Six Sigma Approach for Quality Management in Plastic Injection Molding Process: A Case Study and Review

摘要

Injection molding has been a challenging process for many manufacturers and researchers to produce products meeting requirements at the lowest cost. Its complexity and the enormous amount of process parameter manipulation during real time production create a very intense effort to maintain the process under control. What is more, complexity and parameter manipulation may cause serious quality problems and high manufacturing costs. Determining optimal process parameter settings critically influences productivity, quality, and cost of production in the plastic injection molding (PIM) industry. Previously, production engineers used either trial-and-error method or Taguchi's parameter design method to determine optimal process parameter settings for PIM. However, these methods are unsuitable in present PIM because the increasing complexity of product design and the requirement of multi-response quality characteristics. Six Sigma is the most fervent managerial methodology not only in manufacturing area but also in the services industry. Many investigations have indicated that Six Sigma can increase organization's competitive capability and enhance the quality of products or services by conducting the projects. Since this program focus on data-driven analysis and rigorous methodology to improve quality, and seem to be gaining significant popularity in industrial settings. This study aims to review the effect of six sigma tools in a plastic injection molding industries along with a case study to improve the quality of nylon-6 bush (KAMANI BUSH) produced by plastic injection molding process. After implementation of the proposed method the lower process capability index CPL for over shrinkage of nylon-6 bush has improved from 0.24 to 1.225, process mean decreased from 0.1015 to 0.0615. While process improved from 2.38a standard to 5.18a standard. This work shows that process was improved closer to six sigma standard by changing the processing conditions only without any change in the part design, mold design, and machine performance. The production equipment employed in this study is a precision injection machine, model: PPU7690TV40G, over all dimensions 856×1500×2480 mm manufactured by the Targor Corporation This study has two advantages. First is to choose the best tools that fit that type of industry. Second is to encourage similar companies to apply the same methodology. The case studies by researchers showed a significant improvement in the rejection rate using the structured DMAIC methodology.