"Caved in" sides in PLA prints

[Multitube 0]

Hi!

 

When printing with Ultimaker PLA on my S5 Pro Bundle and an AA 0.8 print core, the sides of the prints are 'caved in', see attached image.

The middle is around 1,5mm under sized, top and bottom are ok.

 

I've used the default Ultimaker profile, with the only difference being the layer height (0,4mm)

See attached 3mf and ufp files.

 

I've never really experienced any shrinkage using PLA and the problem doesn't occur when printing with Ultimaker Nylon (which is my go-to material).

 

Any idea's?

Thanks!

 

Tim

UMS5_X21-0000079-Rev_-.3mf UMS5_X21-0000079-Rev_-.ufp

[geert_2 558]

I would guess it is because of the heat? PLA print want to be cooled fast to below 50°C, otherwise they sag or deform. If you print 0.8mm wide and 0.4mm high sausages, that is a lot of heat. So I could imagine that they do not cool down and do not solidify quickly enough? So the walls stay somewhat soft, and are pulled inwards? Especially if the bed-temperature would also be quite warm. Molten plastic tends to be pulled into a thick blob. This is a guess, but it is the only thing I can immediately think of.

 

[Multitube 0]

Hi Geert,

 

Thanks for the reply. Temperature would be my first guess as well, but since we have no problems at all with all other profiles I figured there would be something else going on.

[geert_2 558]

When I did print circles (tubes) at 0.3mm layer height and 0.4mm nozzle, I already noticed the layers would stay flexible for some time: upon the next pass of the nozzle, the previous layer would still move a bit. So on your 0.4mm high and 0.8mm wide layers, that effect could be far worse. It could also be the combination of slow layer cooling, plus heat radiated from the bed, plus a warm environment.

 

Have you tried putting a 30cm desktop fan - the same fans we use in summer to keep our heads cool - in front of the printer? Even at low speed it should provide enough air for additional cooling, just to evacuate the hot air. See if that makes any difference?

 

It could also depend on your environmental temperature and humidity: if too hot and moist (e.g. 30-35°C) that would also prevent cooling of PLA. Other materials that print at higher temps, like PET, ABS or nylon, would not be affected. But since PLA already starts deforming from 50-55°C...