Product Quality Improvement in Plastic Injection Process by Statistical Quality Control

Abstract

This research aims to improve the quality of product in plastic injection process of the case company for a new part production by applying the Statistical Quality Control technique. Based on the historical data, the average defects were found at 8,947 ppm, exceeding the company target at 3000 ppm. The research methodology started with applying the quality tools to find problem and to analyze the cause of problems in the production process. It found that the silver streak problem became the highest 95.60% of all defect problems and from the problem analysis; it also found that the main cause as a result of inappropriate parameters setting in the injection molding process. The design of experiment technique was then applied to find the suitable factor. After that, the suitable parameters were implemented for mass production. The P-Control Chart was used to monitor and control the production process continuously. After improvement the production processes and controls, the operation result of the part number 1220402 illustrated that the defect proportion of silver streak problems reduced from 33,748 ppm to 6,084 ppm and when considering the overall average defect proportion of all new parts production, it decreased from 8,947 ppm to 2,320 ppm which can be reduced at 74.06 % achieved the company target which, must be less than 3,000 ppm.