Have you ever wondered what actually goes on in the hotend of your 3D printer? It doesn’t seem like much of a secret – the filament melts, it’s pushed out by the pressure of the incoming non-melting filament and lather, rinse, repeat. Or is there perhaps more to the story?
To find out, a team from the University of Stuttgart led by [Marc Kreutzbruck] has taken the unusual step of sticking the business end of a 3D printer into a CT scanner to take a detailed look at what’s actually going on there. The test setup consisted of a Bondtech LGX extruder and an E3D V6 hot end mounted on a static frame. No XYZ motion control was required during these experiments, but a load cell was added to measure the extrusion force. The filament was somewhat special – high impact polystyrene (HIPS) mixed with some tungsten powder (1% by volume) to provide better contrast to X-rays. The test system was small enough to be housed in a micro-CT scanner that produced both 360-degree computed tomography images and 2D X-rays.
The observations made with this experimental setup were quite revealing. The most important message is that higher filament speed results in a smaller contact area between the nozzle wall and the melt, thanks to an air gap between the solid filament and the metal of the nozzle. They also found an increased tendency of the incoming filament to kink at high extruder speeds, which is consistent with practical experience. In addition, the filament speed is more important for the print quality (measured by the extrusion force) than the heating temperature. Although both obviously play a role, they recommend that if higher print speed is required, it is best to optimize the hot end geometry, particularly an extended barrel to allow for sufficient melting time.
Earth-shattering stuff? Probably not, but it’s nice to see someone doing a systematic study on this topic instead of relying on superficial observations. And the pictures are pretty cool too.
