Mirar
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Q: Printing actual different materials using MMU

Jul 12, 2018 11:35 am

I have failed to get a good answer on this, so I'll try to post it on this forum.

Can you print different materials using the MMU2.0 (or the old MMU even)?
As in rubber-like + PLA, or ABS+dissolvable, with different hot end temperatures?

I have seen prusa videos about working with dissolvable, so I guess that should work somehow?
Which material combinations work? What's the experiences here?

(Or is this a job for a dual extruder, and in that case is there a recommended one to put on a prusa printer? A 2xMMU2.0 dual extruder would be nice...)

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Re: Q: Printing actual different materials using MMU

Jul 12, 2018 2:26 pm

I don't think there's an "official" answer to your question.

Based on my experience using the Palette+ filament splicer with the MK3, I think the answer will be that you can use different materials under limited circumstances:
  • The materials will have to have extrusion temperatures which are reasonably close (within 5-10 degrees). While it's possible to change the extruder temperature as part of the purge cycle, changing more than a few degrees is going to create problems.
  • The materials will have to be fusable so that they stick together rather than falling apart. So no mixing PETG and ABS. PLA and TPU might work (though you may need to design the materials to interlock, since the TPU-PLA bond will be weak).
I'm expecting that soluble support with PLA/PVA will be possible, and I think there's a good chance you will be able to get PLA/TPU to work if you want to mix rigid and flex materials.

But keep in mind that mixing materials with the MMU is going to be varsity-level 3D printing (just like printing with multiple extruders). Maybe after some months of tinkering and refinement it will get to the point where you can just hit Print and get reliable results, but I certainly don't expect that out of the box.

Mirar
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Re: Q: Printing actual different materials using MMU

Jul 12, 2018 4:14 pm

So in general, "multi material" means "different colours, single material" and if not, there'll be lots of tweaking involved...?

peter.l22
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Re: Q: Printing actual different materials using MMU

Jul 12, 2018 5:54 pm

pontus.h wrote:
Jul 12, 2018 4:14 pm
So in general, "multi material" means "different colours, single material" and if not, there'll be lots of tweaking involved...?
Pretty much, yes. That's going to be the case with any "multimaterial" solution for 3D printing at the hobby level, even multiple extruder printers. I see no reason to expect that the Prusa unit will be much different. There's no magic bullet.

Again, this is based on my experience with the Palette+, which splices segments of filament together to give you multimaterial prints from a single extruder. The Prusa MMU is a different approach, but you're still going to struggle if the filaments aren't fusible or have to extrude at significantly different temperatures. Having multiple extruders makes it easier to extrude at different temperatures but doesn't eliminate the need to have compatible plastics, and multiple extruders gives you a whole new set of problems with registration and vertical alignment.

I don't want to be too discouraging. I've done soluble support (PVA + PLA) using my Palette, so it can be done. But it was not a push-the-button-and-make-it-go experience. I had to spend some time experimenting with the materials to find the right settings, and the results were not as consistent as I would have liked. Some of my problems were because the Palette still has some gremlins, and I'm hoping that the MMU will prove to be a better approach. But you just can't get around the fact that trying to build a single print that incorporates multiple different types of plastic is not a plug-and-play process.

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Re: Q: Printing actual different materials using MMU

Jul 13, 2018 7:42 am

There is indeed a question of differents printing temperatures but I think that the MK3 is quite fast for increasing it, especially with a sock. I think a 20 or 30 degrees increasing should be handable during the filament changing process if it's well programmed.

About the compatibility of materials, I think it's possible to combine unfusable ones if you had "traps" for materials in each other, like it's done for overmolding. Personally I design l my own parts most of the time so it's not hard to do that when modeling. It's just a guess, we will see if it works but i'll try for sure, I would love to combine PLA and TPU !

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PJR
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Re: Q: Printing actual different materials using MMU

Jul 13, 2018 8:37 am

This is possible but if the temps are more than 10 degrees different, you will need to use additional G-code to wait for temp changes at certain points during the filament change.

This is not so easy with Slic3r; you would have to manually edit the G-code. KISS on the other hand... :)

Peter
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Re: Q: Printing actual different materials using MMU

Jul 13, 2018 10:30 am

For what I see in this video https://www.youtube.com/watch?v=RA36TOArZq4, the filament change took like 25 seconds, from 1:50 to 2:15, I think it's enough to ensure thermal transitions. But of course you have to set the new temperature as soon as the filament left from the extruder, I think PRUSA will think about it :D

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Re: Q: Printing actual different materials using MMU

Jul 13, 2018 10:53 am

arthur.c2 wrote:
Jul 13, 2018 10:30 am
But of course you have to set the new temperature as soon as the filament left from the extruder
No, that's not correct.

Consider this:

You are printing with a filament at 240 degrees; the new filament requires 200 degrees, but there is still about 40 mm^3 of old filament remaining in the nozzle. If you reduce the temp when you unload the old filament, the nozzle will not be sufficiently hot to purge the old filament with the new.

In this situation, you can only drop the temp near the end of the purge.

Peter
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Re: Q: Printing actual different materials using MMU

Jul 13, 2018 11:39 pm

You're right ...

So the main problem is extruding material with a too low temperature, but too high isn't really a problem on short term.

An idea would be to change the temperature at the begining of the changing process if it has to increase, and at the end if it has to decrease.

Ex :

- Printing PLA at 210°C
-Stop
- Change temperature for 240°C
- Retract PLA and insert ABS (~ 20s)
- Extrude the ramaining 40 mm^3 PLA in purge or infill at 240°C
- Printing ABS at 240°C
- Stop
- Retract ABS and insert PLA
- Change temperature for 210°C
- Extrude the ramaining 40 mm^3 ABS in purge or infill as the temperature goes down
- Printing PLA at 210°C

It doesn't seem too hard to program.

But I agree that high temperature differences like 40 or 50 degrees seem difficult to handle.

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Re: Q: Printing actual different materials using MMU

Jul 14, 2018 12:16 pm

arthur.c2 wrote:
Jul 13, 2018 11:39 pm
An idea would be to change the temperature at the begining of the changing process if it has to increase, and at the end if it has to decrease.
Actually, an ideal situation is to change the temps several times during unload and load.

What you need to do is to unload the filament with a clean tip whilst pulling out as much as possible.

So the "ramming" before unload cools the nozzle slightly to help with this, but I also turn off the extruder heater while moving to the purge tower.

I then turn on the heater near the end of the "ramming" and overheat for the new filament, gradually cooling (to avoid "undershoot") during the purge.

Seems to work quite well:
IMG_20180710_204853.jpg
IMG_20180710_204853.jpg (2.86 MiB) Viewed 795 times
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

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