Troubles with TPU in dual extrusion

[paoletto 3]

Hi, so i'm sort of troubled with a dual extrusion print PLA/TPU.

I had the cura project set up and somewhat successfully printed on UM3 back in 2022.12.
Then i had to leave, and i picked it up now.

However, somehow now printing the tpu topping is pretty terrible, underextruding A LOT..
The only difference i can think of is that ambient temperature is now some 10 degrees higher, and the tpu roll isn't sealed anymore.
I read mr5 suggesting that tpu is hygroscopic? If that's the issue, how do i dry it? In the owen at 50 degrees?
If not, what can i try? slowing down more?

I cleaned the printcore, for the records (somehow it was half clogged not even sure how lol)

 

[paoletto 3]

I think the problem might be lying in the fact that TPU filament compresses a lot, and therefore oozes a lot during the print. Typically the first couple of layers are fine, that is, right after the second extruder, at some point during the print (15th layer or so) is activated, primed, and start with its first layer. After that, once is kept warm, tpu keeps oozing out because of the pressure built inside.

I have done this disabling retraction all the way (also in successful prints months ago). I now tried to re-enable retraction, but the problem is that the filament gets also retracted multiple times during the layer and that fucks everything up, even worse than with no retraction.

So i wonder: is there a way to enable retraction only *between* first and second extruder stints?

 

[paoletto 3]

Seems like i overlooked the settings under "Dual Extrusion" that become available once "enable retraction" is enabled. I managed to use them to improve the quality. Still not great but a lot better than before.
I think extra prime amount might also help, except that i'm not 100% sure what that does

[Dadkitess 16]

I've had multiple issues recently using PLA/TPU and PETG/TPU : TPU in the second AA printcore will trigger the flow sensor. Not sure if it's relevant, I've not seen particular under-extrusion before error.

 

Oh, btw, it's using the new CURA 5.3 interlocking function, maybe it's important to mention.

[paoletto 3]

@Dadkitess thanks for your feedback. I use an Ultimaker3 which afaik does not have a flow sensor. And still cura 4.13 (as long as it does what i need, i'd rather not change. Maybe at some point i'll try 5.x on another machine not to wreck settings and such).
If i remember correctly i ended up disabling retraction for second extruder (by setting it to 0mm though), increasing flow for the same, and enabling/increasing retraction on second extruder on extruder change. After i did this, i managed to print pretty decently PLA+TPU, and also the oozing and the tpu mess left around decreased substantially. Not entirely sure how i managed to print it just fine some 6 months ago without doing this, but alas..