Implementation of statistical process control in a high volume machining center : importance of control charts

Thesis: M. Eng. in Manufacturing, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 83-84).This thesis focuses on application of statistical process control (SPC) and control charts in a high volume machining center at Waters Corporation. The company has a need of a real time inspection and control methodology so that new hires as well as experienced operators can produce machined parts with high quality and low scrap rates. This thesis project was conducted by Zhu, Zhang and Udayshankar as a team, developing and applying multiple components of SPC at Waters. Zhang's thesis focuses on Gage Repeatability & Reproducibility and Udayshankar's thesis focuses on standard operating procedures (SOPs). An SPC methodology flow chart is designed specifically for the company based on theoretical review of SPC methods and baseline data collection. Initially, the column machining process was out of control due to existing assignable causes such as tool breakage and tool wear. After an SOP is designed and operators trained to follow the SOP, the process was brought back into statistical control. A sampling plan is determined and individual control charts are used to achieve real time inspection in the long term. As a result, scrap rate was reduced from 8% to 4% and potential savings in the column area is higher than $200,000. The SPC methodology will be scaled up to the entire machining center in the near future, which will have a potential annual savings of $600,000. At the end of this thesis project, recommendations are made to Waters Corporation to help it maintain its status as a world class manufacturer. Major recommendations are to implement a database system for quality control, root cause analysis, training program and continuous process improvements.by Haipei Zhu.M. Eng. in Manufacturin