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I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!

Posted by JazzyB 
I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 28, 2013 06:35PM
Hi!

First up, I'd like to say I'm unsure that my thermistor is reading the correct temperature at the hot end (I've found the min extrusion temp for some coloured ABS I have to be 170deg, which to me seems very low - by minimum extrusion temp I mean, if I go any lower than that the extruder stepper motor stutters or stalls). Could it be normal for ABS to still be slowly extruded at 170 or not?


Next, my main question!

I'd like to find out - does anyone know what exactly causes the effect shown in my pictures?




I've JUST repaired my reprappro mendel and this was the first print since, it was all looking flawless about 2 hours into the print but things took a turn for the worse after I turned off the lights and went to bed. I am printing in ABS, the parts stick to my kapton-tape-covered bed like GLUE, but I understand that as each layer cools it "pulls inward" while contracting and that this causes stresses.

I think this is what I'm seeing, stresses from the contracting are literally delaminating or 'pulling apart my layers' - and then I get what looks like a crack in the part (actually it's the topmost layers pulling so hard that they pull one of the middle layers apart)

What is the reason for this? the part sticks to the kapton like GLUE as I said - but it doesn't stick each layer to the last layer very well. How can I get a stronger bond between layers? I'm about to try turning the temp up, but, is there anything else I should change/check? E-steps is well calibrated and amount of plastic / layer heights etc seem spot-on...

Cheers,

JazzyB
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 28, 2013 08:07PM
Ot
De-laminating? You work in printing huh?
/ot
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 28, 2013 08:17PM
LOL :-) Nope!

Just figured that they were separating like plywood or something similar which is made up of multiple layers - that's called delamination, figured it would be the same term here!
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 28, 2013 08:38PM
hmmm I do get something similar when I finish my prints and take them out in the cold... I think its because I didn't heat the PLA enough for it to bind. but don't quote me on that... I'm still trying to debug my own bugs tongue sticking out smiley

cheers
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 28, 2013 08:51PM
Wow! With pla?

Id say your probably not printing hot enough OR not enough plastic... if theres not enough plastic the layers wont bond either, they will just sit on top of each other... they do need to "squish together" a bit...

My problem is different though, pla works perfectly. But ABS is a different beast, as it cools it REALLY pulls on itself as it contracts... this contracting/pulling force is whats causing my problem... it really curves and bends once it has delaminated too where pla tends not to...
VDX
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 28, 2013 11:27PM
... rise the temps and try with a box around the printer for higher ambient temperature - this will reduce warping and mechanical stress during cooldown ...


Viktor
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 29, 2013 04:06AM
"Turkey bagging" hey? I'll have a look for a good sized box for next time I print this sort of object, I had moderate success tonight though! Pushed the temperature from 180ish up to around 220-230 and I only JUUUST have a tiny crack on one side, but it's the best attempt so far and 200% better than the last, the part is useable, but still could be better.

I also noticed at 230 degrees (my starting temperature) there were many tiny holes in the walls of the print. These were lessened by turning the temperature down to 220. I'm almost sure then, that these holes are related to heat in some way.

Pic attached showing the holes, left side of the pic was mostly 230 degrees, right side (probably 1/3 of the part) was done at 220...

I really would love to do this WITHOUT turkey bagging the machine, I like to watch, to monitor the progress... especially during these early stages where I have a LOT of failed prints (ones that would ruin the machine if I let them continue unattended) BUT - If it really helps the situation, I might as well optimise the process! Cheers Viktor, I'll try that when I can ;-)

JazzyB
Attachments:
open | download - IMG_20130129_220547(2).jpg (450.4 KB)
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 29, 2013 04:21AM
My understanding is that the amount of contraction of the plastic - PLA or ABS - increases dramatically as the temperature falls rapidly below the glass transition temperature of the particular material which is one of the reasons for a heated bed - to maintain the temperature at or just below the glass transition temperature rather than at room/ambient temperature. As the glass transition temperature for ABS is so much higher than that of PLA, (around 140C compared to 70C), printing with ABS is quite a problem.
The solution which is often quoted is to effectively enclose the printer - put it in a box - being careful not to compromise safety of course! Richgain, ( [mynext3dprinter.tumblr.com]) and NumberSix ( [numbersixreprap.blogspot.co.uk] ) have described this on their respective blogs.
Alan
VDX
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 29, 2013 04:29AM
... the tiny holes could be caused by humidity, the filament accumulated - with preheating it in an oven at around 80 degC for an hour (or storing in a box with dehumidifiers) this can be avoided ...


Viktor
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 29, 2013 04:56AM
Ah crap.... that probably is humidity, I've been carelessly storing my filament :-(
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 29, 2013 06:32PM
I have also had success post heating the part. What I do is when the print is over turn the HB to max and put a small cardboard box over the print, after 15 mins or so set the HB to 80C then in another 15mins or so I turn it off but leave the part under the box untill its about room temp. This has helped on a couple parts that I needed to not crack during warming.
But if they are cracking during the print you are going to have to raise the ambient temp with a turkey bag or enclose your printer as others have said.
Re: I call this "De-laminating" or "Thermal Cracking" - but, how do I stop it!
January 29, 2013 07:46PM
Gulf Wrote:
-------------------------------------------------------
> I have also had success post heating the part.
> What I do is when the print is over turn the HB to
> max and put a small cardboard box over the print,
> after 15 mins or so set the HB to 80C then in
> another 15mins or so I turn it off but leave the
> part under the box untill its about room temp.
> This has helped on a couple parts that I needed to
> not crack during warming.
> But if they are cracking during the print you are
> going to have to raise the ambient temp with a
> turkey bag or enclose your printer as others have
> said.


Ha! Heat-treating ;-) nice!

All this talk of enclosing the part in a heated chamber was making me think that way, it helps with steel parts at my work, so I guess it's worth trying out! Thanks ;-)
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