Here’s my situation – I’m attempting to make carbon fiber parts using a mold and caul plate for compaction. It’s a net resin epoxy pre-preg system and the problem is that the parts are coming out with a lot of porosity. The parts are bagged super tight with “Mud” so that no resin gets out, so I’m wondering if the air is not able to get out either. They are autoclave cured to spec.
Parts come out the proper thickness, with no resin loss, but with porosity. Anyone have any suggestions?
Vacuum pulls out the trapped air.
Try some air ports until resin starts to come out and then clay it up?
I’m a little confused. You have a mold, and caul plate, and then bagged with “mud” What is Mud?
And if you “bagged” it, with an autoclave, then what kind of question do you have of the air not getting out?
are you vacuuming it? Are you using breather? Then you should have no problem with air getting out.
Got pics of process/parts?
If you’re using a resin dam, it may also be trapping air in the layup. This is something I often have to explain to new engineers. They want to keep the resin in, but in doing so, air stays in too. A semi-permeable membrane is needed to solve this.
Where is the location of the vacuum draw? Is the porosity only against the tool surface, or through the thickness of the laminate?
“Mud” is like extra thick vacuum tape that completely seals the gap between the caul plate and the tool surface. The bag is pretty much just holding the caul plate down until autoclave pressure is applied. Breather is applied on top of caul plate. It’s a pre-preg material right, so unfortunately we cant just vacuum it until the resin flows, and I’m not going into the autoclave mid-cure to clay it up 
The parts are carbon but with one layer of glass on each surface. The glass has been turning white, and there is air all throughout the finished laminate. This has happened to several different shaped parts, from flat parts to L shaped parts ect.
So TET you recommend, for example, laying up the part, placing the caul on, but instead of putting a resin dam, for example run a perforated release film from the caul plate to the main tool like the attached picture, and then bagged like normal with breather. The location of the vacuum outlet has not changed but all of a sudden we are getting this porosity. other then the shown picture does anyone have any suggestions im going to try some test panels on monday.
If nothing in your process seems to have changed, could it be that resin content is lower in a new batch of material?
Perforated release film held down with flashbreaker tape may do the trick.
gases need a way to escape the part. Net resin means you dont need bleeder to take any resin out.
Try making a plate like you show in the picture, air weave on top, and bag it.
Else, what I do is completely seal the prepreg with non-perf release film in 2 sections, overlapped in the middle by a few inches. this way, gases and air can be sucked through, but resin will not escape so easy.
Caul on top of that, breather, vac. bag.
Pre preg has the right amount for the CF PP only…the added fiberglass will need more resin to wet it out.
I had my former Plastics ROP students to make CF PP clip boards with 1x layer FG Cloth (don’t use mat as the binders will not melt out with epoxy resins) on the inside. It wa a little old PP and would work but a little dry…the FG was soaking it up!
But yet the new HS Principal stated I was only teaching a crafts class and nothing educational! :rolleyes: