Help: permanent vertical blobs along stringing test (TPU)

[edankleef 1]

Hi everyone,

 

 

I am on the verge of giving up with Cura for printing TPU. I have a Sovol SV01 printer and it prints eSUN PLA and eSUN PETG perfectly fine using Cura.

When I try my eSUN TPU 95A however, I get large blobs at a distance next to the walls.

I have tried tuning retraction distance and speed separately ranging from 3 to 6.6mm (limit) and 18 to 39 mm/s (limit) respectively. I have also tried ranging the temperature from 220 to 230 degrees, various coasting and all combing mode settings (also "Max Comb Distance With No Retract"). Printing speed is with 27mm/s already pretty low.

 

I have attached a picture of the print with blobs, the stringing test STL file and my Cura profile that I use for TPU.

 

After having printed too many stringing tests, any help would be very appreciated!

 

 

Best,

Ewald

Stringing_Test.stl tpu_95A.curaprofile

[geert_2 557]

The cause is filament leaking from the nozzle while traveling through the air, due to the pressure in the nozzle not immediately dropping to zero. Especially with flexible, compressible filament. This leaking causes a sort of "insect antennas": the drop on the nozzle is deposited on the edge of the next wall the nozzle encounters. And then on the next layer, it is deposited on the previous drop, and so on, creating these antennas. However, you have a peculiar form of it.

 

Rubbery materials (when molten) like PET also have this tendency.

 

Maybe print still slower, cooler and in thinner layers? So there is very little pressure build-up  in the nozzle and bowden tube? And the filament leaks less due to being cooler? Printers with bowden tube are more prone to this obviously than direct drive printers, due to their long feeding traject under pressure.

 

A close-up of these "insect antennas":

 

For comparison: ruler next to the item with antennas is in mm and cm.

Edited April 9, 2021 by geert_2

[edankleef 1]

Hi geert_2,

 

 

Thanks a lot for getting back to me. The "insect antennas" from your pictures are indeed very similar to mine!

 

The Sovol SV01 printer has a direct drive extruder and should therefore have less pressure issues with TPU.

I have tried printing at 220°C instead of 230°C and 15mm/s instead 27mm/s printing speed. The results are unfortunately exactly the same:

 

 

 

Could there be any other reason you can think of?

 

 

Best,

Ewald

 

[Gero 54]

I print TPU on one of my Ender 3s all the time. Took me quite some time to get the settings right. I also have a direct drive one which needs some different settings, but is also working great now.

 

I use a retrac distance of 2.5mm with a speed of 50mm/s.

I also enabled z hop with a height of 0.4 mm to avoid any "antennas".

All printing speeds are set to 20mm/s with a hot end on 225°C. 

[geert_2 557]

I haven't printed with TPU yet, so no personal experience about its characteristics. Maybe set more retraction, or make sure you did not accidentally switch retraction off in the slicer? If "nothing else makes a difference", then disabled retraction might be the reason? Just guessing...

 

[AndersK 59]

TPU isnt the easiest material to print so dont give up

 

To add to the other good advices you can also experiment with Z-seam settings . It wont remove the blobs completely but can spread them to avoid building antennas

[edankleef 1]

Hi Gero,

 

Thank you very much for z hop suggestion! It was not working how I wanted it to. Disabling "Z Hop Only Over Printed Parts" made the antennas disappear, as this forces z hop to always work. This way the oozed filament blob will not crash into the wall after a travel move.

 

Best,

Ewald

Edited April 13, 2021 by edankleef