Green lean six sigma for improving process-level operational and sustainability: a case study in an auto parts manufacturing industry

Purpose This paper aims to explain how process improvement initiatives in manufacturing often struggle to address identified inefficiencies without introducing new trade-offs. This study presents a new approach that integrates the sustainable stream method (SSM) and the theory of inventive problem solving (TRIZ) into green lean six sigma (GLSS) to address this challenge. Through this integration, operational process problems can be addressed and trade-offs resolved, while overall operational efficiency and sustainability performance are enhanced. Design/methodology/approach This study adopts a data-driven case study approach conducted at an Indonesian auto parts manufacturing company. The SSM is developed by integrating value stream mapping (VSM) with the sustainable performance metric (SPM), enabling the identification of low operational sustainability performance. TRIZ is then applied to resolve technical contradictions and generate inventive improvement solutions, which are systematically implemented through the GLSS using the define–measure–analyze–improve–control (DMAIC) method. Findings The results indicate that the proposed method can be effectively applied to process-level improvement in the automotive parts manufacturing industry. This finding is particularly relevant because it addresses operational processes that previously performed poorly in terms of sustainability. For the company studied, its application identified the drilling process as the primary bottleneck, with an initial SPM of 83.79%. Following implementation, the improved process achieved an SPM of 93.79%, reflecting a transition from an adequate to an excellent level of sustainable performance, resulting in approximately US$2,429.44 in monthly cost savings and an increase in customer satisfaction to 96.58%. Originality/value This study introduces SSM, which extends traditional VSM by integrating sustainability metrics through the SPM. The proposed GLSS–SSM–TRIZ integration provides a structured and replicable framework for data-driven, sustainable process improvement, contributing to both sustainable manufacturing theory and practical process-level applications.