At the DFMEA level, it is usually recommended to study each subsystem separately, and each component separately. Their inter-relations can be evaluated in the System FMEA.
The System FMEA examines system deficiencies caused by potential failure modes between the functions of the system. This includes the interactions between the systems and the elements of the systems.
The PFMEA is conducted on a process, whether it be in a manufacturing or a service environment. It is generally recommended to study each machine or sub-process separately. Their inter-relationships can also be studied in a System FMEA. Service FMEAs are usually not preceded by a DFMEA.
The key difference in the objectives between the two is the focus of the FMEA. When conducting a DFMEA, the team must remember to think in terms of the causes and effects of failure modes due to the design itself. The causes usually involve product design variables that can be specified by the design team.
Design for Manufacturability/Assembly All other (DFM/A/(X) considerations should be included in the DFMEA as well, e.g., tooling access, robustness to sources of process variation, ability of product to be produced at planned production rates, maintainability, etc. In a PFMEA, the team will be focused on those failure modes and causes that could result from the production or service process itself rather than from the design of the product.
the responsible designer will lead the DFMEA team. It is important to have cross-functional participation on the team, including at least some of the members from the after PFMEA team.
Usually, but not always, the leadership of the team changes to the responsible process engineer. This person ideally would have also been on the DFMEA team; and the DFMEA team leader would stay on as a member of the PFMEA team. Several other team members, but not all, could change to reflect a heavier emphasis on the process under study.