Author Topic: Bed heating and avoiding PLA warping  (Read 9352 times)

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Offline InfravioletTopic starter

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Bed heating and avoiding PLA warping
« on: May 06, 2023, 07:28:47 pm »
Especially for prints with high density or solid infill, but also for anything with several wall lines...

I've had issues quite often with prints peeling up at the corners when printing in PLA, and yet the two things which have fixed them on different occasions run completely counter to each other. That is to say sometimes a hotter bed helps, other times a colder one helps, and I've no way to know which in advance for planning future print jobs.

I'm using PLA, I don't have an enclosed build chamber, I have a textured bed with a flexible texture sheet which is magnetically held to the rigid heating element plate.

I always print with rafts, Cura does them with a first layer f thicker over-extruded lines, then a criss-cross of normal amounts of extrusion, and then starts printing the actual part and any support struts on a layer atop that.

I usually work at 205 degrees (C) nozzle, 65 bed* for the first layer, and then start the bed cooling to a lower temperature as soon as the first layer is down. For some parts though, particularly wider parts taking up a good fraction of the build plate (this issue never applies for small parts in the central few square cm only), I've had them warp up from the bed at the edges, and as they are mechanical parts for robots this isn't acceptable, a bit of warping and the whole part is useless. I usually had the bed cool to 60* degrees and stay there for the full print, this lead to warping of big parts. So I tried cooling to 45*, and it worked.

But then for another part, which I knew was a wide job, I pre-emptively set it to be 45* degrees throughout the print, except 65* on the first layer, but this warped up, so badly infact it fell off the bed. And when I say warping, I mean the raft layer coming up rom the print bed, with the part still firmly attached to the raft, not the raft staying on the print bed and the model peeling away from the raft. I tried widening the excess "brim" of the raft, but it didn;t help at all, even when the edge of the rat was several cm beyond the edge of the model the whole thing still warped up at the edges, with this warping travelling towards the centre until the whole raft detached from the bed. This print job however then did work when I ran it with the bed at 60* for everything but the first layer.

What on earth is going on here?

What is the trick to avoid warping with PLA and wide high density prints?

Thanks

*this is the temperature of the heated element plate, I'm sure the actual surface where the printing happens is rather cooler though due to some insulating effect of the flexible magnetic textured layer, 65 as the printer regards it is infact cool enough on the top of the surface to be almost but not quite on the pain threshold when one holds a hand against it, 65 on the heated element layer itself is rather painful if one catches it when peeling away the magnetic layer to remove a part.
« Last Edit: May 06, 2023, 07:36:49 pm by Infraviolet »
 

Offline Lindley

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Re: Bed heating and avoiding PLA warping
« Reply #1 on: May 07, 2023, 08:48:19 am »
Curious problem, though the first thought would be to fasten a thermometer to the bed surface to check what the temperature really is and if its maintained when the print is running.
Have not had and need to do this on our Ender3 but will check it out later today.

Normally do not have to use a raft or brim for smaller PLA parts, though wonder what is the typical base size of what you are printing ?

Is this a new problem to just this reel or PLA or have you always had it ?

When you say you have no enclosure are you printing inside the your house, so would assume it is a resonably stable 20c -ish with no really cold drafts.
 

Offline Whales

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Re: Bed heating and avoiding PLA warping
« Reply #2 on: May 07, 2023, 10:48:11 am »
Cleaning the bed with non-alcohol: I've had situations where alcohol was useless but cleaning the bed with water and ordinary dish detergent suddenly made things stick properly.

Increase first layer contact area: Brims and brim-like shapes are useful for small terminations of large items.  I also run my first layer very thick (0.35mm thick on a 0.4mm diam nozzle and "Extrusion width" set to 200%), this makes it much easier to get right.

Glue-stick + isoprop spreading: I've only tried this once recently but it seems to work.  Apply a small bit of ordinary glue stick to the bed, spray with isopropanol (apparently this is important) and then spread around on the bed with a piece of paper towel.

Masking tape: I'll cautiously note this one.  It can work great.  it can also work like shite.  It depends on the brand of the tape, some brands stick better to the prints than the bed (especially when heated) which is very frustrating.  I did this for a long time, only occasionally replacing bits of tape when they wore out or were torn off.  Required regular cleaning with soap and water. 

