Hello, 

I'm part of a student design team looking to make kevlar enclosures from a negative mould. I've done work in the past with carbon fibre in an MDF mould, which I sealed with gelcoat. However, gelcoat was a huge pain to work with, didn't sand well, poor surface finish, etc.

This time I'm looking to use either aluminium or closed-cell polyurethane foam, which I will be machining on a CNC router. What sort of mould release agents should I use? Is just a wax and some PVA ok? Are there better mould materials to use? These are very low volume, room-temperature VARTM process moulds, 2-3 pulls max so I'm not concerned about long term durability, just ease of machinability and low price. The parts are also very small, largest is about 150x125x54mm. 

Thanks for your help!

Your parts are quite small, you could probably buy appropriate size tooling board from Easy Composites and it wouldn't cost too much to ship? I've bought epoxy tooling board from Easy Composites before, and shipping to Australia wasn't too bad. 

Otherwise, you can use a polyurethane foam but these are not the same composition, and even the high density versions will be very porous on the surface. To seal these you would have to skim it with bodyfiller or cover it in fibreglass etc. Not great for dimensional accuracy.

Honestly, tooling board is your best solution. Aluminium will be miles more expensive. Everything else will require a lot of refinishing to get a good finish.