I have been working on a project for a while now, with a final goal of a flying solar powered airship. I have built a few flying scaled prototypes, the latest of which is about 20 feet long.

The plan is to fit under the FAA ultralight specifications, or if that ends up being impractical, use the homebuilt / experimental regulations.

Anyway, at first I was approaching 3d printing for helping me make parts for prototypes more precisely and easily. But the the wild notion hit me to try to print the entire superstructure from interlocking components, and end up with a pattern others can use and print.

How crazy is this idea? Size of parts doesn't matter, so I don't need high hardness / density. Weight is incredibly important. Are there any materials that might be strong enough? I saw the video about the bike that was printed, but wasn't very strong. But I don't need the high density strength a bike needs.

Feedback / criticism wanted.

Edit: this would be for the gondola / body, not the envelope / gasbag.

Edited 2 time(s). Last edit at 11/04/2012 12:25PM by msummers.

I have just been doing some trials for a printed core for a carbon fibre bike frame. I printed in ABS which is less dense than PLA. My idea was to try to get a core that was as light as PU foam over which I could skin carbon fibre for strength. I failed miserably even though I went to very thin walls with 5% fill. I wasn't going to use the ABS for strength, just for shape, the carbon skin would provide the strength. PU foam was still much lighter.

See here check the post for 22/10/2012 Commuter bike

What I was trying was an order less of what you are proposing, so I don't think it will be practical, unless you use powder printing as in the SULSA aircraft. Even then it might not be as light as you want.

SULSA AIRCRAFT

An alternative might be to print moulds (molds) for the parts you want, then use expandable foam to fill the cavity. PU expandable foam is the stuff you get at diy stores for gap filling around pipes. You can also get two pack mixable stuff used in boat building. I was thinking of using cling film in the mould to help release of the part. You could also add in balsa or carbon spars inside before you fill with foam. This would make a light and rigid gondola. Having said that you might be just as well using conventional balsa and tissue.

Sounds like practical printed aircraft may have to wait for stronger printing materials to become less expensive. Too bad, it would have been cool

While you may not be able to print strong materials, you can distribute material smarter. You can effectively make a "material stronger"(per unit weight). Using a process called topology optimization you can find the strongest, lightest way to distribute material in a part, you can often increase the specific strength of a part by about 1.5.

Of course, this isn't the only thing you can do as Martin mentioned is wrap your prints in carbon fiber. This is actually being investigated as a means of making carbon fiber parts by the aerospace industry, as there are significant cost and time savings associated with not having to produce molds.

Though I haven't gotten much details of the exact process used, I believe they print an ultralight 3d lattice most likely produced via laser sintering(though I suppose if you sparse your prints you might get similar results), or they use a fugitive process and dissolve/melt the inside away after the resin's hardened.

Or you could just print complex connecting components for carbon fiber rods that'd you'd have hard time machining.

I too am thinking about building an airplane with the help of a 3D printer and a CNC router but I don't know that you could ever get to the point of printing an airframe, bolting an engine to it and rolling it onto the tarmac. However, if we could figure out a way to 3D print polyurethane foam, it would be a good day for the aviation industry, especially for home builders (like me). I'm sure you're all familiar with the conventional process (painstakingly shape a foam mold, wrap in it glass, sand, wrap again, sand again, etc) but you might be able to cut construction time in half if you could start with a printed foam mold and it would produce far less waste to boot.

Sadly, I haven't heard of anyone 3D printing foam, yet... In the mean time, the lattice idea might work as a suitable mold for composite construction. The only problem I can see with the lattice is that it might limit your options as far as construction method. Namely that you would probably be stuck with the 'moldless' method wherein you produce a non-loadbearing shell, wrap it in whatever composite cloth you choose to produce an exoskeletal 'skin.' Not that there is anything inherently wrong with that method but in my opinion exoskeletal airframes won't fail quite as gracefully as something with an internal, loadbearing frame with non-structural formers and skin. At any rate, I'll have to continue looking into this.

Sorry to raise an old post, but thinking it through further there may be a way to produce light structures more simply.

1) Print a mould (mold) using a reprap. You could do this in sections for a large item such as a wing or airship hull and bolt them together or mount them to a wooden board. You could also position spars and reinforcement such as cardboard tube in the mould or smaller reprapped parts for mounts or hinges.

2) Use a release agent in the mould such as wax.

3) Mix and pour hard expandable foam into the mould. Use foam such as this which goes hard when cured.
Hard cure foam

4) Once cured you separate the sections and remove the part complete with internal reinforcement. The mould is reusable many times.

5) For extra strength, wrap with carbon fibre or leave as is.

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Helium Frog Website

Hi Martin,

thx for sharing your ideas ... I'm also very interested in having a method of building molds in a fast and accurate way for model RC planes and other stuff.

Have you already that idea?

cheers robert

martinprice2004 Wrote:
-------------------------------------------------------
> Sorry to raise an old post, but thinking it
> through further there may be a way to produce
> light structures more simply.
>
> 1) Print a mould (mold) using a reprap. You could
> do this in sections for a large item such as a
> wing or airship hull and bolt them together or
> mount them to a wooden board. You could also
> position spars and reinforcement such as cardboard
> tube in the mould or smaller reprapped parts for
> mounts or hinges.
>
> 2) Use a release agent in the mould such as wax.
>
> 3) Mix and pour hard expandable foam into the
> mould. Use foam such as this which goes hard when
> cured.
> Hard cure foam
>
> 4) Once cured you separate the sections and remove
> the part complete with internal reinforcement. The
> mould is reusable many times.
>
> 5) For extra strength, wrap with carbon fibre or
> leave as is.

I have been wanting to create a carbon bike frame for a while now and have been looking for a way to utilize my reprap to save foam sanding. Trouble is I only want one bike not a production run, so making a mould is not really necessary. I think it could be used for RC planes. Use expanded foam over a carbon fibre centre spar.

I imagine this technique could also be useful for large items built from repeated shapes. Perhaps a large water wheel for the third world or maybe a wind turbine where you have some repeated shapes.

Perhaps there is another mouldless way by making some cross sections with a reprap, longitudinal ribs from 3mm filament. This would make a weak open structure. You could then infill with expanding foam and sand it back to the ribs for the final shape. It would take the guess work out of sanding the shape. Cover with heatshrink film for a fuselage. It might also work for boat frames or car body bucks.

---

Helium Frog Website

I know I am new but figured I would throw my 2 cents in here as I have done a lot of work with carbon fiber. The F1 car teams use a similar procedure whereas they essentially CNC machine a block of foam that is then dissolved. You can absolutely use Martin's idea but it does somewhat disrupt the intended structural integrity of using carbon fiber for light weight. The ultimate way to create a lightweight strong product is through vacuum infusion that uses a negative to create a part rather than a positive mold that ends up in multiple parts. If using a positive then you really want everything cast in the same piece and using an autoclave is preferred. Have you considered printing a negative that incorporates the wall thickness of the part being considered? In my opinion this would be best for strength and precision and would be similar to an abs injection molding frame.

Thoughts on my comments would be appreciated since I am not a pro but always looking to learn!

have you heard of " nano cellulose " super lightweight and super super strong...

It is cheap to manufacture & abundant. I envision this material becoming the perfect filament for so many high strength, light weight structures.

NANO CELLULOSE LINK