Chris,

The "big boys" will typically cure the outer skin first, at high temp
and pressure (for say.. a carbonfiber indycar chassis), then follow up
with a honeycomb (nomex or alu) and inner skin at a lower pressure.
The pressure chosen depends on quite a few factors; honeycomb crush
strength, cell size, quality of fittment. Basically honecomb is a
real pain from a manufacturigng standpoint. If you accidentally
expose the edge of the honeycomb to pressure, you will 'walk' the
honeycomb sideways like an accordian; not good. People I've worked
with in the racecar world avoid foam, as it's got no real shear
strenght or stiffness compared to honeycomb so it would be kind of a
waste as a core in a carbon composite structure if stiffness is a
concern. If you were to do a foam core, i'm sure you could find a
resin that cures at a temp below that which the foam can handle, while
keeping the pressure really low. The part would be a low temp part
however.

-Alex
www.nextstepcad.com


On 30 Mar 2004 09:41:25 -0800, (Chris) wrote:

Hi everyone,

I'm just trying to educate myself about composite construction
techniques, and I'm a little confused on the process of using prepreg
materials in an autoclave. Could someone who has done this help me
understand the process?

Assuming I have prepreg cloth and access to a large autoclave and I
want to make a part, say a seat for lack of a better example, what
would I use for core material, and how do I keep it from getting
crushed in the autoclave? Typical foam that I am familiar with will
melt under the 250F curing temperatures, and it seems that a core like
Nomex honeycomb will be crushed when the pressure is applied. I can
imagine how to do a mold, but it seems like any core material will
come out a molten, flattened mess.

Can someone help out a novice understand how this is done? What do the
big boys do when they want to make a high temperature part? I'm having
trouble visulizing how this actually works.

Thanks for educating me. This is just for my own enjoyment and
edification, but alot of people I've asked have the same question.

Chris