CHAPTER 18 Statistical Process Controls



Statistical Process Controls: Please solve and submit the following questions (50 points).

1. A major record-of-the-month club collected data on the reasons for returned shipments during a quarter. Results are: wrong selection, 50,000; refused, 195,000; wrong address, 68,000; order canceled, 5,000; and other, 15,000. Construct a Pareto diagram and recommend what are the major problems that demand investment .

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2. Calculate the average, median, mode, range, and standard deviation for each group of numbers.

(a) 50, 45, 55, 55, 45, 50, 55, 45, 55

(b) 89,87,88,83,86,82,84

(c) 11,17,14,12,12,14,14,15,17,17

(d) 16,25,18,17,16,21,14

(e) 45,39,42,42,43

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Descriptive Statistics: C1

N for

Variable Mean StDev Median Range Mode Mode

C1 50.56 4.64 50.00 10.00 55 4

Descriptive Statistics: C2

N for

Variable Mean StDev Median Range Mode Mode

C2 85.571 2.637 86.000 7.000 * 0

Descriptive Statistics: C3

N for

Variable Mean StDev Median Range Mode Mode

C3 14.300 2.214 14.000 6.000 14, 17 3

Descriptive Statistics: C4

N for

Variable Mean StDev Median Range Mode Mode

C4 18.14 3.72 17.00 11.00 16 2

Descriptive Statistics: C5

N for

Variable Mean StDev Median Range Mode Mode

C5 42.200 2.168 42.000 6.000 42 2

3. Control charts for X and R are to be established on a certain dimension part, measured in millimeters. Data were collected in subgroup sizes of 6 and are given below. Calculate the trial central line and control limits. Assume assignable causes and revise the central line and limits.

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Subgroup Subgroup

Number X R Number X R

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1 20.35 0.34 14 20.41 0.36

2 20.40 0.36 15 20.45 0.34

3 20.36 0.32 16 20.34 0.36

4 20.65 0.36 17 20.36 0.37

5 20.20 0.36 18 20.42 0.73

6 20.40 0.35 19 20.50 0.38

7 20.43 0.31 20 20.31 0.35

8 20.37 0.34 21 20.39 0.38

9 20.48 0.30 22 20.39 0.33

10 20.42 0.37 23 20.40 0.32

11 20.39 0.29 24 20.41 0.34

12 20.38 0.30 25 20.40 0.30

13 20.40 0.33

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4. The following table gives the average and range in kilograms for tensile tests on an improved plastic cord. The subgroup size is 4. Determine the trial central line and control limits. If any points are out of control, assume assignable causes, and determine the revised limits and central line.

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5. The Get-Well Hospital has completed a quality improvement project on the time to admit a patient using: XC- and R charts. They now wish to monitor the activity using median and range charts. Determine the central line and control limits with the latest data in minutes, as given here.

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6. The viscosity of a liquid is checked every half hour during one three-shift day.

What does the run chart indicate? Data are 39, 42,38,37,41,40,36,35,37,36,

39,34,38,36,32,37,35,34,33,35,32,38,34,37,35,35, 34, 31, 33, 35, 32,

36,31,29,33,32,31,30,32, and 29.

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The viscosity of the liquid breaks down over time and from shift to shift and its not symmetrical.

7. Determine the trial central line and control limits for a p chart using the following data, which are for the payment of dental insurance claims. Plot the values on graph paper and determine if the process is stable. If there are any out -of-control points, assume an assignable cause and determine the revised central line and control limits.

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#5 has assignable cause. My hand calculation was different than Minitab at centerline was .04 and revised was .03

8. Determine the trial limits and revised control limits for a u chart using the data in the table for the surface finish of rolls of white paper. Assume any out -of-control points have assignable causes.

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9. A quality technician has collected data on the count of rivet nonconformities in four meters travel trailers. After 30 trailers, the total count of nonconfonnities is

316. Trial control limits have been determined and a comparison with the data shows no out-of-control points. What is the recommendation for the central line and the revised control limits for a count of nonconformities chart?

If the data is not showing no out of control points then shift the control points along with the UCL and LCL and establish a new set of specifications moving forward once mass production begins.

10. By means of a scatter diagram, determine if a relationship, exists between product temperatures and percent foam for a soft drink.

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There is a moderate positive correlation between temperature and foam percentage.

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