Slicing adds holes/cracks to my object

Question

I recently got started in 3D printing but here's an issue I can't seem to find a solution for (I don't know what exactly to look for).

Here's what I did:

• I used InkScape to convert an emoji in to a svg and imported it in to Blender
• Used the Solidify modifier to make the curve a solid and converted it in to a mesh
• Extruded the mesh a bit, fixed a few non-manifold vertices and erroneous faces and saved the whole shebang as STL
• Imported the STL in to my printers software:
• After slicing it looks like this:

Is the software making a mistake during the slicing? Or is my mesh screwed up?

I have a FlashForge Finder and using the software that came with it: FlashPrint.

Edit: I uploaded everything to Thingiverse for those who are interested.

Answer 1

here is just a addenum to Tom van der Zanden's answer

this is (an example of) what you may design - nice object with virtual outline, and virtual fill so this is what you see (and what you potentially expect)

but here is what you get (and probably not really expect)

red parts are the areas which are not covered by fill because nozzle cannot reach there

solution is

• to redesign your object in smart way or
• to use smaller nozzle or
• to use smarter app (like Slic3r)

and of course you can use all 3 options together to get best results ;)

EDIT here is simple explanation why smarter app could do the thing

and here goes the difference

green parts are new covered areas

not much but somthing extra

Answer 2

This is likely not a problem with your mesh. It's a problem in the slicer software.

Because your 3D printer prints with a (for example) 0.4mm nozzle, it lays down lines of plastic that are around (for example) 0.5mm wide. The slicer has to create a pattern, consisting of 0.5mm wide lines, that fills in your object. The gaps shown in your object are likely smaller than this, and thus can't be filled.

I am not familiar with the flashforge software, but different slicers have different ways of dealing with this. Some offer a "gap fill" option that uses tricks to be able to fill in these very tiny gaps by rapidly moving the extruder back and forth over the gap. However, even then, it is sometimes unavoidable that tiny gaps remain. Some gaps are just too small to fill with the comparatively large nozzle.