By default, when you create a sub-assembly, it is rigid. Within the parent assembly, the sub-assembly acts as a single unit and its components do not move relative to each other.
However, you can make sub-assemblies flexible. This allows movement of the individual components of a sub-assembly within the parent assembly.
An example of the benefit of this function is when you want to move the components of a piston sub-assembly in a motor assembly. You can move the individual components of the piston while still grouping the components as a sub-assembly.
Please note the following regarding flexible sub-assemblies:
Mates. The mates in a flexible sub-assembly are solved simultaneously with the mates of the parent assembly. Therefore, moving or rotating a sub-assembly component does not violate the mates in the sub-assembly or its parent. A component moves only within its degrees of freedom according to its mates.
Multiple Instances. You can insert more than one instance of the sub-assembly in the same configuration of the parent assembly. You can make some instances rigid and others flexible, and the different instances can have different positions of the sub-assembly components.
To make a sub-assembly flexible:
Right-click a sub-assembly in the FeatureManager design tree and select Component Properties.
The Component Properties dialog box appears.
Under Solve as, select Flexible, then click OK.
In the FeatureManager design tree, the icon changes to to indicate that the sub-assembly is flexible.