การปรับปรุงกระบวนการประกอบผลิตภัณฑ์ตัวล็อคชุดหัวอ่านเพื่อลดข้อบกพร่องประเภทระยะความสูงของบอล / เพ็ญประภา กล้ากสิการ = Improvement of assembly process of head stack assembly latch to reduce ball height defects
The thesis applies Six Sigma approach to improve assembly process of head stack assembly latch with the aim to decrease the defects due to ball height. The thesis follows improvement method of Six Sigma. Firstly, in the define phase, the survey was conducted to define problem. Hence the objective to decrease ball height defects from 27,600 DPPM 500 DPPM is determined. The scope of this improvement project covered the assembly process of latch GZ8063V1 only. Secondly, in the measurement phase, measurement system was analyzed in terms of its accuracy and precision. The analysis result revealed that the measurement process passed AIAG standard. Then the potential causes of ball height problem were analyzed using Failure Mode and Effects Analysis (FMEA). Next, in the analysis phase, the Design of Experiment (DOE) was applied to specify the significant factors affecting ball height. The result of experiment showed that the significant factors affecting ball height were the erosion of POM’s assembly jig, the push length of assembly pin, the assembly mold method which caused the hole on workpiece, the interaction between the erosion of POM’s assembly jig and the push length of assembly pin, and the interaction between the erosion of POM’s assembly jig and the assembly mold method which caused the hole on workpiece. In the improvement phase, the most suitable factor levels were determined. Finally, in the control phase, the most suitable factor levels were applied in the assembly process for one month to confirm improvement results. Moreover, control plan was developed to monitor and control key process inputs and response. After improvement, it was found that defective rate decreased from 27,600 DPPM to 80 DPPM - in other words, the defects decreased from 2.76% to 0.008%. In addition, according to the production forecast, it is expected that the improvement could reduce cost up to 1,509,850 baht annually.