In the domain of software product lines, Feature Models (FM) play a central role in variability modeling, completed by configuration collections (from concrete software product lines), logical representations, constraint programming or conceptual structures, coming from the field of Formal Concept Analysis (FCA). The development of feature models may take several forms, including their synthesis from configuration collections or their design in several steps (by several teams or with different concerns). FM composition (merge) operators are part of that design activity as they assist their iterative building. In this paper, we describe an approach, based on two main merging semantics (intersection and union), which assists designers in merging several FMs. This approach benefits from the help of FCA to represent all the FMs with the same configuration set through a canonical form. We describe the implementation of our approach and present a set of concrete examples.