Prints bend (not warping) when taken off Smooth PEI Sheet, even at room temperature
I am using the Smooth PEI Sheet, that comes as standard with every Prusa printer.
I am printing large miniature houses, lets say 1/5 to 1/2 of the sheet size, high and stable
objects.
Everything works, there is really no warping during and directly after printing (checked carefully under
harsh light), even as I take the sheet off the printer and put it onto my desk- the print sticks perfectly up to
the extreme corners.
Then, after cooling down to room temperature, I bend the sheet very carefully, no force really, the
print pops off, like in those nice Youtube videos.
AND - the bottom is very slightly bent, when checking against an absolutely flat surface.
I have now tried 5 prints in a row, let the sheet untouched for up 20 minutes after printing - all prints
were perfect, no warping - but they all got bent when detaching.
Without slightly bending the Smooth PEI Sheet they wouldn't come off, unfortunately.
I am coming from another brand, where I had massive problems with actual warping during printing
(so I know what it looks like, more or less). Despite being a first time Prusa user, I do have some
experience (especially with failed prints 🙂
Does anybody have an advice to share / similar problems ? Would the Satin sheet work better
when dealing with these issues ? Do you bend your sheets (even slightly) to get your prints off
or do they pop off without any movement ?
Thanks!
RE: Prints bend (not warping) when taken off Smooth PEI Sheet, even at room temperature
You forgot to tell us which filament are you using .. PLA, PETG, ASA ? It makes a world of difference for warping questions.
I understand that these houses are of medium size and relatively tall. In spite of bending the steel plate, they shouldn’t deform at all after being removed. In some cases, if the adhesion to the plate is very strong, rigid filaments like PLA might crack when you bend the steel plate too far, if the part is small and thin, but not be deformed permanently.
Have you tried to check the prints against the bed surface after being removed ?. Maybe the bed itself is a bit bent, so the bottom of the print takes the curved shape of the bed.
RE: Prints bend (not warping) when taken off Smooth PEI Sheet, even at room temperature
( Edit time has expired so I write a new post ..).
If you find that your bed is flat, then the issue is warping. Yes, the part might be perfectly stuck to the bed when the print ends, but it curls a bit after cooling down. Let’s say it’s a case of ‘post-warping’. It happens mostly on large, squarish and flat parts. Printing stencils from PLA I have this problem sometimes, It depends a lot on the specific brand of filament, or even different colors of the same brand. For instance, I never had trouble with Prusament ‘plain’ PLAs, but I had some warping with several Prusament ‘blend’ PLAs ( pearl white, Oh my gold, royal blue)
Solutions for ‘warping-after-the-fact” ?
Try to improve adhesion. The smooth plate is better than satin or textured. Adhesive helps (Magigoo, hairspray or similar ),
If you use an enclosure, after ending the print close the doors and let cool it down very slowly for several hours. If you don’t have an enclosure, there isn’t much you can do about it. Anyway, if you intend to print high temp. filaments like ASA, PC or nylon, an enclosure is almost mandatory. It doesn’t needs to be the Prusa. There’re other reasonable cheaper alternatives.
On the slicer settings, add a brim to the model and/or discs at the corners.
Experiment with several brands of filament. As I said, there’s a noticeable difference between them,
Try different bed temperatures,
RE: Prints bend (not warping) when taken off Smooth PEI Sheet, even at room temperature
It seems like that parts you are describing will always have some inherent built-in tension.
-they print flat
-the steel sheet holds them flat
-once removed, the inherent built-in tension reveals itself
It's like a slightly warped piece of wood - you can tape it down flat to a table, but remove the tape, and it will spring back up.
I like the recommendations of printing in some type of enclosure - just to keep a little more heat around the part. The further away the layers are from the bed - the more shrinkage will occur (I'm assuming the floors of your little houses are bowing downward). The upper layers of your floor are shrinking more than the bottom layers.
Another thing to consider would be trying to create an annealing chamber. This is beyond what I have done personally, but others have talked about annealing prints before removing from the steel sheet in a heated chamber. It's akin to annealing glass - any blown glass needs to sit in an annealing oven for a slow cool down or its surface tension will be too great it it will self destruct. Picking the right temperature to anneal without deforming your part is beyond my experience - but others may know how to pick a temp based on the material specifications.
Hope you figure it out.
RE: Prints bend (not warping) when taken off Smooth PEI Sheet, even at room temperature
Here's an article on annealing from the Prusa site. This is geared more toward achieving improved material toughness and durability - but it could give you a starting point in trying to anneal and relieve the tension in your prints in a uniform fashion.
https://blog.prusa3d.com/how-to-improve-your-3d-prints-with-annealing_31088/