In: Operations Management
Problem 13-9
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. Use Exhibit 10.13.
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: Use three-sigma control limits.
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 | |
a. Calculate the mean and range for the above samples. (Round "Mean" to 2 decimal places and "Range" to the nearest whole number.)
b. Determine X=X= and R−R− . (Round your answers to 3 decimal places.)
c. Determine the UCL and LCL for a X−X− chart. (Round your answers to 3 decimal places.)
d. Determine the UCL and LCL for R-chart. (Leave no cells blank - be certain to enter "0" wherever required. Round your answers to 3 decimal places.)
e. What comment can you make about the process?
o The process is in statistical control.
o The process is out of statistical control.
Sample | Ob. 1 | ob 2 | ob 3 | ob 4 | Mean | Range |
1 | 1010 | 991 | 985 | 986 | 993 | 25 |
2 | 995 | 996 | 1009 | 994 | 998.5 | 15 |
3 | 990 | 1003 | 1015 | 1008 | 1004 | 25 |
4 | 1015 | 1020 | 1009 | 998 | 1010.5 | 22 |
5 | 1013 | 1019 | 1005 | 993 | 1007.5 | 26 |
6 | 994 | 1001 | 994 | 1005 | 998.5 | 11 |
7 | 989 | 992 | 982 | 1020 | 995.75 | 38 |
8 | 1001 | 986 | 996 | 996 | 994.75 | 15 |
9 | 1006 | 989 | 1005 | 1007 | 1001.75 | 18 |
10 | 992 | 1007 | 1006 | 979 | 996 | 28 |
11 | 996 | 1006 | 997 | 989 | 997 | 17 |
12 | 1019 | 996 | 991 | 1011 | 1004.25 | 28 |
13 | 981 | 991 | 989 | 1003 | 991 | 22 |
14 | 999 | 993 | 988 | 984 | 991 | 15 |
15 | 1013 | 1002 | 1005 | 992 | 1003 | 21 |
Mean of means xbarbar =999.1
Mean of range values Rbar =21.73
UCLxbar = xbarbar + A2*Rbar = 999.1+0.729*21.73 =1014.94
LCLxbar = xbarbar - A2*Rbar =999.1-0.729*21.73 =983.25
UCLR = D4*Rbar =2.282*21.73 =49.58
LCLR = D3*Rbar =0
Process is in control as all values are within limits