PLA layer separation after switching from TPU
I have a design that prints roughly 20 mm high of TPU (Fiberlogy FiberFlex 40D) and then switches to PLA. The PLA appears to print fine but when the part is done, the PLA is weak just after the transition from TPU to PLA. To clarify, the first 1-2 layers of PLA adhere well to the TPU and each other, but then the PLA snaps apart between layers 2-3…across most of the layer, not just in a localized spot. The rest of the PLA layers appear to print well with normal strength and adhesion. Because the properties somewhat overlap, I’m printing the entire job (TPU and PLA sections) using PrusaSlicer’s profile settings for FiberFlex 40D and using a “change in color” to pause the print and swap filaments. Any thoughts as to what is causing the layer separation within the PLA layers 2-3?
RE: PLA layer separation after switching from TPU
Are you purging the tpu on your colour change ? Could be contamination from a mixture in the nozzle which is why its weak for a few layers. Also are the settings from the TPU filament profile suitable for the PLA. A colour change (M600) doesn't usually alter the filament profile so that's something else to consider.
RE: PLA layer separation after switching from TPU
I wondered the same thing about contamination, but yes, I am purging on the color change. I would also expect contamination to affect the adhesion immediately, not after a couple layers. Is that a poor assumption?
The TPU settings differ from the PLA settings but appear to be at least somewhat acceptable. I get good adhesion on all PLA layers after the 2/3 problematic layer as well as first layer (bed to PLA). My filament stack is print bed > 5 mm PLA > 20 mm TPU > 3 mm PLA. I get the PLA separation a little over 2 mm from the top (the final 3 mm). I haven't played with manually changing the nozzle or bed temps when I swap filaments...yet. I wanted to check here to see if I'm missing something first before I go spend the time and filament.
RE: PLA layer separation after switching from TPU
Posting for completion…
So, I tried printing the entire PLA/TPU stack at profile settings for Fiberlogy FiberFlex 40D (as mentioned above) and got mixed results. Large sections (length and width) were able to be printed well with good adhesion across all layers. However, "thin walls" of 1.8 mm wide by 100 mm long is where the adhesion between layers continues to be an issue. I also tried printing the entire PLA/TPU stack at profile settings for Prusament PLA with similar results, although the adhesion seemed just a bit stronger on the thin long runs. I ran another set of prints where I used the profile for Prusament PLA but dropped the nozzle temp down to 220 deg C for the Fiberlogy 40D layers because I was getting some stringing across 90 deg corners.
That all said, unless anyone has additional suggestions, I’m done trying to get the thin long runs to adhere for now and will work on finding another way to get my designs to work. Thanks for looking…
RE: PLA layer separation after switching from TPU
Interesting follow-up. Have you tried printing the part only in PLA to rule out geometry weaknesses of your model? Sounds like you were almost there, or you did and I mis-read your follow-up.
Remember many silk filaments are a blend of PLA and TPU. Also remember that many silk filaments have poor layer adhesion. You might need to purge more than you expect?
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