Statistical process control (SPC) in a high volume machining center : gage repeatability and reproducibility study

Abstract

The purpose of this project is to set up a statistical process control (SPC) system in a high volume machining center to reduce the scrap rate and improve the manufacturing quality. The system is demonstrated on a machining center at Waters Corporation as part of a team internship project. This thesis focuses on the gage repeatability and reproducibility study (Gage R&R study) for the implementation of the SPC system. Based on the knowledge about the machining processes and the gages available, we select the proper gages for different dimensions to conduct the Gage R&R study. Gage capabilities are analyzed and root-cause analysis for incapable gages is performed. Related reaction plans are developed and implemented in order to improve the gage capabilities. Discussion about tolerance redesign leads to the adjustment of specifications in the manufacturing area. As a result of these efforts, we find that the existing measurement system is capable for the SPC real time inspection system. As for the final result for this entire project, we demonstrated that with the SPC system, we successfully reduce the scrap rate by half and thus offer substantial cost savings as well as improved product quality.