Enhancing product quality in precast concrete spun pile through the Six Sigma DMAIC

Abstract

Defects in precast concrete spun pile production pose risks to structural reliability, operational efficiency, and project costs. The Company has experienced recurring defects that increase the cost of poor quality and reduce customer satisfaction, highlighting the need for a systematic improvement approach. This study applies the Six Sigma DMAIC methodology to analyze and reduce defects using production data from 25,206 units manufactured between 2020 and 2022. Statistical analysis using P-chart control limits, DPMO calculations, and sigma-level evaluation revealed an overall defect rate of 0.63%, dominated by Broken PC Bars, Cracks in the Stock Area, and Dry Concrete, which together contributed 62.5% of total defects. The initial process performance averaged 3.4 sigma (approximately 2,150 DPMO), which improved to 4.67 sigma following the proposed corrective actions. Root cause analysis identified human factors, unstable machine calibration, procedural inconsistencies, and material variability as the primary contributors. Improvement recommendations include operator training, biweekly machine maintenance, digital standardization of work procedures, and stricter material control. The findings demonstrate the effectiveness of a data-driven DMAIC approach for enhancing product quality in precast manufacturing. Future improvements may incorporate IoT-based monitoring and stronger supplier collaboration to support long-term process stability and operational excellence.