When inventories are not financial losses: a comparative analysis between lean and theory of constraints concepts for production synchronisation

Studies involving the combination of Lean and the Theory of Constraints (TOC) are scarce. Some possibilities may justify this scarcity, such as the different concepts and orientations of Lean and TOC regarding buffer and synchronisation issues. This study compares Lean and TOC concepts for production synchronisation on an automotive assembly line. System Dynamics (SD) modelling was utilised to develop comparative scenarios. The simulated scenarios were compared with the empirical data. From the computational model analysis, Drum-Buffer-Rope (DBR-TOC) was implemented, and empirical intervention data were observed. Potential competing factors were isolated to increase the reliability of the empirical evidence. The economic results highlight that implementing DBR-TOC synchronisation can provide a 14% reduction in labour cost, a 17.8% reduction in overall production cost, and a 48% increase in production volume. We show that the production system may enjoy benefits such as flexibility, increased reliability, and quality that would improve the company's competitiveness. We propose a novel decision aid model, based on system dynamics and the integration of TOC's Drum-Buffer-Rope and Lean concepts, to support the design and management of production systems under variability.