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.