Some materials seem to need minimum flow

[fuh 1]

I tried to print a pretty much "precision part" with ultimaker.com's black PLA. So I sliced with 0.1 mm and printed with just 25mm/s – but failed! This material, though molten, seems to be much less fluid than others, for example the light blue one, at the same temperature. The effect was that it seemed to disintegrate to droplets when it left the extruder, resulting in an ugly, "torn" structure. I aborted the print job. Then the idea came to my mind that there might be some kind of minimum flow, so I tried again with 0.2 mm and 50 mm/s. The problem is gone, the result looks perfecty even!

My conclusion: Fine slicing or slow speed doesn't guarantee a better result!

 

[yellowshark 132]

Hi FUH, I have tried over 20 plus different colours of PLA, spread across 2 suppliers, Faberdashery and Colorfabb. I have not read this anywhere but I am convinced that the pigments used to dye the filaments affect the flow characteristics.

Without doubt it is true that filaments of different colours from the same manufacturer may have different flow characteristics let alone filaments from different manufacturers. I have found that normally the difference equates to a 5 degree difference in extruder temperature from the manufacturer norm (norm being established by myself), but I have experienced 15 degrees. I am not including in this any “funny” filaments like woodfill.

Whenever I get a new filament I always run a series of tests to try and establish the optimum setting for a variety of layer depth/print speed combinations.

As for your problem of droplets, that sounds to me as if maybe you had the filament in a heated extruder not extruding for too long before starting the print and not manually extruding the filament before staring the print. Sometimes you need to extrude 50mm+ before starting. Of course it may not be that but I have experienced that myself.