Applied control charts for analysis of quality control

In this paper we used an expected cost model for a process whose mean is controlled by X(bar) chart and whose variance is controlled by an R chart in the Textile Industry Oeste Ltda. in the State of Santa Catarina. The expected cost comprises the fixed and variable costs of sampling, the cost of investigating and correcting the process when at least one control chart indicates that the process parameters have shifted and the cost of producing defective units. The cost of the optimal design has been compared to the cost of Shewhart´s design for case where large shifts in the mean and variance occur and where the optimal k for Shewhart´s design is known.