Authors: Dr. Debasis Sarkar
Statistical Process Control helps in systematic reduction of variability in key quality characteristics of a product. Online quality control refers to controlling and monitoring during the production process. In this paper attempt has been made to apply some of the advanced and modified process control charts like CUSUM (Cumulative Sum), Multivariate Cusum (MVCUSUM) and Exponentially Weighted Moving Average (EWMA) control charts which can be effectively applied for online quality monitoring of Ready Mixed Concrete (RMC). A proactive approach enabled to detect the causes leading to the variations and other problems associated with the production process at a much early stage of the process. Thus the cost of quality involved in bringing the process within control can be minimized. These control charts can be used as daily / weekly monitoring tool, which can improve the efficiency of the production process. Case studies of commercial batching plants in two metro cities of an emerging economic nation in South Asia have been considered for this research work. Multivariate CUSUM control charts provide unified scheme in monitoring process mean and variability. This Statistical Process Control tool is particularly useful when there is multiple process or multiple streams of processes that can be monitored to track the problem causing a change in the quality characteristic of the process. It has been observed that, though all the charts are sensitive to small process shifts, CUSUM technique along with V-mask and particularly MVCUSUM appear to be a better tool for quality monitoring of RMC. As the concept is generic the methodology developed in this research work can be applied to all batching plants across the globe.
Keywords: Statistical process control; Cusum; Quality monitoring; Ready mixed concrete; Multivariate Cusum.