Operations Mgmt 4 Questions Assignment

6. C-Spec, Inc., is attempting to determine whether an existing machine is capable of milling

an engine part that has a key specifi cation of 4 6 .003 inches. After a trial run on this

machine, C-Spec has determined that the machine has a sample mean of 4.001 inches

with a standard deviation of .002 inch.

a. Calculate the Cpk for this machine.

b. Should C-Spec use this machine to produce this part? Why?

LO13–2

7. Ten samples of 15 parts each were taken from an ongoing process to establish a p -chart

for control. The samples and the number of defectives in each are shown in the following

table:

Samples n Number of defective Samples n Number of defective

Items in a sample Items in a sample

1 15 3 0 10 2

2 15 1 6 15 0

3 15 0 7 15 3

4 15 0 8 15 1

5 15 0 9 15 0

a. Develop a p -chart for 95 percent confidence (1.96 standard deviation).

b. Based on the plotted data points, what comments can you make?

8. A shirt manufacturer buys cloth by the 100-yard roll from a supplier. For setting up a

control chart to manage the irregularities (e.g., loose threads and tears), the following data

were collected from a sample provided by the supplier.

Sample 1 2 3 4 5 6 7 8 9 1 0

Irregularities 3 5 2 6 5 4 6 3 4 5

a. Using these data, set up a c -chart with z 5 2.

b. Suppose the next five rolls from the supplier had three, two, five, three, and seven irregularities.

Is the supplier process under control?

9. Resistors for electronic circuits are manufactured on a high-speed automated machine.

The machine is set up to produce a large run of resistors of 1,000 ohms each.

To set up the machine and to create a control chart to be used throughout the run,

15 samples were taken with four resistors in each sample. The complete list of samples and their measured values are as follows:

Sample Number Readings (in ohms)

1 1010 991 985 986

2 995 996 1009 994

3 990 1003 1015 1008

4 1015 1020 1009 998

5 1013 1019 1005 993

6 994 1001 994 1005

7 989 992 982 1020

8 1001 986 996 996

9 1006 989 1005 1007

10 992 1007 1006 979

11 996 1006 997 989

12 1019 996 991 1011

13 981 991 989 1003

14 999 993 988 984

15 1013 1002 1005 992

Develop an

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X - chart and an R -chart and plot the values. From the charts, what comments can you make about the process? (Use three-sigma control limits as in Exhibit 13.7.)