Feeling the bed surface temp with your hand: keep in mind your ability to judge 65degC depends on the thermal conductivity of the item you touch (they have to heat your fingers to reach your thermoreceptors, you can only sense the temperature of your fingers not what's outside them).  Some materials are safe to touch at 90degC, but metals can burn you down near 40degC.  A contact thermometer and a bit of sticky tape is probably the best option.
« Last Edit: May 07, 2023, 10:56:42 am by Whales »
 

Offline Lindley

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Re: Bed heating and avoiding PLA warping
« Reply #3 on: May 07, 2023, 07:04:44 pm »
Just checked the bed temperature with a metal tipped digital thermometer and when set at 55c it reads 51c when covered and held down with some cloth, but it does take some minutes to get to that temperature.    TA -  18c

Wonder if you are starting the print off very soon after powering up,  though the control panel shows its temp sensor reaches 55c in a couple of minutes think it needs at least 10mins+ for the whole bed /surface to get fully heated.
 

Offline InfravioletTopic starter

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Re: Bed heating and avoiding PLA warping
« Reply #4 on: May 07, 2023, 07:36:56 pm »
There might be an effect there, the top surface of the bed taking rather longer to come up to temperature than the part of the bed where the inbuilt temperature sensor is. I haven't any handheld thermometers to hand, but I might have some thermometer ICs buried in a box somewhere, I'll see if I can find them and then run a test with one of those on the top surface and see how it compares to temperatures the printer measures from lower down in the bed structure.
 

Offline Ian.M

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Re: Bed heating and avoiding PLA warping
« Reply #5 on: May 07, 2023, 08:45:27 pm »
Its easy to make a surface thermometer: Take a DS18S20 or other convenient TO-92 package temperature sensor, and wire it up with very thin wires, long enough to conveniently reach anywhere on the bed, to an Arduino or other device that can read and display the temperature (google for a sketch!), then take a cube of closed cell packing foam or similar, cut a small cavity for the sensor, and tape it down in the cavity flat side out with aluminum or copper foil tape for better thermal coupling. The square of metal tape should be smaller than the face of the foam cube to leave an approx. 5mm (3/16") margin all the way round.  You'll need to insulate the wire to lead joints so the tape doesn't short it out.  Then it only takes a minute or so to press the cube down where you want to measure so the foil is held flat against the bed and wait for the temperature readout to stabilise. 

Another approach is to use an IR camera or IR spot thermometer.  If the bed isn't matte black, you will need to cover it with something high emissivity to get an accurate reading, e.g. black vinyl electrical tape.

Don't be surprised if there is a 10°C or greater difference between the center and the edge of your usable print area, even after half an hour warm-up time, and don't expect the bed thermistor to be anywhere near accurately calibrated!  Adding a tape 'wall' between the edge of your bed and its support (if that's solid) to prevent drafts under the edges of the bed can help considerably to even it out.  There's not much you can do about the calibration unless you are prepared to take a *lot* of measurements to create a custom thermistor table for Marlin, and recompile the firmware, but at least you can note the offset at the glass transition temperature of your filament, and adjust the bed temperature accordingly in your slicer settings.
 

Offline Lindley

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Re: Bed heating and avoiding PLA warping
« Reply #6 on: May 08, 2023, 08:56:32 am »
Just been following up on some points raised by your question and these two links seem to explain things well, the second one directly addressing your warping problem.

https://core-electronics.com.au/guides/Printing_Perfect_First_Layers/

https://core-electronics.com.au/guides/Ultimaker_Cura_Troubleshooting_your_Models/

 

Offline hli

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Re: Bed heating and avoiding PLA warping
« Reply #7 on: May 08, 2023, 01:09:08 pm »
I can second the cleaning part. Clean your build place with dish detergent and lots of hot water, do not touch it afterwards. IPA cannot clean all residues (even worse: IPA on a hot build plate leaves its own nasty residues). Most of the warping issue come from insufficient bed adhesion due to wrong cleaning.
Maybe look at at https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-assembly-and-first-prints-troubleshooting/life-adjust-z-my-way/ for an explanation of getting a good first layer.
 

Offline InfravioletTopic starter

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Re: Bed heating and avoiding PLA warping
« Reply #8 on: May 08, 2023, 04:41:14 pm »
Useful links, but a "shiny and flat" bottom surface is never going to happen for me due to my build plate being textured, I has thought this texturing improved adhesion? I have this style of bed:
https://www.amazon.co.uk/Official-Creality-3D-Flexible-Magnetic/dp/B07GXJNK38

Also, as a note, I use in Cura some starting gcode which first lays a line along one side of the bed, then a line back the other way rather than a prime blob. This line is usually fairly well stuck down but can be peeled up as a whole once something has been used to pry up one end of it. I don't know if this gives any useful indications about bed adhesion?
 

