I'm trying to import a .stl file to Blender, but it doesn't work!

This is how I do: I open the .stl file in Freecad and I select everthing, then I export it as an .obj or .dae file, but when I import the file into Blender, I only get parts of the object and some of the parts are in wrong position. Very frustrating and the client is waiting.

Can someone give me some advise how to solve this?