Evaluating a design for assembly-expanded modular function deployment method: a retrospective SME case study

Abstract Modular product architecture creation methods often fail to fully account for assembly constraints, limiting their practical applicability. This challenge is spread across industry but has greater consequences for small and medium-sized enterprises (SMEs), where design decisions must align with constrained production capabilities. This study examines how the integration of Design for Assembly (DfA) principles into Modular Function Deployment (MFD) can enhance the development of modular product architectures. Through a retrospective, case-based analysis of the Senseair RDS (refrigerant detection system), the research reconstructs key design and organisational decisions and evaluates how a DfA-expanded MFD method could have influenced them. The analysis combines document review, two participatory workshops, and entry–exit surveys to map decisions, challenges, and barriers. Results show that early modular reasoning was constrained by resource pressure, compliance demands, and departmental separation, leading to duplicated work and late clarification of interfaces. Application of the proposed method highlighted opportunities for earlier identification of assembly trade-offs, clearer justification of architectural choices, and improved cross-functional communication. Participants found the method conceptually useful but effort-intensive, emphasising the need for lightweight training and adaptation to existing SME routines. Mapping of workshop findings to the Technological-Economic-Regulatory-Organisational (TERO) framework revealed that organisational and economic barriers dominate over purely technical ones. The study concludes that structured approaches such as the DfA-MFD method act most effectively as sense-making tools that formalise existing knowledge, promote assembly-oriented design decisions, and support incremental improvement of modular architectures under industrial constraints.