18/11/2018
The work presents the new charting technique for complete process analysis from both the stability and capability points of view. Stability evaluation is performed using the true control region on a two-dimensional graph of the measures of the central tendency and spread of the process. The region boundary represents the locus of points with the same probability density function value and is characterized by a one-dimensional statistic, depending on the standardized sample average and standard deviation. The chronological record of the statistic can be used for testing the statistical behavior of the process, a procedure characterized by reduced adjustment errors compared with the conventional Shewhart charts. Capability assessment is based on time-sequence analysis of the quality loss point estimator, which value depends on the sample variance and the squared distance from x-chart centerline to the sample average. The proposed approach allows to apply the charting technique for simultaneous analysis of both the statistical and quality behavior of the process and, thereby, optimize process control.