It seems that this conversion mainly represents an export of individual parts from Inventor assembly files (.iam) and saving them as separate models in Universal 3D format (.u3d). As far as we know, this should be doable with some dedicated 3D modeling tool or converter program.
Convert Autodesk Inventor assembly file to Universal 3D format graphics.
We found one software available in the database for this conversion.
Microsoft Windows software - convert iam to u3d on Windows
A 3D CAD translation softwate
Convert from iam file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.