Printing airtight with PETG

[shcenator 0]

Hi all

 

I am trying to print some small airtight containers on my UM3. My normal settings are just PLA settings with some minor changes:

 

temp: 250

bed temp: 95

speed: 40

flow: 90

no fan

 

I read somewhere on ultimaker that an idea would be to increase flow (I changed it to 100 %) and reduce speed to half (20 in my case) while also having no fan. However, when doing this I get horrible results with minimal layer adhesion. Anybody have an idea what to do and perhaps a better solution for airtight prints with PETG?

 

[geert_2 556]

On my UM2 (=single nozzle) I get watertight PET parts by printing at low speed, low temp, thin layers, no fan. Usually 25...30mm/s, 215°C, 0.1mm layers, bed 80...90°C, 0.4mm nozzle. But 0.06mm layers are even better.

 

At slow speed, print cool to prevent the PET from decomposing and getting brown. Layer bonding is excellent: when overloaded, fractures run diagonally through parts, disregarding layers.

 

Main disadvantage of no fan, is that overhangs and bridges are terrible since the material won't bridge well. But for my long flat models, this usually is no problem.

 

If you would use PVA-supports on an UM3, any PVA strings might cause holes in the PET. Consider using PET for supports (thus a single material).

 

Print a few small test parts before doing a large real part.

 

Pictures:

 

Test blocks in PET, layer height from left to rigth: 0.4mm, 0.3mm, 0.2mm, 0.1mm, 0.06mm. Top row printed at 50mm/s, bottom row at 10mm/s. All 0.4mm nozzle. Slowest and thinnest-printed test blocks are getting brown due to slow material flow in nozzle.

 

Testblock at 10mm/s and 0.06mm layers, left as printed, right polished. Transparency indicates good layer bonding and very few internal voids. Absolutely watertight.

 

The 3D model. Text is a hollow watermark, sitting halfway in the testblock.

 

Keychains in PET. Ruler units are in mm and cm.

 

Fractured carabiner hook: fracture pattern radiates in all directions, mostly not following layer lines, indicating good layer-bonding.

 

Idem, other side.

 

----- end -----

 

[shcenator 0]

Hi Geert_2

 

That looks super nice. What are printing temps for your 10 mm/s and 50 mm/s prints? You do not change your flowrate? is it the same for all speeds? Do you see any variation in parts strenght between the different layer heights?

[geert_2 556]

No, I didn't change the flowrate, so it was the standard for PET on my UM2, and I left it at 100% on the machine.

 

I had to look up temperatures for these test blocks (I had written it down somewhere):

- all were 215°C, except:

- 0.06mm layers at 10mm/s (unpolished block) = 210°C

- 0.06mm layers at 10mm/s (polished block) = 200°C

- 0.4mm and 0.3mm layers at 50mm/s = 225°C due to the much higher extruded volume

 

The recommended temp range by the manufacturer is: 215...250°C, so I am at the lower edge. I once tried higher temps too, but that gave more bubbles and more stringing, and faster decomposing and browning.

 

By the way: test blocks are 10mm x 20mm x 10mm, and watermarktext is 3.5mm caps height.

 

I don't really know about part-strength vs. layer-height. But from these tests it was clear that thicker layers and faster speeds gave more "frosted glass effect". That means more voids, and probably less strength (but I am guessing now). Printing at 0.4mm layer height was still possible, but then cooling became an issue: the block didn't cool down fast enough and it started deforming.

 

I would suggest you run a similar test, but maybe with a testmodel more suited for your application and more similar to your final models (e.g. with overhangs and bridges if you need these). This gives good understanding of your printer and your filament, and you will win back that time investment very fast.