The NX Command "Simplify Assembly" sounds like what you are looking for. This tool has the ability to unite bodies, fill gaps, and remove unwanted internal (or external) geometry. It can be associative, although I generally prefer to do it unassociatively because it is faster.
There is also "Delete Face" command which matches some of the youtube Solidworks videos posted by cubalibre00.
I have seen several instances where people using other CAD systems have used the simplification tools and sent the results to their customers. Unfortunately, the data is really horrible and causes downstream problems. Please be courteous and respectful to the people you are sending your data to. Don't send them junk. The NX command "Simplify Assembly" has lots of options, but it takes some time to fully understand it. Don't forget to read the help pages for useful information.
Ladies and Gentlemen,
Thank you Rick for putting me back on track from drifting away in my eagerness of trying to find alternatives based on the original stated issue regarding the speed of the Simplify Assembly…
Attached is a couple of movie files explaining the Simplify Assembly as well as Linked Exterior. The movies shows and example based of a Gearbox Assembly. The first movie shows the Simplify Assembly and the current state of the application while producing a main solid body as well as additional exterior bodies. The second movie shows Linked Exterior application as an alternative and a rather fast solution only producing the representative exterior sheet body.
The movies are intended to show the functionality as well as a comparison and that it is difficult or more or less impossible to create a “magic” one step/button simplify assembly function as manual input is allways required.
Please have a look all you good people and for specific areas where you have an idea of where you see potential improvements please file potential ER’s for proper handling.