Scholarly articles on PLA and Strength of PLA prints vs nozzle size and layer height.  

RE: Scholarly articles on PLA and Strength of PLA prints vs nozzle size and layer height.

Nice, some reading material for when I'm not randomly wasting my time on youtube.  Thanks! 

RE: Scholarly articles on PLA and Strength of PLA prints vs nozzle size and layer height.

I finally got to spend some time with the Strength of PLA article. By coincidence, I'd watched Stefan's CNC Kitchen video on the same topic recently. He concluded that a 0.15mm layer height was optimal, but I was not convinced because he didn't seem to take the extrusion width into account. Wider nozzles confined to narrow widths will produce more rounded extrusions, so I was hoping for more data. Looks like this article provides more, even if the methodology differs. Stefan pulled his parts apart vertically, looks like these guys whacked them with a hammer of some sort.

My takeaway:

• The test part was 20x10x150mm with 2.4mm thick walls printed vertically with no top or bottom layers and no infill.
• 6 perimeters were printed for 0.40mm, four for 0.60mm and three for 0.80mm nozzles (presumably with extrusion width = nozzle size) to achieve a consistent 2.4mm wall thickness.
• The only layer height tested across all 3 nozzle sizes (0.40, 0.60 and 0.80mm) was 0.20mm. 0.15mm parts were noticeably stronger at 0.15mm layer height with 0.60 and 0.80mm nozzles, so I wonder why they didn't include that height for the 0.40mm nozzle.
• Nozzle width (so presumably extrusion width) made a significant difference in part strength at 0.20mm layer heights at the identical wall thickness. Fewer wider extrusions performed better. This appears consistent at all layer heights. (No surprise there.)
• Higher layer heights result in rapidly declining part strength, at roughly 50% between 0.20mm and reasonable maximums for each nozzle size (0.6mm for 0.80mm nozzle, 0.45mm for 0.60mm nozzle and 0.30mm for 0.40mm nozzle). As layer height is increased above 0.15mm, part strength using any nozzle size drops off dramatically. (This one was a surprise for me.)
• The testing used widely varying extrusion rates. I'm not sure what the reasoning behind this was, but the higher tests were done with nearly double the amount of filament flow as the lowest layer heights.
• Testing was limited to PLA only. Would be very interested in results for filaments meant to be "strong".

The article does note that their findings contradict other research indicating that higher layers result in stronger parts (within reason), so some sort of final conclusion would be nice. I don't have any means of doing a formal test other than whacking parts with a hammer.

I also casually follow some of the miniatures printing groups, and recently watched a video indicating that using detail levels much below 0.10mm don't result in significantly better prints (although this was on a different printer).

Based on this, I have to reconsider my position on Stefan's recommendation for 0.15mm layer heights. Other than gaining print time (which is important), thicker layers may not be optimal. Or they are. One of those.

RE: Scholarly articles on PLA and Strength of PLA prints vs nozzle size and layer height.

The "Impact of FDM on PLA" article wasn't so interesting. Apparently additives impact print quality. I suppose this one underscores the importance of food-safe handling. Additives seem to collect in the gaps in PLA prints, so presumably are in more contact with food than if they were blended throughout.

RE: Scholarly articles on PLA and Strength of PLA prints vs nozzle size and layer height.

I too thought that it appears additives migrate to the surface of PLA during printing, but then again maybe squashing an polymer bulked out with say chalk, would do this!. Also agree, shame more materials were not tested.

Personally I don't use PLA, but PETG mainly so these findings did not really help me, but the drop off in layer height, did also surprise me, but could this just be down to the particular PLA they used and temperature?. I know with PETG, I can print exactly the same part at one temperature and it will be strong as hell, yet increase the temperature a bit and it becomes brittle.

RE: Scholarly articles on PLA and Strength of PLA prints vs nozzle size and layer height.

Some more general information about different materials used in FDM printing:

https://edutechwiki.unige.ch/en/3D_printer_filament