I have been printing with Firaflex TPU 70A for about 6 months, and I keep running into the same issues: a lot of stringing, blobs on the walls, and some unusual “delamination” between the walls — almost like an adhesion problem.
I’m using the H2D, with TPU 70A in the right nozzle and generic PLA in the left nozzle. I’ve already done flow calibration, stringing tests, and several other tests in Bambu Slicer, but nothing seems to solve the problem.
I’m printing this for a university project, which consists of printing a bronchial tree in a single piece. That’s why it’s incredibly important to maximize the internal print quality as much as possible.
This are my setting on the current print:
For TPU 70A
Flow rate:1.15
Desity:1.24
Nozzel temperature: 230
Max volumetric speed 2.5
Colling -
Min fan speed 10% - 100s
Max fan speed 40% - 8s
Auxiliary fan speed: 10%
Retraction: 2mm
z hop when retract: 0.2mm
z hop type: normal
lenght when change hotend: 14mm
wipe when retracting - checked
I don’t think you can achieve a perfect surface with foaming TPU. It’s just not capable of doing that. I’m not sure if this 70A filament is foamy or not but it’s likely.
Putting this aside, have you dried the filament? How did you dry it?
Any foaming filament is inherently prone to some degree of stringing, and foamed variants of TPU/PEBA will tend to string to some extent even with highly optimized settings. If a normally behaving TPU/PEBA suddenly starts stringing more than usual, it is a strong indicator that the filament has absorbed moisture. I always print TPU/PEBA from a heated container, typically my AMS HT, so the filament can dry continuously during printing. With my setup, excessive moisture does not first show up as stringing; instead, the filament swells in the PTFE tubes and causes a blockage.
IMO dry it further. Do yourself a favor and measure weight of the spool so you can have some idea of when it stops losing weight. Your flow rate seems high [and higher flow can lead to strings], but if thats what it tested at, thats what it tested at.
At max flow of 2.5mm3/s, any oozing is going to be a huge % of the volume of material coming out the nozzle and needs to be “put somewhere”. Strings and clumps. You can think of wet ooze as an uncommanded, constant 0.5mm3/s of flow - or whatever number suits your scenario - it’s a near-constant rate, and going to screw with you proportionally way more than if you’re squirtin PLA at 20mm3/s.
Are your bronchial tubes open at the far end? Fill that up with butane and light it up, be ready to blow it out. It’ll destroy all fine stringing inside the structure, but it needs to be much more fine than in the current photos. There’s a macabre joke about smoking cigarettes in here somewhere, but I’m too dumb to find it
Kudos. I have not dared a 70A (yet) as I found the 85A to be enough of a challenge. So only a few questions:
I assume both “wipe on retract” check boxes are checked? Occasionally, I forget about the second one.
I have not had much luck with any type of z-hop at all. It usually seemed to decrease string thickness but increase string count for me. Have you tried disabling it?
Did you adjust the retract speed (yet)?
Do you have avoid crossing walls enabled? The screenshot is truncated. It may not actually affect this particular print but you can check the slices travel moves before printing.
Other thoughts:
Could you try a harder TPU and reduced line widths/number of walls? (Of course, also considering @Gerrit recommendation first.)
A bit far fetched but just to look at all possibilities: A harder but foaming TPU for flexibility?
& 