Offline thm_w

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Re: Bed heating and avoiding PLA warping
« Reply #9 on: May 08, 2023, 08:38:38 pm »
Don't use rafts, it should be fine to print directly onto the bed. No you won't get a perfectly shiny glossy surface, but it will still look nice.

As mentioned you may need to wait a while for the bed to reach an even temperature before beginning your print. I have a 2min wait command in the gcode after bed temp is reached, and temp of ~65C for PLA, but, its a thick glass bed.

Usually with the magnetic bed you don't want to be prying parts up, once the bed has cooled, you pull the sheet off and flex the bed to release the part (if it didn't already pop off).
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Offline Lindley

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Re: Bed heating and avoiding PLA warping
« Reply #10 on: May 09, 2023, 08:50:06 am »
Which model of the Ender do you have and is this Warping problem something you have always had  or just started recently, eg with a different reel of filament ?

As those links above indicate, it does suggest your bed is not properly levelled and /or you need to adjust your Z offset to put more 'squish' on the first layer to aid adhesion.

We initially had problems with bed levelling on our Ender3 V2 and it only seemed to become stable once we changed the bed spring to the Yellow ones,  but never really sure if the springs fixed the problem or that we just got better at  level adjusting ?
Our bed is a glass one with a black textured finish which they originally shouted out as the best thing etc, yet the later V2 Neo has a  flexible steel magnetic plate ?!

Have you tried re-levelling your bed with a test print like Chep uses ?

 

Offline InfravioletTopic starter

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Re: Bed heating and avoiding PLA warping
« Reply #11 on: May 09, 2023, 12:28:29 pm »
Bed levelling is weird for me. My printer is a "CR20 Pro", it uses common Ender parts (so spares are easy to get), but it comes as a pre-assembled unit rather than a kit. The very weird part is it has no bed springs, all it has is an automatic bed levelling sensor, based on probing a grid of 9 points during the starting gcode of each print.
 

Offline Lindley

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Re: Bed heating and avoiding PLA warping
« Reply #12 on: May 09, 2023, 04:19:25 pm »
Its a bit of a different beastie to our Ender3 and so , it seems, is its set up.

Have you run this set up proceedure for your CR20 Pro  ?


If not recently, worth doing again  and when doing that 'squares' print the filament rubs off too easily, then typically you need to reduce the Z setting by a small negative amount to move the head closer to the bed and so squish the first layer more, then retry the print to note any improvement.
You need to do it in small amounts as too much and it could cause the nozzle to hit the bed !
 
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Offline ebastler

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Re: Bed heating and avoiding PLA warping
« Reply #13 on: May 16, 2023, 09:01:00 am »
One more thought, which I did not see mentioned yet: What room temperature are you printing at? If it is too cold, the bulk material might shrink too much after printing; the common recommendation seems to be "not less than 15° C". I run my printer in the basement and, depending on the season, sometimes have to heat the room a bit to avoid problems.
 

Offline hli

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Re: Bed heating and avoiding PLA warping
« Reply #14 on: May 16, 2023, 09:47:26 am »
due to my build plate being textured, I has thought this texturing improved adhesion?

It doesn't, its actually the other way round (mostly): quite a lot of filaments stick too well to a flat surface (e.g.a PEI sheet or glass plate). This does not happen on a textured plate. (this is also the reason for using glue stick - for most prints that's not there to _improve_ adhesion, but to be able to lift off the print afterwards).
On the Prusa printers, where you can get both the PEI and a the textured sheet, its well known that the textured sheets does not work well with PLA (and in contrast printing PETG on the PEI sheet will ruin it). Fortunately Prusa also has the satin sheet which is a great middle ground and works well with most  filaments.
 

Offline Jeroen3

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Re: Bed heating and avoiding PLA warping
« Reply #15 on: May 16, 2023, 11:57:14 am »
I usually work at 205 degrees (C) nozzle, 65 bed* for the first layer, and then start the bed cooling to a lower temperature as soon as the first layer is down.
Yeah, don't do that. It creates shear stress due to material shrinkage in hard materials like PLA. This is especially troublesome on textured plates where any shrink generates a mismatch in texture pattern and releases the print. It's actually an amazing feature of the prusa plates, when the plate cools, the print literally just falls of when using PLA. This is also a problem with thin prints, the fan cools it too much and generates warping where it lifts from the bed.

