Sustainability-driven optimization of np chart for enhanced process monitoring

This study introduces a sustainable approach for monitoring manufacturing processes by optimizing the np chart to account for the environmental and economic impacts of inspection processes. Unlike traditional methods, which focus solely on quality control, the proposed approach integrates the costs associated with recycling, reworking, and disposing of nonconforming items, thus addressing sustainability concerns. The optimal np chart enhances the detection of increasing shifts in the fraction of nonconforming items, leading to significant reductions in emissions, rework, disposal, and recycling costs. The novelty of this study lies in its ability to optimize the np chart for both quality control and sustainability. An application on fire extinguisher manufacturing demonstrates a 50% reduction in overall sustainability costs, when using the optimal chart compared to a conventional np chart. Sensitivity analysis further examines the impact of design parameters on total sustainability costs, providing practical insights for manufacturers aiming to reduce carbon emissions and inspection costs while maintaining high-quality production standards. The results reveal that the optimal np chart achieves 59% and 62% better performance under uniform and Rayleigh distributions, respectively.