strength vs weight in 3d printing

[jferguson]

I do not yet own an M-2, other than an ancient Leica, but have been much impressed by the intelligence and creativity in the posts I see here. My ongoing project is design and construction of very small fixed-wing autonomous aircraft. I had expected structures to be carbon fiber composite and mylar made by moulding. It occurs to me that I might be able to print composite structures and in reading here i see reference to some fairly stiff prints made with particular filaments. But how about weight?

Do any of you have experience with optimizing strength to weight ratios in 3d prints? If this isn't the right place to ask a question like this, can you recommend one?

Finally, is there a description somewhere of how the filament is moved through the M2 printer head to the nozzle?

thanks for any help you can provide,

John

[jsc]

I haven't seen any rigorous tests with numbers. A quick search gives a rough estimate of 60% strength of injection molded plastic for a printed part, but I don't know if that's the result of tests. The real test is to try it in different materials and see how well it holds up You might try sending off a few designs for test parts for printing by someone off of 3D Hubs and see if it will meet your needs. That first link from that search gives some discussion of varying designs to increase strength for weight.

We have/had some members who were into things like discus launched gliders, and I recall that they still all just use balsa as its strength to weight can't really be beat.

Finally, a few people have been getting into the new nylons recently, which look promising for toughness: viewtopic.php?f=11&t=2109&start=10#p10882

[rsilvers]

I have a laser cutter and I think that is of key importance to making a fixed-wing aircraft. You can cut out Balsa wood. 3D printer is useful also.

[jimc]

one of the members here, pyronaught, makes small scale rc blimps and he deals alot with weight and strength on those parts. maybe he will chime in on this. there are some filaments stronger than others and some weigh more than others. i guess its all in how you design the parts you need. if you take a stronger but heavier filament but now you can model the part to use less material than the weaker stuff, ehhh, who knows really which will be lighter in the end. i guess it would all vary.

[rsilvers]

Maybe look at Polycarbonate as it will be strong and stiffer than PETG and ok for small parts?

[jferguson]

Guys,
This has been very helpful. Thanks much for the ideas.

John

[jferguson]

An outfit is marketing a printer with two extruders one of which lays down a filament with a "continuous" carbon fiber/fibers. Their site shows pretty good strength by testing. The carbon fiber is encased in thermo-setting plastic. System is operated with Cloud proprietary software which is written to support the sorts of things you would want to do with their system. cost of system is +/- $6k and cost of filament is also high, but certainly worth it if you need these qualities.

There is no description of how the continuous carbon reinforced filament extruder works. I would think that in addition to feeding and heating the filament, it would need to cut it at the end of each pass, and tamp down the loose end. It might be a little messy, but if the ends are subsequently encapsulated in conventional filament and the adhesion between the carbon reinforced filaments is good, it wouldn't matter.

I'm sure their system is proprietary and patented.

It sort of makes one want to whip up his own. You'd end up buying your filament from these guys and once they realized that they hadn't sold you a printer, they might ask what you were doing with it.

[thecadman99]

If you could come up with some accurate material simulations (whatever material you wanted to print with), many software packages will let you simulate loads on your designs. The scary thing with printing would be having to assume every layer had perfect adhesion, and that there were no manufacturing variances in your filament.

[jferguson]

There's also the issue of scale, maybe granularity. if you want to make small components, you have to face the fixed size of the filaments. It may be that 3d printing isn't suitable for every part. I'm tossing all of this around because I'd like to identify blind alleys before I spend more money. As to the question of repeatability and adhesion consistency, I suppose that it would be best to test and then discount the results to cover inconsistencies and hidden issues in fabrication -- or non-destruct test every finished component.

sorry if there's too much thinking out loud here.

i do appreciate the discussion -- a lot.

[jsc]

There is also this tool which claims to reduce weight in printed objects while retaining strength: http://www.3ders.org/articles/20141209- ... tware.html