Modelling Bee Foundation Mould I am having a bit of a hard time understanding why the STL export differs from what I see in my model. 

Currently I am trying to create a 3D printable mould to create beeswax foundation. I have created a small example of the problem I am facing. 

In Blender my model looks perfect, each hex has 3 edges meeting in the center of the cell, the mid point is then moved up 1mm to form the indent in the mould.  Here is what it looks like in Blender, you can clearly see the three faces.


However when I export as STL and pull it into Prusa Slicer, I end up with 6 faces, which is not what I am after. 


You can find my blender file here

Any suggestions welcome.
What you see here is automatic triangulation. You have quad faces in your model that are not planar and polygonal faces that are not planar cannot be printed so they are triangulated and since there is no way for a computer algorithm to determine where to insert the edges it sometimes fails to guess. 

The solution would be to enter edit mode with your object selected(tab) and use something like the knife tool(k) to triangulate the mesh manually so it fits your expectations. you can also join vertices with an edge by selecting 2 vertices and hitting j.