SIX SIGMA IN PLASTIC INJECTION MOLDING: REUSE DEFECTIVE PARTS IN NEW ARTICLE PRODUCTION AS RAW MATERIAL INPUT OR NOT?

Abstract

In production plants, re-processing of defective products and re-incorporating them into production as raw materials provides the advantages of reducing scrap and efficient use of material. However, using recycled defective plastic parts as raw materials in the production of new parts in plastic injection processes can create aesthetic problems for the final product. On the other hand, the aesthetic dimension of quality that fulfills customer expectations provides competitive advantage. Considering this, in this study, the root cause of the aesthetic problem that occurs as discoloration of a particular component manufactured in a plastic injection facility operating in the white goods industry was revealed and improvement was made. Six Sigma DMAIC methodology was applied to reduce high scrap rates caused by discoloration errors, and it was determined that the error was caused by reusing scrap plastic parts as raw materials in the production of new articles. With the elimination of this cause, the process capability was improved, the 3 sigma process capability was increased to the level of 4.7 sigma and the aesthetic appearance of the product was improved. This study has shown that the reutilization of defective plastic parts as raw material input in new article production is not a viable approach for particular products such as white goods products.