Vacuum Bagging Thick Parts

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wsimpso1

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I have been vacuum bagging my doors and roof structure in a female mold.

The normal technique for building male and female parts using a mold or caul plate works great. The bag is put on using short extra sections of mastic to put in extra folds of bag film, which allows the bag to conform and follow concave and convex surfaces, cover places where the laminated part has thickness greater than just a few thousandths, etc.

But when I went to build my doors, well the parts are thick. The door frames are built like beams with UNI tape in top and bottom caps and BID at +/-45 for a hat section shear web. Foam cores an inch thick separate the caps. Conventional layups worked fine for getting the skin and skin side UNI tape plies on the mold. But I only wanted 4 BID where the windows fit. How to make a clean break with the vacuum bag moving the plies around a bit as it drew down?

Trick Number One! – A tool was built in the mold with 2 BID against the mold, and then foam to get 1 3/8" thick. It was trimmed to just slightly larger than I what I wanted for windows, buttered with micro, sanded to perfection and covered in release tape. Then several wooden blocks were hot glued to the mold to establish position of the tool. When I did the first door layup, I put down peel ply, 2 BID, and then set the new tool in place over the 2 BID, and duct taped the whole thing to the mold. Then we applied the several plies of UNI tape and vacuum bagged it all. The tool kept the UNI tape from reachign the places where I needed everything to stay thin. After it cured, the tool was removed, the glass was trimmed and faired, and the tool was reinserted.

The cores were applied on top of the UNI tape in layers using hot glue and rested against the tool too. Then came applying the inside caps and shear web. Making the vacuum bag conform to the 1 ¼" deep section began to be a problem. We deliberately left lots of extra bag film in the areas where the par changed thickness. And it worked OK on the doors.

To do the roof, I built it right over the doors in the mold - that way we know they will fit each other. I applied ¼" foam as a surrogate for weather strip, and then followed that with duct tape, both as an adhesive and as a release layer. We then proceeded to laminate the roof in the same manner as the doors. But now instead of the surface that we were bagging being single steps from mold to the top of the part, we had two raised areas with ¾" space in between that was much lower.

The bag could not follow the profiles and ended up bridging the gap between door and raised parts of the roof! And excess epoxy would run down to the local low spot and pool there! And the glass had excess epoxy in it!.

Trick Number Two! – Well, after going in with a mallet and chisel and very delicately chipping the pooled epoxy out of the part, and doing lots of itchy sanding, my creative juices got flowing. When each layup was finished, we started applying peel ply and perforated ply in short strips overlapping each other and that ran across the new and old raised areas. In this way, the peel ply and perforated ply could be driven into good wet contact with the entire new shape. Then we twisted "ropes" out of batting to force down into the gaps between door and roof just like caulking a wooden boat hull, except that we did not use a mallet to put it in place. Then the rest of the batting and bag film would go on, and the parts came out nice, with minimum epoxy and no pooled epoxy in local low spots. We figured all of this out and demonstrated how well it worked just in time for the last layup of the roof...

Ah well, I now have two big gullwing doors at about eight pounds and a fourteen pound rollover cage that is ready to fit to my tub and decks, so I should not complain.

Billski
 

wsimpso1

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I have tried. The pictures are busy with details and just do not tell the story, even to me, the guy that is doing it... I shall try.

Billski
 

Midniteoyl

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Speaking of doors, composites, pics, etc., here's something I thought was cool; using different materials to achieve a cool effect. Like using Kevlar inlaid to Carbon:
 

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etterre

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Speaking of doors, composites, pics, etc., here's something I thought was cool; using different materials to achieve a cool effect. Like using Kevlar inlaid to Carbon:
:ban: Cool :ban:
Is that a Lancair? How was it done? It looks like the Kevlar was cut and laid on top... but I thought Kevlar was supposed to be a real bear to cut - so how were the crisp edges on the letters done?
 

Joe Kidd

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I'd say your correct WB. From my experence's with kevlar reinforcement lay ups on white water boat's as well as fitting body armour I'll be the first to say it doesn't like to cut very cleanly and will fray on the edges while working with it.
 

Gray Out

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My guess is a sheet of kevlar was laid up and laser cut, then placed on top of the carbon for the final lay up. Any other guesses?
I would venture to say the carbon was cut and overlaid on top of the Kevlar? Kevlar is a bear and even laser cuts could leave 1 fiber sticking straight up. Good job whichever way it was done though.
 

orion

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I've seen some pretty good work being done using a water-jet cutter. The fabric is placed between two sheets of sacrificial material (usually thin ply) then weighed down in order to minimize the chance of voids. The water-jet cuts through like a warm knife through butter, leaving clean, sharp edges. It works best with prepregs since the resin acts as a binder, reducing the chance of fraying edges.

The number of layers between the ply sheets can be substantial so that most, if not all of a layup schedule can be cut at the same time.

Due to the nature of the cutter, edge contamination is virtually non-existent and the material can be used almost immediately.
 

Midniteoyl

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Yep Lancair IV.. I got this from a website promoting its sale. Here is what the caption read:

Every experimental aircraft is required by law to display the word "EXPERIMENTAL" in 2 in. high letters near each entrance to the cabin. Most Lancair IV's display the word in the upper part of the door by using an adhesive decal or stitched letters in the upholstery. In order to maintain a consistent look in the door, I decided to cut the letters from a sheet of Kevlar®-Epoxy composite. The letters were then laminated to the door during the final vacuum-bagging process and afterwards embedded in the clearcoat.
So 'in-laid' was my mistake, but the effect is pretty cool.
 
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