Annealing PLA

[BigJimSlade]

When assembling larger pieces together, I am often finding bending as the PLA strands cool.

Is there any safe way to anneal the PLA to relieve that stress?

[Tim]

Do you mean that the pieces are warping on the heated bed as they cool down, so that they don't fit together as well as they should? If that's the case, then make sure you've got really good adhesion to the bed. PLA is just about the best plastic for its lack of warping. I usually find that if I can just keep it stuck to the bed for the duration of the print, there won't be any warping. Of course, it's all easier said than done.

[BigJimSlade]

The problem is after they cool down. The flat pieces then start getting bend to them.

[jsc]

Zheng3 claims you can straighten warped PLA by using a warm skillet: http://zheng3.com/2014/06/05/zhengs-garden-guardian/
Not much detail, but it seems pretty self explanatory.

Tim should recognize that model.

[willnewton]

You did not mention pieces warping while printing, just after removal.

Are using the bed heater? Are you removing the print as soon as it is done?

If so, then you should wait for the bed to cool down before removing the piece. Removing a warm print will cause warping just from the removal process. It will then warp further because there is nothing keeping it place while it cools.

The top of the print is cool and bottom is still hot from the bed and will contract as it cools, so you will get warping as it reaches room temp.

It should only take about five extra minutes to wait for your piece to cool, depending on size and density. I keep a small fan nearby and turn it on to help cool prints and the bed down quickly if I am in a rush.

In some cases I will simply peel the print off while hot and hold it down on a cool surface to stiffen, but I wouldn't try this on anything where you need dimensional accuracy.