Woes of ABS and part warping
Posted by dlc60
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Re: Woes of ABS and part warping September 20, 2017 02:04PM |
All good suggestions, but I have some questions.
How do you get the beds that hot? It is all my system can do to reach 105C, and that takes half an hour at least.
If you don't use a glass topper for the bed (so it is really flat, aluminum beds are always warped in slight amounts) do you apply your tape/slurry directly to the bed plate? If you use some other liner for the bed, how do you hold it down? Is the stuff easily cut? There are lots of bed sizes out there and they are not all square either...
I have avoided a complete enclosure because the electronics are under my bed. If I put my whole unit in a box I guarantee the driver electronics will fail. I have a fan blowing across the heat sinks over the stepper drivers to avoid this. And this solution was needed for a printer that isn't fully enclosed! If I put my delta in a box and raise the temperature I am pretty sure my drivers will over-temp limit. How do you avoid that?
My last run had this configuration:
Bed: 100C, nozzle: 240C, Infill 40%, "Mouse ears" on the sharp corners, 5 rings of brim, 0.3mm layers, 40mm/s print speed, 20% speed first layer
Glass topper with Kapton tape and plenty of glue stick
Walls around the printer with a vent for the electronics fan, the top was 80% enclosed, the sides fully enclosed - No clue of internal temperature.
Results:
Less than 1mm warp on the corners (pretty good from my experience).
Several layer separation cracks, one severe.
Analysis:
Higher infill % might reduce, but not remove the cracks. Higher nozzle temp might improve layer adhesion. However, this setup works fine on parts that are only 10-20mm high. This part is probably 100mm high. There are serious stresses as the upper levels cool and shrink, the base level is not cooling as much and not shrinking much - This means high stress on those sharp edges, if the part cannot warp because it is solid to the bed, then something is going to give, hence cracks. This implies that I should get those first layers to cool and shrink right away so that upper layers don't pull apart. But the "wisdom" that I read says we need to slow the cooling process. Huh? The ABS is gonna shrink whether it cools fast or slow, so I am experiencing cognative dissonance here.
The common wisdom doesn't seem so wise in the face of these conflicting needs.
So.
It seems to me that what needs to happen is that I need to bring the entire environment to the same temperature as the print bed (100C or so) and hold it there for the entire print, then cool the bed and the air inside down at the same rate. IOW, I don't need to heat the bed, I need the entire build volume enclosed in a temperature controlled chamber or have no hope of getting this to work.
In my mind, heating my electronics to 100C is a bad idea. Temperatures over 60C will seriously stress most commercial components, so THIS means I need the electronics to be outside of the temperature chamber. This means also that I need to have stepper motors that can survive temperatures around 100C comfortably to provide long term service. Chinese steppers do not provide their specs, so this means getting lots of steppers for replacements or spending $$ on quality steppers that are warrented at these temperatures. This is not sounding like a hobby anymore, now it is an engineering challenge.
I will work on this and see what I come up with. I need to find a supplier of cheap ABS for all this experimentation.
Either that or move to PETG as my building material - At least PETG doesn't smell so bad...
Keep the ideas coming, I am listening closely,
DLC
How do you get the beds that hot? It is all my system can do to reach 105C, and that takes half an hour at least.
If you don't use a glass topper for the bed (so it is really flat, aluminum beds are always warped in slight amounts) do you apply your tape/slurry directly to the bed plate? If you use some other liner for the bed, how do you hold it down? Is the stuff easily cut? There are lots of bed sizes out there and they are not all square either...
I have avoided a complete enclosure because the electronics are under my bed. If I put my whole unit in a box I guarantee the driver electronics will fail. I have a fan blowing across the heat sinks over the stepper drivers to avoid this. And this solution was needed for a printer that isn't fully enclosed! If I put my delta in a box and raise the temperature I am pretty sure my drivers will over-temp limit. How do you avoid that?
My last run had this configuration:
Bed: 100C, nozzle: 240C, Infill 40%, "Mouse ears" on the sharp corners, 5 rings of brim, 0.3mm layers, 40mm/s print speed, 20% speed first layer
Glass topper with Kapton tape and plenty of glue stick
Walls around the printer with a vent for the electronics fan, the top was 80% enclosed, the sides fully enclosed - No clue of internal temperature.
Results:
Less than 1mm warp on the corners (pretty good from my experience).
Several layer separation cracks, one severe.
Analysis:
Higher infill % might reduce, but not remove the cracks. Higher nozzle temp might improve layer adhesion. However, this setup works fine on parts that are only 10-20mm high. This part is probably 100mm high. There are serious stresses as the upper levels cool and shrink, the base level is not cooling as much and not shrinking much - This means high stress on those sharp edges, if the part cannot warp because it is solid to the bed, then something is going to give, hence cracks. This implies that I should get those first layers to cool and shrink right away so that upper layers don't pull apart. But the "wisdom" that I read says we need to slow the cooling process. Huh? The ABS is gonna shrink whether it cools fast or slow, so I am experiencing cognative dissonance here.
