PLA Warping?

So I have been printing a lot with both ABS and PLA but I have never experienced PLA warping to such an extent.

I have designed this toolbox:


Even though I have printed a lot of big parts I have never experienced such warping with PLA. The warping was so tremendously powerful that, since the PLA was sticking perfectly to the PEI sheet, the PEI sheet managed to separate from the cast aluminum heatbed. The PEI sheet is attached with 3M 468MP to the build plate and I thought that it is never going to separate.

Alas, it did on all four edges:



Is it a bad PLA batch or should I just come to terms with the fact that printing humongous parts inevitably leads to warping? Does it make sense to use an enclosure next time (like I do with ABS)?

Thanks

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

Did you print on a cold PEI sheet? Maybe the 468MP sticks better at higher temps?
Changing the pattern of the solid bottom layers might help against warping. Make sure the tracks go zigzag instead of straight.

I would be interested in knowing at what temperature the 468MP released from the bed.

I was printing at 60 degrees C. The 3M adhesive separated from the bed about halfway through the print...

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

This is crazy. I have print PLA at 56C on Vinyl Transfer Paper Tape (medium tack)(similar to blue tape),
Taped to the Top of two different print surfaces and it did not release like you PEI sheet did. However I have not yet printed such a large model.

If the surface was cleaned and dry when the PEI sheet was installed it should not have released. Makes you wonder if that PEI sheet was a fake.

I recently bought some fake PEI. I was using it with an IR probe and so had to cure black spray paint that I applied to the sheet in the oven. The sheet instantly melted and curled. I can't remember my oven temps now, but I do remember it being significantly lower then the glass point of PEI by 20-30c. I calibrated with an external thermometer (not with the oven thermostat).

It could also be that you bought fake adhesive, my PEI sheet also claimed to come with 3M adhesive but who knows what I got.

Saying that, I have seen powerful warp with PLA as well. I think its very easy to underestimate the pulling power of a warping print, regardless of plastic used. Perhaps try using less cooling? I often find some brands of PLA need almost no cooling, yet some need heavy cooling. Find your sweet spot and always be willing to try less cooling. It can only benefit layer adhesion in the end!

Maybe try PETG instead of PLA.

Once you work out the settings and dial it in, you are likely to never look at PLA again......

It can still warp but the amount is far less, layer adhesion is super strong, can print directly to PEI.

Same story with PETG, you can get good or bad quality...
The print speed of PETG is a lot slower ( ~35mm/s ) than PLA. Imagine, how long it would take to print such a huge tool box...

Out of interest, what is the size of the print? Looks like a big bed.
How many solid layers are on the bottom?
I think these issues are caused by shrinkage. The larger the "span" the more stress from shrinkage. If it stays stuck to the PEI so it can't shrink in the X-Y plane it tends to warp at the corners. So your PEI is OK its the glue thats giving up.
If this is true you could try and change your design so the there is a gap in the bottom layers where the dividers are so the first layers are like 4 islands. That reduces the shrinkage stress. Then above these layers you go back to your normal design.

Similarly, how many perimeters does the box have? This could also cause lift.

It sounds backwards, but a raft might help. The raft will insulate the print so that there is not as much of a temperature gradient in the print itself

All good suggestions, thanks

The box is roughly 300 x 220 mm, 3 bottom layers, 2 perimeters. I am going to print the top cover of the toolbox while using some clips to hold down the PEI sheet in the corners so that I don't have to rely solely on the 3M adhesive.

All in all, the ready part doesn't look so bad because it is so big the warping can barely be recognized.

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

The cover warped a bit as well but it was not that bad. Here is the finished box:

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6