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JLiang
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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!
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Hanaldo
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Group: Forum Members
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Tooling board is ideal for what you are wanting to do, much better than polyurethane foam. You can get a range of densities, basically the higher the density the more durability and the better the surface finish will be, but also a higher investment price. But if you get something around a 600kg density, this will be plenty sturdy for 2-3 pulls (depending on draft and geometry), great surface finish, and still quite affordable especially at the sizes you are looking at.
Sealing wise, you can either prime and topcoat the tooling board, or you can seal and gloss it directly with a sealer like the S120 you can get from Easy Composites. Sealer has a bit of a learning curve with its application, but once you get the hang of it it works pretty well.
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JLiang
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Group: Forum Members
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+xTooling board is ideal for what you are wanting to do, much better than polyurethane foam. You can get a range of densities, basically the higher the density the more durability and the better the surface finish will be, but also a higher investment price. But if you get something around a 600kg density, this will be plenty sturdy for 2-3 pulls (depending on draft and geometry), great surface finish, and still quite affordable especially at the sizes you are looking at. Sealing wise, you can either prime and topcoat the tooling board, or you can seal and gloss it directly with a sealer like the S120 you can get from Easy Composites. Sealer has a bit of a learning curve with its application, but once you get the hang of it it works pretty well. I looked into tooling board fairly early on, but unfortunately I can't find it for an affordable price in Canada. Most of the sites are selling it in 48" panels, which run over $300. By 'topcoat' do you just mean a 2-part paint like polyurethane? I can't find any of what you mentioned in Canada unfortunately, which is why I'm looking at alternatives. Thank you for you insight!
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Hanaldo
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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.
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JLiang
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Group: Forum Members
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+xYour 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. I will look into that! Thanks. As for sealer, is something like a Duratec 707-002 fine? Just to fill in micropores and polish to a shine, correct?
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scottracing
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you will be surprised at the cost of ali tooling against epoxy tooling board,a lot of the tools I make are now made out of aluminiumbescuase of the overall cost is much cheaper.
A good machined and polished ali tool will give very good results with chemical release agents.
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JLiang
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Group: Forum Members
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+xyou will be surprised at the cost of ali tooling against epoxy tooling board,a lot of the tools I make are now made out of aluminiumbescuase of the overall cost is much cheaper. A good machined and polished ali tool will give very good results with chemical release agents. I looked into a few metal moulds, the trouble with my particular part is it's fairly deep, so the stock needs to be quite thick. It does seem easier to work with though! What sort of surface treatment do you do? Just wax and PVA? Sounds like it would save a ton of time.
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KLComposites
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Agreed. Been buying a lot of aluminum from Xometry here in the US, and the price is amazing, even compared to PU board, let alone epoxy.
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JLiang
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Group: Forum Members
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+xAgreed. Been buying a lot of aluminum from Xometry here in the US, and the price is amazing, even compared to PU board, let alone epoxy. Sweet. I'll look into it more. What sort of surface prep do AL moulds need? Just wax and PVA? Thanks for all the help guys.
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Chris Rogers
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I'll second (third?) the aluminum - it's awesome to deal with and at that size it will be a wash money wise. You'll want to sand it to at least 320 grit - more if you need things shiny. Once the machining marks are gone, Scotchbrite works pretty well. Can you split the mold so that deep feature is easier to machine? I'd recommend a mold release system other than wax though - if you can get it Frekote, Chemlease, or other semi-permanent system. Wax will work though if you buff it out and do a few coats. You shouldn't need the PVA - but it will certainly make demolding easier if there's any doubt. Good luck with the kevlar! If you've been doing MDF in the past, any tooling board will be like a dream - but it is so expensive! Gelcoat to seal the MDF is a real hassle though. I wrote up a post about how to get the best out of MDF - if you find yourself doing bigger parts it may be helpful: https://explorecomposites.com/articles/tooling/using-mdf-for-composites-tooling/
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