You can activate the join
in the IGES section of the Preferences.
When this check box is selected, the system tries to knit the surfaces from an importable file into
a shell, even if the file contains Groups (402).
Notes:
- The tolerance value is that of the input file resolution, limited between the modeler resolution and 100 x the modeler resolution.
- The model must be made of one part.
- The Join operation may fail in specific topological
configurations.
- This option does not apply to Manifold Solid Brep (IGES type
186): The faces are always imported into a join.
- When the Import as a Product Structure option is
active, the option Join surface of the model is
selectable but has no effect.