Analysis Of LPG Tank Defect Control Using the Six Sigma Method at Pt. Metal Hitech Engineering

الملخص

Quality control in the welding process plays an important role in ensuring product quality and production cost efficiency. This study aims to analyse the defect rate, process performance, and effectiveness of the Six Sigma method in welding quality control at PT Metal Hitech Engineering. The research data was obtained from radiographic inspection results during the period 2024–2025. The research methods used included calculating Defects Per Million Opportunities (DPMO) and sigma levels to measure process capability, analysing process stability using C-Chart control charts, identifying defect causes through cause-and-effect diagrams (fishbone diagrams), and analysing quality costs and sigma level interpolation as a basis for improvement planning. The results of the study show that the quality control system implemented by the company is still reactive and focuses on final inspection, so it is not yet able to prevent defects from occurring at the beginning of the production process. The dominant types of welding defects include incomplete fusion, incomplete penetration, porosity, and undercut. Process performance measurements show a sigma level of 3.94 in 2024 and 3.84 in 2025, indicating that process capability is in the intermediate category. Control chart analysis shows that the process is still within statistical control limits, but there are observation points approaching the upper control limit. Interpolation results indicate that an increase in the sigma level has the potential to significantly reduce the number of defects and repair costs.