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How to improve print quality at higher speeds?

Posted by ruyvieira 
How to improve print quality at higher speeds?
December 20, 2018 10:30AM
I'm used to printing at 70mm/s tops, but at 150mm/s and beyond I get bad corners and either bad overhang curling (at temp high enough for flow to be good) or underextrusion (if I lower the temperature to decrease the curling).

What could I do to improve this? I'm using a regular MK8 extruder and two 5015 blowers. Would a geared extruder, 32 bit board and a better fan duct help me here?

Re: How to improve print quality at higher speeds?
December 20, 2018 01:36PM
better fan ducts will help in any case, to be honest lower your expectation a little or just slow down with small objects,,, at these speeds a 32 bit board be nice but you gotta allow the layer to cool enough before the next.
at 150 mm/s squirt of liquid nitrogen may help smileys with beer
gotta say though the printer sounded good at those speeds if I attempted that kind of speed I loose a nut or two.
Re: How to improve print quality at higher speeds?
December 20, 2018 05:06PM
If you want clean surface finishes, it becomes hard to cool the extruded plastic quickly enough. High powered fan ducts help but printed geometry redirects airflow. Identical layers that have received a different amount of cooling will display a different amount of smearing.

I've found that if you care about detail there is a fairly low hard limit on PLA print speed (40mm/s?). Lower accelerations will slow down the printer in detailed sections, but then you need to worry about pressure advance. ABS probably behaves better.

Its a pain to talk about print speeds because most people don't understand the relationship between toolpath, acceleration, and speed; and think their printer is running far faster than it actually is.

Edited 1 time(s). Last edit at 12/20/2018 05:06PM by 691175002.
Re: How to improve print quality at higher speeds?
December 20, 2018 05:32PM
I have found it advantageous to lower printing temperatures by up to 5 -7 degrees C for some projects and some particular filament types in order to maintain print quality at higher speeds.

The curling issue you mentioned is particularly noticeable when printing flexible material especially at sharp points .

To solution I used was to increase barrel pressure to compensate for potential under extrusion issues (which was an issue for both flex and rigid filament), to achieve this I found a more powerful extrusion system to be essential.

More power = More Hotend Barrel Pressure = Improved printing capabilities.

Re: How to improve print quality at higher speeds?
December 21, 2018 09:02AM
as some other members have indicated layer height and temp play a big roll in quality of corners. lowering the mass of the printer head might help clean up jagged edges,
but if surface of part is warped, then better cooling or running at lower temp might work, however lower temp does mean more drag on the nozzle.

one option is to reduce weight of moving parts in system. this would only partially fix issue of uneven corners.

lowering temp quicker to reach glass transition temp, either by lowering temp or by blower fans. (lowering temp increases drag on nozzle, so my choice would be more air flow)
filament becomes harder to push out the nozzle at lower temps as well. a geared extruder would improve flow, as long as the mass is still kept low.

my ideal suggestion: find a way to cool faster while heating up the hot-end more. higher temp means less drag, less pressure required for nozzle. and just have highest speed blower fans at nozzle,
also have nozzle coated in kapton tape, the blower should focus around the exit point of the nozzle. the nozzle should be insulates so it keeps heat.
the goal is cool material as fast as possible when it exits nozzle.

these are just my suggestions.
Re: How to improve print quality at higher speeds?
December 22, 2018 10:51AM
Ways to heat the hotend more: use a 12v heater instead of 24v. I used to do this, the nozzle heated really quickly, then I changed it for a 24v cartridge and well it slowed things down a lot to say the least

How to increase the extruder force: I guess with a 1:2 reduction? I have a 1:3 Titan clone and it skips steps when the extruder feedrate is above 15mm/s. For that feedrate I need about 300 steps per mm, which is about 4500 steps per second, which the arduino mega should be able to handle but something isn't right. Need to figure out a way around this

Improve cooling: with a different duct design? Maybe a smaller opening for increased air pressure?

How to decrease moving weight: maybe if I made a gantry out of CFRP or GFRP but I'm not too concerned with ripple since it's more discrete than my larger CoreXY at slower speed (pic below). I could try this once I get my CNC router moving. The only problem is it would cost twice what I paid for all my aluminum plates
open | download - corexy stripes.JPG (40.8 KB)
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