Discussion:
Statistical Quality Control- Mean and Range Chart
Q: A new machine has just been installed to cut and rough-shape large slugs. The slugs are then transferred to a precision grinder. One of the critical measurements is the outside diameter. The quality control inspector randomly selected five slugs each hour, measured the outside diameter, and recorded the results. The measurements (in millimeters) for the period 8:00 A.M. to 10:30 A.M. follow:
Outside diameter (mm)
Time 1 2 3 4 5 Mean Range
8:00 87.1 87.3 87.9 87.0 87.0 87.26 0.9
8:30 86.9 88.5 87.6 87.5 87.4 87.58 1.6
9:00 87.5 88.4 86.9 87.6 88.2 87.72 1.5
9:30 86.0 88.0 87.2 87.6 87.1 87.18 2
10:00 87.1 87.1 87.1 87.1 87.1 87.1 0
10:30 88.0 86.2 87.4 87.3 87.8 87.34 1.8
a. Determine the control limits for the mean and the range.
b. Plot the control limits for the mean outside diameter and the range.
c. Are there any points on the mean or the range chart that are out of control? Comment on the chart.
[use Megastat, quality control process charts or use Phstat, mean and range control charts.