To Remove internal faces in the Main Menu select Repair - > Remove internal faces.

This operation removes all shared faces from given solids to obtain one or more bigger solids from a set of smaller solids.

Arguments: Name + one or more shapes containing solids.
Advanced option: Set presentation parameters and sub-shapes from arguments.

Note: Only shared faces will be removed. Coincident but not shared faces will stay as is, use Glue Faces or Partition before Remove Internal Faces if you need to remove them.

TUI Command:
geompy.RemoveInternalFaces( theSolids ),
where theSolids is either a compound or a list of solids.

Our TUI Scripts provide you with useful examples of the Remove Internal Faces functionality usage.