Chapter 12 Quality Control 517
- True or false, and why? The purpose of
statistical process control is to eliminate
all variation from a process.
- True or false, and why? As long as the
process values lie between the control
limits, the process is in control.
- Calculate the control limits for an
x chart where
a. n 59 , m 550 , and s55.
b. n 59 , x 550 R 58 , and s is
unknown.
- Calculate the control limits for a range
chart where
a. n 54 , R 510 , and s 54. (What is
the value of the center line?)
b. n 54 , R 510 , and s is unknown.
- Calculate the control limits for a C chart
where
a. c 516.
b. c 522.
- Calculate the control limits for a P chart
where
a. n 52 5 and p 5 0.5.
b. n 52 5 and p 5 0.2.
- Return to the Teacher workbook from
this chapter and perform the following
analysis:
a. Open the Teacher workbook from
the Chapter12 folder and save it as
Teacher Control Chart 2.
b. Redo the x chart; this time do not
assume a value for s.
c. Create a range chart of the data; once
again, do not assume a value for s.
d. Examine your control charts. Is there
evidence that the teacher’s grades are
not in control? Report your conclusions
and save your changes to the workbook.
8. A can manufacturing company must be
careful to keep the width of its cans con-
sistent. One associated problem is that the
metalworking tools tend to wear down
during the day. To compensate, the pres-
sure behind the tools is increased as the
blades become worn. In the Cans work-
book, the width of 39 cans is measured at
four randomly selected points. Perform
the following analysis on the data:
a. Open the Cans workbook from the
Chapter12 folder and save it as Cans
Control Chart.
b. Use range and x charts to determine
whether the process is in control.
Does the pressure-compensation
scheme seem to correct properly for
the tool wear? If not, suggest some
special causes that seem still to be
present in the process.
c. Report your results, saving your
changes to the workbook.
9. Just-in-time inventory management is
an important tool in project manage-
ment. The OnTime workbook contains
data regarding the proportion of on-time
deliveries during each month over a
two-year period for each of several
paperboard products (cartons, sheets,
and total). The Total column includes
cartons, sheets, and other products.
Because sheets were not produced for
the entire two-year period, a few data
points are missing for that variable.
Assume that 1,044 deliveries occurred
during each month. Perform the follow-
ing analysis on the data:
a. Open the OnTime workbook from the
Chapter12 folder, saving it as OnTime
Control Chart.
b. For each of these products (Cartons,
Sheets, and Total), use a P chart to
Exercises
