Vacuum bagging for molded composite pieces...are there any decent training videos out there??

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Jay Kempf

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Wax and PVA are chemically in different worlds. That is why. I use urethane paint on the mold so I can see what I am doing as I polish it in. If you have an epoxy surface mold and you are putting epoxy laminates on it you want all the insurance you can get to make sure they are isolated from each other.

So for me a mold is CNC cut foam, coat with epoxy, wet sand, paint, polish, wax, PVA, lams... Wax is an isolator the way I use it not a release per se.

I lay up flat parts right on my epoxy surfaced table. I wax the area, the PVA, then lams. Means I don't glue things to the table.
 

Jay Kempf

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Never tried it but dry teflon spray cures a lot of things in other worlds. Wonder if that would work as a simple mold prep. I'll try it on a sample panel.
 

autoreply

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Frekote 700NC (silicon based) is amazing. The first few pulls are ridiculously light compared to wax/PVA even with severe draft angles and multiple pulls between recoating the mold. I will never go back to wax.

O and if you have single-curved parts, just use cheap mold material (MDF) and a single layer of foil as the release mechanism. Dirt-cheap and simple.

A lot of what you wrote is good advice, but I can't agree with that statement! With a squeegee it is easy to introduce micro-faults into the reinforcement (especially glass) and weaken the part. There is no ideal inexpensive method, it all takes some level of skill.
What works great is putting the fabric on foil, pooring a big chunk of epoxy in the middle and add a 2nd layer of foil on top. Then squeegee out the resin towards the edges. The first bit that comes out along the edges is a bit foamy due to air inclusions.

Results are on par with professional hand laminators. Maybe I should've added that you draw your templates on the foil, such that you can cut the wetted fabric to size before you peel off one layer of foil. But the wet fabric with the outer layer of foil attached in your mold, squeegee again, then remove foil.

I still prefer infusion ;-)

BTW silicone coated/treated peel ply is verboten in aircraft structural work. Causes all kind of problems with secondary bonding.
Not neccesarily. We use it everywhere on certified aerospace, just not where you're going to do secondary bonding (glueing).

Billski,

Are you using peel ply on the tool side? Is this to create a bonding surface on the outside of the part? Or did I read that wrong.

Regarding 29" Hg every single industry person I know is using as full vacuum as they can get. But most are doing infusion or high temp stuff and/or prepreg. Maybe not the right benchmark. We used to use small numbers like 8-12" for model airplane stuff when vacuum laminating was brand new 30 years ago. My first rig was a free refrigerator compressor and an empty freon bottle for an accumulator. Worked great. Used it til just recently before I upgraded across the board. What I have now is overkill but I have been doing small scale stuff for customers.
Going to very low pressure, combined with peel ply on your laminate can also suck out too much resin. Better to use perforated foil with breather on top.

Going too low can also make the resin or catalyst (PE/VE) boil away. Most pumps can't go that low, but I have to be careful if I don't have a little head above the part. This is easy to check, if your pump can't boil water by applying max vacuum to water that's 30 degrees centigrade, you're usually fine.
 

Rik-

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Wax and PVA are chemically in different worlds. That is why. I use urethane paint on the mold so I can see what I am doing as I polish it in. If you have an epoxy surface mold and you are putting epoxy laminates on it you want all the insurance you can get to make sure they are isolated from each other.

So for me a mold is CNC cut foam, coat with epoxy, wet sand, paint, polish, wax, PVA, lams... Wax is an isolator the way I use it not a release per se.

I lay up flat parts right on my epoxy surfaced table. I wax the area, the PVA, then lams. Means I don't glue things to the table.
Once you put the PVA down, nothing will stick nor come into contact with the other side.

Thousands of Boats, RV, Airplanes and such are pop'd out of a wax'd mold no PVA.

An isolator between the Epoxy and the polyester can be a barrier layer of primer that can adhere to the mold sufficiently to not pre-release and the epoxy will adhere to and still kick off.
 

Jay Kempf

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Hi Jarno!

Guess you're off the road and working from home like the rest of us. We'll I'm working from the hangar at the moment. Got a set of wing skins in the mold right now. 3D printing internals like spar blanks and servo boxes aileron parts and hinges. Works great on the UAV or scales prototype level. Working my way up to full size at the moment. So much learning.
 

Jay Kempf

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On my layup table 11' x 5' level and airtight and smooth. I used bartop epoxy to level float seal. Tried just wax, tried just PVA. Both had creep and I had to scrape epoxy from around the edges before the sealing putty. Wax only I can't stick tape well to it. But I can put PVA right over the tape and peel it up later. So I do that as a barrier around a flat panel if I have to do it on the table. Maybe my methods due to equipment.

Interesting drawing off too much resin with too low pressures.
 

Jay Kempf

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Jarno,

Foil is release film? Not perforated film? I have used trash bags to make my own prepreg in the past the way you describe. Lately I have been doing lam wet layups in the tool. Have an order of perforated film inbound.

