การลดผลิตภัณฑ์บกพร่องในกระบวนการผลิตชิ้นส่วนเครื่องประดับโดยใช้เทคนิคซิกส์ซิกม่า

Abstract

The case study company produces jewelry products for export. One of the problems found in its production lines is product defects. The main objective of this research was then to reduce defective products in the case study company production process using Six Sigma Technique. This research was conducted following 5 steps of DMAIC: Define, Measure, Analyze, Improve and Control. The company is giving prior attention to reduce defective products occurring in the top part item manufacturing process, since it is a process that is produced regularly. The Define step aimed to define the scope of the project using Pareto Chart. It was found that the most frequently encountered product defect was hole type. This research then focused on solving the hole type defect problem in the top part item production line. Next, the objective of the Measure step was to evaluate and understand the current state of the process. Key metrics, e.g. percentage of defective product, were studied for comparison with the results after improvement. In addition, the measurement system was analyzed using Attribute Gage Repeatability and Reproducibility technique. Next, the Analyze step aimed to find the root causes of the problem. Root causes of defective product were determined using Process Mapping, Fish Bone Diagram, and Cause and Effect Matrix. The Improve step was aimed at eliminating the root causes of the problem using Design of Experiment Technique. Full Factorial Design of Experiment with 4 factors, each with 2 levels, was conducted to find factors affecting the occurrence of product defects and appropriate conditions of each factor. The factors studied were burning temperature, number of pieces per mold, metal casting temperature and pressure of metal injection. Finally, in the Control phase, the objective was to maintain the conditions of the improvement. Control chart (p chart) and standard operating procedures were developed and used. In conclusion, the research results were able to reduce the hole type defective products from 7.82% to 1.84%