The common wisdom doesn't seem so wise in the face of these conflicting needs.
So.
It seems to me that what needs to happen is that I need to bring the entire environment to the same temperature as the print bed (100C or so) and hold it there for the entire print, then cool the bed and the air inside down at the same rate. IOW, I don't need to heat the bed, I need the entire build volume enclosed in a temperature controlled chamber or have no hope of getting this to work.
In my mind, heating my electronics to 100C is a bad idea. Temperatures over 60C will seriously stress most commercial components, so THIS means I need the electronics to be outside of the temperature chamber. This means also that I need to have stepper motors that can survive temperatures around 100C comfortably to provide long term service. Chinese steppers do not provide their specs, so this means getting lots of steppers for replacements or spending $$ on quality steppers that are warrented at these temperatures. This is not sounding like a hobby anymore, now it is an engineering challenge.
I will work on this and see what I come up with. I need to find a supplier of cheap ABS for all this experimentation.
Either that or move to PETG as my building material - At least PETG doesn't smell so bad...Keep the ideas coming, I am listening closely,
DLC
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Re: Woes of ABS and part warping September 22, 2017 12:56AM |
Line power requires extra safety precautions. Use a fuse to protect against broken/shorted wires. Ground the printer's frame. Add a TCO to the heater or bed plate to prevent thermal runaway if the SSR fails. Here's the wiring diagram for the bed heater in my printer:
I used a Keenovo 750W heater and Crydom D1225 SSR -an expensive part that I got for free, but there are plenty of others that will work just fine for lower cost. The Keenovo heater seems to be very well made.
Full details of the bed mechanical design are here: [drmrehorst.blogspot.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
I used a Keenovo 750W heater and Crydom D1225 SSR -an expensive part that I got for free, but there are plenty of others that will work just fine for lower cost. The Keenovo heater seems to be very well made.
Full details of the bed mechanical design are here: [drmrehorst.blogspot.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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Re: Woes of ABS and part warping October 02, 2017 09:58PM |
I print almost exclusively ABS. With the brands I've been using the build chamber must be >45c and <50c. I have a vent at the top of my enclosure that is partially blocked by a piece of cardboard. I leave a multimeter thermocouple in the chamber and open/close the vent to adjust temperature.
In my experience there is really no way to reliably print ABS if the chamber is <45c. I used to play with ABS juice and other tricks, but even if you keep the first layer in place the print will just delaminate somewhere else and you end up chasing your tail trying to improve layer adhesion while maintaining crisp print quality.
I print on bare Kapton at 95c and scale my parts up to 100.6% to compensate for shrinkage. The parts pop off the bed themselves as the bed cools.
Here are some examples of challenging ABS prints:
I find that ABS is a very nice plastic to print in because aside from the warping it is very well behaved. PLA and PETG are very goopy when hot whereas the ABS kind of slides through and off the nozzle and overhangs/bridges very well.
I've also had problems with PLA creeping under load over time. When I'm printing functional components I can't risk them bending out of shape if left in the sun on a hot day.
(I wish slicers would let you define a per-filament scaling factor because sometimes I forget to print ABS at 100.6%. I mean I could change my firmware steps/mm but that screws up prints in other plastics and is a pretty dirty hack that could have other consequences.)
Edited 1 time(s). Last edit at 10/02/2017 10:00PM by 691175002.
In my experience there is really no way to reliably print ABS if the chamber is <45c. I used to play with ABS juice and other tricks, but even if you keep the first layer in place the print will just delaminate somewhere else and you end up chasing your tail trying to improve layer adhesion while maintaining crisp print quality.
I print on bare Kapton at 95c and scale my parts up to 100.6% to compensate for shrinkage. The parts pop off the bed themselves as the bed cools.
Here are some examples of challenging ABS prints:
I find that ABS is a very nice plastic to print in because aside from the warping it is very well behaved. PLA and PETG are very goopy when hot whereas the ABS kind of slides through and off the nozzle and overhangs/bridges very well.
I've also had problems with PLA creeping under load over time. When I'm printing functional components I can't risk them bending out of shape if left in the sun on a hot day.
(I wish slicers would let you define a per-filament scaling factor because sometimes I forget to print ABS at 100.6%. I mean I could change my firmware steps/mm but that screws up prints in other plastics and is a pretty dirty hack that could have other consequences.)
Edited 1 time(s). Last edit at 10/02/2017 10:00PM by 691175002.
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