Infusion is in my future.

Nice thing about this whole worldwide crisis is I get to spend all my time doing R&D with no distractions from clients.
 

Gene Young

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Since PVA is basically a glue, wax makes the PVA release easier. Pulling a mold off a plug with steep angles, I usually melt the PVA out with hot water. If you are making a polyester mold off a rare, expensive, or for any other reason you don't want to risk damaging the plug, use PVA so the plugs surface is protected from the solvents in the polyester resin.
Also if your making a polyester mold and it gets too hot for your wax, the PVA will help it from sticking.
 

Rik-

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Since PVA is basically a glue, wax makes the PVA release easier. Pulling a mold off a plug with steep angles, I usually melt the PVA out with hot water. If you are making a polyester mold off a rare, expensive, or for any other reason you don't want to risk damaging the plug, use PVA so the plugs surface is protected from the solvents in the polyester resin.
Also if your making a polyester mold and it gets too hot for your wax, the PVA will help it from sticking.
Water.. Just like with Jello is all that is required to make PVA disappear. Wax has more effort in the wax than it does in getting the PVA off of wax.
 

Kurt Ayres

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Kitplanes had a series of articles about this back in 2010 or 2011 if you have access to their archives.
 

autoreply

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Jarno,

Foil is release film? Not perforated film? I have used trash bags to make my own prepreg in the past the way you describe. Lately I have been doing lam wet layups in the tool. Have an order of perforated film inbound.

Infusion is in my future.

Nice thing about this whole worldwide crisis is I get to spend all my time doing R&D with no distractions from clients.
Foil, release film, or vacuum bagging material. As long as it doesn't stick to your part you're fine. Use thicker foil for rougher plugs/molds.

Hi Jarno!

Guess you're off the road and working from home like the rest of us. We'll I'm working from the hangar at the moment. Got a set of wing skins in the mold right now. 3D printing internals like spar blanks and servo boxes aileron parts and hinges. Works great on the UAV or scales prototype level. Working my way up to full size at the moment. So much learning.
I'm actually at work, leading a prototyping team building aerospace parts. Picture attached ;-)
 

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12notes

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Frekote 700NC (silicon based) is amazing. The first few pulls are ridiculously light compared to wax/PVA even with severe draft angles and multiple pulls between recoating the mold. I will never go back to wax.
Holy crap, you are right about this stuff. I just used it for the first time, and the part literally fell off before I could even finish unsealing the the vacuum bag.
 

BoKu

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Holy crap, you are right about this stuff. I just used it for the first time, and the part literally fell off before I could even finish unsealing the the vacuum bag.
Watch out, though, it's not a superpower. I have one or two molds where, for whatever reason, Freekote just doesn't work, even when I apply the FMS sealer and then the 700. My vinylester primer still sticks to those molds right through the Freekote products, and I have to scrap the part and carefully scrape and sand out the primer and try again. For those few molds, several coats of carefully-applied was is the only thing that works. Bottom line, I'd do a quick test pull on each mold before doing a full size part.
 
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On the tool side of big parts, I go peel ply, peer ply, peel ply, Triax, foam, Biax, peel ply, perfect ply, blanket, bag. The big pieces (wing skins, fuselage pieces) require a crew of willing inexperienced volunteers to get it all done and under vacuum in an hour. I expect too much resin on the mold side, and I need all the help I can get on removing excess resin from that side. I went with two peel ply under there to help get excess resin out. Once the wing is built, there will be a tape along the leading edge, then fill and fair, so I want the peel plied surface.

Billski
Would it be possible or practical (in colder climates anyways) to limit big layups to winter months so you can have a longer window to complete layups therefore reducing the need for extra help? If so is there a lower limit to this? Eg. How cold is to cold?
 

cblink.007

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How cold is to cold?
My experiences have told me with 'absolute certitude' that anything below 65F is a no-go for layup work.

I use EcoPoxy at present for my subscale build, and they have told me 50 ways from Sunday that their product will cure at 55F. So I tried a sample layup. They were technically correct, but the surface was extremely tacky, despite the curing being structurally sound.

So, as a matter course, in my tiny workshop, I set my space heaters to 72F. I have not had not any issues with my layup work. At least with this EcoPoxy product, where post-curing is not necessary.

However, with EcoPoxy unable/unwilling to share mechanical properties data, and the fact that the product I use is now discontinued, I will be using AeroPoxy for my full-scale build.

The folks at PTM&W (who make AeroPoxy) recommend absolutely no lower than 68 for initial cure, then 150F post-cure for 8-12 hours.

If in doubt, call the companies who manufacture the resins of your choice, and they should be able to give you some good guidance on the right temperatures for your particular applications. I can tell you that the folks at PTM&W and FibreGlast are an open book, so take advantage!!

Good luck and be safe!!

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