Extrusion multiplier = f(extrusion rate)
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To achieve a certain extrusion rate over a wide and varying speed range, it is necessary to adjust the "target" extrusion rate, because the difference between "target" and "real" extrusion rate depends on the extrusion rate itself.
The picture below shows an example of PLA extruded with a e3d v6 type nozzle 0.5mm, a titan full metal throat, air active cooled e3d cold end heat sink and varying extrusion rates.
With increasing extrusion rate the pressure/force needed to extrude the filament increases and because the force transmitted to the filament is not only done in an elastic way, the real filament feedrate starts to drop and need to be compensated non linear.
To be able to improve the print quality vs speed ratio, we need to compensate these effects. It could be done by applying a second extrusion multiplier, with is adjusted according to the extrusion rate. This second extrusion multiplier needs to be multiplied with the normal used one to achieve the compensated extrusion rate.
The in the diagram shown trend lines are just an indication, a piecewise linear approximation or whatever fits would be fine. The curves below show, that in the low speed range (e.g. < 15 mm^3/s) the deviation real vs target extrusion is small up to a point where it start to increase significantly. I guess this is the point where the forces applied to the filament by the extruder exceeds the "elastic" part and the filament surface (tick marks) start to "flow" (plastic deformation) in the extruder. Therefore a piece wise linear approximation using 3 points should improve the situation already noticeable.
The orange line in the picture shows the area where the filament start to slip, grind etc. in my case. This area cannot be used for e.g. outer perimeters, but still without big problems for solid top and bottom layers.
The dependency real vs target extrusion rate would have to be determined for a nozzle, filament and temperature combination manually or by using the filament monitor it could be done online automatically.
In case somebody tries to reproduce this curves, be aware that especially when using a full metal hot end and high temperatures you will end up with a jam, if you don´t stop early enough.
If somebody is interested, this topic is discussed here: https://www.duet3d.com/forum/thread.php?id=3693
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Very interesting…. Great works, congratulations.
