Composite Vacuum Resin Infusion

[buzzard]

Looking over the forums upcoming at Oshkosh this summer, I see one by the name "Composite Vacuum Resin Infusion". It is being presented by a guy that is building a composite scale replica of an F4-U Corsair. Anybody familiar with this technique or what it is?

 

I also see that Marc Z. is presenting on the Cozy. Hopefully, lots of builders will be there to support him!

[Wayne Hicks]

I believe the class might be about SCRIMP or VARTM.

 

SCRIMP = Seeman Composites Resin Infusion Molding Process

VARTM = Vacuum Assisted Resin Transfer Method

 

These are two popular methods which infuse the resin by vacuum. Fabrics are laid up as a dry stack of materials onto a mold. The fibre stack is then covered with peel ply and a knitted type of non-structural fabric. The whole dry stack is then vacuum bagged, and once bag leaks have been eliminated, resin is allowed to flow into the laminate. The resin distribution over the whole laminate is aided by resin flowing easily through the non-structural fabric, and wetting the fabric out from above.

 

It's worth bookmarking this site:

http://www.netcomposites.com/Education.asp

 

There's a picture of each process on that website. The pictures are worth a thousand words.

 

...Wayne Hicks

[douglasrfix]

...It's worth bookmarking this site:

http://www.netcomposites.com/Education.asp

 

There's a picture of each process on that website. The pictures are worth a thousand words.

 

...Wayne Hicks

Several thousand more words

 

http://www.fram.nl/workshop/controlled_vacuum_infusion/cvi.htm

 

and we think we do big layups

[mjgundry]

Yet another link:

 

http://home.houston.rr.com/pieceofwork/

[velocity dreamer]

I have a couple questions regarding infusion. everything I see on the net have to do with building boats in molds and not aircraft wings where there are no mold edges to seal the bag to. Lets say I wanted to do the bottom of my wing, I position the fiberglass, peel ply, and distribution layer. After putting my hoses in place what would I seal the top plastic to.

 

Second item.

the plans say leave 1/2 inch or so around just hanging over the edges to be trimed later, obviously this wont work if putting a vacuum to the area. Can you trim even with the edges before putting In the bag, or Is there a reason for leaving that 1/2 in .

 

Thanks

Lynn

[Jon Matcho]

I can't imagine how this approach would be worthwhile in the context of what we're trying to accomplish. You're talking about making molds (a project in itself), which would only make sense if you were looking to create a kit business or make a half-dozen planes for some reason.

 

Basic vacuum bagging, on the other hand, is in the gray area. If you've never done it, try your hand in the inexpensive "LoVac" technique. You can achieve some very good results that way.

 

Even less complicated is what I call "pressure bagging", where you do your hand layup per plans, cover w/peel ply, cover w/6mil plastic, cover with an old fluffy quilt, and then cover with a slightly weighted board. Of course this is only most useful for flat parts -- I did a couple bulkhead sides this way -- but it gives you some experience.

[velocity dreamer]

From what I have read, if your going through the hasstle to vacuum bag it why not infuse it also. Add another hose or two and give yourself more time to make sure everthing is perfect. Its cleaner, and possibly save on resin. Im not into it for the weight savings as it may be minor, but Im into safety. lesson the risk of delamination, stronger parts.

 

Im not wanting to make molds. My question was how to seal a bag for infusion without a mold. example the wing, only glass one side at a time. I'm willing to put a little more money and setup time into the process if it makes the overall job a little easier and gives me a peice of mind of how well its built the day I fly it the first time.

 

Sure there is a learning curve. But once again I feel there is a learning curve on hand layups. I can picture myself squeeging the heck out of it only to have to add more resin or leave to much on in fear of having dry spots. It takes practice eiter way.(correct me if Im wrong).

 

One thing ive noticed reading these threads, is that there is a better way of doing just about everything stated in the plans. Heck the long-ez plans are what 20 years old. Major imporvements since then. How many people have bought electric scissors to make trimming easier. Or going to try post curring to make the part stronger. We are all out to improve our planes.

 

Thats just my oppenion though. I could still be miss informed

[Jon Matcho]

From what I have read, if your going through the hasstle to vacuum bag it why not infuse it also.

