Significant under extrusion with TPU 95 HF?

[Zhapox]

Hi all,

After lots of hours with PLA, PETG, ABS & Co. I started playing around with TPU 95 HF. I used it for small use cases like small key chains, etc. I use the external spool holder on the left to feed the primary nozzle (0.4 hardened Steel). The roll has two cycles of drying at 65 degrees Celsius for each 12h in the AMS 2 Pro behind.

I found early though that there’s significant under extrusion going on. I’m aware that the X2D tends to struggle with slight under extrusion. Hence I looked into the manual flow calibration. The result to me looked off though. A closed surface was only achieved at +20 where details and corners seem to suffer in quality significantly though accompanied with stringing. To me it seems like I’m fighting a symptom but not a root cause.

I tried various different parameters like reducing the volumetric flow by half, increasing nozzle temperature by 10 degrees but it doesn’t seem to help. Dynamic Flow Calibration was disabled at the prints as recommended in the wiki.

Does anyone have any ideas what I can look into?

Thanks a lot in advance!

Kevin

[Eponymous]

I have successfully printed 95A using “generic TPU” settings and setting volumetric rate to 4mm^3. It needs to be printed very slowly.

However TPU is ridiculous to print because it’s so squashy, it does not want to get rammed into an extruder. I would instead use “Foaming TPU” as it’s rigid until heated and by changing the nozzle temperature you control the softness. Bambu doesn’t offer this filament, but others do.

[EnoTheThracian]

The tension in the filament is visible between the roll and the inlet. A common cause of TPU printing issues.

Most use a low friction top mounted roll holder (there should be few on MakerWorld also for the X2) or the TPU assist module.
With the former, I (slowly!) printed down to 85A on my X1.

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