Green Lean Six Sigma for Smart and Sustainable Manufacturing: A Comprehensive Review and Strategic Framework in the Industry 4.0–5.0 Era

The transition toward smart, sustainable, and human-centric manufacturing is reshaping how organizations integrate operational excellence, environmental responsibility, and digital transformation.Green Lean Six Sigma (GLSS)-which synergizes Lean waste minimization, Six Sigma's data-driven methodology, and green manufacturing principles-has emerged as a robust approach for improving sustainability and operational performance.However, its strategic integration within the evolving Industry 4.0-5.0landscape remains conceptually fragmented and insufficiently structured.This study presents a comprehensive review of GLSS and its convergence with advanced digital technologies, including the Internet of Things, cyberphysical systems, artificial intelligence, robotics, cloud computing, blockchain, additive manufacturing, and big data analytics.The review synthesizes key implementation drivers, performance impacts, organizational and technological challenges, and critical research gaps, with particular emphasis on sustainability integration, digital maturity, human-technology collaboration, and the progression toward resilient, circular, and human-centric manufacturing systems.Building on these insights, the study proposes an integrated strategic GLSS framework tailored to the Industry 4.0-5.0context.The framework extends the traditional DMAIC methodology by embedding circular economy principles, sustainability-oriented performance metrics, digital intelligence, and human-centric innovation across all phases.Structured around five interrelated pillars-Technological Enablement, Human-Centric Management, Sustainable Materials and Processes, Policy and Governance Alignment, and Operational Integration-the framework provides a structured roadmap for deploying GLSS to achieve eco-efficient, socially responsible, and highperformance smart manufacturing systems.