Question

sls: dimensional accuracy
use the information below to answer the question
bin cool down
like fused filament fabrication, there is a possibility of shrinkage or warpage in sls printing. this is caused by differential cooling that occurs as each layer is printed.
the time it takes the powder bin to fully cool down after running a build can be up to 50% of the entire build time. during this cooling period, the form is often quite prone to warping.
reducing shrinkage and warpage
in extreme situations where the temperature gradient in a build causes material warpage, an edge may curl high enough to block the path of the re - coater arm. if the arm makes contact with the printed form, this can cause serious damage to the machine. there are several ways to prevent that from happening:

• when the laser sinters the powder, the area where the laser beam is making contact with the material is much hotter than the portion of the powder bin down below, where the material has had time to cool. to diminish the temperature gradient, the powder bin is heated which creates a more stable environment for the powder and reduces the possibility of warpage or shrinkage.
• another technique used to prevent material warpage is to change the orientation of the parts. instead of having flat planes parallel to the print bed, forms can be positioned at various angles or placed vertically. this reduces the cross - sectional area and the amount of material variance that can be created in each layer.

what causes shrinkage and warpage in sls prints?
differential cooling
an improperly sized bin
excessive heat
an under - powered laser

Explanation:

The text under "Bin Cool Down" states "Like Fused Filament Fabrication, there is a possibility of shrinkage or warpage in SLS printing. This is caused by differential cooling that occurs as each layer is printed." So the cause of shrinkage and warpage in SLS prints is differential cooling.

Answer:

differential cooling