524 Samples of six items are taken from a service process at

5.24 Samples of six items are taken from a service process at regular intervals. A quality characteristic is measured and bar x and R values are calculated for each sample. After 50 groups of size six have been taken we have bar x = 40 and bar R = 4. The data is normally distributed. a. Compute control limits for the bar X and R control charts. Do all points fall within the control limits? b. Estimate the mean and standard deviation of the process. What are the +-3 standard deviation limits for the individual data? c. If the specification limits are 41 +- 5, do you think the process is capable of producing within these specifications?

Solution

As range R =4

x bar can vary +2 or -2 on either side

Hence control limits for x bar = (38, 42)

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b) Mean = 40

and std deviation = 2/3 = 0.67

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c) If 41+ or 5 means x moves from 36 to 46

Not within the range.

Hence not capable