Vacuum bagging is much more involved than a hand layup. Resin infusion requires a mold of some sort -- as does vacuum bagging -- as well as a special type of resin (more watery).

 

Its cleaner...

I'm sure it's cleaner at the Cirrus factory, but be prepared to get dirty in your shop. Epoxy is messy business, but nothing that you can't deal with. Have a jug of vinegar around and a can or two of acetone and you'll be fine.

 

...Im into safety. lesson the risk of delamination, stronger parts.

There are thousands of these planes built "the old fashioned way" of hand layups that have no delamination. What cases do you know of where delamination has occurred?

 

Im not wanting to make molds. My question was how to seal a bag for infusion without a mold.

You need a mold. Open foam is not a good mold for high-vacuum operations.

 

I'm willing to put a little more money and setup time into the process if it makes the overall job a little easier and gives me a peice of mind of how well its built the day I fly it the first time.

Vacuum infusion will NOT make anything easier and I would not be confident that anything would be safer. These planes are built tough -- they don't suffer catastrophic failures aside from when they meet the Earth at high speeds.

 

Sure there is a learning curve. But once again I feel there is a learning curve on hand layups. I can picture myself squeeging the heck out of it only to have to add more resin or leave to much on in fear of having dry spots. It takes practice eiter way.(correct me if Im wrong).

Let's not say that you're wrong -- you just haven't done a hand layup yet. Treat yourself to the practice composite kit at Wicks or Aircraft Spruce and do a couple hand layups BEFORE you spend $$$ on vacuum bagging supplies.

 

Everything can be made better, and some things work just fine as-is. My opinion is that vacuum infusion is "out there" and it will definitely NOT be worth your time. You can get everything you're looking for through well-done hand layups. If you're adventurous, you can try your hand at "regular" vacuum bagging (some think this is very overkill). The key is NOT to over-think step 10 before you even start step 1.

[chasingmars]

Jon's got some good advice above... Advice I should have taken... Don't get me wrong, I'm still happy and having fun getting my vacuum setup going, but I've spent about $2000 I probably needn't have on good vac bagging supplies and such. I've spent a good long time trying to get it to work, made a bunch of test panels and no parts yet save for lots of carved foam for when the setup works right.

 

I've done precisely one hand layup, hit wieght near enough to exactly what I'd like to build to, and had I just done this and skipped vac bagging, I'd probably be mostly through chapter four by now.

 

Flip side, resin and glass, while pricy, aren't the predominant cost driver on the aircraft and an extra $2000 is only about 5% if it's worth it. It has yet to be so, but that will hopefully change once I fix my vacuum regulation issues...

 

we shall see... I may have a bunch of vac bagging stuff to sell you

 

Anyhow, as for infusion, that's a whole different level of complexity. The vacuum needed for it to work well may be too much for some of our foams, especially wings, and you might need complex modeling software or a dozen trial runs to get the flow pattern right to produce good results. infusion is not really a one-off production technique suitable for aircraft... looked at it in some detail anyhow, and that was what I came to.

 

For what it's worth...

 

Craig.

Plans #1457

[Jon Matcho]

Advice I should have taken...

Me too.

 

...but I've spent about $2000 I probably needn't have...

Don't beat yourself up, I think everyone does. Still, I can't imagine what could cost $2,000. A super duper pump? Tons of supplies?

 

I have since been told, "Don't buy anything in advance, including parts, tools, and supplies. Buy as late as you can, and only then will you know what you NEED."

 

Personally, I found 95% of my investment in the LoVac (cheap) approach to vacuum bagging to be worth every penny (I bought one silly tool and over-built another).

 

...$2000 is only about 5% [of the aircraft] if it's worth it.

You may want to check yourself --the airplane you want to build costs much more than $40,000. That's a nice baseline/target though.

[chasingmars]

Me too.

Don't beat yourself up, I think everyone does. Still, I can't imagine what could cost $2,000. A super duper pump? Tons of supplies?

.

Tons of supplies... my supplier is a five hour drive away and by yard is about twice the price of by roll, and I'm a jump in the deep end with both feet kind of guy sometimes...

