An approach for integrating performance evaluation and environmental sustainability assessment for hybrid additive-subtractive manufacturing

Manufacturing systems that integrate additive and subtractive unit processes within a unified workflow aim to leverage the respective strengths of each technology. This study presents a modeling framework for assessing the environmental performance of hybrid manufacturing systems, explicitly accounting for stochastic system-level dynamics such as blocking (when an upstream process is forced to stop because the downstream buffer is full) and starvation (when a downstream process remains idle because the upstream buffer is empty). The model is applied to a case study combining wire arc additive manufacturing and 5-axis CNC milling, under three different process scenarios and multiple system configurations. Increasing buffer capacity reduces idle states and enables the system to operate closer to its maximum throughput, at the cost of higher work in progress. As productivity increases, specific energy consumption and emissions per part decrease. These findings extend traditional process-level models to a multi-stage context, highlighting the importance of system integration. Overall, the study demonstrates that applying the proposed model can improve energy efficiency and carbon footprint by jointly considering process strategies and system configuration, supporting more informed, sustainability-oriented design and planning decisions.