Thinkin about pre-preg compression moulding

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#1

Just wondering if many have experience of it. Ive been looking at the likes of this thread which briefly touches on void removal which is what Im mainly thinking on.
http://www.compositescentral.com/showthread.php?t=2501&highlight=compression+moulding&page=4

Are there many void problems with the process? ive seen a few papers that seem to suggest that addition of a vacuum (im guessing seals around the mould) assist in void removal but surely this would need to be done prior to application of full pressure, etc.
Also, with thicker parts, would a flow media be needed or has anyone experience with what you can get away with size wise without additional vacuum? Or maybe even de-bulk prior to moulding. sorry for the brain dump - just thinking out loud here!

How do compression moulded pre-pregs (woven) differ from standard pre-pregs? Im assuming they are designed primarily for minimal resin loss/bleed.

#2

Void removal on prepregs is a major issue. Debulking the first, and then subsequent 5 layers or so helps…press molding requires 2 molds, and till define the EXACT shape, including thickness, and density of part. The mold design must factor in production, along with the pressure induced will spread the fabric out a bit. Adding vacuum would not be as effective because there isn’t a full surface to draw out voids. Using membrane, or even perf-release film helps…but that leaves a unfinished surface.
I think compression molding is more for quick production parts. Also the only real way to go for thermo-plastic prepregs. Else using RTM/RTM-lite would be the way to go.