 

So yeah, $100 bucks for a homemade resevoir system, $400 for a nice compressor pump that I justified half as "I can use a big compressor" and half as "I can draw vacuum with this", a thousand feet of 15 mil plastic that I use for just about anything needing plastic cause in bulk it was "only" a buck a yard, a 100 yards of bleeder breather, a hundred yards of coated peel ply (in addition to the 10 yards uncoated that'll make the tapes called for in the plans), 40x 25 foot rolls of vac bag tape (like chewing gum) which when I first tried thought "why didn't I just use tape" but now love cause it works so well .... list goes on...yep, a good $2000... vac bagging is expensive if you buy in bulk, and more expensive if you don't. I'm a perfectionist, so I'll take the time to get this working, but knowing what I know now, I can't honestly say I wouldn't rather just be hand laying. But I am having fun with it, and that's more important to me (and better I think for completion) than just doing the hand layups and wondering if I'd be having more fun the other way... and of course there's one more reason I'm bagging, also part of being a perfectionist... I can't leave well enough alone... if I hand layed, I know I would be messing with it until it had cooked and probably ruin things for overworking something that should have been left well enough alone. With the bag, once the vacuum is on, it *has* to be left alone, and you can't mess with it, it's done, for better or worse, and you'll find out which when you tear of the peel ply and plastic.. oh yeah, that's the real reason right there... it's like christmas every time, unwrapping the parts when they are done, even just the test panels I've done... but is it rationally worthwhile? No.

 

 

You may want to check yourself --the airplane you want to build costs much more than $40,000. That's a nice baseline/target though.

Oh yes, that's true, but as you say, baseline target, of the sort it's the most I'm willing to commit to at any point in time, so now that I'm 6K in, and 40K to go, I'm ok on budget

[Jon Matcho]

Yikes, that's a ton of $$$. You should be able to do some nice stuff with it, but I personally feel the LoVac route is so much better for an introduction into vacuum bagging. Now you have to get yourself through chapter 4. I don't recommend vacuuming chapter 5, but you can try at risk of having to redo the whole chapter (I only vacuumed one small part). My point is that there are some steps in the plans that are best done as-is, without vacuuming.

 

oh yeah, that's the real reason right there... it's like christmas every time, unwrapping the parts when they are done...

Believe it or not, the same joy is had w/pulling the peel ply from cured hand layups. I know what you mean though. Watching the atmosphere GENTLY press down all over your layup is a wonder in itself. Seeing what actually happened the next day -- and having that turn out to be GOOD -- made it worthwhile for me (the $200 I invested).

[Maarten Labordus]

Vacuum infusion will give you a better quality laminate than hand lay-up with respect to void content and fibre volume content. But only when performed correctly. It all depends on the details and a basic knowledge of what you are doing. That's why I always start by giving my students or new clients a bit of theory (Darcy's law, some fundamentals on vacuum vs. pressure infusion etc) before I show them the process. My personal experience is that is far easier to have inexperienced people achieve good laminate qualities by vacuum infusion than by hand lay-up. Yes, there are some requirements to tooling (airtight). No, the process does not need to be expensive. Most stuff can be bought in simple hardware stores. Determining infusion strategies can be done by sophisticated simulation software, but common sense and maybe some simple lab tests will get you there aswell.

 

Some papers on infusion projects can be downloaded from our website: www.lightweight-structures.com

[Jon Matcho]

Welcome Maarten...

 

My personal experience is that is far easier to have inexperienced people achieve good laminate qualities by vacuum infusion than by hand lay-up.

That's very interesting...

 

Yes, there are some requirements to tooling (airtight).

That might be the deal breaker here. Our building process -- one that is not easily changed, although it can be with a bunch of effort -- does not allow for tooling. The tooling, in our case, is often rather flimsy foam. Many of our parts are flat, so maybe there is an opportunity.

 

No, the process does not need to be expensive. Most stuff can be bought in simple hardware stores.

That's critical for this crowd -- many of us are building airplanes from plans rather than kits.

 

Some papers on infusion projects can be downloaded from our website: www.lightweight-structures.com

Nice site. Looks like fun stuff.