Composite mold making questions Options

[TonyAKAVW]

I want to make a diffuser/engine pan for my car, and last night I started gluing foam sheets together to make a mold. My plan is to form the foam into the shape I want and then seal it with body filler, and then primer and polish. I have been reading up on making molds for composite work and most seem to talk about making a copmosite piece for the mold rather than what I am planning. If I make my mold as described will my composite part rip the mold apart when I seperate the two? (assuming I use a PVA mold release film).

Also, if I make the part with carbon fiber, how do I finish the edges of the piece when I'm done?

I would like to vacuum bag this part because the part will be visible from the top and the bottom... Can I get away not bagging it and get a decent finish? (I'm not super concerned that it has a perfect surface really).

-Tony

Finished part will look something like this...

With the long straight edge meeting up against the firewall and the two tunnels exiting right under the bumper.

[TonyAKAVW]

Felix: Not sure about what you mean in terms of what I'm making. The mold that I'm working on should end up looking like this:

Basically its a foam piece (with sealer and primer, etc. on the surface) and then I will layer the cloth on top of that. I will probably use some kind of mat between CF layers to reduce cost, but this large foam piece won't be part of the finished product. The whole foam piece will be glued to a 1/2 inch MDF board. Which in turn will be supoprted by 2x4s. I figure that should help during the vacuum bagging, to prevent mold warpage.

-Tony

[okieflyr]

My experience is vacuum bagging 60" composite model sailplane wings panels.
We use mylar for the surface finish which can come out beautiful when doing paint design transfers.(no pinholes)
My suggestion is to bag ALL your individual precut pieces flat, and lay in your spars and predetermined attatchment points within your lay-up.
Then you can assemble the pieces. You may have a hard time getting the bag to conform to your concave 90's and get some flooding. (not the worst place though).
Blue or pink extruded foams work well with the epoxy finishing resins, and there is no sealing requirement, but it won't deal with direct heat well.

Kevin

Felix: Not sure about what you mean in terms of what I'm making. The mold that I'm working on should end up looking like this:

Basically its a foam piece (with sealer and primer, etc. on the surface) and then I will layer the cloth on top of that. I will probably use some kind of mat between CF layers to reduce cost, but this large foam piece won't be part of the finished product. The whole foam piece will be glued to a 1/2 inch MDF board. Which in turn will be supoprted by 2x4s. I figure that should help during the vacuum bagging, to prevent mold warpage.

-Tony