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

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cblink.007

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I know this is probably a stupid question, but are there any good videos out there that are a good/great "how to" with fabricating & vacuum bagging molded composite pieces? We all know about Building the Rutan Composites and the Mike Arnold AR-5 videos (I have them all and watched them ad nauseum before I did my first-ever layup many years ago), but of the videos I have seen on vacuum bagging and fabricating molded composite pieces, it feels as if alot of detailed steps are missing, namely regarding setup and preparation, and the materials needed. We need good practical input, and unfortunately, my EAA chapter lacks a molded composite SME (I'm actually the resident moldless SME...lol).

I have alot of text on the subject...alot of it, and sure I can probably figure it out on my own, but it would be great if there were some videos out there to help bridge the knowledge gaps and gauge our comprehension.

Thx all in advance, and be safe!!
 

wsimpso1

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FiberGlast has videos.

The single most helpful piece I ever got into is the West Systems booklet on vacuum bagging. It is now available online at their website.

I too am the SME on composites in two chapters... But I do have what looks like an airplane going together in my shop.

I recently found out that a dentist/pilot friend had a bunch of experience in tooling and then in vacuum bagging big sailboats in a boatyard, and he is part of a project to resurrect three gullwing Stinsons, including new carbon fiber cowlings for them.

Billski
 

cblink.007

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FiberGlast has videos.

The single most helpful piece I ever got into is the West Systems booklet on vacuum bagging. It is now available online at their website.

I too am the SME on composites in two chapters... But I do have what looks like an airplane going together in my shop.

I recently found out that a dentist/pilot friend had a bunch of experience in tooling and then in vacuum bagging big sailboats in a boatyard, and he is part of a project to resurrect three gullwing Stinsons, including new carbon fiber cowlings for them.

Billski
I'll take a look at West's site! I have my subscale proof of concept bird coming together...all moldless sandwich construction. But, on the full scale design, we are planning to do all moldless on the prototype...with the exception of the engine cowling. I know how to make a great plug, and even have learned the art of making a mold. I just need to learn how to make a nice molded part. I was hoping that there was some instructional video out there like the ones I mentioned above; it is difficult to grasp the concepts in any of the sub-10 minute videos out there.

Should our design prove itself well in testing, the production variants will be made from molds!
 

Jay Kempf

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I'm a little farther along the curve than you but I agree a real practical hands on blow by blow treatise on the subject would be a lot better than suffering through a lot of unrelated YouTube videos and some texts I have. I have some industry guys that I call and lean on when I get stymied. So far I have managed to get a CNC router to directly cut out female molds and wet layup and bag carbon structural cloth into them. I built a really nice airtight table with manifolds underneath and a regulated vacuum source with reservoir. All that works great. So far laminate trials have been good and bad. I know know what it takes to get a good part out of the mold with good surface finish and make sure it won't stick. Learning about different peel ply vs. release film, breather, bag, etc... to use to get what I want and to prep for secondary bonding. A lot of it is inventing while you go and just trying what you think seem like the right approach. Fortunately my projects have been scale mockups and largish UAV stuff so walk before running is always good. If you need any sources I might have them for both equipment and supplies. Just ask.

Maybe we can all just learn together as we go.

I am heading toward infusion rapidly. I use 3D printed parts for components like bag taps and other things you have to buy or you want to have a different design. Been working so far.
 

Gene Young

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I am new to the site and aircraft construction, but I have been doing motorsports composites for 10+ years.
Here is one of my composite projects, all the panels are carbon fiber.
IMG_5351.JPG

I can give you tips on how to make parts the best and easiest way.


You don't need an expensive vacuum pump. Here is mine, it's a compressor from a water cooler I got for free. I have been using it for ten years.
You can see I have a small fan to keep it cool, you should have a switch so you can turn the fan off, to reduce the noise when you are trying to find leaks in your vacuum bag. I have a shutoff valve, I never use it, a vacuum gauge, and a automotive fuel filter hooked to the inlet of the pump.

