Defective product reduction for a plastic injection process

Abstract

The objective of the thesis is to reduce the defective product for a plastic injection process in a smple company by using the quality improvement tools. This research focuses on the process of raw material, plastic injection, self inspection and process quality control, not including painting process and screening process. Reduction of defective products for a plastic injection process starts from using cause and effect diagrams to explore all the potential influence factors affect on the defect product. Then, the Failure Mode and Effect Analysis is used to analyse the factors and shown the risk priority number. After that, the relation diagrams are used to illustrate the relation between each flaw. Finally, the Why-Why analysis and the decision tree diagrams are used to find the root cause of the highest risk proiority number and find the solutions before we do the implementations. After the proper implementations are applied, the defective products or silver streaks reduction are achieved. Those are the defective products reduced from 6.68% on August to 1.94% on the second week of October 2003, which equal to reduce 277,270 baht within six weeks. From the study, the best alternative to reduce the number of silver streaks defects is the mechanic-shut off valve system. In addition, the new risk priority number is lower than the former over 50%. However, some of the risk priority number cannot reduce because that is an uncontrollable factor. The observation on this research is the collaboration from every related person is an important thing to get the goal even though the controversies are happened sometimes.