I have saved a flat face on my solidworks model as a dxf file and it all looks fine. But when I got on Techsoft 2D Design, I go: File> Import> and select the dxf file. Then it opens an options window and I select mm and then press ok. Then it imports all the straight lines fine but not the splines. Why doesn't 2d design import the splines?
It might be a limitation of Techsoft 2D Design, or there may be an import option needing adjusted. The pcba design software my colleague uses has in the past experienced issues with importing splines, but in his current version it works.
When exporting the DXF from solidworks you may want to try switching the 'spline export options' to 'export all splines as polylines' and see if that works well enough for your purpose.
As a test, try making a new sketch on your flat model face. In the sketch, convert all of the model edges to sketch geometry. Save the sketch as a DXF, and import it to your 2D program.
Attached is a DXF created from a sketch. It contains 2 lines, 1 circle, 1 arc, 1 spline, and a 12 sided polygon (lines and circle). Does it import correctly?
I encountered a similar difficulty with a laser cutting supplier. After several attempts, I had to redraw all the splines into arcs of circles.
I even came to think that some laser cutting software require files only in arcs because the splines require to be converted into arcs, which too many files.
I have not encountered this problem with CNC machines.