Part Count and Design of Robust Systems

Dan Frey, Department of Mechanical Engineering, Massachusetts Institute of Technology

Systems engineering frequently includes efforts to reduce part count with the goal of cutting costs, enhancing performance, or improving reliability. This paper examines the engineering practices related to part count, applying three different theories -- the Theory of Inventive Problem Solving, Axiomatic Design, and Highly Optimized Tolerance. Case studies from the jet engine industry are used to illustrate the complicated trades-offs involved in real-world part count reduction efforts. The principal conclusions are that: 1) part consolidation at the component level has generally been accomplished as technological advancements enable them which is consistent with the “law of ideality” in the Theory of Inventive Problem Solving; 2) part count reduction frequently increases coupling among functional requirements, design parameters, and processing variables while also delivering higher reliability which conflicts with the theory of Axiomatic Design and; 3) at the overall system level, jet engine part count has generally increased in response to escalating demands for system robustness as suggested by the theory of Highly Optimized Tolerance.