Appendix Control Chart Analysis for Average and Range Charts (n>1) • Calculate the average and range of the data values in each subgroup. • Plot the average values on one chart and the range values on another chart. • Calculate the grand average (average of the averages) and the average of the ranges . These are called the central lines on the two charts. Draw these lines on the charts. • Calculate the limits on the chart for average values using the following formulas: UCLX = X + A2R LCLX = X – A2R • Calculate the limits on the chart for ranges using the following formulas: UCLR = D4R LCLR = D3R Control Chart Analysis for Individual and Moving Range Charts (n=1) • Make a run chart of the individual data values in time order. • Compute the moving ranges and chart them in time order. Moving ranges are the absolute difference between adjacent data values that are in time order. • Calculate the average of the individual values and the average of the moving ranges. These are called the central lines on the two charts. Draw these lines on the charts. • Calculate the limits on the chart for individual values using the following formulas: • Calculate the limits on the chart for moving ranges using following formula: UCLR = 3.268mR Capability Analysis: The Technique • Collect data from a process and plot the data over time. • Analyze the data using a process behavior chart. • If the process is predictable, go to the next steps. If not, work to get the process predictable. • Make a histogram of the individual data values. • Calculate the Natural Process Limits and mark them on the histogram to show what the current process is capable of producing. • Mark the customer specifications on the histogram. • Can the process meet the specifications? Calculate Cp. • Is the process meeting the specifications? Calculate Cpk.
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