Warping of selective laser sintering

I am a newbie in 3D printing. I am wondering what causes warping in laser sintering? For a single layer, which direction will it warp in? (towards or away from heat source), and how big is the deflection is it usually? I am figuring how to better design my piece.

Thanks!

Hum, with my humble process and physics knowledge, I can think somethink like that:

Whatever the process is, if there is heat involved, a difference of temperature causes deformations, and most of the time, it's due to a difference of thermal inertia, which is linked to the difference of mass of material of the piece.

Typically, the print of a large plan surface causes warping at the edges because the center have still some heat gathered, while the edges are cooling easily. The warping happens in the cool direction: when you cool something, it generally retracts. If you have piece of material, the cooled part will retract while the still hot one will stay larger.

... with SLS this is a little bit complex ... when melting the particles, they will expand slightly, but when cooling down this would shrink more, so it would tend to curl up.

But an even stronger effect is the 'wetting' of not melted particles with molten material, what tends to generate a sort of attracting force, what too will curl up or bend the actual slice up.

Depending on the stiffness of the solid material this can be some percents shrinking/warping, so good support structures to the building basis are essential!

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Viktor
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