Prepreg mould surface voids

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#1

So, new here, and looking to get some opinions of an issue we’re having at work regarding voids on the surface of our moulds.

Basically, at the moment we’e been struggling to produce our moulds without large levels of surface porosity. Changing a lot of things in the process hasn’t seemed to help too much.
Running the mould cures to high pressure (600KPa), although at relatively low temp (70C ish) due to the tooling board. Debulks after surface ply every time as well.
My personal opinion is that it is a surface breathing issue during cure (and there is one part made that supports that), with minimial vacuum connection to the surface of current parts, but having difficulty convincing my colleagues.

Any thoughts on if thats a good line of thought? or is there something else?

#2

What are the materials you are using and do you have any pictures? We had a similar problem a while ago.

#3

how is your master made? the build up of heat can be different, and much slower than the airtemperature (do you have sensors on your surface? )

I had a problem with parts, with poor surface quality on several spots. The part had foam core on that areas, wich delayed the heating. slowing ramp rate fixed that problem.

#4

Pre Preg ( ESP low temp ) tooling resins are very sensative to cure inhibitors any fillers using BPO hardeners and the like will cause reactions in the surface quality so will tooling board sealers if not properly applied “more of an art form than a science I believe”.
If you are using a well know tooling system contact the manufacturer they should be able to assist. We have had the same issues before and ACG has sent a rep out that made it look so simple. That couldn’t be farther from the truth. The process and prep materials and prep processes have to be followed to a T.

You can repair the surface quality issues with surface fillers and sealer but does require a bit of elbow grease.

Regards
KJC

#5

You did not mention whether you are venting your cures? It helps with reducing gaseous voids. Also, is your material handling up to scratch as excessive moisture in the material will create voids during the cure as well? You could try having glass tows under the release film and protuding from the edge of the laminate to try and facilitate a better breathe!