Exploring Extrusion Limits - Soft (64D) TPU
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David has already implemented non-linear extrusion via the M592 command which will be appearing in the next release. I am using it already and it works well. So far I have used it for PLA, PETG and TPU.
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Cool, I'll await the wiki page before asking much more about it then. I presume what I was discussing was the driver for it's development?
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Links for others who stumble across this post:
G-Code Wiki
Reprap Forum Post (also linked on above page)
Duet Forum Post -
Yes, good links. Here's what I discovered that made me interested in this topic and it explained why I was struggling to get uniform extrusion on walls/skin/etc.
http://www.extrudable.me/2013/04/18/exploring-extrusion-variability-and-limits/
This guy was ahead of the curve.
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Thanks for that. I've found TPU is a real slow material compared to the others. It's pushed me into the needing to process faster zone when I'd much rather be working with bog standard parameter sets.
Didn't say in the original post but spec is:
0.4mm nozzle.
E3d V6 Hot end.
250mm of bowden tube
E3d titan extruder with E3d's standard motor (current high, temp 52C) -
I love these threads…investigative 'tweaking' and pushing the limits to find the low/high limits.
Thanks for doing the research and sharing...Keep it coming!
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Changed spool and it threw out my figures. Foolishly thought diameter would be similar with the same batch number! I'm going to adopt the following procedure when setting up materials from now on. I checked the gcode and Slice3r was calling for extrusion widths varying from 0.4 to 0.7 for 0.2mm layer thickness.
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Best effort extruder calibration
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Measure filament with micrometer looking for light drag of the filament in the micrometer jaws
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Run a 20mm square, 10mm high cuboid with 1 vertical shell and 0% infill to get a thin wall
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Set all extrusion widths to 0.4mm and run a range of eight parts with increasing volumetric extrusion rate.
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Do the same for 0.7mm
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Measure wall thickness on all parts taking enough samples on each part to get an average.
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Compare the calculated extrusion multiplier that would be required to correct the 0.4 and 0.7mm wall thickness to the correct width. Pick the volumetric rate that has the most similar required correction for the 0.4 and 0.7mm wall thickness. Apply the calculated extrusion multiplier
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rebuild the 00.4 and 0.7mm walls with the chosen parameters.
The 20x20x10 samples take minutes each. Normally takes me longer to measure two points on each side than it does the printer to print them!
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Since doing the above I've noticed the muck that accumulated in the extruder has all but disappeared. In retrospect this was an obvious sign that I was pushing things far too hard.
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I've just realised that I think I'm struggling with something else here.
Yes, I can see a non linear relationship between requested volumetric output and a required correction on a 0.7mm wall.
But; I'm currently using autospeed on Slic3R and the problem is at the same requested volumetric output 0.4mm walls need a greater correction than 0.7mm walls. The 592 feature won't help here. Because I am requesting the same volumetric rate the formula from the duet wiki will apply the same correction:
(1 + min(L, Av + Bv^2))
Any more hints apart from have a little filament bonfire in the car park!
I'm getting tempted to force Slic3R to use the same extrusion thickness for all the different types of deposition (e.g. perimeter, infill, outer/inner, etc.). I can bodge the extrusion multiplier to get that right and it should make something then…
Edit:
Titan Extruder
E3D V6 Hotend
0.4mm Diameter Nozzle
0.2mm Layer Thickness -
I've been testing volumetric extrusion rates from 1.6 through to 3.4mm3/sec.
I'm beginning to think the opaque appearance is the polymer overheating. I had a filament jam late last week that was cause by over extrusion on the first layer blocking the path out of the nozzle for the polymer on the second layer. With a bit of a shove it started feeding again for the third layer, but in a white colour and almost frothy.
I'm currently thinking that;
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Running slowly increases the time the polymer spends in the nozzle and it over heats and begins to bubble slightly giving an opaque appearance to the think walls, and white to the parts.
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Running fast reduces the time in the hot end and so reduces the ultimate melt temperature, and makes clearer parts.
I've been increasing the nozzle temperature to reduce polymer viscosity, but perhaps the polymer is just particularly crap at taking heat from the hot end. Maybe a longer melt zone at a lower temperature would have the same effect without risking over heating the melt?
I had shear thinning floating around in the back of my brain but at the higher speeds, particularly on the thinner walls the parts didn't only look bad but there were holes in the walls, so if that was a thing for this polymer and I hadn't reached the extrusion rate where that occurs it was well in excess of where I am working.
Edit: Recommended processing temps were 230-250°C and the polymer does ooze out of the hot end at 230°C.
Edit 2: I think I may also be suffering with the polymer having next to no melt strength.
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