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Unformatted text preview: b. Plot the 20 points on the chart and determine which ones are in control. c. Is the process stable enough to begin using these data for quality control purposes? 4. A process for producing electronic circuits has achieved very high yield levels. An average of only 10 defective parts per million is currently produced. a. What are the upper and lower control limits for a sample size of 100? b. Recompute the upper and lower control limits for a sample size of 10,000. c. Which of these two sample sizes would you recommend? Explain. 5. Widgets are made in a two-shift operation. Management is wondering if there is any difference in the proportion of defectives produced by these two shifts. They suspect that the second shift has a higher rate of defectives, since the workforce is not as highly trained and supervision may be lacking. a. How would you use the p control chart to determine if there is a difference between the two shifts? Explain. b. On the first shift, samples of size 200 have been used and p-bar = .04. Calculate CL, UCL, and LCL for the first shift. c. On the second shift, six samples of size 200 have been taken with the proportion of defectives .04, .06, .10, .02, .05, and .03. Using the samples from the second shift, has the process mean shifted upward or downward? Explain. 6. In a control chart application, we have found that the grand average over all past samples of size 7 is x-bar-bar = 30 and R-bar = 5. a. Set up a control chart for this application. b. The following measurements are taken: 38, 35, 27, 30, 33, 28, and 32. Is the process still in control? 7. The producer of electronic circuits in problem 4 has reconsidered the method of quality control and has decided to use process control by variables instead of attributes. For variables control a circuit voltage will be measured based on a sample of only five circuits. The past average voltage for samples of size 5 has been 3.1 volts, and the range has been 1.2 volts....
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- Fall '13
- UCL, LCL