This paper introduces an approach to synthetize new CAD assemblies from existing STEP files. The algorithm first generates linkage graph by detecting linkage between components. Then it detects linkages similarities between components of different assemblies while analyzing the associated graphs. Finally, it exchanges the similar components. The similarities in a family of components must be formalized by the user. Then the similar components can be replaced by the other through smart placements. This method allows to automatically generate a wide variety of new consistent assemblies sharing the same semantics, in order to create databases of CAD assemblies ready for machine learning applications. It has been validated on several cases.