Difficult mold to work with, help?!

[Dienqtran]

Hey guys I'm new to this forum but I have been working work carbon composite and fiberglass for about a year now, but still need much need help on this subject.

I been working on a plug that has very sharp turns and there are area where I can't figure out how to get the fibers into the small "V" shaped crevices. I just need some advice in this matter before I even start making the mold. I have been using vacuum bagging and I'm considering infusion process too. But are there any techniques to prevent bubbles and Voids in the difficult areas that aren't flat and easy? Your advice is much appreciated.

 

[Compositepro]

This is handled by the use of cauls or pressure intensifiers. I'm not sure of the origin of the term caul, and pressure intensifier is really a misnomer but that is what people call it. It refers to placing a male mold piece over a lay-up into a female corner. Its usually made of rubber so that it doesn't have to exactly match the mold curvature. In effect you create a two sided mold in small areas where you have bridging problems under the vacuum bag. You may also need to use intermediate debulk cycles and cut the fibers near the corner to get things to nest into place.

 

[ESPcomposites]

Perhaps this is too obvious, but why not add a large enough radius to help yourself out? I remember having the same problem early in my career. A larger radius, hardly even noticeable, made all the difference.

Brian

http://www.espcomposites.com

 

[berkshire]

One sneaky little danger with caul plates, is that you can over do it with a poor design, and get a resin starved area in your layup.You may have to run several parts and redesign your cauls,to get it right.
ESP has it right, try to get away from the sharp corners in the first place, if you can.
B.E.

 

[Dienqtran]

Thanks guys for the quick reply. Much appreciated, I was actually thinking about using a cual. My concern was What birk, pointed out the part being starved of resin. Maybe using infusion would cuase that but using normal vacuum bagging process instead will prevent this? Becuase resin is already manually applied. Also I wish I could try to avoid this but the design Just will not allow to increase the radius, but I will try to add as much that I can. I think I will go with Compositepro! Most off the process to getting the perfect piece is trail and error, trying to keep error to a minimum that's all!

 

[ESPcomposites]

I would think you would use a caul either way as this is standard practice for what you are describing. I was suggesting to increase the radius as much as possible to increase your chance of obtaining an acceptable result. Depending on your problem, the caul will lose effectiveness over time (silicone does not like heat and pressure). So if you optimize your tool, you could get more life out of it in addition to increasing the acceptance rate.

Brian

http://www.espcomposites.com

 

[bellx1]

Infusion may not fix your problem either. If the radius is too small the resin may not permeate the fabric and fill the gap. If you can't widen the gap you could try prepreg which is can be shoved into corners.

http://www.compositescentral.net

 

[Dienqtran]

Thanks guys all very great advice. I will get this started this coming up weeks and post the result for our entertainment.

 

[Dienqtran]

Ohh yeah and one more thing i have a project wing I been working on how would you guys handle making a mold of it? I usually mold half of the wing on top and bottom then make both sides and put the half together with epoxy. I was wondering is there any othere Megiddo of doing this?

 

[berkshire]

Is this for a model , or a full sized aircraft?
B.E.

 

[Dienqtran]

Model, but I would like the wing to be as strong as possible, I'll be using it for a wind turbine.

 

[Corrosiondoc]

Not sure your part or mold will allow it but make a simple putty to fill the tight radius. Add chopped fibers if you need additional strength. Putty should be applied wet and cure with the overall layup.

 

[Compositepro]

A putty fill will help prevent problems due to vacuum bag bridging but will not help where the problem is bridging of the reinforcement fibers.

 

[MotoMike]

Why not try making a reusable bag from silicone instead of a normal vacuum bag. The brushable silicone from smooth-on works real well. Brush a few layers over your mould and you have a vacuum bag with the exact contours of your plug. Since you are doing wet layup you don't have to worry about resin flow and starvation.

Mike

 

[MotoMike]

Dienqtran,

For your model airplane wing design, check out season 8, episode 5 of how its made on the discovery channel (the model jet episode). They discuss the procedures for bonding wings and the design of flaps in the initial layup that are trimmed post cure. You should be able to find on demand video through Dicovery channel or hulu.

Mike

 

[Dienqtran]

Thank you every one for the help, I have the parts mold so far and about to remove it today or tomorow from the plug! Wish me luck.