CAD tip # 8183:

First convert your surface (mesh) model to format directly readable in Inventor. For 3DS files use AutoCAD (3DSIN, SAVEAS DWG), for STL format models use our web service STL2DWG.

Drag-n-drop the resulting DWG or DXF file into the Inventor window, or use the standard Open. In the import wizard (the 3rd step) use the option "Destination: New part", check "3D solids", "Use the default file names". Complete the import. Your model will be imported as a surface part. (If you load the surface in another way, you may need to use "copy to construction" in the browser tree.) Now you need to "stitch" the surface to a watertight 3D model.

Run the command Stitch (the ribbon Model > Surface > Stitch) and enter the tolerance for stitching of the surface facets. If neccessary, switch off the original surface model and assign material properties to the new solid model.

An example of a STL model in AutoCAD (faces only) and the resulting solid model in Inventor:

Note: precision of the resulting solid model is limited by the precision of the original facetted 3DS or STL file