The creality plates are just sandpaper, prints will be stuck regardless, so if your print let's go from that you just have PLA with a very high shrink factor.
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Offline HobGoblyn

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Re: Bed heating and avoiding PLA warping
« Reply #16 on: May 17, 2023, 11:45:58 pm »
If I have either the ceiling fan on or the front window open in my living room (living room and dining room knocked into one) I get this problem.

Printers against back wall in dining room.

Window must be 8 meters away, ceiling fan about 6 meters.

In the summer I use 3 bits of thin ply duct taped together .

Once I start the print, I place them around it to protect from drafts.



 

Offline InfravioletTopic starter

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Re: Bed heating and avoiding PLA warping
« Reply #17 on: May 18, 2023, 03:38:23 pm »
Jeroen3, that's an interesting thought. Put like that then maybe even making the slightest (5 degree) bed cooling during the print is a mistake. Perhaps keeping it at the initial temperature throughout might be a betetr move.
 

Offline mendip_discovery

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Re: Bed heating and avoiding PLA warping
« Reply #18 on: May 24, 2023, 06:25:24 pm »
Glass has a low temperature coefficient of expansion but some of the steel stuff is a fair bit and that could be contracting at a different rate to the plastic or just the contraction might be enough to break the bond.

I borrowed a temp logger from work and taped some thermocouples to the glass and got quite a variation over the bed. But that wasn't helped by the printer also blowing air onto the bed.

Also had a chance to borrow a customer's thermal camera and got some interesting measurments as the bed doesnt heat up uniformly. Talking with other we came the the conclusion that the glass onto a painted bed is having some issues due to flatness. Some have found just adding some tinfoil in the middle has made the contact better. After all the glass is being clamped on the outer edges.

My plan was to get some of that thermal pad stuff and stick that to the metal bed to aid with transferring the heat quickly and uniformly as it would get into all little bits to make up for the lack of flatness.
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Offline janoc

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Re: Bed heating and avoiding PLA warping
« Reply #19 on: May 24, 2023, 07:32:39 pm »
I usually work at 205 degrees (C) nozzle, 65 bed* for the first layer, and then start the bed cooling to a lower temperature as soon as the first layer is down.

Yeah absolutely don't do this. Either keep the bed cold (PLA can be printed on some materials like that) or keep it warm but never change bed temperature during print.  It doesn't affect only the first layers directly touching the bed but also the changing the temperature of the air right above the bed, causing warping stresses as the plastic cools.

Key things to prevent prints peeling up at corners:

- Stable temperature, I am printing PLA with the bed at 80 degrees C. Keep in mind that the printer showing 80 means the bed is likely at 70 at best due to the thermistor calibration being fairly approximate, generally poor thermal transfer between the heater and the print surface and the bed moving around. So you likely need more and not less temperature! 65 degrees is very low so the print is not sticking to the bed properly and will curl up as it cools. 45 degrees bed temperature is pretty much useless, that you can as well leave it cold. The bed must be hot enough to keep the plastic soft/sticky, PLA needs at least 60ish degrees for that - so the bed needs to be set to 70-80 for that to work. Otherwise you leave it cold and rely only on the surface adhesion of the plastic to the print surface. A lot of cheap PLA-only printers don't have a heated bed at all and work fine.

- Clean print surface. PLA can be printed even straight on glass but it is important the surface is not greasy (fingerprints, etc.)

- No drafts - if you don't have enclosure or at least some sort of screen, you do need to make sure the printer is in such location where you don't have air currents from people moving around, open doors/windows, etc. That will reliably cause layer delaminations and warping.

- For small parts or things that have small surface area it helps to use brim. There is no need to use rafts these days, as long as your machine is properly leveled and square. I don't think I have ever used a raft on my old Mendel, despite the machine being almost 10 years old now and built from a kit.

And as a general issue - the bed absolutely needs to be level and the machine square. If you can't put down an uniform first layer because the machine is out of square then the print will not stick to the bed properly either and you will have problems.
« Last Edit: May 24, 2023, 07:42:27 pm by janoc »
 

Offline mikerj

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Re: Bed heating and avoiding PLA warping
« Reply #20 on: June 02, 2023, 09:47:57 pm »
I had a nightmare with parts warping and lifting off the bed in the corners until I realised it was a draft caused by the open fireplace in the room.  PETG was the worst for this but PLA also did it, some brands worse than others.  I have a partial enclosure around the machine now to shield it and that completely stopped the problem.

I've not had too many issues with the soft textured build surfaces, but my textured PEI build surfaces requires fairly regular scrubbing with dish soap and a pan scrubber to make prints stick well.
 


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