Process Monitoring in Production Systems with Large Diversity of Products

The main objectives of Statistical Process Control (SPC) are monitoring and analyzing the capability of processes. Traditionally, the analysis of the process capability is performed at the end of Phase 1 (preliminary) and periodically during Phase 2 (monitoring) of the SPC, using the indices Cp and Cpk. SPC and capability analysis of production systems with a large diversity of products present difficulties in implementation. In order to meet the needs required by the current production systems, this paper presents methods for both the statistical control and capability analysis of the processes. These methodologies include two situations, when there are sufficient data to estimate the process parameters (mean, variance) and when it does not exist. In the first case, it is suggested the implementation of control charts Z and W and capability indices ZL and ZU. In the second case, when there is a limited amount of data, the authors suggest the implementation of control charts Q and capability indices QL and QU. The methodologies are illustrated with two case studies, concluding that they allow streamline the statistical control of the various processes and reduce the downside, in Phase 2 of the SPC, where the capability analysis is made only periodically.