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Quartile Deviation Based Process Capability Analysis
M S Prabhuswamy, P. Nagesh
Abstract
The process capability analysis helps in quantifying the process variability and assists manufacturing by reducing the variability. Process capability of a manufacturing process can be assessed through the computations of various process capability ratios. The usual method of process capability analysis involves large Computations and requires more time. The usual method of process capability analysis uses range and average range, which is more sensitive and affects by fluctuation of sampling and is not a stable measure of dispersion. Quartile Deviation (QD) based process capability approach can be used to compute capability ratios. Quartile deviation can be obtained graphically. This graphical approach of the process capability study is more rigid, consumes less time and has its own advantages over traditional method and gives quick information for further computation and analysis. The limitations of usual method of process capability analysis can be overcome by using quartile deviation based analysis. Using the quality characteristic of observations draws the cumulative frequency curve and hence Median and Quartile deviation is obtained. The traditional grand mean computations are replaced by median. Quartile deviation is used to compute process standard deviation through empirical relation. Quartile deviation based process capability analysis is more rigid and gives quick information. The process capability results using median has less affect by extreme values. The process variability is recorded in median chart, which indicates on-line variability.
Keywords
Process Capability, Quartile Deviation, Cumulative Frequency Curve, Graphical Approach
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