Why does warping occur?

My PLA prints have a minor warping. I was wondering what is the reason that objects wrap. My initial thoughts were:

• Temperature difference between layers. Bottom layers are hot due to heated bed and upper layers cool down after a while, and this difference causes warping.
• Plastic tension. Corners tend to warp because of the tensions pulling it together

However, I printed a part (attached) which is circular and I turned off heating in bed completely and the part still wrapped (minor warping, not visible from the photo angle). This indicates that both the reasons I listed are not responsible for warping in my case.

Any thoughts?



Edited 1 time(s). Last edit at 09/16/2014 02:43AM by demetris.

What is your bed? Some can have good first-layer adhesion with bare glass, some use blue painter tapes, some use diluted white glue.

Bed is just glass. But I try to understand why this happens.

Warping is caused by hot plastic being extruded onto cooler plastic. It then cools and contracts, exerting a force on the layer below. This causes the object to curl up at the edges.

With a heated bed the bottoms layers are kept warm so they contract at the end and cause warp in the opposite direction.

To build an arbitrarily large warp free object you need a heated chamber kept just below the glass transition temperature so the whole object contracts together at the end of the build.

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[www.hydraraptor.blogspot.com]

Printing in ABS requires a chamber to prevent uneven cooling. PLA requires the opposite - a fan directed at the print can help prevent warping.

@nophead: Heated chamber becomes more and more attractive as fine tuning proceeds! Do you have any suggestions for Mendel90 chamber?

You're printing PLA, you don't need a heated chamber. The heated bed temperature typically at around 60 to 65 degC is enough.

Your problem is caused by bad bed adhesion. If cleaning the glass thoroughly with isopropyl alcohol doesn't work, try using blue tape or diluted white glue. Also, you should consider adding a fan to cool the print if you don't have one already.

I'd suggest posting a picture of the bottom of your print, but it sounds like poor adhesion. Better adhesion equals less warping (because it can't pull loose).

Personally, the best results I've gotten have been from:

* proper calibration
* clean with isopropyl alcohol
* lightly coat with "disappearing purple" glue-stick
* heat bed slightly (45-55C for PLA. Other materials require higher temps)

Most difficult part? Removing print from HBP.

For truly insane adhesion, try blue tape lightly rubbed with isopropyl alcohol. Works better than glass + glue-stick, but the tape will probably have to be scraped off the bottom of the print.

Hi,
for PLA printing I'm using blue painter tape with best results.
The print will hold very tight. Mostly I have to pull the tape off to get the print from the plate.

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RepRap Electronics, Mechanics, NEMA 17, Filament you find here: [www.my-home-fab.de]