Welcome to the forum, it is definitely possible with freecad, but you need to "get your hands dirty" and dive in scripting territory.
I've only been using FC for a few weeks, but I was itching to try to give back to the community a bit. So I started to work on the cross section macro to make it work with my project (0.18 with body and parts) and so because the changes were pretty small to do a multi cuts like Tilli is talking about so I gave it a try. Here is my first script contribution...
I hope you can understand the english it's easier for me to type than in french but we could work a translation later
So here is a proposal with a bust of another nice lady (don't judge ok!):
1/import the STL with file/Import, it will create a mesh
2/ select the workbench "Part" in the drop down menu
3/ select the mesh object in the tree and use the part/"create shape from mesh" tool
this will create a shape that can be sliced later
Then download the macro file joined
4/ from the menu macro/macros, browse to the folder of the macro, select it and run
5/ go grab a coffee especially if the model is large...
6/ the slices will be created in a cross section object
You can then export them to DXF:
7/ select the cross section object then file/export to DXF or other format that your CNC is taking
8/ you will have to move the slices to separate them and they are not numbered so it's going to be a pain...
but hey that was only 20min of fooling around python and I'm not a pro so...
The macro is all hard coded, but you can change the orientation of the slice by editing:
self.axisX = 0.0
self.axisY = 0.0
self.axisZ = 1.0
And the number of slice is controlled by:
numSlice = 10
I would recommend you try on a simple model first to make sure everything is working for you.
Also I should probably make something to lay out the slice nicely to help with the laser cutter/cnc later but no time today...
I will start a git-hub to keep track of all these things...
Credit to all the authors of the cross section macro that made my job easier!
OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.13509 (Git)
Build type: Release
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.2.0
Locale: English/UnitedStates (en_US)