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Under Water printing

Posted by tprime 
Under Water printing
September 28, 2012 05:32AM
A crackpot idea: Has anybody ever attempted to print in/into water? Like under water printing.

Since PLAs density is close to that of water, I could imagine it removing the support issue - and,
if the water's heated, wrapping.

Obviously, there's a number of obstacles and issues with this approach
- PLA absorbs moisture (but I guess, all printed parts will eventually be saturated anyhow)
- The nozzle is hoter than the boiling point of water - a diving bell might be used
- Immersing electronics in water is a hazzle (diving bell again)
- Can't use a moving bed due to the weight (->delta design? - Need's a bigish water space though)

Well, my google fu hasn't pointed me to anybody experimenting with it, but y'all have been around
a lot longer winking smiley
Re: Under Water printing
September 28, 2012 05:53AM
... some 4-5 years ago there were some ideas about using oil as 'support-medium', but AFAIK nobody tried this confused smiley

Some problems when printing into a fluid are the heat-transfer and the complete different behaviour because of surface-effects between filament/material and fluid, changing the adhesion ...

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Re: Under Water printing
September 28, 2012 07:55AM
As suggested water may not be an option, but oil such as cooking oil etc might be worth a try. Cooking oil has a flash point of around 300 degrees c if I remember rightly, so having a hot bath at around 140 degrees you might be able to deposit PLA at 160 + without too much loss of heat or boiling of the liquid. It would also be good to stop warping if printing with ABS using a hotter bath, but you are a bit too close to the flash point at 275 degrees for comfort!

I also previously suggested using high temp grease as a support medium. This could be extruded rather than using a bath.

As Viktor suggested I could see that depositing material onto a surface wetted with oil could be a problem, but this is easily tested.

Pause a print, paint it with oil then try printing the next layer. I think you may get a part that easily splits apart. If this is the case, it might be a way to print support material that crumbles away or separates easily. I was thinking over the idea of injecting powder into the filament via the extruder to change its mechanical properties, but there is no reason why fluid wouldn't work as well as an alternative method to using a bath.

In conclusion I think its worth some investigation. I am looking forward to hearing others thoughts on the subject.
Re: Under Water printing
September 28, 2012 08:38AM
While I'm always a fan of empirical testing I'm a bit dubious about the adhesion between layers. Through my time learning how to get successful prints with PLA on heated glass I found that even the tiniest finger smudge would prevent the PLA from sticking to the glass. This is a very thin film of oil from contact with skin, many magnitudes different than printing IN oil / water / grease. If you can somehow keep the printing layer just barely above the surface (build plate lowers into the oil bath?) of the liquid then maybe I could see this working. Another issue you will run into is that while water / oil may have a similar density to PLA it certainly does not provide the same mechanical properties. I don't see how you would be able to print, for example, unsupported cantilevers or "free air" (or "free oil" in this case) extrusions. The printed filament will just drag around through the liquid a little bit slower than it would in air.

The reason printed support works well is that within seconds of being laid down it becomes a rigid body able to not only support the next layer but also control lateral movement by providing a rigid bonding surface.

I'm also worried about the idea of printing into a high temp liquid. Having a 1-3cc object (print head) heated to 200C is potential enough for a painful burn (I've done it to myself several times) but I'd be very worried with 8000cc's of 140C (300F) oil potentially spilling everywhere. A liquid at 60C will give you a 3rd degree burn in 5 seconds and we are talking about temps twice as high as that! I think you could get away with a PLA oil bath of around 60C (heated bed temp) but you still run into the disadvantages listed above.
Re: Under Water printing
September 28, 2012 09:18AM
@Martinz; I remember a blog post about trying to paint oil on top of the supports to get them to split from the main partapart very easily. Fortunatly,
to prevent all wrapping, we only need to stay above the glass transition temperature. For ABS, it's still too high for water (105 C), PLA would be ok (60C),
but as archistrong has pointed out, that' still plenty dangerous (though I guess the figures are for submerging?).

My hope is that the improved heat transfer will allow the filament to turn solid much faster, which in addition with the buyoancy
would improve bridging.

I think I'll give (cold) water a try, just for kicks.
I'll start with a relatively flat dish and will add water slowly while the head retracts.
If that produces decend adhesion, I'll investigate the diving bell
and support less printing smiling smiley.
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