Rapidform XOR/XOS can create a body on a mesh using “Auto Surfacing” command. This method can quickly and automatically wrap the mesh and create a surface/solid body with just one click of a button, but it might be possible for gaps to be created between patches on complicated and sharp areas of a mesh. [...]

If you’re importing reverse engineered models into UG NX via IGES, there are some settings you’ll want to pay attention to.  (Note: we recommend using XOR’s liveTransfer tool when possible, rather than IGES files)
Problem
When you import an entity in IGES format from Rapidform, it may import into NX with many split bodies even when you export it as [...]