Manufacturing Process Optimization to Increase Products Reliability by Control Charts

Document Type : Research Paper


1 University of Kurdistan

2 Industrial Engineering, Kermanshah University of Technology, Kermanshah, Iran



The production process must be monitored to produce highly reliable products, and in this regard, control charts are one of the most important and widely used process monitoring tools. In this study, it is assumed that the quality characteristic that is monitored is the lifetime of the products, which follows the distribution of Weibull with a variable scale parameter and a fixed shape parameter. The purpose is to monitor the average lifetime of the products, which is conducted by monitoring the Weibull distribution scale parameter. To design a control chart, first, the control limits of the chart for different parameters are obtained and presented. Relationships and values regarding control limits show that the control limit of a one-sided chart is always larger than the control limit of a two-sided chart. To evaluate the performance of the proposed control chart, the average run length in the out-of-control mode for various parameters is presented and sensitivity analysis is performed. The computational results show that the one-sided control chart has better performance in detecting reduced lifetime compared to the two-sided control chart. One of the most important parameters that increase the performance of the control chart is the number of failures in the failure censored life test, as the number of failures increases, the test continues for a longer time and therefore it increases the chances of detecting the changes. Finally, a practical example is provided to show the performance of the proposed control chart.