McDaniel Shipyards wants to develop a control chart to assess the quality of its steel plate. They take ten sheets of 1" steel plate and compute the number of cosmetic flaws on each roll. Each sheet is 20' by 100'
Based on the following data, develop limits for the 3-sigma control chart, plot the control chart, and determine whether the process is in control.
Sheet Number of flaws
1 1
2 1
3 2
4 0
5 1
6 5
7 0
8 2
9 0
10 2
Total units sampled 10
Total defects 14
Defect rate, c-bar 1.4
Standard deviation 1.183216
z value 3
Upper Control Limit 4.949648
Center Line 1.4
Lower Control Limit 0
Sample six is above the control limits; therefore, the process is out of control.
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