About 3D printing

[afernan]

3D printing is something that I saw in exhibitions and news but really never put a lot of attention on that. I thought the printed results were not so good for the use in our bussines of copters. I was totally wrong.

Now I have one 3D printer (the cheapest, yet very good: Prusa i3, 500€) and results are really impresive. After several months of use, I can summarize my experience here for others that still doubt on this must-have tool.

In the image below is shown my last HEXA with all bracketry fully built in 3D printing.

Main advantages are the following:
- high strenth material (ABS), and low density (1000Kg/m3). Specific strength is 39MPa/1000 Kg/m3 that is the same of a standard aluminum! (95MPa/2700Kg/m3). So, one of the best material selection for aircrafts. See strenth analysis in the figure below for the motor bracket, pulled up with 10Kg. I did a real test also to confirm results .
- Density can be variable. Printing process (mainly for thick parts) let select the inner density (from 0.1 to 1). So Mass can even be reduced more without loosing performances. For instance, my motor bracket weights 12g and withstand a load of more than 30Kg each!. Inner density is 0.3, with three full layers externally.
- Endless design posibilities. Infinite creativity.
- Very cheap.

Some engineering skill is needed to take full advantage to this manufacturing tool in terms of design and structural concepts. But intuition is also a good support, and "trial & error" is very easy.

Hope this help you to get a better idea of this manufacturing tool, perfect for copter construction.

Angel

[LPR]

Angel

Thank you for the good information.

Larry

[JussiH]

I think I must be readjusting my opinions on 3D printing and get one sometime soon....My problem with it has always been the way the extrusion printers work and the surface finish they leave behind. But I can see that it could be a very useful tool.

What is the typical extrusion nozzle size? How fine can it get?

How long does it take you to print one of those motor mounts?

Good work!

[Trnquill]

After playing around with 3D printer for about 1,5 years I have came to conclusion never to design parts that are under extreme pull, bend or twist. Extruded 3D printed parts tend to break in those circumstances after a while. Compression on the other hand is very much OK. So, When ever I need a part with extreme strength, I design it so that the load gets carried by for example a CF plate and the 3D printed part is just a "filler" or "adapter" between differently shaped parts (for example a boom and a plate).

I would never for example fly with motor mounts like the one pictured above. When printed "standing up" (boom hole straight down, motor mount plate facing to side) the extrusion layers build up in direction that is worse for this kind of application. The force of motor pull one end of the part up, which tries to pry extrusion layer away from each other on bottom side of the part. Bond between layers is commonly the weak spot of 3D printed parts. So, If the design was mine, I would maybe print it laying down (to have horizontal layers) and add a load bearing CF plate on top of the printed part and some boom clamps to tie the plate to the boom. You could still have ESC32 mounting bracket under that plate as 3D printed part etc.

[afernan]

@Trnquill:

sorry, but I don´t fully agree with your comments.

First reason is that I´ve demonstrating the load capability of a 3D part by analysis, by test ( I´ve done several load test) and the more convincing one : flying many times (none a single issue)

Of course, 3D parts must be "well manufactured", and this is not easy for several reasons:
- the "way" is printed: parts have some kind of "fiber" direction were strength is better, so it´s important to design and manufacturing choosing the "right" way. Knoledge in structural and material strength is a key factor.
- Interlaminar strength should not be an issue. Layers are "welded" in between. I you have problems on that for sure you have a bad tuned machine. Distance between layers (typically 0.3xxx mm) is critical and must be tunned with every especific batch of material. Initial distance of hot end is critical (0.1mm about), temperature of fusing is critical also, etc, etc

3D machine is NOT straight forward (like AQ). Is not industrialized for public use today. It´s still a kind of "art" (this is a great thing for me. Like AUTOQUAD, if you get it working properly, oh man, this is a wonderfull tool. No doubt on that.

Angel

[afernan]

@Jussi:

nozzle sizes are tipically 0.3mm and 0.175mm. I use 0.3mm because surface finishing is good enough (some kind of small rugosity, perfectly aceptable). The small nozzle takes double time to print.

One of my motor mounts takes 50 min about. 3D printing It´s clearly not for masive production use, but in one day you can fully built a copter part set.

ALM (Aditive Layer Molding) is today one of the more important developing technologies in manufacturing processes. We´ve bought already ALM machines in AIRBUS not only for plastic parts, but metallic : Alu, Titanium, Steel, etc ...a bit different than my small Prusa!

Angel

[Trnquill]

[afernan]

@trnquill
3D analysis was done with solid elements (tetrahedron) with "elfini" (the calculator inside CATIA). Obviously this was done for a "quick" check of stress concentration zones and general stress levels (took me 5min). For that goal is more than enough. Considering the material is built "fusing" one layer over other the approach of using solid elements (tetrahedron) is not too bad, (although tetrahedron is not the best solid element, but hexahedron as you probably know). Results from a super-detailled FEM using directional elements representing the 3DPrinting process probably will give very similar results, but many hours of math model preparation.

Angel

[srinath]

Angel

How long does it take to make a part like the esc32 bracket?
Can it make limited series production ( like enough parts for 1 or 2 craft a day?)
How is the power consumption and material cost? Where do you buy the ABS from?

[afernan]

@srinath:
An ESC32 bracket printing takes about 30min. The whole set of parts for one quadropter take me 30h in total. So not possible 2 copters/day (an hexa has 3/2 more parts). I´d say something like 1 copter per week to be confortable with 3D printing.

Material cost is negligible (20€/1Kg). For one copter can be around 5€ total.

There are many plastic companies that perform "rapid prototyping" or "pre-series" for small quantities (5-200) with a limited cost. You should check that options instead.

Angel