Ultimaker 3 Extended TPU Print

[SinoscanCJ]

I am experiencing issues with printing multiple parts in TPU95+. If I print 1 part it works perfectly fine, with no issues whatsoever.
As can be seen in the picture, it actually starts fine with no issues. But when it gets to the top half of the parts it begins being to loose.
IMG_20200624_074755.jpg

I am using the following settings:
AA 0.4 Nozzle.
Layer Height: 0,2mm
Wall Thickness: 1,1mm
Top/Bottom Thickness: 1,1mm
Infill: 6%
With PVA support.

I am hoping some of you have experienced an issue like this, and is able to help me.
Below you can see a bad and a good part.
IMG_20200624_093653.jpgIMG_20200624_093702.jpg

[curious aardvark]

retraction settings are wrong.

Each time the printhead moves from one print to another it retracts the filament. and feeds back to start printing.

Now, you have a bowden tube based printer, so need longish retractions.
With a flexible filament there is ALWAYS some contraction and expansion when you retract.

So you need to use very slow retractions - and weirdly counter intuitively - as short as you can get away with.

Looking at it that part should normally print all the way through without needing to use retractions.
So the single part prints fine.

It's only when you start using retractions between models for each layer, you get problems.

Sooo, SLOW your printspeed right down (slower than you were just thinking :-)
say somewhere between 10-20 mm/s.
Reduce the travel speed of the printhead - say 50mm/s to start - slower if necessary. This gives more time for both the retraction and re-extrusion to work properly.
And reduce the speed of your retractions to around 30-40mm's. Less if it's already at that.
Retraction length wise. basically as short as t#you can get away with. start at maybe 3mm and work your backwards till you start to get stringing - at which point it's too short.

You do have an advantage in that you are using 3mm filament - which reduces the compression of the filament. But obviously not sufficiently :-)

Getting multiple prints with flexible filament is something of an artform - so good luck :-)

[curious aardvark]

although, it seems odd that the bottoms look okay.

How many solid shells do you have on the bottom of the print ?
It might be when the infill starts to kick in and that usually prints faster on multiple prints than on a single print - actually most layers tend to.

Hmm, odd.

[SinoscanCJ]

Hi!Thank you for your replies, i tried your idea last night.It did improve the quality to do it slower, but it is still not perfect. So I believe if i reduce the speed further, it might help with the quality. I agree that is seems odd the print gets worse over time. i believe it can have something to do with how well the material sticks together, and when it gets more time to do this it works better.There is 7-8 layers in the bottom on the print.I hope when i reduce time further, it will improve more as well!

[Davo]

Alternately, you can opt to print one model (the furthest from home) first, and then another, etc.

[curious aardvark]

Yeah but on a square build plate with a fixed height extruder the odds are the printhead will crash into the already completed model.
You can get away with it on a delta, but not usually on this style of printer.


If slowing down helped then increase the printing temperature.
One thing I've never had any problems with in flexible filaments is layer adhesion.
The flexible pla I prefer to use the later adhesion is perfect. The prints are unbreakable without using power tools.

Tpu is weird stuff, it can often print best at temps much higher than the manufacturers state.

And NEVER use manufacturer or slicer standard profiles :-)

[SinoscanCJ]

Yeah i am starting to get that experience, that it is preferable to use a different setting than what the manufacturer says. Actually the print is very good now, although it of course takes a lot of time, because of the changed settings.
So thank you for your help on this topic!

[curious aardvark]

glad to help :-)

Flexible stuff is brilliant - but don't be in a hurry :-)