DSCF1838.JPG

Don't ever wet out your carbon in the mold with paint brush a , unless you want a heavy, weak part, wet it out on a table with a squeegee and the blot out the excess resin with paper towels, then you can put the wetted out carbon in the mold like pre-preg and use paper towels to press it in place and to remove wrinkles. Also this method is the only way you can use honeycomb core, every other way will fill up the core cell with resin, making it very heavy.
I will try to make a video of this, I am getting ready to layup a part soon.
Loctite Frekote 770-NC is the best release agent I have ever used, use it with the FMS mold sealer, and you parts will fall out of the mold and have the best surface finish.
Use silicon coated release fabric, "peel ply", the perforated release films will not remove the excess resin as well as peel ply.
Use two layers of breather cloth to soak up the excess resin. You will always be battling excess resin unless you are using real pre-preg, which requires an oven to cure.
Excess resin will cause the part to be heavy, weak, and have a bad surface finish.
DSCF1847.JPG
If your parts have places that look like this , first you have too much resin, second the carbon fabric was not pressed down into the corner of the mold and "bridged" the corner. Another cause of bridging is not using a slippery release agent like Frekote. If you don't use Frekote and use a release agent like PVA the vacuum force can clamp the fabric and not let it slide into the corners of the mold.


20200329_204415.jpg
Here is a louver panel I did using Frekote, and silicone coated peel-ply, no bridging, or bubbles, and the part is light, just a few ounces.

I will try to add some other tips when I get a chance. There are a lot of tricks to make a good vacuum bag.
 

User27

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Don't ever wet out your carbon in the mold with paint brush
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.
 

Hot Wings

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micro-faults
I haven't heard of that issue,
I too had not heard this. Kind of made a little sense to me since I have managed to break BID carbon cloth during dry handling so I did a little looking. Found this:



BTW silicone coated/treated peel ply is verboten in aircraft structural work. Causes all kind of problems with secondary bonding.
 

cblink.007

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I too had not heard this. Kind of made a little sense to me since I have managed to break BID carbon cloth during dry handling so I did a little looking. Found this:



BTW silicone coated/treated peel ply is verboten in aircraft structural work. Causes all kind of problems with secondary bonding.
FibreGlast has a DVD on composite construction- all different aspects and techniques to teach. Only hangup is that its $99. I am going to try reaching out to them to get more info, as its only just over an hour in length. Given how potentially complex some of my texts indicate vacuum bagging and infusion can be, I'm averse to dropping a hundred clams on a subject video thats only an hour long, you know?

Rutan's video is over an hour long and barely scratches the surface on moldless construction...
Each of Mike Arnold's videos, all five of them, are well over an hour each...

Based on the input you all are giving, it looks like there are alot of ways to skin the proverbial cat!

The questions I am trying to get answered correctly are:

1. I want to do a fiberglass sandwich layup over/inside a mold. How should I set up for this?

2. There is a plethora of blanket, perforated sheet and peel plies available. Which ones do I need for fiberglass layups? Carbon?

3. Mold release materials. Is wax under PVA acceptable or not?

4. Vacuum pressure; what setting? I keep reading about 10-15 psi for alot of layups. If that is the case, why do I need a vacuum pump powerful enough to suck a golf ball through a braided hydraulic hose?

5. Are there any sure-fire "rules of thumb" in bagged/infused layups, like there are in moldless construction?

Like I said, apparently there are alot of ways to do this. Texts are great...but a good video to help close the gaps would make for a more efficient learning experience! We do not expect to be perfect at this right out the gate...but we want to be on the right path!!

Thanks all!
 

Jay Kempf

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Wax under PVA works fine. Never stuck a part in a mold.

10-15" Hg is not enough for wet layup parts in a mold. You will not get into small details and you won't extract enough excess. My rig regulates at 29" Hg.

Peel ply and breather combos help to extract excess and distribute vacuum to all areas. Perferated release film (PETG I think) is really designed for prepreg but it can be used for wet layups but you might trap some resin you wanted to get out of the plys. It gives a smoother surface than peel ply (Dacron).

I'm still experimenting with all this stuff. Wish there were rules of thumb.

Haven't tried FreKote or FMS sealer. Getting the bag into tight corners is always a problem. I intend to try 3D printed preforms to go in small details. Or cut off the sharp corners and glue them on later like fillets.
 
