Conversion from FreeCAD to Unigraphics is not supported yet :(

FreeCAD is a customizable, open-source paramentic 3D CAD and BIM software with FEM support, built on the Opencascade geometric kernel. It was created primarily for product design and mechanical engineering, but it can be used in a wide range of industries, such as electrical engineering, or architecture. It runs on Windows, Mac OS, and Linux.

FreeCAD is made to craft real-life objects of different sizes and is perfect for a home user/amateur, programmer, experienced CAD software user, or educator. This software provides tools similar to those of SolidWorks, Catia or Autodesk Revit.

Unigraphics is a former name for Siemens NX, an advanced CAD/CAM/CAE software application suite. However, veterans are still using the Unigraphics name.

In 2002, the new version of Siemens Unigraphics, merged with I-DEAS software, was released and called NX, which means "Next Generation". In fact, it was the last version of the software released under the Unigraphics name. All further releases became known as NX. So the addition of I-DEAS functionality to the core code of the Unigraphics has become the basis of the existing NX product line.

Siemens NX / Unigraphics use a .prt extension, which contains 3D CAD parts.