Managing for Quality and Performance Excellence 9th Edition by James Evans,William Lindsay

Exercise 44

Note: Data for many of the problems in this chapter can be found in the Excel workbook C08Data.xlsx on the Student Companion Site. Click on the appropriate worksheet tab as noted in the problem (e.g., Prob. 8-6, etc.) to access the data.
The data in worksheet Prob. 8-30 in the C08Data.xlsx file represent processing time values for 40 samples of size 4 that were taken from Rapid Check Kiters, Inc.'s check processing firm over a 20-hour period.
a. Compute the mean and standard deviation of all 40 samples for the sample data.
b. Calculate the control limits and construct the
and R -charts, using the first 20 samples. Is the process under control at that point?
c. Specifications for the process are 1.065 ± 0.14. If the process is under control, calculate the capability indexes based on the first 20 samples. Cpu , Cpl , Cp , and Cpk using the part of the
and R -charts Excel template that calculates the process capability. What do the indexes indicate?
d. After calculating the control limits, the last 20 samples were collected. When plotted using the control limits calculated earlier, does the process appear to be in statistical control? Why or why not? What should be done if it is not under control?