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User27

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micro-faults
I haven't heard of that issue, can you tell me more about it?
Some years ago someone smarter than me was wondering why glass composite does not achieve anything like its predicted strength. The reason is handling of the dry glass cloth introduces small "micro-faults" into the fibres that reduce their strength, and so the strength of the laminate. Therefore minimize the handling of the cloth from the roll to the mould. The same is true to a lesser extent for carbon. Using a squeegee without much skill will do the same. I almost always use a brush, except where I have a large reasonably flat layup to wet out. Yes it requires care to ensure the layup is not too resin rich, but resin starved is as much a problem. I rarely use a vac bag as I am mostly moulding small parts and carrying out repairs.

I don't think it matters exactly what is used. Most of the texts show the various layers required. I have on occasion made my own perforated release film from polythene sheet (or bagging film) with holes punched in with a pad of nails spaced an inch apart. Peel ply is not always required - it depends if anything will be laid up on the part. Start experimenting on smaller flat parts that are expendable. Figure out what works and what doesn't.
 

wsimpso1

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So much information, and so much of it can be misleading. While there seem to be some standard things you need to do, I gotta say it, it is largely a matter of what works for you with your materials, processes, and shop.

29" Hg? I go for 22" Hg and am happy with 20". My current pump came to me with two cylinders plumbed in series to get big vacuum. I swapped it around so the two cylinders pull in parallel. I can pull down a part quickly to 22", and then it cycles there. With it in series, it takes twice also long to evacuate the bag, and it can have a hard time getting to decent pressures if I have even the tiniest of leaks.

My big parts are made of "knitted" cloth, peel ply on both sides, perforated ply between peel ply and batting, and the come in about 35% resin by weight. Using twill cloths, my parts are more like 40% resin by weight. That works... Get into complicated parts and your resin fractions will go up some. All of these have tested stronger than book values...

Perforated plies are great in my mind. All resin that can be squeezed off by compacting the cloth can come off, and that is good. Put batting directly on the part and the batting can wick resin from the stack. When I left out the perforated ply, my stuff got only a little lighter, was a bear to peel, and looked really dry. When I tested those sorts of layups, they came up short on strength, with inter-ply fractures.

Wax and PVA. Molds should be made smooth. The smoother the better. Once they are perfect for shape and close to perfect for surface, then you wax and buff. Do not leave any wax un-polished, as it can get into your part. After it is waxed, PVA is a great thing to add as it helps get the part out of the mold.

I have never found the expensive peel plies to be worth the extra money, and you need to make sure that they are compatible with your resins. If they dissolve in your resin, you have scrap parts. They might look fine, but they are scrap. For most of my stuff, Wicks used to have cheap polyester cloth that worked great.

As to how to make molds and such, you can look up my stuff. The folks at West System have a lot of info. I have done molds and make many of my parts. They work. Other people may do better. Experience is something you have after you have made bad parts and fooled around and finally started getting good parts.

Billski
 

cblink.007

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Perforated plies are great in my mind. All resin that can be squeezed off by compacting the cloth can come off, and that is good. Put batting directly on the part and the batting can wick resin from the stack. When I left out the perforated ply, my stuff got only a little lighter, was a bear to peel, and looked really dry. When I tested those sorts of layups, they came up short on strength, with inter-ply fractures.
Your points make a ton of sense...but what is batting? Is it the same as the "blanket" material I see by the metric ton at FibreGlast?

At this stage of the game, we are working solely with fiberglass...but will likely go carbon fiber down the road...
 

Jay Kempf

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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.
 

wsimpso1

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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.
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
 

cblink.007

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Triax, foam, Biax
Just out of curiosity, whose biax and triax do you use? We are planning a single ply of 20 oz triax on both the top and bottom exterior wing skins of our full scale prototype (slated to be done in moldless form as of this writing), with variations of BiD and Uni on the interior structures. We are sourcing ours from VectorPly.
 

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Rik-

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Why is everyone waxing if your using PVA? PVA is a mold release itself and sprayed over a waxed surface or a rough surface doesn’t make a difference.

Polish the mold, wax the mold and spray your gelcoat or if you like fixing pin holes, spray primer or nothing and deal with all that extra work.
 
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