PETG Bonding issue when using PLA interface layer

Bambu Lab P Series Troubleshooting
1

A particular layer comes apart after printing, reproducibly. I need help on fixing that.

I’m trying to print a large rectangular case (22x22cm) that I designed.

Using a P1S and BambuStudio 2.8.1.55.

It prints a 4-sided wall of 3mm thickness in PETG, which is fine. But then the wall gets a wider lip (10mm), which is supported on the outside with a PLA interface layer.

And right there, the bonding isn’t working. Here’s how it comes apart when I pulled a bit on it:

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Here’s an image of a smaller sample I made, upside down so that you can see better where it comes apart:

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Here’s the print layers:

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The dark green is the PLA interface layer.

I suspect that, after printing a part of the 3mm wide wall, when the P1S switches to the PLA, too much time passes, letting that PETG wall layer cool down too much, so that, when eventually the next PETG layer on the 3mm wall gets printed, the new layer doesn’t bond well with the cooled one below it.

Also, it made no difference if I close the P1S or not - same problem, so the heat in the chamber hardly matters.

How is this best solved?

2

My feelings would be that it’s not so much of a cooling issue, but a purging one. Without purging enough, you are going to see layer bonding issues.

Maximize your purging between PLA and PETG and see if that makes a difference.

3

PLA isn’t getting fully flushed out after printing the interface layer. Best to try maxing the purge volume. Even then it might not completely flush out the PLA, so you will end up with some PLA in between the layers of the PETG part, reducing the layer adhesion.

4

Did you not get a wiki link ? because you are mixing filaments ?

5

Purge as high as your slicer will allow you to take it. Single nozzle multiple material type is asking for contamination

6

It was indeed the flushing. And only setting the PLA-to-PETG to 900 wasn’t enough either. Only after setting both transitions to the max, it worked well, and the layers stick now properly.