM structure and support. Also, it will be mounted to the car properly so there are no issues there. My concern is more with the thickness of the material.

Vacuum Bagging
I’m under the impression that vacuum bagging is a must for a good final product, which has given me more questions than answers since it seems there are many different approaches to vacuum bagging.
1)Since I will have the mold framed I was going to tape the bagging material on the outside edges of the frame itself.
2)Since the shape is concave and the underside is more complex I was looking to use a high stretch vacuum bagging film.
3)I was going to use two “EZ-Vac" Connectors at the two points of the hood that connect to the hinges closest to the windshield. Connect the two 1/4” lines by means of a “T” going to the vacuum.
4)I’m confuzed over which release film to use between the hood and the bag. I was thinking a Non-Porous bag film was what I wanted but advice here is welcome.
5)I was looking into the “EZ-vac electric vacuum pump”
a. Has anyone else used this or have comments on it?
6)Does the vacuum need to be constantly running or can you use a valve to shut off the system once the vacuum has reached its full potential?

I think I covered it all, though I may have skimmed over some of the finer processes.

With your welcomed responses could you please refrain from not identifying acronyms, as I’m not in tune with all of their meanings.

Thank you for your time and help

#2

I would recommend against the ez vac connectors. They get clogged up, are a pain to use, tiny and easy to misplace. Get the standard twist type. They’re way better

http://www.acp-composites.com/images/C/L%20-%20V-13C%20High%20Temp%20Vac%20Bag%20Connector.jpg

#3

4 layers of the common fiberglass weights will not be enough to make any sort of strong mold, especially the size of a hood. I’d recommend a thickness of at least 100oz/sq yd. Thats 17 plies of 6oz, or 10 plies of 10oz, or 5 plies of 20oz, etc…

For the hood, 3 plies of 6oz carbon/epoxy will barely be adequate even with the inner frame attached. I’d recommend 6oz plies top and bottom, with an 11oz or 19oz middle ply laid up with ±45* fiber orientation.

What will help you most is to practice on some smaller projects. Make a few simple molds, and try vacuum bagging parts in them. Guaranteed you’ll scrap some material, but at least only in small amounts!

#4

1: yes, make sure you have several inches of flange to tape too. Makes working with the tape and any vacuum tubes easier to work with. Nothing sucks more than having ONLY enough room to do what you need to do!!
2:that works, but also making sure you have enough bagging material and pleat it. You can find many youtube videos on how to pleat bagging (or dog ears, etc)
3: i suggest just using a plastic tube. Any sort of quick connect will get clogged with resin. I only use a tube wrapped with tacky tape along the bag seal line. I then use spiral tube around the edges…this way I get a better air/resin flow out of my part, and then I can throw all that away (there is ALOT of investment material used in composites)
4: for wet-layup and vacuum bagging, use a perforated release film over the composite surface (you can use peelply, and THEN release film if you plan on bonding something else to that surface), and then a few layers of bleeder/breather on top of the release film to soak up the resin that sucks out. The hole spacing and how much bleeder/breather you use, is all part/process dependent.
5: do not know. as long as it can run as in the HIGH 20s ( inch of mercury), and as long as it takes fo ryour part to harden
6: run the vacuum as long as it takes for your part to gel and harden. Running it maintains NO AIR gets in your part!!! I’ve heard of people running tanks along with a vacuum switch. I perfer the vacuum pump stays on, and pumping at 29" the entire time, until the part cures! There are debates and preferences on this, but in the end, you want your part to see full vacuum as long as it is wet.

#5

I have some concerns about the thicker plies of CF (the 11oz or 19oz) and it conforming to the mold that has some intricate sections. Is this an issue? or will doing 4 layers of 6oz for the top and for the bottom pieces be an adequate substitution?

#6

As long as you can get the layers to stay in place, and you have a good bag that will compensate for any odd shapes, it will go where you want it to. Can you post pics on where you think you might have problems? If you can, use thinner but more plys in those areas.

#7

Shouldn’t be an issue, especially with a vacuum bag.
We lay up multiple 36oz plies into molds with tight corners and compound curves without a problem.

#8

If you were to use the lighter cloth with say 4 ply’s and put some paper nomex honeycomb in the flat areas (if you have the clearance) then it should be plenty stiff enough and a little lighter also.

#9

paper OR Nomex…not paper nomex. They are different materials.

#10

Sorry used stupid shop talk, I ment Paper or Nomex H/C

#11

for your mold construction.
After laying down 7-8 plies of 10oz over the gelcoat I’ve often used some wood cut to the shape of the part (with a flat bottom so it can be set on a bench) and then glassed the wood supports into the mold with another 2-3 plies. The added support helps with the stiffness and you then have a stable base on curved parts.