Import 3D Shape (surface)

I'm trying to import a surface into FlexSim.

I have a DXF which I moved everything to 0,0,0 coordinate. I've tried importing the DXF, converting to STL, WRL, 3DS. I didn't have luck with any the formats that I've tried.

The only one that showed something in the 3D scene was 3DS, but it didn't have any lightning, so it looked very flat (it's a mine surface with ramps, benches etc).

What's the best 3D format to import in FlexSim? And how to prepare the file to be imported?

For drawings, dwg and dxf are both good. Right now FlexSim can import dwg with multiple layers pretty easy. And also you can control layers in FlexSim.

For 3D models, 3DS is best. Google sketchup files are also good.