Continuous prints between TPU spool changes and quality problems

Bambu Lab H2 Series
1

Hello to the community,

My setup is the following :

Printer H2S. On top of the printer, I have this 3D printed mount. On top of this mount, I have an AMS-HT. For the current project I only use TPU 95A from various brands like TINMORRY, SainSmart, kexcelled, CCTREE, YOUSU. I use this PTFE Guide in the AMS HT bypass port to feed the TPU filaments directly to the extruder. Of course, the top glass of my printer is absent, for this setup to wor k.

The objects I have to print are fairly large. Each object needs 16 – 32 hours to be printed. Before putting any TPU filament to the AMS HT, I dry it in a Creality SpecePi X4 at 75oC for 18 hours. Then I load it in the AMS-HT and I also dry it while printing at the same 75oC for as long as the print lasts. The mean humidity of the filaments throughout hole process is ~10-13% as far as I can see from both the AMS HT and the Creality SpecePi X4. Of course I have not set the AMS-HT as active feeding, I have declared it just as external spool which is passively rotating when the extruder feeds the filame nt.

I use this setup because as far as I read, I cannot feed regular 95A TPU using active feeding through any type of AMS that is far away from the extruder, using long PTFE tub ing.

Now I have two questions:

1) Sometimes I have to produce multiple objects of the same color TPU. Ideally, I wanted when one spool of TPU comes to its end, to be able somehow to feed the next spool of TPU automatically. With my current setup, I can not even do this manually because I face another silly problem. Some TPU spools have the inner side of the filament hooked into the spool itself. This tiny detail cause the whole print to fail because the printer throws a feeding error, it cools down, and when I replace the spool my print has for sure a defect and it is useless. My question here is if there is any solution to print TPU continuously by an automatic manner or even by a manual manner but without having to destroy the obj ect.

2) Printing defects. I can not explain why certain objects exhibit the same print defects in the same spot every time. In the following pictures you can see the left and the right side of a symmetrical TPU object. I have printed this object twice. Both of the times the right side printed nicely and both of the times the identical (CAD mirrored) left side of the same object has these defects. (This slice uses fuzzy skin by the way) Do you have any idea?

defect
defect960×606 127 KB

Thank you in advance!

2

A couple of things here:

You mention numerous brands of TPU that you are using. Are you intending to switch brands during one print job?

What’s the reason for using so many different brands? All probably need some calibration before printing.

Have you looked at the TPU feeder from Bambu?
Definitely for TPU 95A but even softer runs perfectly without the complex setup that you have.
It would probably make swapping spools on runout a lot easier.

If some TPU manufacturers have the filament hooked to their spools, stop using that brand or respool the filament to prevent this issue.