Autodesk Inventor Tutorial Chapter 3

Assembly Modeling
With the exception of very simple objects, such as ruler, most objects have more than one part put together to form a useful whole. The set of parts put together is called an assembly. When you design the parts for an assembly, the relative dimensions and positions of parts, and how they fit together, are crucial. You need to know whether there is any interference among the mating parts. if there is interference, you need to find out where it occurs; then you can eliminate it. Apart from fitting the parts together, you also need to validate relative motions and check clearances if there are moving parts in the assembly. Moreover, you should critically evaluate the parts and the assembly as a whole to ensure the assembly functions correctly in accordance with the design intent. To shorten the design lead time, you construct virtual assemblies in the computer to validate the integrity of the parts and the assembly.