ABSTRACT Using Shewart charts to control multicavity processes is not, in general, reliable when there are small deviations in relation to the total variability and when there is a large number of cavities. For this reason EWMA charts have been used to control averages and standard deviations in some of the cavities. The quantification of the improvement in the reliability of the processes has been done as a result of studying a simulation in which the cycle mean length to detect an out-of-control signal, under different experimental conditions, has been tested.