Questions about creating fiberglass and carbon fiber die and LARGE parts

[osakamitsu]

Hello, I am new here and absolutely new to the fiberglass mold and carbon fiber mold ideas. Never touched the stuff before. I did watch a video on youtube about the process of making a car roof and it didn’t seem too hard. I would start with making dies for smaller parts. But I have a few questions.

I am building a hovercraft. It will be made of wood and foam in the end. But I had an idea that I may be able to make a fiberglass die of the entire body (or most of it), so that when I make a second one I could just pop the body out of a mold and half the entire thing carbon fiber. The upper portion of the craft anyway. I wouldn’t say there is any complex curves or geometry in this craft. But I was hoping it would be possible to make a die for the entire main shell of the body so that there were no seems. It would extend from the entire front, sides, around the xxxxpit area, and to the engine in the back. I may have to make a seem in that area. My question is, would this be hard to do? Or just plain stupid? I’m new to the idea after all. Would it be unwieldy and hard to lay the fiberglass/carbon fiber in such a large area without screwing it up?

My other question is if I buy fiberglass and carbon fiber in yards it obviously won’t cover the entire hull of the craft. So I would have to lay multiple strips down next to each other. Does it look bad when they are not made from a single piece? I know I could paint it but in case I want to leave the carbon fiber look to it.

Also which is heavier wood or fiberglass/carbon fiber? Wood right? This craft has to stay light. I read somewhere that its 3 time lighter and 3 time stronger than steel. I considered making the frame that holds the giant shell out of carbon fiber a well. Bad idea? Would a metal skeleton work better? I’m mainly concerned with weight. I mean if it truly is stronger than steel then making a frame out of it wouldn’t be a bad idea if its stronger than steel, right? I know the stuff isn’t cheap but I am still considering it.

Also if this idea is possible what type of carbon should I go with? Or which to avoid?

Thanks for your time.

[riff42]

Many questions. Let’s start off by saying HIIIII!!!

Yes, carbon fiber is lighter and stronger if done right, and yes, you can make the entire shell out of carbon, or carbon/foam sandwich construction. Now, not knowing what you mean by shell, I will imagine something like a large half-bubble type of deal, like the shell of a RC truck.
I think the easiest way to do that, is to make a foam master tool. If it’s large, you can make a wood frame, add foam to that. THen you can shave/sand the shape you need. Cover it in a filler, like bondo. Sand it smooth as hell, seal the bugger out of it, and add a release agent.
Then you have a master tool. At this point, you add a gelcoat, then start adding layers of tooling resin and fiberglass. After this (And depending on the size), you can add a frame to it with wood/metal, so the thing doesn’t warp, and stays dimensional stable.
Once the mold is done, you can start laying up your shell itself. Carbon, glass, foam core, etc. There are MANY videos on how to make molds, and then how to lay up in a mold.

Now, as to say, what can be stronger than steel, depends on the part you are making. Remember, you can add as much reinforcement in one area that you need it, and only have a thin skin in another where you only need a simple aerodynamic area. You can attach the finished shell to your frame many ways. You can even add in bolts/nut flanges so your frame can bolt right onto the shell. Or just drill holes in the shell.

What carbon you need to use/avoid depends on what you are doing. Again, if it’s a simple shell, that will not see high-loading, you can stick with “low modulus” carbon. IM3/T300/AS4, etc. The cheap stuff. If you are adding a carbon support, engine mount, walking area, you can go with mid-high modulus carbon. Also, using a foam core can build up stiffness, without needing tons of layers of carbon. (google foam sandwich theory to understand)

Price, yes, this is expensive. Start building small molds first to understand the process. There is nothing worse than spending 500$ on mold making materials, only to screw it up half-way through because you didn’t understand something.

Laying carbon down in strips. 1: as long as not all seams are in the same area, or you lay some strips 0 to 180deg, and the next layer, 90 to 270deg, your part will maintain stability. Depending on the shape, it might not look good, or it might not be possible. You can design this in by placing seams in certain areas that might not be visible, can be painted over with stripes, etc. Else, it’s a part of life, and you just live with it. composite fabrics shear slightly, so you CAN sometimes match seams up, but many times you HAVE to dart them.