Quality Control
CHAPTER 10
QUALITY CONTROL
PROBLEMS
Note:
Control chart factors can be found in Table 102 of your textbook
P1.
The Perfect Circle Company manufactures bushings.
Once each hour a sample of 125 finished
bushings is drawn from the output; each bushing is examined by a technician.
Those which fail
are classified as defective; the rest are satisfactory.
Here are data on ten consecutive samples
taken in one week:
Sample no.
1
2
3
4
5
6
7
8
9
10
Defective
15
13
16
11
13
14
20
25
30
45
a.
What type of control chart should be used here?
b.
What is the centerline of the chart?
c.
Assume the chart will include 3 standard deviations on either side of the centerline. What is
the lower control limit (LCL)?
The upper control limit?
d.
What statistic should be plotted on the control chart in the future for
?
e.
Draw the control chart on a piece of graph paper.
f.
Is this system under control?
g.
What should the quality control engineer do?
P2.
Use the data in Problem P1 in this problem.
Assume that an assignable cause has been found for
Sample #10 and has been corrected.
a.
What is the value of the centerline of the revised control chart?
b.
What is the lower control limit of the revised chart?
c.
What is the upper control limit of the revised chart?
d.
Compare the revised control chart to the original control chart.
P3.
The TakeCharge Company produces batteries.
From time to time a random sample of six
batteries is selected from the output and the voltage of each battery is measured, to be sure that
the system is under control.
Here are statistics on 16 such samples.
Sample
Mean
Range
Sample
Mean
Range
1
2
3
4
5
6
7
8
4.99
4.87
4.85
5.26
5.09
5.02
5.13
5.09
0.41
0.57
0.59
0.74
0.74
0.21
0.56
0.92
9
10
11
12
13
14
15
16
5.01
5.19
5.40
5.15
5.00
4.89
4.99
5.05
0.49
0.56
0.44
0.63
0.35
0.45
0.54
0.33
a.
What type of control chart should be used here?
Why?
b.
What is the centerline of the chart?
c.
What is the lower control limit?
The upper control limit?
1
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Chapter 10
d.
What statistic should be plotted on the control chart for each sample?
e.
Draw the control chart on a piece of graph paper.
f.
Is this system under control?
g.
What should the quality control engineer do?
P4.
Use the data in Problem P3 to draw an R chart.
a.
What is the lower control limit?
The upper control limit?
b.
What statistic should be plotted on the control chart for each sample?
c.
Draw the control chart on a piece of graph paper.
d.
Is this system under control?
e.
What should the quality control engineer do?
P5.
Assume that an assignable cause has been found and corrected for sample # 11 in Problem P3.
a.
What is the value of the centerline of the revised control chart?
b.
What is the lower control limit of the revised chart?
The upper control Limit?
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 Spring '08
 WILLIAMCOSGROVE
 Standard Deviation, Control Chart, UCL, LCL

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