Wednesday, December 19, 2012

Warping - Some Findings

Today I tried some settings in Slic3r. Doing so I printed a U-shaped testcube of PLA on a heated mirror. I printed the first layer at 200°C and the subsequent layers, too. It looked quite well, but at one corner it hadn't stuck to the bed as perfectly as I wished. Actually I wouldn't call it warping already, but maybe the very very beginning of it.

So I cleaned the mirror with alcohol. Then I printed a second cube with 200°C at the first layer and the other layers at 170°C. My expectation was a reduction of the warping, as a layer with a lower temperature wouldn't shrink that much like a hotter one.

The result was puzzling. The second cube showed strong warping.

To be sure I repeated the printing and printed a third cube with 200°C/200°C and a fourth with 200°C/170°C. While the third one again showed no warping, the fourth cube warped so much that it got off the heated bed and I had to abort the print.

Obviously the reduction of temperature at the second layer weakens the bond of the first layer to the bed. Maybe the "cold" second layer cools down the first one and causes it to shrink. Once the first layer got off the bed the whole part is an easy prey to warping.

Possibly this temperature difference explains a lot of cases of mysterious warping. A little option in the slicing software turns out to be a trap ...

I guess I will repeat this with ABS soon.


  1. It is only the shrinkage from the glass transition down to room temp that causes warping. From the deposition temperature to the glass transition the plastic shrinks but it isn't hard, so doesn't stress the layer below.

    So when you reduce the deposition temperature it doesn't reduce the shrinkage that matters, which explains why it didn't get better.

    I suspect it warped more simply because each layer cooled quicker so started exerting force on the layer below sooner.

    1. Well, after looking through a lot of p-v-t diagrams of polymer plastics I am afraid that I missed your point.

      For an amorphous polymer like ABS the change of volume below Tg (glass transition temperature) is less than above. Shouldn't we expect warping forces to be higher above Tg then?

      For a crystalline polymer the case is very different. Crystallization depends (among other factors) on the cooling rate. The p-v-t diagrams have some very non-linear parts around (Tg + Tm)/2 where the crystallization mainly takes place. But they do not change much around Tg.

      The literature isn't very clear about if PLA is to be regarded as amorphous or crystalline.

      But in both cases it is not clear to me why you believe that warping takes place only below Tg.

  2. i have had the same experience with warping. Setting first layer temperature to the same like the others solve it.
    Now i dont have any warping effects in my prints.

    I am printing PLA on Glass with HBP 60 degrees.

    Thanks for share your experience in your blog.
    It saved many of my nerves :-)

  3. I've resolved this issue by lowering the headbed temperature from 80 to 55 degrees. I print at the lowest temperature possible, usually 185 degrees. This totally reduced any warping. I clean the mirror with a mixture acetone/water and wipe them dry till they fell quite tacky. On large objects with small footprint I add a skirt layer without a distance to the object. Called brim in slic3r. This adds additional adhesion.