Failed TPU Prints

Bambu Lab P1 Series Troubleshooting
1

Hello,
yesterday I tried printing TPU (Jayo) for the first time. I tried to calibrate it in Orca slicer as I do it always with new filament. But the calibration prints look like this:

IMG_2928
IMG_29281822×1822 2.14 MB

What I already tried:

  • drying the filament at 70°C for 8h (it lost about 6g of weight)
  • increased the flow rate by .1 ( thought it looks like underextrusion)
  • tried higher and lower temp
  • did the retraction calibration and changed retraction to 0,6mm
    • the strange thing was that the retraction test looked pretty good
    • another strange thing is that some areas of the first layer are good and some are bad
  • built a spool stand that decreases the force the extruder needs to unspool the filament
  • unspooled the filament for one calibration run
  • checked if the nozzle is clogged (it is not, PETG prints perfectly)

As you can imagine, nothing helped…

I ran out of ideas, any thoughts?

Thanks in advance.

2

I bought a roll of inland TPU. Loaded it as an external spool, set parameters to generic TPU and it ran fine. Also printed on blue painters tape because I read it sticks strongly to the build plate. I would just try to print using stock settings.

3

Hello! The issue with printing TPU is that it’s very different from other plastics due to its flexibility. TPU does NOT like speed, at all. TPU needs to be printed slowly. These profiles helped me start with TPU and I did some small tweaks from there. Please experiment for yourself and see what works.

X1C: Printables
P1: Printables

4

Printing the (Probably 95A) TPU should be relatively easy.
Did you cancel the print after the first layer, or did it stop extruding there?
The first layer usually looks like that. I suspect Bambu Studio tries to prepare a reliable base for the test.
Your TPU should also be okay with less than the 240C set in the generic TPU profile.

1 Like
5

Alright thanks for the links, I will give them a try.

6

I had the same thought so I tried to print a normal part with the standard profile only increasing the max flowrate to 6mm3 (I am using a cht nozzle) and setting temp to 215C (as the temptower showed me beforehand). It nearly stopped extruding at the half of the first layer
Look:

IMG_2944
IMG_29442261×2658 3.01 MB

I started the same print again and it started printing the thin lines later on but also in the first layer

7

Maybe try to print hotter and with less flow.
You could also manually set the nozzle temp and extrude some TPU for a while, maybe that helps identifying the issue. I did not try any CHT nozzle on my Bambu Printers. You could also try to switch to the stock unit and try again.

1 Like
8

That’s exactly what I did. Well I unscrewed the CHT nozzle and put in a normal 0.4mm nozzle. I used the Generic TPU setting and changed nothing but the retraction length to 0.9mm. The only issue I still have is (at some point heavy) stringing. What causes this? The retraction length doesn’t seem to fix this. Apart from that the print finished quite nice so the CHT nozzle definitely caused the problem. I found this thread on reddit, it also says that the CHT nozzle can cause problems when printing TPU(https://www.reddit.com/r/3Dprinting/comments/r5a9r9/anyone_use_bondtech_cht_nozzle_on_tpu_and_see_a/).

If someone is interested in the CHT nozzle:

Zusammenfassung

I can highly recommend you the cheap one from AliExpress you can change the nozzle within 1min with a 4mm wrench. The quality is as good as the quality of the stock one and all parts (heater, thermistor, fan) fit perfectly to it. The length is the same as well. With the highflow nozzle I was able to print PLA (Jayo recycled) at 30mm³ vol. speed and PETG (Jayo) at 27mm³.
The system works even better when printing abrasive materials, because it’s way easier (1min, nearly no disassembly) and cheaper (6€) to replace the nozzle.
I bought the V2.0 from IdeaFormer.
https://de.aliexpress.com/item/1005005291012768.html?spm=a2g0o.order_detail.order_detail_item.6.5a366368llSRsA&gatewayAdapt=glo2deu

9

Did you try the retraction test in orca slicer?
More retraction is not automatically less stringing.

10

Yes I did, the best looking result was at 0,6mm - I’ve adjusted it.
What else can cause stringing except wet filament?

11

Maybe retry the test with your travel speed dropped to something like 20mm/s and keep a close eye on the nozzle to find the ideal spot.

I recently had some stringing issues with PETG and solved it by disabling the “Reduce infill retraction” option.
Another thing to check would be your flow ratio. It’s possible that you extrude too much material leading to buildup on your nozzle, causing stringing.

If that is not helping, try to drop your nozzle temp a bit or adjust the retraction speed.